Threatened Habitats
Learn more by visiting the links to threatened habitats, below. Learn more at Threats to Forests and Wildlife under the Fire and Forest Ecology menu to the left.
Aquatic – Riparian Conservation
April 5, 2012
Fifteen years after the Sierra Nevada Ecosystem Project (SNEP), what is the status of aquatic conservation within Sierran national forest lands today? This new report is a compilation and summary of a workshop convened in December, 2011 and sponsored by Sierra Forest Legacy and our partners. This information will inform our Conservation Strategy for forest plan revisions. Download the report here.
Frissell, C.A. M. Scurlock, and R. Kattelmann. 2012. SNEP Plus 15 Years: Ecological & Conservation Science for Freshwater Resource Protection & Federal Land Management in the Sierra Nevada. Pacific Rivers Council Science Publication 12-001.
Portland, Oregon, USA
Below, read a history of grazing and other reform measures in the 2001 Sierra Framework, and a discussion about our concerns with the 2004 revisions. Our partners at Pacific Rivers Council successfully challenged those changes in court, resulting in a favorable decision on February 3, 2012, that requires the Forest Service to return to the 2004 Framework revision and properly analyze the environmental impacts on rare and endangered fish species.
Aquatic and riparian habitats are linked in direct and complex ways and are fundamentally dependent on natural flows of water. Californians have engineered extensive control over the waters of the Sierra Nevada changing these natural flows. Aquatic ecosystems are very important to species of the Sierra Nevada with 17% of Sierran plant species, 21% of the vertebrate species, and almost 100% of aquatic invertebrate species dependant on riparian or wet areas.
Due primarily to human activities and disturbances, aquatic and riparian habitats have been severely altered and continue to deteriorate, leading to the loss of native species, ecosystem functions, and services to human society. Of sixty-seven types of aquatic habitat categorized in the Sierra Nevada, almost two-thirds (64%) are declining in quality and abundance, and many are at risk of disappearing altogether.
The Sierra Nevada Framework Plan was designed to protect these important natural areas by creating Critical Aquatic Refuges and Riparian Conservation Area management guidelines to preserve, enhance and restore water quality and key habitats for sensitive or listed species that will contribute to their viability and recovery. This includes restrictions on grazing and peer review of any activities that may affect aquatic resources. The revisions to the Framework Plan weakened grazing standards in aquatic areas and will not be developed at the bioregional scale. Furthermore, mechanical treatments will be used on more acres for fuels reduction and “forest health” logging, despite the Forest Service knowledge that mechanical treatments “have more potential for adverse effects” on aquatic habitats. Aquatic and meadow-dependent species that are at-risk include a variety of native fish, the Yosemite toad, Mountain yellow-legged frog, Willow flycatcher, and Great Gray owl.
The revisions to the Framework Plan weakened the grazing standards in aquatic areas and have not been developed at the bioregional scale. Furthermore, mechanical treatments will be used on more acres for fuels reduction and “forest health” logging, despite the Forest Service knowledge that mechanical treatments “have more potential for adverse effects” on aquatic habitats.
Multiple stressors have negatively affected rivers, streams, and wet meadows in the region. Dams and water diversions throughout the region have profoundly altered stream-flow patterns, increased water temperatures, and degraded aquatic ecosystems. Dams and reservoirs have also blocked animal migration routes. Livestock grazing, eroding forest roads, timber harvest activities, development, and recreational activities have also contributed to the fragmentation of riparian habitats, caused bank erosion, and increased sediment and nutrient runoff into aquatic ecosystems.
One of the main threats to aquatic and riparian habitats is poorly managed and excessive grazing. Riparian habitat is often trampled by cattle seeking water and cool shady areas in the hot Sierra summers. Additionally, the increased erosion from cattle and the resulting siltation into aquatic areas is of great concern for species dependent of clear, clean water. In some areas grazing needs to be eliminated altogether, while in others, a significant reduction on the amount of grazing is necessary to ensure that these critically threatened habitats are given the chance to recover.
