Signs of Fall 4: Prairie Dogs (another keystone species)!

Photo by J. Ravi, Wikimedia Commons

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This past summer Deborah and I had the pleasure of going for a walk with my daughter and her husband along a beautiful hiking trail that followed the Cache de Poudre River just west of Greeley, Colorado. There were many things to see on this hike including osprey and red-tailed hawks and old venerable cottonwood trees. We also had two energetic dogs with us that kept us on our toes. The creature, though, that most strongly captured my attention was a single prairie dog that bravely kept his body above ground to bark and whistle at us as we walked past the extensive colony of burrows in which all of his compatriots were hiding.

I hadn’t been close to a prairie dog in over 40 years. Back at Texas Tech when friends and I would go play golf on the Lubbock public golf course, prairie dogs would regularly run out onto the fairways, grab our golf balls and take them off to their burrows. The Lubbock course, according to their score cards, was the only course in the country that had prairie dogs listed as a “no stroke penalty” hazard.

Prairie dogs are ground squirrels that were once astonishingly abundant on the Great Plains of North America. Prairie dogs live in colonies (or “towns”) with clusters of complex burrows that can have 30 to 50 burrow entrances per acre. The prairie dogs in a colony have complex social behaviors and communication systems. They also have significant impacts on their habitats. Lewis and Clark described prairie dogs and their extensive colonies in one of their journal entries (September 7, 1804) when they passed through what is now northeastern Nebraska. They marveled at the depth and nature of their burrows and the elusiveness of the prairie dogs themselves. They did capture one of the prairie dogs but only after great time and effort. That prairie dog, kept as a pet, was later presented to President Jefferson as a gift.

National Park Service, Public Domain

Exactly how many prairie dogs existed in the pre-settlement Great Plains is very hard to determine. They were so abundant and so common that few early settlers took the time to even mention them let alone count them. Estimates of 80 to 100 million acres, though, are often offered for the extent of land initially occupied by prairie dog colonies. One well documented prairie dog colony in Texas covered 250 square miles up into the Texas panhandle and contained, possibly, 400 million individuals!  Using present day observations of land occupied and numbers of individuals present (2.4 million acres and 24 million individual prairie dogs) we can extrapolate that could have been well over a billion prairie dogs living on the Great Plains prior to European settlement.

All five prairie dog species are only found in North America. The most abundant and most widely distributed of these species is the black tailed prairie dog (Cynomys ludoviclanus) whose range extends from southern Canada, down the Great Plains with the Rocky Mountains as the border in the west all the way to northern Mexico.

Prairie dog colony near Bozeman, Montana. Photo by M. Lavin, Wikimedia Commons

Prairie dogs live a variety of dry grassland habitats including shortgrass prairies, mixed grass prairies, sagebrush steppe, and desert grasslands. Vegetation in prairie dog inhabited grasslands is kept short (between 3 and 5 inches tall) to keep from interfering with their constant, visual monitoring for approaching predators. Prairie dogs also rely on these grasses for their food (75% of their diet are grasses), and their impacts on the quality and quantity of plants growing within the boundaries of their colonies are substantial.

Photo by D. DeBold, Wikimedia Commons

Coyotes are the most significant predators of prairie dogs, but swift foxes, American badgers, golden eagles, red-tailed hawks and ferruginous hawks also readily take and eat them. A highly specialized predator of prairie dogs that actually lives within the prairie dog burrows is the black-footed ferret. This ferret is an endangered species primarily due to the great reduction in prairie dog colony sizes and distributions. The evolution of a specific predator for prairie dogs implies that prairie dogs have lived in their grassland habitats for a very long period of time.

Prairie dogs were first and foremost looked upon as pests by European settlers. They assumed that the prairie dogs ate the same grasses as their introduced cattle and sheep and were, therefore, direct competitors for a limited food resource. Massive programs of extermination involving shooting and poisoning were undertaken reducing the prairie dog distribution from the 100 million acres of the pre-settlement plains to just 364,000 acres in 1961. It was observed, though, that the quality of the rangeland suffered when the prairie dogs were excluded, and the prairie dog’s role as a keystone species became apparent.

The keystone nature of the prairie dog has both obvious and subtle aspects. One of the most obvious features of their impact on their habitats is their construction of their extensive systems of burrows. These burrows can be 4 or 5 feet deep and are typically branched into a large number of side tunnels and specialized dens (sleeping dens, defecation dens, mating and brood dens, etc.). Many other animals use these shady ground burrows for both protection and to get relief from the winter cold and summer heat on the plains. Hundreds of species of both vertebrates and invertebrates rely on prairie dog burrows as components of their preferred habitats. Some of these other species may even have tightly evolved tight, commensal connections to these burrows. The mountain plover and the burrowing owl are two bird species with very significant reliance on prairie dog tunnels.

Equally obvious is the importance of prairie dogs in the food webs of their grassland ecosystems. Their abundance, mitigated more than a little by their high levels of alertness and elusiveness, makes them a significant source of food for a large number of small to medium sized mammalian and avian predators.

Llano estacado (near Ralls, Texas). Photo by Leaflet, Wikimedia Commons

The more subtle aspect of the prairie dogs’ influence on their ecosystems, though, involves a closer examination of their alleged negative impacts on their sustaining grasses. These assumptions of competition with other grazers and degradation of range quality led ranchers and sheepherders to initiate their programs of extermination. Prairie dogs, though, through their activities actually increase soil nutrient levels and water retention potentials which, in turn, lead to an accelerated rate of grass growth within the borders of their colonies. Further, the increased soil heterogeneity around and in between the burrow openings provides a more diverse growth medium for a broader range of grasses and forbs which in turn increases the diversity and ecological stability of the grassland ecosystem. Further, by keeping the grasses closely cropped around their burrows, prairie dogs keep the plants developmentally suppressed, thus maintaining a higher nutritional density in the plant tissues.  Also, in many of the grasslands inhabited by prairie dogs, they actually consume plant species not favored by grazing, domesticated cows or sheep.

A telling observation concerning the increased quality of the range forage within a boundaries of a prairie dog colony is that wild bison and pronghorns and even domesticated cattle will preferentially graze in and around prairie dog burrows rather than in adjacent non-prairie dog inhabited range lands. They go where the food is better!

Prairie dogs are often in the news because of a human introduced calamity that can decimate an entire prairie dog colony. “Sylvatic plague” (plague in wild animals) is caused by the flea-borne bacterium Yersinia pestis. This bacterium is the pathogen that also causes both bubonic and pneumonic plague in humans. In the early 1900’s plague bearing rats arrived in western ports of the United States, and their fleas carrying the Yersinia bacteria, spread to wild rodent populations (including prairie dogs). Plague, then, became established in wild rodent species throughout California and Oregon and all across northern Arizona, northern New Mexico and southern Colorado.

An outbreak of plague typically kills an entire prairie dog colony. The danger of this disease spreading to humans and/or their pets via the transmitting fleas is a frequently disseminated news story in the west. This past summer, plague was detected in a prairie dog colony near Denver and news alerts quickly went out announcing the closing of the affected area to hikers and campers.

The transition of prairie dogs from pest to keystone species is still being debated, but there is no question that their influences on their grassland habitats are profound.






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Signs of Fall 3: Keystones in our Biotic Communities

Forest elephant family. Photo by USFWS, Public Domain

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A “keystone species” is a species that has a large influence on the other species within its biotic community. It is often defined in terms of loss: “if this species is removed from a community” or “because this species was removed from its community” the entire community, all of the populations of all of the other species, were seriously affected and degraded. There is a subjective tint to this definition due to the individual interpretation of how “large” the influence of a particular species might be or how “serious” a particular loss might reverberate through an ecosystem, but the term has come into widespread use especially in discussions of the rampant species extinctions going on in our Anthropocene times.

Forest elephants are a species that has recently been described as playing a keystone role in its African tropical rainforest habitat (The New York Times, August 19, 2019). The African rainforest is second only to the Amazon rainforest in its size and scope and also in its influence on global water and carbon cycles. The lack of large herbivores in the Amazon, though, is one of a number of interesting differences between these two great, tropical ecosystems. The Amazon’s “elephant-like” herbivores (which included giant ground sloths and gomphotheres and glyptodonts) went extinct 12,000 years ago. As a consequence, there is no animal in the Amazon biotic community capable of trampling or uprooting small trees, and, logically, there is a much higher percentage of small trees in the Amazon rainforest and a reduced overall mass of above ground vegetation compared to an elephant inhabited African rainforest.

