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Wildlife and Habitat
Nevada is home to West-wide common species of wildlife and plants, such as mule deer and sagebrush, as well as endemic and rare species that have adapted to unique habitats, such as the Railroad Valley springfish (Crenichthys nevadae) and Las Vegas bear poppy (Arctomecon californica).  The Nevada Division of Wildlife (NDOW) and U.S. Fish and Wildlife Service (FWS) have primary responsibilities for protecting and managing wildlife according to various state and federal regulations and special management designations. Most of the wildlife habitat is managed by the BLM, USFS, and FWS, which combined control the use of land on about 80 percent of the state. The Nevada Division of Forestry also has certain vegetation protection and management responsibilities on state and private land for designated plant species.
Before state and federal agencies regulated hunting and fishing, populations of many native species plummeted due to lack of awareness and carelessness. Now that state and federal agencies oversee hunting and manage wildlife and habitats, better data are available on the numbers and distribution of game species. NDOW routinely gathers information from hunters and fishers, and with fees paid by hunters, conducts surveys and models population dynamics of game species. In addition, scientists have gained more knowledge about imperiled animal and plant species. However, these species constitute a small fraction of Nevada's total biodiversity. A frequently stated theme regarding our biological resources is the dearth of information on the vast majority of plants and animals that populate our ecosystems.
One way to report on the overall status of Nevada's wildlife and plants is to group species according to designations that indicate their management or conservation status (Table 3-1). For example, native and endemic species are classified and tracked to account for the state's overall and unique biodiversity. Game species are wildlife that are hunted, fished, or trapped by sportsmen.
Federally threatened and endangered species are those whose numbers have dwindled and are believed to need special protection and recovery actions in accordance with the Endangered Species Act of 1973, as amended. Rare and sensitive species are identified during periodic review of the state's inventory of native species that takes into consideration the population size and distribution, level of threats and corresponding management attention, and the biology of the species.
Each species that has become extinct or extirpated (i.e., no longer exists in part of its native range, i.e., Nevada) represents an unfortunate loss and a reminder that careful resource management and development is essential for maintaining Nevada's biological diversity. The number of mapped rare species per thousand square miles is greatest by far in the Sierra Nevada ecoregion (81), followed by the Mojave (16), Great Basin (6), and Columbia Plateau (5) (Nevada Natural Heritage Program, 2001a).
Adequate habitat availability and quality largely determine the abundance and distribution of all wildlife species. Over the short term, wildlife populations and distribution fluctuates with winter precipitation patterns that in turn dictate seasonal plant growth and habitat conditions. Successive drought years can be particularly stressful. Generally, the larger and more mobile animal species have adapted to extremely variable conditions by moving among suitable habitats, thereby maintaining healthy, widely distributed populations.
Wildlife species restricted to small, unique habitat patches or with limited mobility are more sensitive and vulnerable to human alteration of the environment. Some of the most immediate wildlife diversity concerns occur where loss of unique, specialized native habitats is imminent. Yet, even mobile species are vulnerable to the cumulative fragmentation and deterioration of natural habitats. The range-wide decline of sagebrush ecosystems and sage grouse population is an example. Another example is found in the Mojave Ecoregion, where unique pool, spring, and pupfish populations that occupy widely distributed springs have been federally listed as threatened and endangered.
The vast openness of our state can give the impression that much remains wild and untrammeled. The practical reality is that the cumulative effects of land use and resource management activities, historically and today, have altered the structure, function, integrity, and biodiversity of wide-ranging and small, unique ecosystems. Progress in managing and improving remnants of native aquatic and terrestrial habitats, must keep pace with rapid population and economic growth. Otherwise, the likelihood grows that more species will be designated for mandatory protection under federal and state laws. By the time listing of a species as threatened or endangered has occurred, substantial ecological and economic losses and regulatory costs already are incurred, which are likely to extend far into the future.
Interest in balancing the land and water needs of human activities with those of native ecosystems has grown with Nevada's population. State, federal, and local government, industry, and citizens are working on joint conservation plans intended to ensure that viable populations of vulnerable species will be sustained.