The Sierra Nevada Ecosystem Project highlighted aquatic and riparian ecosystems as vital to the sustenance of wildlife diversity. Deterioration of these vital aquatic and riparian habitats has contributed to the decline of native fish and amphibians as well. Wildlife species that depend on these habitats, including the Sierra Nevada willow flycatcher, Mountain yellow-legged frog, California red-legged frog, and the Yosemite toad are either declining or facing an uncertain future. In the Sierra Nevada, of the 83 terrestrial species dependent on riparian habitat, 24 percent are at risk. Aquatic insects and other invertebrates, important prey for fish and amphibians, have also been affected by habitat changes. Six of the 40 native fish of the Sierra are listed as threatened or endangered and only half of the 40 species have secure populations (Moyle et al. 1996). Among the fish species at risk in the region are several of California’s native trout, including the Little Kern golden trout and Lahontan and Paiute cutthroat trout. Half of the 29 native amphibian populations of the region are at risk of extinction. Decades of stocking fish for recreational fishing have contributed to the decline of native fish and frog species in the region. Stocking of trout into historically fishless high mountain lakes has contributed to the extirpation of native amphibians in some basins, with particularly severe consequences for the once-common mountain yellow-legged frog.
Scientific Research
Aspen Groves
Aspen are medium-sized deciduous trees, often referred to as “quaking” aspen. The leaves of the aspen tree shake and shimmer in the wind and provide and accompanying sound easily identified once heard. Aspen trees usually do not live more than 150 years, though they may persist more than 200 years. It grows on many soil types, especially sandy and gravelly slopes, and is quick to pioneer disturbed sites where there is bare soil. It grows best where soils are moist and sunshine is plentiful. Aspen is intolerant of shade, and does not compete well with more shade-tolerant conifer species.
Quaking aspen are scattered across the Sierra Nevada, usually in stands of fewer than five acres and usually adjacent to streams, springs, lake shores, and meadows. Aspen is found within a wide range of elevation in the Sierra, from the lower elevations of western juniper on the east side to higher zones of fir and lodgepole pine, generally along creeks or meadows.
Aspen groves are often out-competed by conifers in the Sierra Nevada, due to extensive livestock grazing and the absence of regular fire. As a result, the health of aspen has deteriorated and estimates suggest its extent in western North America has been reduced by as much as 96%. Aspen habitat, especially when associated with riparian vegetation, is the single most species-rich avian habitat in the Sierra Nevada.
Aspen is an especially desirable component of riparian areas where it contributes to the stability of streams, provides shade, nurtures a diverse and abundant understory community, and contributes a pleasing aesthetic component. Like other riparian communities, aspen communities comprise only a small portion of the landscape but provide habitat for many species. The multilayered herbaceous vegetation and shrubs that thrive beneath aspen canopy provide nesting, denning, and foraging habitat for insects, birds, amphibians, and mammals. The fruits produced by this diverse plant life and the insects that are abundant in the moist aspen environment provide food for a wide variety of birds. Northern goshawks, owls, and other raptors rest in the upper canopy and hunt adjacent habitats and cavity-nesting songbirds make use of all layers of the canopy and brush of aspen stands.
Livestock Grazing Impacts
Livestock grazing has a direct impact on aspen trees in this forest community. Through the early sapling stage, grazing reduces aspen growth, vigor, and numbers. Historic grazing consumed vegetation around aspen stands, reducing fuel available for fire. Also, under conditions of moderate-to-heavy livestock grazing, both livestock and wildlife graze more heavily on vegetation in aspen stands, including any emerging aspen shoots. The aspen forest type produces an abundance of forage, as much as many grasslands and more than 10 times that produced under associated conifers. Cattle and sheep grazing the aspen understory has been the primary consumptive use of the aspen forest in the Sierra Nevada.
Fire Dependence
Aspen is considered to be a fire-induced successional species that will dominate a site until it is replaced by less fire-enduring and more shade-tolerant species, such as conifers. Fire reduces the overstory, stimulates shoots to sprout, and kills invading conifers growing in the aspen grove. Fire also reduces conifer encroachment, opens up the tree canopy, removes shrub cover, and stimulates sucker release. In some areas, many aspen stands are the same age, dating from a single great fire or a year of widespread fires. Fire appears to be necessary for the continued well-being of aspen on most sites. In the absence of fire, many aspen stands are replaced by grass, forbs, shrubs, or conifers. Less-frequent fire over the past century has limited the regeneration of aspen groves.
Aspen is an aggressive pioneer species. It readily colonizes burned areas and can persist even when subjected to frequent fires. In the Sierra Nevada Mountains, the extensive stands of aspen are usually attributed to repeated wildfires. It may dominate a site until replaced by less fire-enduring but more shade-tolerant conifers. The soil water tapped by conifers has contributed to the drying of meadows, reducing water available for aspen. Pine and fir trees eventually tower over the aspen stands, shading them from sunlight.
