Arapaho Bend. Photo by D. Sillman
Audio of Natural Areas of Fort Collins
Last week I described Deborah’s and my drive over to Fort Collins from Greeley. Our destination, on the north side of Fort Collins, was one of the “natural areas” that have been established and maintained by the city. On this trip we visited Riverbend Ponds while previously we had hiked around Arapaho Bend just a bit to the south.
The centerpieces of these natural areas are ponds and lakes that have primarily been created from the reclamation of old gravel pits. Gravel eroding down from the nearby Rocky Mountains over many millennia accumulated in great deposits all along the courses of the mountain-sourced rivers. Mining the gravel created deep pits which, through the foresight and efforts of environmental groups in Fort Collins and Greeley, have been flooded and transformed into very productive aquatic and riparian habitats.
Over 200 species of birds feed in, nest in or migrate through the ponds and wetlands of these natural areas, and about a fourth of these species can be seen here year-round. The local and national Audubon Societies have designated these natural areas as “Important Bird Areas,” and their presence has transformed the spring and fall migration patterns of many dozens of species (including Canada geese, American white pelicans, double crested cormorants, pied-billed and western grebes, American avocets and many more waterbirds!) and provided birdwatchers with a rich venue for observation and discovery.
Riverbend Ponds. Photo by D. Sillman
The ponds are stocked by the Colorado Division of Wildlife with warm water fish including large-mouth bass, crappie, channel catfish, yellow perch, sunfish and bluegills. They are very popular spots for recreational fishing and, in spite of the relatively heavy rates of use are very well maintained and remarkably free of litter.
Walking around the ponds in these natural areas you can feel the looming presence of the dark foothills to the west and can view the tallest peaks of the Rockies in their
Foothills from Riverbend Ponds. Photo by D. Sillman
gaps. You can also see pieces of the original ecosystems of the site: there are glimpses of short grass prairie and dry sagebrush steppe and suggestions of a riparian forest dominated by cottonwoods. You also see very clearly, though, the impact of human use of the area (about a third of the plant species in these sites are exotic species many of which are classified as invasive).
There are 238 different plants at the Arapaho Bend Natural Area and 150 of them are native. Looking down the plant list, it is notable that 48 of the plant species are grasses reflecting the grassland history of the site. Of the 17 exotic grasses, Kentucky bluegrass and tall fescue (major components of suburban lawns) are quite prominent. Also, smooth broom (another exotic grass species) has made a continuous cover along several of the waterways. This grass cover will inhibit the establishment of cottonwood seedlings and disrupt the potential regeneration of the cottonwood-riparian forest since cottonwood seeds require wet, bare soil along with direct sunlight for germination.
Cottonwood tree. Photo by A. Gordon, Public Domain
The cottonwood tree is a keystone species in these plains, riparian ecosystems. Many species of plants and vertebrate and invertebrate animals depend upon it for food, shelter, shade and protective refuge. The growth patterns of the cottonwoods here in the natural areas are quite different from the “natural” conformation of a cottonwood forest (which is also called a “bosque”). The trees in Riverbend Ponds and in Arapaho Bend are mostly growing as single, isolated trees along the pond banks or edges of the streams. There is little clustering or clumping of trees into an integrated forest stand, and, therefore, little synergistic impact of a complex forest habitat on the physical and biological components of these ecosystems. Further along the Cache la Poudre River (which is the stream that runs through these natural areas) there are some newer bosques that extend ten or twenty yards away from the stream. There are also a few older bosques that extend eighty to one-hundred and eighty yards away from the stream. These younger, narrower bosques reflect the extent of the relatively recent, engineered control of flooding along the river (flooding being essential to the germination and growth of the cottonwood seedlings), while these older, wider bosques reflect the historical extent of the seasonal flooding.
Rabbitbrush in fall (with honeybee). Photo by D. Sillman
Rabbitbrush (Ericameria nauseosa (formerly called Chrysothamnus nauseosus)) is another plant of note in both the Riverbend Ponds and Arapaho Bend Natural Areas. Often called “gray rabbitbrush” or “rubber rabbitbrush,” this plant is a perennial, deciduous shrub that typically grows to heights of two to four feet. Through most of the spring and summer, rabbitbrush, with its gray-green leaves and rounded growth pattern, looks a great deal like sagebrush at a distance. In fact, many on-line pictures of summer “sagebrush” are actually pictures of rabbitbrush! Up close, though, the two plants are very different. Sagebrush leaves, when crushed have the rich, herbal scent of sage, while rabbitbrush leaves, when crushed have a pungent, and to many, foul odor. Also, sagebrush leaves are rather wedge-shaped and have three distinct “teeth” on the distal, free edge (these three teeth, in fact, generate the species component of the scientific name for sagebrush (Artemisia tridenta)). Rabbitbrush’s leaves, on the other hand, are long and narrow and lack “teeth.”
In late summer and on through the fall, though, rabbitbrush stands out clearly from any surrounding sagebrush because of its abundant display of large, yellow flower clusters. These flowers are an important source of late summer and fall nectar and pollen for a large number of insects including many butterflies and bees. Last September, as we walked through Arapaho Bend, we saw numerous, Monarch butterflies who were completing the final legs of their fall migration down to the mountains of Mexico, feeding avidly on the nectar from the rabbitbrush flowers.
A great diversity of subspecies make up the broad rabbitbrush community which extends all across the western portion of North America. Rabbitbrush grows on arid soils, disturbed soils, abandoned farmlands, roadsides, gaps in montane forests, and is extremely tolerant of drought and low nutrient, alkaline soils. Few grazing animals feed on it extensively although mule deer and pronghorns do consume it more readily than any domesticated grazers like cattle or sheep.
Rabbitbrush in spring. Photo by D. Sillman
Rabbitbrush has been called a “chemical factory” because it synthesizes so many different chemical compounds (many of which, undoubtedly, function to inhibit the magnitude of grazing animal damage). Native Americans used rabbitbrush to make a yellow dye and also to brew a medicinal tea. The U.S. Military in World War 2 explored the use of rabbitbrush as a non-tropical source of rubber. The sap of rabbitbrush is rich in rubber compounds (hence one of its common names). There is also ongoing research to see if any of the compounds made by rabbitbrush can be used as insect repellants, or anti-malarial drugs, or nematicides!
Rabbitbrush is an extremely important plant in arid soil systems. Its very deep root system not only supplies the plant with water but also brings important nutrients up from very deep layers of the soil profile. The deciduous nature of the plant then cycles these nutrients to the soil surface in its abundant seasonal leaf fall at the onset of winter. The nutrients released from these decaying leaves are then readily available to a large number of other plant species.
It is interesting that although this plant is called “rabbitbrush,” rabbits have very little to do with it. Rabbits seldom eat its leaves, but likely utilize the dense shrubby growth as a shady refuge in their hot, dry steppe and grassland ecosystems. Maybe someone just happened to see a rabbit running out of a cluster of bushes and named them accordingly! Maybe some abundance of rabbits and an abundance of these plants just caused someone to make a mental connection.
Photo by D. Sillman
After our walk around Riverbend Ponds we went to a wonderful nursery to look for yuccas and cactuses. Here is a picture of the ones we adopted!