Relatively new tools include multi-species habitat conservation plans, conservation agreements, and the acquisition of conservation easements, land, or water rights. Also, resource managers are re-examining approaches to the control of floods, fires, and other natural disturbances for the purpose of determining how ecological benefits of such phenomenon can be safely and economically obtained. Species benefiting from specific collaborative initiatives include the Desert tortoise and other sensitive Mojave Desert species, the Amargosa toad, Columbia spotted frog, Lahontan cutthroat trout, Virgin River spine dace, and Greater Sage Grouse. However, 644 animal and plant species currently are considered to be rare or sensitive. Keeping these populations at safe levels while demand for land and water development expands will depend upon greater investment in coordination and advance planning to sustain existing high quality habitats and restore suitable sites.
Plants
The foundation of healthy wildlife populations and habitats is a diverse mix of native plant communities. Nevada's floral diversity is enormous. Botanists estimate roughly that 2,800 native species live in the state, of which 139 are endemic. The great variability in vegetation provides many different habitat niches and promotes diversity of associated animal life found here. Many plants
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A Wyoming big sage / Sandberg's bluegrass community type in Eureka County is pictured. Sagebrush ecosystems have been altered slightly to severely throughout the state. Sparse occurrence of forbs and grasses between shrubs is indicative of the reduced plant diversity and cover found in intensively used sagebrush. Ecological changes can be subtle but substantial over time. Removal of understory cover reduces exposes soil to sun and erosion, invites nonnative weeds to invade, oversimplifies the food web, and alters the availability of usable forms of nutrients and energy.
Photo by Eric Peterson, NNHP. 2002. |
are annuals, only living above ground for a short period of time - a necessity where daytime temperatures can exceed one hundred degrees and annual evaporation exceeds four feet to eight feet north to south. Trees and shrubs have many physical adaptations to access and conserve water, such as enormous root structures, waxy leaves, and the ability to drop leaves and become dormant during extreme dry periods.
Vegetation occurs in broad patterns, or zones, that reflect physical and biological factors, including climate zone, geology, landform, soil type, and inter-relationships with other plants and animals. Vegetation zones consist of commonly associated species and are often classified by dominant plant species or position in the landscape. Since precipitation and temperature strongly influence the distribution and species composition of vegetation, the zones transition from south to north and from warm, dry valleys upslope to cooler, moister mountain canyons and ridges. In Nevada, vegetation zones are identified as alpine, montane, pygmy conifer, sagebrush, blackbrush, saltbush or shadscale, Lower Mojavean, and absolute desert. Sand dunes, riparian, and lakes and ponds are "azonal" features that occupy a relatively small area of each vegetation zone, but occur frequently. Within a zone, distinctive plant communities can be found, which are generally characterized as forest, woodland, meadows or grasslands, and shrublands (Charlet, 1998).
Because vegetation zones describe broad, landscape scale patterns of floral diversity, relatively rapid or distinctive changes in species composition, boundaries, continuity, or ecology of a vegetation zone should be seen as signals that significant natural or human stresses are at work and special management attention may be needed. The vegetation zones showing signs of extensive changes are the sagebrush, pinyon/juniper woodland, saltbush, and riparian zones. Contributing factors variously include excessive grazing by livestock, wild horses, and wildlife; expansions of non-native grass and weed species; suppression of wildfire in fire-maintained ecosystems; bigger and more frequent wildfires; a warming in certain climate zones; fertilization effect from higher atmospheric carbon levels; deteriorated watershed conditions; and, conversion of land for urban, agriculture, mining, and transportation developments. Two zones of special statewide concern are the riparian and sagebrush zones.
Historical loss and deterioration of riparian zones and wetlands is extensive. Occupying a small fraction of the landscape, riparian and wetlands contribute greatly to biodiversity, as well as the production of clean water. These areas produce large amounts of biomass that provide food and habitat for many forms of wildlife. Riparian zones are found in moist soil zones between open water and drier upland sites, and traverse all vegetation zones. Since water supplies are limited, the much wetter riparian areas have a greater concentration of birds, fishes, bats, insects, and plants. Riparian corridors are critical habitat for breeding, feeding, and migration, yet are also the most impacted by water diversions, grazing, and various other uses. According to one reconnaissance level study, more than half of the state's riparian and wetlands have been converted to other land cover types (Dahl, 1990).
The sagebrush is the state flower, but that is not why declining land coverage and quality of sagebrush habitats is of general concern. The sagebrush zone contains many subtly different plant communities covering an enormous portion of Nevada, about 30 million acres.