Scientific Research
Montane Meadows
Montane meadow ecosystems are associated with seasonally moist to waterlogged soils in valleys, flats, gentle slopes, and filled-in lake basins in the higher elevations of the Sierra Nevada. Both wet and dry types occur, and their plant species composition and stability are largely dependent on the underlying hydrology. These ecosystems are the most botanically diverse in the Sierra Nevada, and they have high wildlife values because of their abundance of food and cover.
Mountain meadows play a key role in effecting watershed condition and water flow in the Sierra Nevada. Restoration of degraded meadows is the first step in improving overall watershed function and could have major effects on surface and subsurface flow regimes influencing water delivery downstream, far removed from source watersheds.
Montane meadows also play a unique and crucial role in the ecology of many bird species found in the Sierra Nevada. A substantial subset of Sierra species is dependent on meadows for breeding habitat, and the population density of many forest-inhabiting species is often highest at meadow edges. Perhaps even more importantly, montane meadows serve as critical molting and pre-migration staging areas for dispersing birds (particularly juveniles) of a broad array of species, some of which do not actually breed anywhere near the meadows.
Historic and current human activities (most notably livestock grazing, but also water management, recreational activities, logging practices, agriculture, and fire suppression) have compromised the viability of meadow habitat throughout much of the Sierra. Two of California's endangered bird species, Willow Flycatcher and Great Gray Owl, depend critically on montane meadows.
Recent research suggests that meadows may have an important role in carbon storage. Research at the University of Nevada found that restored meadows in the Northern Sierra Nevada averaged 20 percent more soil carbon capture than those that did not receive restoration treatments, with one site increasing by 80 percent. The downside of this, from the perspective of climate change, is that meadows that are dried up and no longer functioning are net emitters of carbon dioxide. Between 60 and 70 percent of the meadows in the Sierra Nevada have been dried out due to human related activities. Reversing this trend is one way to reduce carbon emissions in California, and the state has funded additional research activities towards achieving that end.
The Sierra Nevada Meadows Data Clearinghouse hosted by University of California, Davis, highlights the recent and ongoing assessments, research and restoration on meadows in the bioregion.
The Sierra Meadows Partnership has produced the Sierra Meadows Strategy (2016).
Scientific Research
Oaks and Other Hardwoods
While plant communities known as oak woodlands occur primarily in the Sierra Nevada foothills, the conifer forests of the Sierra also contain magnificent stands of oak and other hardwood species. Montane Hardwood is a type of forest plant community where oaks form a major component of the forest.
Oaks and other hardwoods form the foundation of the forest food web in the forests of the Sierra Nevada. They provide forage as well as abundant crops of acorns, berries, nuts, and other fruits that are essential for wildlife. They provide structural habitat for concealment, resting, nesting, denning, and birthing. Their flowers provide nectar and pollen that are essential for the survival of countless species of butterflies, bees, and beetles. Together they comprise the beautiful and diverse forest understory of the conifer forests of the Sierra. Many species of shrubs and trees are endemic to the forests of Northern California, and do not occur anywhere else on the planet.
Unfortunately, oaks and other hardwoods are declining throughout the Sierra Nevada, due to logging practices and mismanagement of natural fire cycles. The loss of hardwoods in the forests of the Sierra Nevada was identified in the 2001 Sierra Nevada Framework forest plan as one of five priority issues which must be addressed in order to sustain the viability of Sierra forest ecosystems.
The loss of oaks in particular was identified by Forest Service scientists as a serious threat. Oaks provide essential food and habitat for hundreds of species of animals which inhabit the Sierra Nevada. While most people don’t associate oaks with old-growth forests, black oaks (Quercus kelloggii) are found at elevations up to 2,400 meters or nearly 8,000 feet in elevation! Acorns are consumed by a variety of animals in every forest habitat type, from squirrels to acorn woodpeckers, black bear and black-tailed deer. They support the prey species that in turn are eaten by rare animals like the Pacific fisher, American marten, Northern goshawk, great gray owl, and California spotted owl—species which are associated with old-growth forest habitats. Many animals fatten up on acorns in the fall, providing them with the necessary fat reserves to survive the winter. Without oaks, animals throughout the Sierra would literally starve.
