Western range issues can be seen from space
BILLINGS, Montana––No one needs to take anyone else’s word about the condition of the western range. Monitor Google Earth for a while and ancient sages will tell you all about it.
First, though, it is necessary to understand the evolutionary and ecological relationships among sagebrush, grasslands, and forest.
Sagebrush, grasslands, and forest are all essential components of the western wildlife ecology, from the northern Rocky Mountains of Alberta south to the Sonoran desert of northern Mexico. All three habitat types are clearly visible from space, often intersecting and partially overlapping.
Sagebrush, grassland, or forest?
Advocates for controversial species––including wild horses, beaver, bison, bighorn sheep, elk, mule deer, sage grouse, wolves, grizzly bears, prairie dogs, and pumas––are all in gist disputing with ranchers over how much habitat, of which types, should be allocated to wildlife by federal and state land management agencies, as opposed to sheep and cattle.
But underlying the frequent furors over the animals and their specific habitat needs is the ecological reality that whichever animals are favored, the actual choice to be made is among whether sagebrush, grassland, or forest is to be most encouraged.
Rainfall and runoff from snowmelt, or lack thereof, often limits the leeway for choosing.
Why beaver & prairie dogs are “keystone” species
Certain species, especially dam-building beaver, help significantly to slow the rate of water loss to runoff and evaporation, and therefore improve the habitat for many other species.
Several other species, notably prairie dogs and ground squirrels, dig burrows that help water to soak into the earth, as well as providing habitat for species including badgers, blackfooted ferrets, burrowing owls, snakes, and tortoises.
Species who eat and transport acorns and pine seeds, mostly birds and rodents, help to replant tree cover that shades and cools habitat, eventually encouraging more rainfall. The tree roots then help to retain the runoff.
But this process requires from decades to centuries to transform any given locale, and is easily set back by drought, insect infestations that kill trees, wildfires, or premature logging, meaning logging that is done before enough leaves or needles accumulate on the forest floor to nourish regrowth.
No species regulates rain & snow
Though some animal species help to conserve water more effectively than others, no animal species directly increases the amount of rain and snow that falls.
Grass-grazing animals, in general, tend to help grasslands to regenerate. Grasses have evolved to be grazed, relatively rapidly regenerating if allowed a few weeks to grow back after being eaten down. But grass-grazing animals can expand grasslands only if there is precipitation and topsoil enough for windblown seeds and undigested seeds in droppings left at the margins of the habitat to take root and grow.
Most of the controversies pertaining to the presence and relative abundance of cattle, sheep, bison, elk and horses on the western range amount to disputes over which species will be allowed to eat the limited grass supply and drink the relatively scarce available fresh water.
Just grow more grass?
In abstract theory such conflicts could be prevented, if enough grass could be grown to feed all of the animals who want and need it.
Reality, though, especially since the effects of global warming became evident, is that most of the western range does not get enough precipitation to grow grass at an optimal rate.
Suppose all the cattle and sheep now on range leased to ranchers by the Bureau of Land Management were to be removed and sent to slaughter tomorrow, as many conservationists have vocally wished since the heyday of EarthFirst! in the 1980s.
Suppose those cattle and sheep were never replaced by other domestic stock, and that cattle and sheep were never again fed with hay and grain collected from the western range.
Even if all of that somehow came to pass, despite the political reality that such changes have a a snowball’s chance amid global warming of occurring within the foreseeable future, rain-and-snow-irrigated pasture enough no longer exists to keep millions of bison, elk and wild horses grazing, defecating seeds and fertilizer, and then moving on before their hooves damage the topsoil, as these species did for hundreds of years in pre-settlement times.
When sagebrush succeeds grass
Parched grasslands, if overgrazed, tend to go toward sagebrush (some say “revert” to sagebrush, but most sagebrush habitat has not been grassland within millennia, and the converse.)
Like “grasses,” which in nature rarely grow as a single-species monoculture, the habitat called “sagebrush” is a constellation of species, many of them closely related, growing in partially competitive, partially symbiotic confluence.
Sagebrush in general tends to thrive in dryer soils than grasses, grows more slowly, and is less nutritious for most grazing animals than grasses, though cattle, sheep, wild horses, elk, and bison all will consume sagebrush after the grasses in their range area become depleted.
Sagebrush is also less nutritious than leaves and green twigs for browsing species such as mule deer and whitetail deer, but mule deer in particular often depend on sagebrush to sustain them when seasonal browse is depleted.
Pronghorn: a special case
Only pronghorn antelope, the least numerous and least controversial hoofed species common to the western range, seem to consume sagebrush as their food of preference.
Mostly smaller than mule deer, though their size range overlaps, and much more thinly distributed, pronghorn may be the only western grazing or browsing species not specifically represented by an influential dedicated interest group.
By far the fastest North American mammal, evolving to evade the long extinct North American cheetah, pronghorn have been on the western range since before the Ice Ages, longer even than coyotes, who with pumas are their major predators.
Unregulated hunting appeared to threaten pronghorn a century ago, but at present pronghorn appear to be among the species best adapted to the effects of global warming.
Sagebrush did not evolve to be fodder
Because sagebrush regenerates slowly, compared to grass, sagebrush is poorly suited to sustain intensive consumption by hooved animals who––unlike pronghorn––eat a lot before moving on.