Rain forest near Konimbo, Liberia (West Africa). Photo by J. Atherton, Flickr

Looking more closely at this, researchers studied the tree distributions and carbon compositions of the tropical rainforests in the Democratic Republic of Congo (which have not had forest elephants for the past 30 years) and in the nearby Republic of Congo (which has only recently lost its forest elephants ). They found that forest elephants regularly trample trees that are less than a foot in diameter, and that they primarily eat the soft-wooded, relatively fast growing tree species. As a consequence of their trampling and tree consumption more sunlight reaches the forest floor (stimulating tree seedling growth) and water availability to forest plants is increased. Larger, slower growing, longer-lived tree species were subsequently favored in an elephant impacted rainforest, and these trees store significantly more carbon than their smaller, faster growing counterparts.

Researchers estimate that the widespread extinction of forest elephants will result in a 7% loss in African rainforest vegetation (the equivalent of three billion tons of stored carbon). The storage of this carbon is valued at $43 billion!

Forest elephant populations have decreased by 62% in the first decade of the 21st Century! They are functionally extinct from most of their 850,000 square mile, natural African range. Poaching along with habitat loss are the main reasons behind the widespread decline of this critical, rainforest keystone species.

American alligator. Photo by D. DeLoach. Wikimedia Commons

Another keystone species found closer to home is the American alligator. The American Alligator is a large reptile that was once found abundantly from wetlands and lakes of Texas, all across the states bordering the Gulf of Mexico, and up the U.S. Atlantic coast as far north as North Carolina. Freshwater and brackish water open and marshy habitats could be occupied by this apex predator. By 1967, though, primarily due to widespread, uncontrolled hunting, the numbers of wild American alligators were so low that the species was teetering on extinction. Placement of the species on the endangered species list in 1967 and the passage of the full Endangered Species Act in 1973 provided sufficient protection to allow the American alligator to recover and to re-inhabit much of its former natural range.

Why was it important to re-establish this formidable reptile in its former ecosystems? The answer revolves around the keystone nature of this species.

First and foremost, the American alligator is a predator. It broadly and opportunistically takes almost any prey species that come available. It especially consumes relatively large prey species that live in their aquatic habitats (especially large fish), and they also take a wide range of terrestrial species that wade or swim across their aquatic habitats or come to the edge of their pools, ponds or streams to drink. American alligators have been known to take black bears, panthers, deer and wild boar but more commonly capture and eat smaller terrestrial prey like raccoons and muskrats. Wading birds may also be taken but they are not a typical part of an alligator’s diet. Control of these prey species is a very important ecological role of the American alligator.

One very interesting “unintended consequence” of the extirpation of the American alligator from wetlands in Florida (which was motivated in part at least to stop the alligator consumption of game fish) was the precipitous drop in game fish populations after the alligators were gone. Researchers determined that the alligators preferentially consumed the larger fish (like gars) that ate the game fish and that without the alligator control of the gar population, game fish numbers drastically declined.

Gator hole. Photo by A. Gould, Flickr

American alligators also construct “gator holes” or “gator ponds” in their wetland habitats. The alligator uses its snout and tail to dig down through the accumulated muck and vegetation to create a relatively deep water pool in which it can hide and hunt. These pools fill up with freshwater and are often the only water sources that persist during times of drought. Many animals rely on these gator holes for drinking water during times of low rainfall (although they have to keep an eye out for the lurking, hunting alligator!).

Female American alligators also modify their wetland habitats via the construction of nesting mounds. These mounds can be as much as 3.5 feet high and up to 7 feet wide. These mounds serve not

Alligator mound. Photo by L. Oberhofner, Wikimedia Commons

only as incubation sites for the alligator eggs but can also can significantly add to the topographic complexity of the wetland habitat. A variety of plant species that require slightly drier soils can grow on these mounds thus increasing the vegetative diversity of the wetland. Also, a significant number of bird and mammal species can use these mounds for their own nests and dens.

So, forest elephants and American alligators both function in their ecosystems to increase biotic diversity and stability. They are keystone species whose influence and importance was not recognized until they were almost gone!

Next week, another keystone species that humans tried very hard to exterminate: the black tailed prairie dog!



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Signs of Fall 2: Week of the Canids!

Red fox. National Park Service. Public Domain

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Last week I had three encounters with wild canids down on the Roaring Run Trail!

The first was Monday morning: I was out for an early bike ride and had just pedaled up the hill to the junction of the right turn that drops the trail down to its last mile into Edmon and the gentle left curve that leads over to the waterfall near where the railroad used to cross over the creek. About 60 yards ahead of me I saw a red fox laying on its side, back towards me, right in the middle of the trail! My first thought was, “oh, no! A dead fox!” But, then I thought I saw it move! About 20 yards away from the still recumbent fox I shouted, “hey, fox!” and the fox leaped up, saw me barreling toward him, and raced off into the nearby thicket of knotweed. He was a very handsome animal with a beautiful coat and great agility and speed! Why he was napping in the middle of the trail, I have no idea!

The next day, I was back on the bike trail about the same time of the morning. Pedaling up the hill, I got very excited about seeing the fox again, but he was not in sight when I reached the trail intersection. I rode down to the turn-around at the waterfall and got a quick drink from my water bottle. When I started back down the hill the fox ran across the trail right in front of me and plunged into the knotweed patch and disappeared!

Two days and two fox sightings!

I went back out biking Wednesday morning, but I did not see the fox.

Eastern coyote. National Park Service. Public Domain

Wednesday afternoon, though, I was walking on the trail with Carl when we heard a rustle and crash in the underbrush across the river. We could see the tops of the knotweed moving as if something was chasing/being chased through the dense vegetation. Suddenly, a coyote popped out of the knotweed onto the open bank of the river and then just as suddenly leaped back into cover. The crashing went on for a couple of seconds and then it was quiet. Was the coyote hunting on his own or with other coyotes? Was it/they after a woodchuck or rabbit or muskrat or maybe a deer? Did it/they get it?

Three days and three canid sightings!

There are four types of canids in Western Pennsylvania: dogs, red foxes, grey foxes and coyotes. All four are very similar, but they are easily distinguishable from each other.

Kozmo. Photo by D. Sillman

Dogs can come in a wide range of sizes (5 to 150 (or more) pounds!) and a great range of coat colors and hair lengths.   Most dog breeds, though, have floppy ears, short muzzles, and steep foreheads (to make room for their large, domesticated brains!). They also typically hold their tails in an upward curve when they run. Dogs also look a bit bulkier and shorter legged than their wild counterparts because they have larger, deeper chests and slightly shorter upper leg bones than their wild relatives.

Coyotes here in the east are actually hybrids of western coyotes and the eastern gray wolf with a little bit of domesticated dog thrown in. Eastern coyotes can weigh up to 50 pounds and are about 33% to 50%  larger than the western coyotes. They are much larger than either red or gray foxes but are right in the middle of the size range of domesticated dogs. Coyotes have pointed ears, a long, pointy muzzle, a flattened forehead, and shorter, though often bushy (usually black-tipped) tails that they carry below their backs when they run. Coyotes have a lean, leggy look due to their shallower chests and longer upper leg bones (as compared to those of a domesticated dog).

Red foxes are smaller than most dogs and almost all coyotes. They typically weigh between 8 to 15 pounds. They have pointy muzzles, flat foreheads, pointy ears and long, bushy tails. As their name implies, they are usually a reddish-brown color but some individuals may actually be in a  range of browns and even grays. Most red foxes, though, will have black legs (their “stockings”) and a white tip on the end of their tails. Red foxes are the ultimate canid generalist! They can be found in almost any habitat (wild or human-modified) all around the world. They also eat almost any type of food from small mammals, to birds’ eggs, to fruit, detritus and carrion.

Grey fox. Photo by California Department of Water. Public Domain

Grey foxes are about the same size as a red fox, and, as their name implies, they are usually grey in color (especially on their backs), but they can have a great deal of reddish-brown hair on their sides. Their back coats usually have a dappled pattern of gray and black (this color pattern makes the gray foxes I have seen in the wild seem to shimmer as they move along!). Grey foxes also have a black stripe down the middle of their backs that extends on down to the tip of their tails. They don’t have black leg stockings or a white tail tip. Grey foxes are also seldom seen in human modified ecosystems. They are animals of the forest.

Both coyotes and red foxes are regularly found in urban and suburban communities. The abundance of food and shelter in these human-modified ecosystems make them ideal habitat choices for both of these types of canids.

Red foxes, being incredible generalists, make use of many types of human foods and also human detritus. They raid garbage cans, hen houses, compost piles, gardens, fruit bushes and trees, and eat avidly from food dishes left out for pets. They also go after small mammal prey (like rabbits, chipmunks and squirrels), and since many of these prey species are active during the day, often shift their activity periods from nocturnal and crepuscular time frames into diurnal intervals. The sight of a fox walking down a busy, city street in the middle of the day is not an unusual occurrence in many cities across the country! Foxes seem to prefer urban/suburban habitats that are relatively open and fairly well developed.