Prior to settlement, native sagebrush communities commonly contained a mix of shrubs, grasses, and forbs. Since settlement, use of the Great Basin sagebrush zone for ranching, wild horses, and big game species has been emphasized. More recently, cheatgrass has invaded millions of acres, forming monocultures where fire recurred and occupying voids in the shrub understory where native grasses and forbs have been removed. In other parts of the sagebrush zone, the shrubs are overcrowded, which, coupled with flammable cheatgrass, creates extensive beds of fuel for wildfires.
Wildfires of catastrophic proportions have become more frequent in altered sagebrush ecosystems. The decline in the state's sage grouse population is one of several landscape scale biological indicators that the functions and values of sagebrush ecosystems are serious and widespread. Comprehensive statewide assessments detailing the magnitude of loss and degradation of riparian and sagebrush zones in Nevada are generally lacking. Public discussion and decision-making about changes in the sagebrush zone would be better informed if more comprehensive scientific documentation concerning Nevada-specific circumstances was available. Detailed mapping and data analyses of the composition, ecological status, and threats to sagebrush and riparian plant communities is necessary to provide a modern information base as part of the planning process to improve land use practices, management strategies, and rehabilitation and restoration techniques.
Fungi
For many people, the mention of "fungi' brings to mind mold in forgotten parts of the refrigerator, or mushrooms at the grocery. In fact, there are nearly 70,000 species of fungi known worldwide, and many thousands more as of yet unclassified. Fungi are very diverse and many are important. Consider the yeasts used to make bread or beer, Penicillium chrysogenum (the source of penicillin), the beautiful but deadly Amanita mushrooms, delicious wild morels that pop up in recently burned areas, and the ubiquitous lichens on trees, rocks, or even soil. While most people think of fungi as plants, they actually form their own kingdom separate from plants and animals. Surprisingly, fungi are more closely related to animals than to plants. However, fungi are far less studied than plants and animals, and this is especially true in Nevada.
No checklist of species exists yet for fungi in Nevada. However, the collection at the USDA's Systematic Botany and Mycology Laboratory in Maryland has nearly 1000 species of non-lichen fungi from Nevada, and there is a preliminary checklist of about 300 species of lichens. The total number of lichens extant in Nevada will likely double to about 600 before surveys are complete. Lichens are unusual fungi that host colonies of algae growing in close association. In this symbiotic relationship, the fungus receives energy stored by the algae through photosynthesis, and the algae reside in a more hospitable environment. While some lichens reveal the green color of the algae growing within them, most have strongly colored pigments, which shield the lichen from harmful UV radiation, much like a sun-screen lotion. Common colors include brown, white, yellow, and orange.
The slow growth of lichens on rocks in arid regions makes them useful to anthropologist for dating cultural events (e.g., the age of a petroglyph). Lichens perform many functions in ecosystems, including forage, nesting materials, and nutrient supply. Beard-like lichens in some of Nevada's conifer forests likely provide foods for squirrels and other mammals. Greater Sage Grouse have been observed eating lichens on rocks during Nevada's cold winters, probably to get liquid water when everything else is frozen. Perhaps the most important function of lichens in Nevada is the formation of biotic soil crusts. These crusts, which also include mosses and free-living algae, form a deeply textured cover over soil in the spaces between plants, primarily in non-forested arid lands. Many crust forming lichens convert atmospheric nitrogen to a nutrient form usable by plants, increasing the nutritional value of forage. Biotic soil crusts also reduce soil erosion and surface runoff by absorbing raindrop impact. Although more research is needed, preliminary data suggest that crusts can inhibit cheatgrass germination.
Crusts are very sensitive to ground disturbances. Intensive livestock grazing nearly eliminated biotic soil crusts from much of the western landscape. Where crusts remain, decades old off road vehicles tracks can be seen. Native grazers undoubtedly impact the continuity of crusts, but their numbers and population densities are much smaller. Crusts are also killed by severe wildfires, though apparently they can survive light fires. In the driest areas of the Mojave Desert, biotic soil crusts may require several centuries to re-occupy disturbed sites. Fortunately, in moister sagebrush habitats, crusts should begin to recover within a couple decades and form reasonably well developed communities after a few more decades.
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