Signs of Winter 10: Bison, Elephants and Whales (part 1)!

My front yard prairie in December. Photo by D. Sillman

(To listen to an audio version of this blog, click on link … Bison, elephants and whales part 1

Looking out at my tiny, front-yard, shortgrass “prairie,” I wonder if the brown, curled-over buffalo and blue grama grasses that are in their very quiet winter phases will need something to release them from their tame domesticity (see Signs of Summer 8, July 29, 2021 for a discussion of my grassland!). There’s not enough grass out there to support even a single bison or pronghorn, but having some grazing mammal occasionally clipping the tops of the grass plants and breaking up the soil surface with their sharp hooves might be just the force needed to stimulate growth and increase water infiltration and root aeration.

We have so many breeds of toy dogs, why don’t we have toy grazing animals for tiny (‘toy-sized”) ecosystems?  Many ecosystems need a touch of creative destruction in order to be sustainable!

Maybe there are no “toy grazing animals” available for sale or rent, but there once were many, regularly sized versions of these keystone species in a wide variety of ecosystems. Sadly, most of them today are greatly reduced in numbers!

American Bison:

Photo by RedGazelle123, Wikimedia Commons

The vast short-grass prairie once stretched across the million-plus acres of the Great Plains of North America. This prairie and its buffalo and blue grama grasses sustained the great herds of American bison up until the end of the Nineteenth Century. Possibly, sixty million bison (or, one per every 12 acres of prairie) roamed, ate, trampled, urinated on and defecated on this great expanse. It is estimated that the bison consumed up to two-thirds of the grass production of this ecosystem (Signs of Fall 5, October 10, 2020) and via their physical impacts and deposition of urine and feces stimulated grass growth and kept the prairies vital and green.

A single bison produces 7300 pounds of feces a year and 11,680 pounds of urine! The National Park Service indicates that over three hundred species and over one thousand individual insects can live in just one American bison dung pat! Also, over a two week period a single bison pat produces three thousand flies (great food for all sorts of birds, bats, arachnids and reptiles!).

Bison dung. Photo by R. Bair, Flckr

The discretely deposited bison dung pats are rapidly spread across an expansive area of soil not only by trampling by the bison but also by the frenetic activity of armies and armies of dung beetles! The dispersal of these vital dung nutrients stimulated grass growth all across the bison’s range which in turn provided fresh forage not only for bison but also for the multitudes of other grazers that also occupied this ecosystem. Further, as the bison trimmed down the grasses more sunlight could reach the soil surface stimulating the germination of new plants and their overall growth.

In a paper published two years ago in the journal Agriculture, Ecosystems & Environment (July, 2019), Hillenbrand et al. found that shortgrass prairie sites in South Dakota that were grazed by bison had increased fine litter cover, improved water infiltration rates, 200 to 300% increases in available forage, improved plant composition, decreased numbers of invasive plants, and decreased areas of bare soil patches! This “bison impact” on these prairie ecosystems was far from subtle!!

But then, suddenly, all (or at least most) of the American bison were gone! By 1889  there were only 541 American bison left, and, fortunately, the mass slaughter stopped. Today there are 500,00 bison in North America. Some 30,000 of these animals live on public lands but only 15,000 or so are wild and free ranging. The great bulk of the remaining bison are kept in private herds where they are culled and harvested for their meat. Most of the Great Plains is bison-free, and we are just beginning to appreciate how much the soils and the natural flora and fauna of the prairie suffer for the lack of this vital, keystone species.

Elephants:

Forest elephant. Photo by N. A. Nazeer, Wikimedia Commons

The two types of African elephants are defined by the ecosystems that they inhabit. There are “forest” elephants that live in the tropical rain forests of the continent, and “savannah” elephants that live in the broad, tropical grasslands.

The keystone nature of forest elephants have only recently been recognized (See, Signs of Fall 3, October 3, 2019). The African rainforest is second only to the Amazon rainforest in its size and scope and influence on global water and carbon cycles. There are a number of interesting differences between these two great, tropical ecosystems, though, and the lack of large herbivores in the Amazon is one of these. The Amazon’s “elephant-like” herbivores (which included the giant ground sloth, the gomphotheres and the 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. Therefore, 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.

Looking more closely at this, researchers in the Democratic Republic of Congo (where forest elephants were extirpated 30 years ago) and in the nearby Republic of Congo (where forest elephants have only recently been removed from their rainforests) examined the tree distribution and carbon compositions of their rainforests. They found that forest elephants regularly trample trees that are less than a foot in diameter and that they feed preferentially on relatively fast growing, soft-wooded tree species. As a consequence of their trampling and feeding more sunlight reaches the forest floor (stimulating tree seedling growth) and water availability to these forest plants is increased. Larger, slower growing, longer lived tree species are favored in an elephant impacted rainforest, and these trees store significantly more carbon than their smaller, faster growing counterparts.

Forest elephant group. Photo by USFWS, Wikimedia Commons

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 21^st 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.

Savanna elephant. Photo by B. Dupont. Wikimedia Commons

Savannah elephants are the engineers of their lush grasslands ecosystems. They create and help to maintain these vast, tropical grasslands via their extensive trampling, the creation of systems of well-worn paths through the countryside and via active destruction of trees and shrubs. They dig and expand deep waterholes, disperse seeds of a broad array of plants and produce astonishingly large amounts of nutrient-rich dung which, like the dung of the American bison, is spread about not only via the trampling of the herds but also by the action of great armies of dung beetles. This dispersed dung then supports vast populations of decomposer invertebrates (which are the base of many food chains) and, eventually, generates the nutrient base for the surrounding vegetative community.

Savannah elephants feed preferentially on grasses but also consume many species of trees and shrubs. They can be quite destructive in their feeding and frequently push over large trees in order to browse tender leaves or ripening fruit. An elephant-browsed landscape is often littered with dozens of downed, up-rooted trees that often have large soil balls still clinging to their roots.

During the dry season, the grasses are much less nutritious than they are during the wet (or “growth”) season. This forces the elephants to consume more and more woody vegetation. Their dry-season browsing often destroys extensive stands of trees and opens up the landscape to the growth of more and more grass.

Savanna elephant. Photo by B. Dupont. Wikimedia Commons

An active, adult savannah elephant can eat 600 pounds of vegetation a day (although a daily average of 300 pounds of forage for free-roaming elephants may be a more reasonable estimate). These almost constantly feeding elephants also almost continually defecate (15 or 20 times a day!) producing two to four hundred pounds of dung per individual per day (each elephant, then, generates 40 tons of dung a year!). The dung beetles really have their work cut out for them on the elephant-occupied savannahs!

There are, according to the World Wildlife Fund, about 400,000 savannah elephants in Africa today. Just eighty years ago, however, there were possibly five million savannah elephants in Africa! The dwindling vigor and stability of the African savannahs is in large part attributable to the decreased presence of these vital “ecological” engineers!

Next week: whales!