Coyotes, on the other hand, tend to keep to their more “natural” types of prey even when they inhabit a human-modified habitat. They eat rodents, rabbits, large insects, birds and birds’ eggs, along with occasional house pet (watch your cats and small dogs, everyone!). They may also may form groups to hunt larger prey (like deer) particularly in the winter. They also tend to keep to their nocturnal activity patterns and usually spend their days well hidden from sight. They usually choose to live in urban/suburban habitats that still have a predominance of “natural” spaces (woods, dense fields, etc.) probably to give them cover to hide during the daylight hours.

Coyotes do not tolerate red foxes in their natural habitats. They will kill foxes on sight in order to remove a potential food competitor from their community. In urban/suburban systems, though, coyotes have been shown to tolerate the presence of red foxes. It is thought that the abundance of food in the human-modified ecosystem (and also, perhaps, the selection of different specific habitats, times of activity and food sources) have led the very energy conscious coyote to the conclusion that tolerating minor food competitors is a more energy efficient strategy than expending their energy reserves to kill them.

If you would like to read more about coyotes and red foxes in urban habitats two excellent articles are: Mueller, Drake and Allen (University of Wisconsin) in PlosOne (January 2018) and Rodewald, Kearns and Shustack (Ohio State University) in Ecological Applications (ESA) (April 2011).



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Signs of Fall 1: Fresh Kill Landfill

Photo by M. Arseneault, Wikimedia Commons

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A landfill is an ancient and terribly simple technology. Wherever people exist, they generate a variety of wastes that they then pile up on the edge of their living space. A great deal can be learned about a society by examining its garbage. Anthropologists comb through the refuse midden piles of ancient villages and cities and develop hypothesis about trade routes, social structures, manufacturing technologies and quality of life of the people who threw their trash in the pile and then went on with their individual and collective lives.

Modern, industrial societies generate wastes in unprecedented amounts, and so much of our collective production involves the synthesis of relatively useless packaging  and trivialities. Our landfills fill up with these materials, and when we can’t jam any more refuse into them, we cover them up and find a new place to dump our trash.

Last week I talked about a small-scale garbage dump that was located on the land donated to Allegheny County to make Harrison Hills Park. That dump was an ecological blight that was subsumed by the power and resilience of the forest vegetation around it. Many people have walked right next to that dump or maybe even right over the top of it, and never knew that it was even there except for a few stray shards of glass and some emerging, rusting pieces of metal. This week I want to scale up our vision a few orders of magnitude and consider a landfill that for 46 years was the largest landfill in the world: The Fresh Kills Landfill in Staten Island, New York.

Fresh Kills, Staten Island, NY. Photo by K. Paulus, Flickr

Staten Island is the smallest of the five boroughs that make up New York City. It stretches well to the south of the other four boroughs and has the southern-most point of the entire state of New York (“Ward’s Point”). It is only just barely an island in that its separation from the New Jersey mainland is a narrow tidal channel called “Arthur Kill” (or sometimes, “Staten Island Sound”). A “Kill,” by the way, is a water channel or stream in Middle Dutch. The Dutch influence on site names is very apparent throughout the New York (i.e.“New Amsterdam”) area.

Arthur Kill has been a heavily used passageway for commercial boat traffic ever since the founding of New Amsterdam. The Kill is dredged regularly to allow ocean liners and ships to move up and down the passageway that connects Raritan Bay in the south with Newark Bay in the north and the ports of New York and New Jersey. The Staten Island side (the east side) of Arthur Kill is dominated by salt marshes. These vast wetlands, today, are recognized as valuable, vital “organs” of our ocean ecosystems, but they were once reviled as worthless wastelands. Fresh Kill is a small tidal stream that runs through a section of one of these Staten Island salt marshes, and in the late 1940’s New York City purchased several thousand acres around Fresh Kill to use as a repository for its residential garbage.

Landfill at Fresh Kills, NY. Photo by C. Higgins, Wikimedia Commons

Initially, or, at least publicly, the Fresh Kill Landfill was to receive garbage for just three years, although many memos between city planners and waste managers at the time indicated that a much longer period of use would be require to payback the initial and on-going developmental costs of the landfill. Later a 20 year period of active use was proposed. The landfill, though, opened and received its first garbage scow full of trash in April 1948 and did not officially close until its last garbage scow delivery in March 2001. From 1955 to 2001 it was the largest landfill in the world covering 2200 acres and housing 150 millions tons of garbage. There were four great mounds of refuse in Fresh Kill that ranged from 90 feet to 225 feet tall. At its peak in the 1980’s it was receiving 29,000 tons of garbage a day from the armada of scows arriving on the Arthur Kill from all of the boroughs of New York City.   Cambridge University archaeologist Martin Jones ranks the Fresh Kill Landfill, “among the largest man-made structures in the history of the world.”

From the earliest planning stages the landfill part of Fresh Kills was only the beginning of a long, complex development scheme. Raising the land from the level of the salt marshes up many dozens of feet would allow commercial, recreational and residential development. Layering garbage, incinerator ash and soil in a “layer cake” pattern was intended to seal in the odoriferous garbage and provide a stable base for future surface construction.  The final, layered, sealing cap on the landfill was designed to prevent deep water infiltration into the still rotting garbage and to collect its continually evolving methane gas. Surface layers of soil then provided ground vegetation with a rooting matrix and nutrient base and finished off the garbage containment with a biological surface screen. Much of Fresh Kills was to become a park: a park that was even larger than Central Park in Manhattan.

Pin oak forest, Photo by D. Cerula. Flickr

Last winter, William Bryant Logan went out to Fresh Kills to hike through the former dump. It was a cold, snow-slushy day but Bryant could easily make out the high hills of capped and sealed trash. The hilltops were treeless, but the valleys in between them were densely wooded with a variety of “volunteer” trees. There was a tall, thick stand of pin oaks, a common street tree in NYC. Could their acorns have been gathered up by street sweepers, tossed into waste receptacles and then dumped onto and floated out to Fresh Kills by garbage scow? There were also willows and cottonwoods along the streams of green, sludgy water. Red maples stood tall but were encased by layers and layers of vines. Poison ivy, wild grape, oriental bittersweet and porcelain berry grew denser and denser in the tree crowns as Logan hiked deeper into the increasingly narrow valleys. The trees seemed knitted together into a hideous, strangled vision of a forest growing out of control. Coils of sharply thorned greenbrier covered the ground and snagged onto Logan’s pant legs and boots. It took him 15 minutes to extract himself from one of the brier thickets.

Black cherry tree in forest. Public Domain

A large, wind thrown black cherry tree (almost always one of the first trees to grow in a disturbed area) had flung its six foot diameter root mass up into the air. The roots had grown down through the sealing landfill cap layers into the garbage below and pulled up mangled plastic toys, broken glass bottles, old nylon stockings and unrecognizably fragmented materials from the great hidden mass of sub-surface garbage. Black locust and mulberry trees also grew up into the interwoven forest along with every manner of now winter-dead and dried weed. All of the plants that Logan noted were plants of disturbed ecosystems. They were struggling for their individual existences and for their tiny sections of space and light.

Deer bones in forest. Public Domain

Amazingly, in the slush and snow Logan saw a garter snake coiled up and hissing with attitude. There were also white-tailed deer browsing in the thickets, and deer carcasses in some of the ravines. Many of the carcasses had picked clean by coyotes. There were scattered bones and skulls partially covered by the low weeds.

Many of the trees and other plants that Logan saw were growing out of the damaged or dead remains of other plants. He called it “phoenix regeneration:” (life arising from the ashes of former life). I have seen this before in  the nutrient poor, maritime forests of barrier islands like Assateague Island, Virginia. Great stands of tall pines in these forests often grew in unnaturally straight lines. The line was the ecological memory of a fallen tree whose decaying tissues provided much needed nutrients and water holding potential for germinating, fallen seeds. We called these trees “nurse trees.”

So, Nature is (mostly) covering up even a landfill the size of Fresh Kills. The disturbance forest’s trees and other plants will rage and roil at each other until some semblance of stability is achieved. Tree roots will grow deeper and deeper into the underlying garbage and regularly bring up root-balls full of its rotting substrate when their trees wind throw.

The garbage will be with us probably forever. As one of my old ecology professors so aptly put it: there is no “away” in Nature.


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Signs of Summer 13: Hiding Extreme Disturbances

Trees near overlook point in Harrison Hills Park. Photo by D. Sillman

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The first Europeans to see eastern North America were overwhelmed by the extreme “tree-ness” of the place. Gigantic white pines and hemlocks, immense oaks and chestnuts, and a staggering array of maples, beech, ash, cherry, birch, poplar and more filled almost all of the physical space of this vast wilderness. Trees covered the valleys, the hillsides, and the mountain slopes. Trees grew in the wet-muck soils of swamps and bogs and on the bare rocks that capped the ridge tops. Trees covered the rich, fertile soils of the bottom lands and the thin, acidic soils of the mountains. These trees had had uncounted millennia to find their interactive balances, their points of ecological equilibrium and sustainability, and they were growing and stable in their interactive spaces. These forests would have existed for many millennia more, in  fact,  if not for the appearance of those “more than just observing” Europeans who also brought with them axes, and saws and oxen and eventually logging railroads.