Typically sagebrush will colonize overgrazed and eroded former grassy habitat, but sagebrush in depleted habitat can only thrive if it is not overgrazed as the grasses were.
Herein lies one of the major points of controversy involving cattle, sheep, and wild horses. Cattle and sheep, if not overstocked, tend to be removed and sent to slaughter at the end of each growing season, before grasslands become so depleted that the livestock lose weight and turn to eating less nutritious growth.
Home on the range
Wild horses remain on the range year-round, therefore depleting what grass remains after cattle and sheep are removed. Wild horses then tend to trample sagebrush in search of grass, and finally consume sagebrush until the grass recovers.
This activity tends to offset the role of wild horses––and sheep and cattle––in converting grasslands to sagebrush habitat through overgrazing and dust-bathing.
Meanwhile, and also of note, former grassland that goes to sagebrush rarely returns to grassland without intensive human intervention.
Overgrazed sagebrush tends to go toward severely eroded soil and bare rocks.
Juniper & pinyon pine
In certain regions, such as the Pine Nut Mountains of Nevada, juniper and pinyon pine may grow in cracks that hold moisture, and may eventually mature into forest, but grazing and browsing animals meanwhile struggle or starve.
Bureau of Land Management scientists in 2016 cited protecting sagebrush habitat for a threatened sage grouse subspecies and inhibiting the spread of juniper and pinyon pine as reasons for reducing the wild horse population of the Pine Nut Mountains, now four times the estimated optimal carrying capacity.
Objected Wild Horse & Burro Fund wildlife ecologist Craig C. Downer, “The increase of these ancient woodland communities is a healthy response to global warming. Pinyon pine as well as juniper provide food and shelter to the pinyon jay, Clark’s nutcracker, the pinyon mouse, the black bear, and many other birds, reptiles, mammals and insects, including pollinators.”
Mature forest does not feed many grazers & browsers
But while all of this is true, pinyon pine and juniper do not provide much food to either wild horses, other grazing animals, or browsers, though pronghorn, mule deer, whitetail deer, and jackrabbits will eat juniper bark in absence of other food sources.
Mature forest habitat in general does not favor grazing species, or browsers after tree canopy closes in, keeping understory from receiving sunlight.
What you can see using Google Earth
With all of the above information in mind, it is a relatively simple matter for anyone concerned to go to Google Earth and zero in on grazing and browsing habitats such as the Pine Nut Mountains; the million-acre Fort Belknap Indian Reservation in northern Montana; the Pryor Mountains Wild Horse Range south of Billings, Montana, extending into Wyoming; the National Bison Range at Charlo, Montana; and the greater Yellowstone region of Wyoming, Idaho, and Montana.
Healthy range, whether most heavily used by wild horses, cattle, sheep, or bison, will be covered chiefly by green grass, albeit that much of the grass may be fading to brown and yellow in mid-to-late-summer heat and drought. At maximum Google Earth magnification the resident large animals can often be identified by species and be counted.
What you won’t see, where
Range consisting mainly of dense sagebrush, recognizable as a lighter slightly bluish-green, will tend to have few if any horses, cattle, sheep, or bison on it.
Overgrazed and damaged habitat tends to feature sparse grassy highlands, visibly eroded slopes, and broken patches mixing clump grass and sagebrush below the erosion. In general, as the grassy areas become less hospitable to grass, sagebrush claims the territory, to the extent that it can, but will not become dense if hooved animals continue to trample the sagebrush patches, either to eat whatever grass can still be found, or eat the sagebrush itself.
Also of note, healthy range habitat will have visible water sources, such as streams or ponds. Where streams or ponds have become mere mud-wallows by midsummer, there will usually not again be water enough to sustain either large animals or regenerate grass until winter precipitation begins in late fall.
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In addition to our own observations made during a recent 3,000-mile trek through the rangelands of British Columbia, Alberta, Saskatchewan, Montana, Wyoming, Idaho, and Washington, this article has been informed in part by:
Effects of feral free‐roaming horses on semi‐arid rangeland ecosystems: an example from the sagebrush steppe, by K. W. Davies, G. Collins, and C. S. Boyd, Ecosphere, 22 October 2014; https://doi.org/10.1890/ES14-00171.1
Impacts of Wild Horses, Cattle, and Wildlife on Riparian Areas in Idaho, by Molly M.Kawecka, John P. Severson, and Karen L. Launchbaugh, Rangelands, April 2018; https://www.sciencedirect.com/science/article/pii/S019005281830018X
Habitat Use by Feral Horses in the Northern Sagebrush Steppe, by David Ganskopp and Martin Vavra, Journal of Range Management 39(3), 1986; https://journals.uair.arizona.edu/index.php/jrm/article/download/7975/7587
Influences of Free-Roaming Equids on Sagebrush Ecosystems, with a Focus on Greater Sage-Grouse, by Erik A. Beever and Cameron L. Aldridge, Free-Roaming Equids in Sagebrush Ecosystems, Studies in Avian Biology 38, 2011; http://www.nrel.colostate.edu/assets/nrel_files/labs/aldridge-lab/publications/Beever&Aldridge_2011_Equids&GRSG_SAB_Ch14.pdf
American Wildlife & Plants: A Guide To Wildlife Food Habits, by Alexander C. Martin, Herbert S. Zim, and Arnold L. Nelson, 500 pages, McGraw-Hill Book Company, 1951.