Not much of the untouched forest still exists. In Pennsylvania, for example, only 5% of the original forest, in the form of scattered, small parcels, still stands. Our European ancestors used the wood from the primal forest for fuel, for shelter, and for a myriad of other products. They cut down the forests and often left them to repair and re-grow on their own. The places where these primal forest stood filled up with types of trees that have only had a few decades to work toward their ecological homeostasis. These new forests are made up of mostly quick seeding, fast growing, short-lived tree species that have molded themselves to the less stable conditions of their modern existences.

We can see some features of this robust forest re-growth by looking at land that has been severely disturbed and left to recover on its own. Which gets us to some observations in Harrison Hills Park along the 5.2 mile park trail called the “Scouts’ Trail,” and, next week, to an interesting New York Times OpEd about New York City’s largest landfill!

Just outside the “dump trail.” Photo by D. Sillman

Deborah and I first hiked the Scouts’ Trail 8 or 9 years ago. Along its path you can see almost all of the possible habitats of Harrison Hills. You go from the highest sections of the park (the cell phone towers up on the hill on the north boundary) down into wet, muddy hollows. You walk across open, grassy meadows, past sunny ponds and wetlands, and through shady forests dominated by black cherry, maples and oaks. One section of the trial, though, caught our attention even on our first through-hike many years ago. In the southeast quadrant of the park the Scouts’ Trail  makes a sharp “V” around the edge of an apparent hill. At the point of the “V” there is a bench that looks over the steep cliffside down to the Allegheny River. All along this section of the trail, on both arms of the “V,” there are flickers and shards of broken glass dotting the trail, and all up the bordered hillside glass, metal and ceramic debris are eroding out the leaf-covered soil.

Emerging trash from the old Harrison Hills dump. Photo by D. Sillman

This hill is an old dump that was part of the donated farm that in the 1970’s became Harrison Hills Park.

The Pennsylvania Waste Industries Association indicates that prior to 1968 there were thousands of active, unregulated sites across the state into which municipal waste, industrial waste and toxic waste were indiscriminately dumped. The passage of the Solid Waste Management Act in 1968 and its subsequent amendment in 1980 and then comprehensive re-writing in 1988 (as “The Municipal Waste Planning, Recycling and Waste Reduction Act”) established the regulations and oversight for our current landfill and recycling systems.

Along the dump trail at Harrison Hills. Photo by D. Sillman

The dump at Harrison Hills Park long predates the 1968 regulations and was, undoubtedly, one of those thousands of unregulated dumps that received municipal waste from nearby communities. Few records would have been kept by the landowner of the dump and little monitoring of the nature or even the volume of the waste materials being disposed at the dump site would have been done. Rehabilitation or restoration of the dump might have consisted of simply covering the mounds of waste material with soil and then waiting for something to grow on top of it!

Photo by D. Sillman

The hike to the V-shaped loop around the old dump starts in a parking area near a large, heavily used playground and runs past a Japanese-style bridge that spans a narrow gully. It then follows a narrow trail over the gently rolling terrain. The trail is bordered (like most of the trails in Harrison Hills) by a dense growth of thigh-high stilt grass (an Asian invasive plant that is steady swallowing up almost all of the native vegetation in the park). Black cherry trees are abundant along the trail. Most of these cherries are about 50 years old and most are well pocketed with pileated woodpecker holes. The cherries were among the first trees that colonized the abandoned farmland (and the shallowly covered dump). Birds readily spread the cherry fruits and seeds, and the germinating cherry seedlings grow

Mile-a-minute vine along trail. Photo by D. Sillman

vigorously in the full sun. There are also some northern red oaks along the trail. Some of these may have arisen from bird-transported acorns while others (especially the double-trunked red oaks) may have sprouted from stumps left behind after land clearing. Spicebush also grows thickly along the trail along with scattered stands of multiflora rose (another Asian exotic invasive). Mile-a-minute-vine (a more recent but particularly insidious Asian invasive plant) is also growing over the tops of many of the shrubs and tall plants along the trail.

The packed soil of the trail surface is extensively punctured by clusters of pencil-sized, round holes. These are the emergence holes of the periodical cicadas that dominated the park for three weeks back in June. This section of the trail must have been a robust incubator for these seventeen-year cicadas!

Ravine along dump trail. Photo by D. Sillman

Mixed in with the black cherry and the red oaks are red and sugar maples and black locust trees, and then, as the trail begins to circle around the tip of its “V” there are some large white oaks and chestnut oaks growing on the trailside away from the mound of the dump. The trail is a boundary between the dump and a more “pristine,” surrounding forest: small diameter, evenly aged trees (mostly black cherry) are growing in the soil-covered spoil of the dump while larger (two or three

Silt grass growing over old dump. Photo by D. Sillman

foot diameter) oaks are growing in the undisturbed soil outside the margin of the spoil. It is impressive, though, how thickly the trees and shrubs (not to mention the stilt grass!) are growing on the glass and metal laden spoil! Most of the dump is covered by a dense mass of woody vegetation. The dump, except for the emerging debris, is very well hidden by its entangling vegetation! When I step off the trail out onto the spoil (I am wearing thick soled boots, of course) I feel the solid nature of packed spoil and covering soil. I can’t walk very far into the dump area, though, because of the density and tightly intertwined nature of its covering vegetation.

As I was walking about and paying attention to the trees and shrubs around me, I nearly stepped on a large, still green, big-toothed aspen leaf that was laying in the middle of the trail. I stopped and looked for the aspen tree but only saw black cherry, sugar maple, and various oaks. The leaf must have just recently blown down (it was nearly as green and as full of chlorophyll as it had been while it had been attached to its tree!), but it must have traveled a long way before it came to rest. Unexpected.

Photo by D. Sillman

Signs have been placed at the ends of the “V” around the dump warning hikers of unsafe trail conditions, and a cutoff trail has been opened to allow hikers to avoid most of the debris. There has been some discussion among the park authorities as to whether the eroded glass fragments represented a true hiking hazard or just a curiosity. At a meeting this summer it was decided to keep this trail section open but to establish a set of informational signs to explain the presence of the glass and other debris. The dump is observable only in the glimpses of these fragments. The dump, though, is an important part of the human history of this site! The covering trees and shrubs and herbaceous plants have done an incredible job in obscuring the nature and extent of this unfortunate place. We need, though, to see this “hillside” for what it really is!

(next week: the Fresh Kills Landfill on Staten Island!)








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Signs of Summer 12: The End of Summer

Photo by D. Sillman

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The deer have kept their fawns well out of sight for most of the summer. Up until two weeks ago we had only gotten glimpses of them down at the bottom of our field, but then, one morning, four does paraded out three handsome fawns onto the broad, open lawn across the street. It was hard to tell which of the does were mothers and which were aunts! All four were very focused on the fawns. The fawns were romping and playing with each other, but then the does got tense and alert. The cause of their unease popped into view out of the far woodlot: a young buck with an uneven pair of nubby antlers. The does chased him back into the woods and then herded the fawns slowly across the street to the relative security of my back field. The fawns did not seem to notice the young buck’s visit or any of the tension in their herd.

The dog star, Sirius, the brightest star in our sky, starts to rise with the morning sun in late summer (here in Western Pennsylvania, this year (2019), the initial rise was on August 14). Sirius’ rise signals the beginning of the “dog days.” The dog days are also the usual time for the annual cicadas (called the “dog day cicadas”) to climb up into the trees and begin to sing. This year our local dog-day cicadas emerged a month before the rise of Sirius! It feels, in fact, like many of the usual “summer” ecological events this year occurred weeks ahead of time! I am tempted to think that the periodical cicada emergence back in June was somehow driving events two to four weeks ahead of their “usual” times, but I can’t come up with a logical link between those seventeen year cicadas and everything from bluebird nesting patterns to monarch migration. I’ll keep thinking about it, though.

Goldenrod. Photo by D. Sillman

A friend (who taught in public schools) told me that the dog-day cicadas were her dreaded sign that the summer was coming to an end and the new school year was about to begin. I always watched out for the blooming goldenrod as my indication of summer’s end. The good news is that now that we are both retired, neither of those signs have the power to make us sad!

The mornings are increasingly foggy as summer begins to fade. These ground clouds are called “radiational fogs,” and they are caused by the extensive radiational cooling of the night air due to the longer, clearer nights of late summer. When this cool air comes into contact with soil and surface water that still retain their daytime heat, moisture condenses into fog. These fogs, then, quickly disappear when the morning sun starts to heat up the air. The other morning when I went out to fill the side bird feeders, a small flock of five Canada geese flew over honking loudly and quickly disappeared into the lingering fog bank. I am not sure if they were some of the non-migratory geese that live down along the nearby Kiski River or if they were some of the migratory geese practicing their long distance, V-formations! So many sounds and signs of Fall!

Crabgrass. Photo by D. Sillman

A more mundane sign of the end of summer is the appearance of crabgrass. Although many of my friends and neighbors positively hate this species and do not want to hear anything good or amazing about it, in the diverse mix of plants that I call my “lawn” the rise of crabgrass is an exciting, late summer event.

Crabgrass thrives in the heat and dryness of the late summer because of elegant adaptations in its cellular structure and molecular physiology. In most plants, the cells that carry out the two parts of photosynthesis (the “light reaction” that captures the energy in sunlight and makes both energy molecules and also the “waste” molecules of oxygen, and the “dark reaction” that uses carbon dioxide and the light reaction’s energy molecules to make sugars) are intermixed together. This allows effective contacts and transfers and lets photosynthesis run quite efficiently. When a plant becomes stressed by a lack of water, though, it closes its leaf pores (the “stomatae”). This stops the potentially fatal water loss but also shuts off the delivery of carbon dioxide to the “dark reaction” cells. There is, then, an imbalance between the “light” and “dark” reactions, and one of the consequences is that oxygen begins to build up inside the plant. This oxygen starts breaking down the functional molecules of the dark reaction (a process called “photorespiration”) and the photosynthetic rate (and the growth rate) of the plant plummets.

Crabgrass avoids photorespiration by anatomically separating and isolating the cells that carry out its light and dark reactions. The dark reaction cells are sealed away from the air spaces inside the leaf, and the oxygen from the light reactions, then, cannot break down the dark reaction cell’s molecules. A system (involving the synthesis of a four carbon molecule (hence, they are called C-4 plants!)) then transfers carbon dioxide from the air spaces to the dark reaction cells and keeps the carbon chemistry of the dark reaction cell operating.

At temperatures above 30 degrees C (about 86 degrees F) a C-4 plant is 200% more efficient than the typically photosynthesizing plant (which is called a C-3 plant, by the way!). So, when you see the spiky heads of crabgrass rising about the dead and dying grass plants around them, think about the biological elegance that allowed that event to occur!

Hummingbird in the beebalm. Photo by D. Sillman

The birds around our house have been subtly changing here at the end of summer. We have put the hummingbird feeders back out after our beebalm finished blooming. We were sure that the male ruby-throats had taken off on their southerly migration already and that there would only be female hummingbirds about. But, right after we put out the nectar feeder I was buzzed very aggressively by a male when I dared to stand too close to the freshly filled feeder. We have watched a mature female and what we think is her fledgling regularly rousting around each other for nectar access. The male comes and goes much less predictably: I think, though, that he has finally headed south. The seed eating birds are slowing down their rate of sunflower seed consumption from their mid-summer nestling/fledgling binge cycles, although the goldfinches and house finches (and chickadees and titmice) are emptying my thistle feeder faster than they have all summer! The nearby coneflowers in Deborah’s front flower bed may be drawing them in with all of their dried seed heads.  And, finally, the summer robins have left our yard and field. We no longer regularly hear them singing and fussing in the evening as they settle into their night roosts in the surrounding spruces and hemlocks. Once a week or so, though, passing flocks of robins use our trees for their overnight roosts and grace us with their rolling, “nightly news” songs.

A very hot, wet, busy summer is slowly wrapping itself up. Red maple leaves are starting to accumulate on the grass out back. There is even some hints of color in the tough, spiky leaves of the young black oaks just outside my window. The juncos will soon return, and autumn will really get rolling.



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Signs of Summer 11: Summer Algal Blooms

Lake Erie, Public Domain

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News reports in mid-July of this year talked about the likelihood of another algal bloom in Lake Erie this summer. This is becoming an annual event that poses serious health risks to not only the fish, waterfowl  and invertebrates that live in the lake but also to people (and their pets!) who get their drinking water from the lake or use the lake for recreational purposes.

The National Oceanic and Atmospheric Administration (NOAA) predicts that this year’s bloom will rise to a severity of 7.5 out of a possible 10. The severity index is based on the biomass of the algae over a sustained period of time, and any index value over 5 is considered serious. The bloom last year was rated a 3.6. In 2017, an article in The New York Times (October 3, 2017) described a 700 square mile bloom of bright green algae covering the western end of Lake Erie (see Signs of Fall 13, November 30, 2017). This bloom was rated 8.0 on the NOAA severity index. In 2011 an even more massive Lake Erie algal bloom was rated a full 10.0 on the NOAA index, and then in 2015 a bloom occurred that actually exceeded the index’s upper value and was rated a 10.5!

These algal blooms are primarily caused by the inflow of phosphate-rich, fertilizer and animal waste runoff from surrounding agricultural lands into the warm, shallow waters of western Lake Erie. Lake Erie is the shallowest of the five Great Lakes (its average depth is only 62 feet, and its western basin is especially shallow with average depths between 25 and 32 feet). The consequences of Lake Erie’s shallow depth are multifold: 1. It has the smallest volume of the five Great Lakes, 2. It has the shortest “water residence time” of any of the Great Lakes (only 2.6 years), 3. It is the first of the Great Lakes to freeze in the winter, and 4. It is the warmest of the Great Lakes in the summer. The shallowness and warmth of Lake Erie makes it a particularly ideal habitat for many species of green algae and plankton which serve as the base for a diverse food web of fish. It is estimated that half of all of the fish in the Great Lakes live in Lake Erie!

Photo by C. Fischer, Wikimedia Commons

Unfortunately, these phosphate-fed, summer-warmed algal blooms do not just involve the green algae that are components of the lake’s food webs.  Cyanobacteria (also called “blue-green algae”) also are found, although usually in small numbers, as a part of the rich, complex bacterial community of Lake Erie and most other freshwater ecosystems all over the Earth.

Many species of these cyanobacteria produce complex protein toxins. These chemicals were probably weapons used by the cyanobacteria in the intense, on-going chemical battles with other bacteria in their crowded, resource limited, aquatic habitats. The cyanobacteria have existed for nearly three billion years and, as a result of competition and evolution, have generated an incredibly diverse array of survival strategies. As a result they can synthesize three to four hundred different, toxic peptides. Usually, cyanobacteria are a small, non-threatening part of the freshwater microflora, but they  respond quite vigorously to added phosphates! Also, cyanobacteria need water temperatures above 20 degrees C (64 degrees F). Temperatures that warm can be generated in small shallow ponds fairly easily but will occur in larger (especially shallow) lakes (like Lake Erie!) toward the end of a summer season. The annual , late summer, Lake Erie algae blooms, then, almost always involve significant numbers of toxin-producing cyanobacteria.

Cyanobacteria. Photo by NASA, Wikimedia Commons

There are a few other interesting features of cyanobacteria also come into play during a bloom: 1. Cyanobacteria contains gas filled, intracellular vacuoles (therefore they float!),  2. Cyanobacteria require high levels of sunlight to run their photosynthesis (therefore they NEED to be on the top of the water),  3. Cyanobacteria are not very high quality food sources for zooplankton (they tend to get left behind after feeding and grazing … maybe the peptides have something to do with this, too?), 4. Cyanobacteria clump together into large colonies (which may be too large for most zooplankton to easily consume), and 5. Cyanobacteria can obtain the nitrogen they need to grow directly from the nitrogen gas of the atmosphere (they are “nitrogen fixers”).

So, the floating, clumped together masses of cyanobacteria when they get their population boost from the phosphates and the warm temperatures of the water and since they are already making the nitrogen that they need, tend to survive and accumulate in their ecosystems and crank out their hundreds of different toxic peptides! These toxins then can sicken and/or kill fish, waterfowl, livestock, dogs, and even people! There is also a concern that chronic, low level ingestion of these toxins can lead to liver damage and even liver cancer! Drinking water taken from surface water sources needs to be checked for these dangerous bacteria!

A recent New York Times article (August 12, 2019) described deaths of dogs all across the country who swam in cyanobacteria contaminated ponds and lakes. Dogs when they swim tend to ingest and swallow great quantities of water making them particularly vulnerable to the toxic impacts of the cyanobacteria’s secretions. Some dogs may only have skin rashes when exposed to cyanobacteria contaminated water but neurological damage, respiratory arrest and liver failure are also possible consequences of exposure to the cyanobacteria toxins.

The sizes and durations of these later summer blooms in Lake Erie have been increasing since 1985 as have the levels of dissolved phosphorus in the waters of the lake. Ongoing climate change with its increase in rainfall (and greater volume of phosphate rich river runoff) and elevated summer temperatures is only expected to make these blooms even more extensive and potentially even more toxic. I talked about the biology of these blooms back in 2014 (see Signs of Summer 1, June 12, 2014). On a small scale these algae blooms are dangerous, on a large scale, as we are now seeing in Lake Erie, they are potentially calamitous.

Sargassum on beach. Photo by P. Bourjon, Wikimedia Commons

Another algae that is excessively blooming in our climate changed world is sargassum. As I wrote about back in Signs of Winter 3 (December 20, 2018) great mounds of sargassum are accumulating on the beaches of Mexico, Texas, Louisiana, Mississippi, Florida and nearly two dozen islands of the Caribbean. Since 2011, the amount of sargassum in the Caribbean and Atlantic has greatly increased. A recent paper in Science (July 5, 2018) describes a 8850 kilometer long, continuous mass of sargassum that extends from West Africa across the Atlantic Ocean into the Caribbean and the Gulf of Mexico. It is the largest macroalgal bloom ever recorded.

Causes of this continuing sargassum explosion, like the summer algal blooms in Lake Erie are thought to be the inflow of nutrient-rich (especially phosphate and nitrogen rich) waters into the Atlantic via the Amazon River as it drains the increasingly deforested and agriculturally manipulated Amazon Basin. Fed by these nutrients, the sargassum steadily increases and dominates its open ocean and shoreline ecosystems.

Algae blooms, heavy rains and warmer summer temperatures (and all of their un-intended consequences!)! Welcome to the “new normal!”




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Signs of Summer 10: Aging and Life Spans

Cropped screen shot from Annie Hall. Fair use. United Artists

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In a scene in the 1977 movie “Annie Hall,” Tony Roberts climbs into his convertible with Woody Allen and carefully zips up the body and hood of his protective suit. “Keeps out the alpha rays,” he says to Allen, “You don’t get old.”

Aging is a complex, physiological phenomenon (that is not, as far as we know, caused by alpha rays). Every cell, every tissue and every organ of the body are changed in the aging process. There are two lines of questioning that we could follow concerning aging and life span (“life span” being a nice way of saying “dying”): the first asks “why?” Why do all organisms age and why do they die? And the second asks “how?” How do organism’s age and how does death come about?

“Why” questions are often very difficult to answer scientifically, but aging and death are probably most clearly explained via reference to evolution and, maybe, the purpose of life itself. Richard Dawkins in his book The Selfish Gene describes the purpose of life as a drive to preserve and replicate DNA (or “genes”):

“ We are survival machines—robot vehicles blindly programmed to preserve the selfish molecules known as genes.”

Figure by Radio89, Wikimedia Commons

Once replication and preservation of DNA has occurred, Life (or Nature) has little use for the parental generation. In almost all species, physiological and anatomical changes occur in post-reproductive (“senescent”) individuals that either decrease their chances of survival in their ecosystems or directly cause debilitating diseases and death. Resources need to be available for the next “replication and preservation” cohort rather than for the maintenance of the now evolutionary dead-end group. In a Natural Selection system long, post-reproductive life spans could only be selected for in situations where resources were super abundant and non-limiting, or where individuals had such a slow rate of metabolism that they used very few resources as they aged. Also, and this is the essence of “Grandmother hypothesis” in human beings,  longer life spans could be selected in situations where the post-reproductive individuals contribute in some positive way to the survival of their offspring or their offspring’s offspring.

So why do organisms age and die? Mostly because their job is done, and their continued presence might harm their passed-along DNA.

Looking at the second question, how aging occurs and how death comes about, is much more satisfying path of exploration in that understanding these things may enable us to resist them! In a human-controlled world (one in which cultural values, aspirations and technologies have by and large replaced the “nature red in tooth and claw” world of Natural Selection) we see discussion of and progress toward what Yuval Noah Harari has described in his book Homo Deus: A Brief History of Tomorrow  as the newest “ultimate” goal of humanity: immortality.

So, what do we know about the physiology and molecular biology of aging?

Telomere caps on chromosomes. US Dept of Energy, Human Genome Program

Each strand of your DNA in every cell of your body is marked with a curious feature of aging: the ends of your DNA strands (the “telomeres”)) get shorter each time the DNA replicates. Every time one of your  cells divides, the length of the information molecules that encode the instructions for all aspects of you and is, according to Dawkins’ selfish gene theory the whole reason for your existence, erodes away. It is not known, though, if this shortening of your telomeres is one of the causes of aging or just one of its many symptoms.

It is possible to introduce or activate an enzyme (called “telomerase”) into a cell that repairs these shortening telomeres. This happens in many types of cancer, and the cancerous cells then are able to multiply indefinitely without any DNA erosion.  Some tissue cultures of these cells are referred to as “immortal,” and they continue to replicate and thrive often many decades after the original cell donor has died.  The big (unanswered) question about telomeres is: if telomerase were switched on in all cells of an individual would that individual’s body become an immortal assemblage of cells or would it turn into a seething mass of out-of-control cancerous tumors?

Aging Diagram. Dw001, Wikimedia Commons

Oxidative stress is unquestionably a major factor in aging. Most organisms take in oxygen to allow their cellular energy generating systems to function, but some 2 to 3% of these oxygen molecules end up being reduced by stray electrons that bleed out of the energy-generating metabolic pathways. These reduced oxygen molecules become “reactive oxygen species” (ROS) (like superoxide anions, hydrogen peroxide and hydroxyl radicals). ROS’s then attack a cell’s macromolecules (proteins, lipids, nucleic acids) and cause chronic, cumulative damage to the cell.

Studies in nematodes and fruit flies in which genes are inserted that code for intracellular synthesis of anti-oxidant enzymes or in which drugs are administered that accomplish the reduction of these molecular degrading agents do result in the expansion of life span in both types of these invertebrate organisms. Laboratory and human-clinical studies in which dietary anti-oxidants (like Vitamin C, E, beta-carotene or flavonoid anthocyanins) are administered, however, have not shown any impact on or benefit to the slowing of the aging process or the expansion of life span. It is interesting, though, that some of the oxidative-stress reducing genes that may lengthen life spans may also have deleterious effects on the pre-reproductive survival of these organisms. Recent studies on nematodes showed a greater susceptibility to bacterial infections and higher rates of early life mortality in individuals that possessed the “oxidative stress reducing” “life span enhancing” genes  (Nature Communications, July 27, 2019).

Possibly related to this oxidative stress hypothesis are observations that have been made in lab animals and humans that have been kept under severe caloric restriction (CR). CR not only changes an organism’s regulation of energy metabolism but also may result in the synthesis of metabolic proteins that enhance the cell’s ability to resist both aging and also a number of degenerative processes. Longer life spans and inhibited development of Alzheimer’s and Parkinson’s diseases have all been observed in CR experiments.

Great white shark. Photo by T. Gross. Wikimedia Commons

In aging, the stability of a cell’s DNA declines. There is inhibited recognition and repair of mutated or transposed nucleotide sequences in both nuclear and mitochondrial DNA. These altered base sequences inevitably involve vital sections of the genome  and the failure of important cellular systems. These changes can reduce the ability of a cell to run normal metabolism and maintain normal homeostasis or cause it to significantly degrade in function or grow out of control and become cancerous.  The long life span of the great white shark (70+ years) and remarkable evolutionary stability of sharks as a group (almost 500 million years!) have been correlated to the extensive number of genes they have that participate in DNA control and repair and an equally large portion of their genome that is involved in tissue repair and healing (see Proceedings of National Academy of Sciences, February 18, 2018).

Giant tortoise. Photo by Childzy. Wikimedia Commons

Giant tortoises and parrots are two other types of organisms that have extremely long life spans. Both have been shown to have clusters of genes that control cell growth, DNA repair, and energy metabolism (see Current Biology, December 7, 2018 (parrots) and Nature, Ecology & Evolution, December 3, 2018 (giant tortoises)).  The natural selection systems for these extended, post-reproductive life spans might fit two of our proposed evolutionary models: tortoises have remarkably slow rates of metabolism (and, so, will not over-exploit their ecosystem’s food resources) and parrots with their high levels of intelligence and extensive nurturing of their young, may be assisting in the survival of their progeny or their progeny’s progeny!

Anyway, much is known about lifespans and aging, but very little is known for certain. Philosophically looking at life (and death), I think the best thing is to recognize that life itself is finite and that we should enjoy every minute of it. I would also recommend the “life” advice given to the protagonist in John Irving’s novel Cider House Rules, “be of use!” All of the generations coming after us need our help!

If you would like to read more about the biological and molecular aspects of life span and aging check out these two online sources:  Molecular Biology of Aging  ( by Johnson, Sinclair and Guarente)  and  Biology of Aging    National Institute on Aging (US-HHS).













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Signs of Summer 9: More on Coffee

Photo by J. Scortzman, Flickr

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Coffee is, to me, one of the glorious aspects of life and living. The small trees and bushy shrubs of the genus Coffea yield “cherries” (red to purple, pulpy fruits) that contain the caffeine and flavor-rich seeds (the coffee “beans”) that can be roasted and ground up and then brewed into the wonderful, black beverage that so many of us love.

There are 124 species of Coffea and most grow wild in sub-Saharan Africa. Only two of these species are extensively cultivated to produce commercially traded coffee. Coffea arabica (“Arabian coffee”) makes up 60 to 70% of the coffee grown and sold around the world, and Coffea robusta makes up the remaining 30 to 40%. A study by botanists at the Kew Garden (“Royal Botanical Gardens”) in Great Britain, published earlier this year in both Science Advances and Global Climate Change Biology, determined that 60% of the wild Coffea species are at risk of extinction due to climate change and habitat destruction. The potential loss of this diverse and as yet poorly studied gene pool could leave cultivated coffee without the genes and proteins that it needs to survive in our climate changed world!

Coffea arabica was the first type of coffee to be domesticated. By the early Sixteenth Century it was widely consumed throughout the Middle East. It is native to the southern highlands of Ethiopia and arose, apparently, as a naturally occurring hybrid of two other Coffea species (C. robusta and C. eugeniodes). Most Coffea species have diploid chromosome arrangements, but C. arabica is tetraploid and contains the entire genomes of both C. robusta and C. eugeniodes.

Coffea arabica.Photo by H. Zell. Wikimedia Commons

In its natural habitat, C. arabica grows as an understory plant beneath tall shade trees. It is capable of self-pollination and relies primarily on wind dispersal of pollen (although wild bees greatly increase its overall pollination efficiency both in wild and domesticated systems). The traditional method of cultivation of C. arabica, which is practiced in more than 70 countries around the world, replicates this controlled, shady, growing environment.  In modern parlance this type of coffee growing system generates “shade grown” coffee beans. Coffee trees in shade grown coffee plantations can produce coffee beans for 30 years or more!

In the 1970’s, though, in an attempt to increase the productivity of coffee trees, sun tolerant varieties of Coffea were developed. Coffee could then be grown in vast, open, monocultural plantations that produced what is now called “sun grown” coffee beans. Sun grown coffee systems do have higher yields per tree, but its trees are only productive for about 15 years.

Sun grown coffee plantation in Kaua’i Hawaii. Photo by Lukas. Wikimedia Commons

Sun grown coffee was beset with a myriad of other problems, too. Increased levels of fertilizers, pesticides and herbicides were needed to fuel the increased productivity of the coffee trees and to fight intrusions of insect pests and weeds. Also, removal of the shading, over-story trees destroyed important habitats for a large number of native birds, mammals and reptiles (many of which were quite active in insect control!). A study published last year counted 204 species of birds living in the shade grown coffee plantations in the Western Ghats of India.

Removal of the protective tree cover also exposed soils to the often violent rain storms of the tropics and led to accelerated rates of soil erosion. Also, the quality of the coffee suffered. The accelerated coffee bean maturation rate in the sun grown trees generated beans with lower levels of important flavoring chemicals and higher levels of increasingly bitter acids. It was a lose/lose/lose/lose proposition! In Central America alone, over 2.5 million acres have been deforested to make room for sun grown coffee plantations.

Coffea robusta is particularly well adapted to sun grown coffee systems. Its flavor profiles are not as high in quality as those of C. arabica, but its higher caffeine content makes it a desirable crop. Many sun grown coffee plantations are dominated by C. robusta trees. Interestingly, C. robusta trees are not self-pollinating. They require the spread of pollen from one tree to the next and are much more dependent on insect pollen transfers than C. arabica. The monocultural nature of the sun grown coffee plantations, though, and their inherent dearth of nectar producing wild plants coupled with the extensive use of pesticides in the management of the system greatly reduced the abundance of potentially beneficial pollinating wild insects.

Shade grown coffee in Guatemala. Photo by J. Blake. Wikimedia Commons

Coffee trees of all types need stable environments to grow and thrive. This has been one of the ongoing arguments in favor of planting coffee trees in shade coffee systems. The micro-environments of the shade plantations fluctuate much less than they do in sun grown coffee systems. These more controlled environments may even serve as buffers against some of the predicted temperature and moisture consequences of climate change. The need for consistent growing conditions is also one of the explanations for the superiority of high altitude grown coffee over most low altitude grown coffee. Cooler, less fluctuating temperatures and lower atmospheric oxygen levels slow down the coffee tree’s rates of synthesis and maturation and enable the high altitude grown beans to develop their full flavor profiles and potentials.

Back in 2017 I wrote about some very disturbing studies concerning the sustainability of coffee cultivation. A report by the Climate Institute of Australia explored the impact of climate change models on the global distribution of coffee trees. They found that projected rises in global temperatures would reduce coffee producing land areas by 50% by 2050. Impact of climate change (which includes not only rising average temperatures but also changes in weather patterns and cycles of drought and excessive rainfall) were especially severe at low latitudes and low altitudes. The worldwide, tropical “bean belt” will need to move out of the afflicted tropical zones and up mountainsides in order to find suitable sites to grow coffee. It is estimated that there are 120 million people in these zones whose economic livelihoods depend on coffee.

The recent awareness of the multiple benefits of shade coffee have included not only an economic side (lower production costs), an ecological side (reduced pollution and soil erosion and establishment of complex habitats for birds and other animals), and also an aesthetic side (shade grown coffee tastes better!). Climate change, though,  may be too much even for these coffee ecosystems unless new genetic traits from the wild Coffea species can be found to extend coffee trees’ growth tolerance ranges into the “new normal” of our climate changed world.

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Signs of Summer 8: Among Hemlock Trees

Photo by D. Sillman

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I am standing in the middle of an old growth hemlock stand that is tucked away off a hiking trail in Laurel Hill State Park. This four acre plot probably escaped logging because of confusion about the exact location of a surveyor’s line. Cutting a tree on someone else’s property was an expensive mistake (fines and reimbursement of the owner of three times the value of the logged trees and, possibly, even penalties for trespassing!). So, to avoid doing all of the work and only getting the privilege of paying many times over for it, disputed property lines often generated safe zones for fragments of primal forest.

Many of the hemlocks around me are impressively large. A few measure nearly four feet in diameter and stand one hundred feet tall. According to Kershner and Leverett  (2004) these trees range between 200 and 300 years of age. So, they are not even half way along on their potential life spans of 800 to 1000 years. There is a range of tree diameters and heights within the stand, which, I assume, reflects a distribution of ages.

The forest floor is covered with a thick layer of shed hemlock needles. Deep in the litter layer a slow process of decomposition is going on. The very top needles are relatively dry, but layers just below and on down to the soil surface are increasingly moist. The soil is black and wet. The thick, acidic mulch layer prevents many understory species from growing here. There is an open quality to this part of the forest. It is very easy to walk around. The mulch underfoot is soft and springy. Wood sorrel, wood fern, club moss, and polytrichium moss grow in scattered patches, and radiating out away from the hemlocks is a three dimensional cone of scattered and ever smaller hemlock seedlings.

Photo by Bonnachoven, Wikimedia Commons

The reality of this hemlock stand is an emotional experience. Intellectually, though, I know that these slopes of Laurel Hill were once densely covered with often pure stands of hemlocks trees, and I also know that these hemlocks were cut down in the late 1800’s and early 1900’s for their wood and to harvest their bark tannins. The clear-cut slopes, thanks to the resilience of Pennsylvania’s vegetative communities, reforested themselves in fast growing hardwood trees like red maple and black cherry and stump sprouting red oak but not, immediately, in hemlocks. Standing among these few surviving trees humbles my imagination to try to visualize what this primal forest was like. Contemplation of the immensity of the individual trees, the impact of the stand on the very climate of the site, and the overwhelming continuity of the former forest is awe inspiring. This a beautiful spot, but what a place it once was!

So, why were hemlock trees here? Why did this forest grow, and, very significantly, why is it growing back so slowly? To try to answer these questions, let’s start at the beginning of a single tree and imagine its life over several hundred years:

Photo by N. A. Tonelli, Flickr

To get a hemlock, you have start with a hemlock (to paraphrase Schleiden and Schwann’s Cell Theory statement, “omnis hemlockae et hemlockae” (“hemlocks always come from hemlocks”)). So, a mature, seed-producing hemlock had to have been right here because hemlock seeds do not travel very far from their parental tree source (Goldman and Lancaster 1990). Therefore, the parental trees of the hemlocks around me themselves stood very close to this very same spot. And, the parental trees of those trees, and their parents’ parents’ parental tree, and so on, were also right here or at least very close by. The generations of trees were separated by centuries or even millennia of time, but all of these trees stood trunk to trunk and branch to branch in this very space.  Where we see a hemlock forest there has been a hemlock forest for a very long time.

The parental tree of our example hemlock could have started to make cones when it reached 15 years of age, but if it were growing in the deep shade, reproduction might actually have begun much later on in its life. A hemlock can grow so slowly for one or two hundred years when light deprived that it scarcely makes growth rings (Tubbs 1977). In this suppressed state, energy is used to maintain existence with little left over for growth or reproduction. Removal of the shade suppression (say, when an older, nearby tree succumbs to disease, is thrown over in a wind storm, gets struck by lightning, or simply reaches the end of its possible life span) stimulates the young tree to rapidly grow and eventually reach its reproductive maturity..

Photo by K. McFarland, Flickr

Each hemlock tree has both male and female cones. The male cones’ pollen is dispersed by the wind and mostly falls in places where it will dry up and inconsequentially fail. A very small percentage of these shed pollen grains falls into the open scales of the upwardly directed ovulate cones and are thus given the opportunity to fertilize an ovum. Most of these pollen grains, though, even when they are “lucky” enough to be blown into an ovulate cones, also dry up and fail to accomplish fertilization (Nienstaedt and Kriebel 1955).

So, an infinitesimally small percentage of the pollen grains produced actually fertilize ova inside the female cones and make viable embryos and seeds! When fertilization does occur, the ovulate cone closes its scales around the seed and turns from its upward orientation to a downward, dangling position. The cone grows and then, as it and its seeds mature, turns from an initial yellowish green to purplish brown and then, as it dries, to a deep, dark brown. In mid-October the cone opens, and the seed, with its short, terminal wing, flutters downward to the litter surface probably just beneath or at least very close to the parental tree (USDA Forest Service 1974).

Photo by D. Sillman

Eastern hemlocks make cones frequently (two out of every three years) and a single tree can continue to make cones well into its fifth century of life (USDA Forest Service 1974). That’s a lot of cones and a lot of seeds! Very few of these seeds, though, ever get the chance to become a tree. Many of the seeds are eaten (by rodents, by insects, by squirrels)(Abbott 1962), many of the seeds dry out on the dry surface of the litter, and many others rot away when the litter layer is too wet (Le Madeleine 1980). Conditions have to be just right for seed survival. Many surviving seeds then don’t germinate because the ten week rest period at freezing temperatures didn’t occur so their dormancy was never released. Many other seeds don’t germinate because the temperatures after the dormancy release are too cold or too warm (optimally it should be 59 degrees F, but a range of 44 to 65 degrees F is tolerable). A very precise micro-environment on the forest floor is required to give the hemlock seed its shot at germination!)(Goldman and Lancester 1990). So, a massive number of seeds are needed to get just a couple of them through this dense ecological filter of catastrophic probabilities.

The seeds that germinate might have landed on a mound of soil and litter or maybe on a rotting stump or a rotting tree trunk. Its overstory must keep it shaded, though. Any increase in sunshine on the germination site will increase the rate of moisture loss and will quickly kill the seed or the seedling (Jordan and Sharp 1967).

After a year of growth the seedlings would be about one inch tall with a half an inch of roots extending down into the moist layers of the litter. The upper half inch of litter is very vulnerable to drying so even short period of drought can kill these young seedlings. Any seedling not in the deep shade, or any seedling not growing on a moist enough pile of litter will die (Goldman and Lancaster 1990).

By the second year, the seedling’s roots have extended deep enough into the litter layer that moisture delivery is more assured. The seedling’s chances of survival and ability to grow have greatly increased. Hemlock seedlings, as I mentioned before, can survive in deep shade. Even in conditions in which only 5% of full sunlight is available to the seedling, enough photosynthesis can occur to keep the seedling alive if only barely growing, and the seedling can persist in this state of suppression for one or two centuries (Tubbs 1977)!

When the seedling is 3 to 5 feet tall it is able to withstand the impacts of full, direct sunlight (Gladman and Lancaster 1990). Hemlocks an inch in diameter can be a hundred years old and some that are two or three inches in diameter can be 200 years old (Tubbs 1977)! The tiny trees we see growing around the parental hemlocks in our Laurel Hill site may have been growing and waiting for a very long time.

Photo by Pixabay, Public Domain

These young trees are very vulnerable to tree predators. White tailed deer readily browse young hemlocks as do cottontail rabbits and snowshoe hares (Abbott 1962, Anderson and Loucks 1979, Euler and Thurston 1980, Goldman and Lancaster 1990). The probabilities are very high that in the many decades the young trees sit well within reach of these browsing animals they will be consumed. And hemlocks are not capable of root sprouting (USDA Forest Service 1965), so destruction of the above ground mass results in the death of the tree.

But some trees, somehow and against all probabilities, survive all this, and are present when a light gap opens (a large, shading tree (maybe the young tree’s parental tree?) is wind thrown, struck by lightning or killed by defoliators or diseases). The opening of the overstory then allows young tree to rapidly grow.

Centuries pass. Our tree has steadily grown and is now nearly four feet in diameter and one hundred feet tall. It dominates its space in the forest and rains down seeds onto the forest floor around it every two out of three years. As mentioned previously, a very small number of these seeds ever germinate, and an even smaller number of the seedlings ever grow, but there is a slow, steady wave of hemlock seedlings growing out from around each of the seed producing trees. The limited, seedling nurturing micro-environments under the parent trees slowly expand as the parent trees grow. The seedlings are also encouraged or destroyed by the temperature and rainfall fluctuations of their growth site’s weather and climate patterns.

Photo by W. Hamilton

Hemlock forests grow from hemlock forests. The old trees are needed not only for seeds but also for the control of the forest floor environment. The slow recovery of a logged hemlock forest reflects the very slow return of the influence of the mature trees on the seedling nursery of its forest floor.

Are small hemlock stands like this one in Laurel Hill State Park sustainable? Can they continue to extend themselves at their edges and begin to knit together their old range and scope? Can they be “ecological crystals” that reform the old growth, hemlock forest? Looking at the edges of this site, I see hemlock needles mixing with fallen maple leaves and the slowly growing, outward curve of spreading hemlock seedlings.  I see the beginnings of some possibilities. Hemlocks live in time frames that are so very different from short-lived species like humans. What will happen here? I’ll get back to you in five hundred years and let you know how it’s going.

References for Eastern Hemlock:

Abbott, H. G. 1962. Tree seed preferences of mice and voles in the Northeast. Journal of Forestry 60 (2): 97-98.

Anderson, R. G. and O. L. Loucks. 1979. White-tail deer (Odocoileus virginianus) influence on structure and composition of Tsuga canadensis forests. Journal of Applies Ecology 16: 855-861.

Eckstein, R. G. 1980. Eastern hemlock in north central Wisconsin. Wisconsin Department of Natural resources, Report 104. Madison. 20 p.

Euler, D. and L. Thurston. 1980. Characteristics of hemlock stands related to deer use in east central Ontario. Journal of Applied Ecology 17:1-6.

Eyre, F. H. (ed) 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, D.C. 148 p.

Goldman, R.M. and K. Lancester. 1990. Tsuga canadensis (L.) Carr: Eastern Hemlock. pp 604-612, In, Burns, R. M. and B. H. Honkala (tech coord) “Silvics of North America: Volume 1, Confers.” U.S. Department of Agriculture, Agriculture Handbook 654. Washington, D. C.675 p.

Hepting, G. H. 1971. Diseases of forest and shade trees of the United States. U.S.Department of Agriculture, Agriculture Handbook 386. Washington, D.C. 658 p.

Hough, Ashbel F. 1960. Silvical characteristics of the eastern hemlock. USDA Forest Service, Station Paper NE-132. Northeast Forest Experiment Station, Upper Darby, PA. 23 p.

Jordan, J.S. and W.M. Sharp. 1967. Seeding and planting hemlock for ruffed grouse cover. USDA Forest Service, Research Paper NE-83. Northeastern Forest Experiment Station, Upper Darby, PA. 17 p.

Kershner, B. and R. T Leverett. 2004. The Sierra Club Guide the Ancient Forests of the Northeast. Sierra Club Books. San Francisco.

LeMadeleine, Leon. 1980. Seed-borne pathogens of hemlock seed from Argonne Experiment Forest. Evaluation Report NA-FB/U-8, January. U.S.Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry, St. Paul, MN. 4 p.

Nienstaedt, H. and H.B.Kriebel. 1955. Controlled pollination of eastern hemlock. Forest Science 1(2): 115-120.

Rogers, R.S. 1980. Hemlock stands from Wisconsin to Nova Scotia: transitions in understory composition along a floristic gradient. Ecology 61(1): 178-193.

Tubbs, C. H. 1977. Manager’s handbook for northern hardwoods in the north Central States. USDA Forest Service, General Technical Report NC-39. North Central Forest Experiment Station, St Paul, MN. 29 p.

U.S.Department of Agriculture, Forest Service. 1974. Seeds of woody plants in the United States. C.S.Schopmeyer, tech. coord. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, D.C. 883 p.

Willis, G.L. and M.S.Coffman. [n.d.] Composition, structure, and dynamics of climax stands of eastern hemlock and sugar maple in the Huron Mountains, Michigan. Michigan Technical University, Department of Forestry, Technical Bulletin 13, Houghton, 43 p.

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