Oaks can become massive in size in the Sierra. The oldest giants, particularly black oak (Quercus kelloggii), are important denning and rest sites for the rare Pacific fisher. Black oaks don't start to produce a significant crop of acorns until they are at least fifty years old. The loss of black oak has resulted in long term, significant adverse impacts to Sierra Nevada forest ecosystems.
Forest management practices that favor the production of conifers for commercial lumber production, coupled with fire suppression, have severely impacted the quantity and quality of hardwood vegetation in the Sierra Nevada, especially on the western slope where hardwood diversity is highest. For many decades, foresters and loggers treated oaks and other hardwoods, as well as non-commercial conifers, as weed species that must be eliminated. Oaks are killed during clearcutting, thinning, and during plantation management that includes the use of herbicides.
A lack of understanding of native forest ecology has led to widespread conversion of natural oak-dominated landscapes to conifer tree plantations. Areas which normally would not support conifers are cleared of their oaks and diverse shrub communities, and densely planted with ponderosa pines. Potent chemical herbicides are used to suppress the natural regeneration of the native hardwoods and shrubs.
Scientific studies have shown that young ponderosa pine plantations are the most fire prone configuration—even more fire prone than shrub-dominated sites, and remain so for fifty years or more. Thus, such practices are not only devastating to wildlife which depend upon the rich food source found in hardwood communities, but the practice has greatly increased fire hazard throughout the Sierra.
Oaks are also cut for firewood in rural SN forest communities, but it is difficult to measure the impact this is having. Despite small improvements in forest management and policies on oak management, there is little oversight or enforcement of protective measures, and oak and other hardwoods continue to decline throughout the range.
Fire suppression is another factor resulting in the steady loss of hardwoods and native shrubs that are important for wildlife. Most hardwoods and native shrubs are dependent upon fire returning regularly to SN forests. All are adapted to survive under the conditions that occur in the fire-prone interior of the western slope of the Sierra Nevada. Seeds that can readily germinate after exposure to fire, and the ability to sprout from the base after fire has killed the tops of individuals, are two common adaptations. Fire also reduces disease and insect outbreaks. Most importantly, regular fire return keeps conifer species from shading out the hardwoods in the understory. This is significant for production of vital wildlife habitat.
In areas where oaks naturally predominate (west side lower elevation forests, where fire return intervals are short—between 5-30 years), fire suppression coupled with logging of all the old-growth has resulted in forests that are overly crowded. When fire does occur, as we know it will in these environments, the old oaks may be killed due to fire intensities that are too hot. Oaks are somewhat fire resilient, but can easily be killed if there is a build up of fuel at the base. While they may sprout from the base if the fire is not too hot, they will not produce abundant acorn crops again for decades. Thus it is essential to sustain wildlife viability to maintain and protect healthy oak populations.
Conservation Measures
There are a number of steps that should be taken to ensure the survival of oaks and other hardwoods in the Sierra Nevada.
- Set limits on the amount of clearcutting permitted in each watershed on private timber lands as well as on public lands, as recommended by the California Department of Fish and Game in the State Wildlife Action Plan (2007).
- Oaks should also be protected during thinning operations on both public and private lands. The 2001 Sierra Nevada Forest Plan Amendment requirements for protection of westside hardwoods must be enforced.
- Restore fire resilient landscapes. Before fire can be returned, in places that are unnaturally overgrown with dense conifer cover in previously heavily logged environments, some mechanical thinning must be undertaken prior to allowing fire to return. Great care must be taken to ensure that fragile soils are not further harmed, and to protect legacy oaks and other important structural components of the forest during thinning.
- Introduce fire through prescribed/managed fire and allowing wildland fire use (letting fires proceed whenever possible, where property is not at risk), also known as appropriate management response (AMR).
Oak Woodlands
Oak woodlands also are among the most biological diverse communities in the state, supporting 5,000 species of insects, more than 330 species of amphibians, reptiles, birds and mammals, and several thousand plant species.
The oak woodlands of the western Sierra foothills are one of the most imperiled habitats in all of California. These oak woodlands, where approximately 70 percent of the region’s population lives, have been hardest hit by development. Less than 1 percent of the foothills are protected from development, and much of the area lies within commuting distance of rapidly growing cities in the Central Valley.
The Sierra Nevada Ecosystem Report of 1996 reported that "The oak woodland communities of the western Sierra Nevada foothills are the most vulnerable of the widespread vegetation types as a result of greater access by humans and of their continuing potential for urban development,”"(Vol I, page 18).
More than 65 percent of the oak woodlands in the Sierra Nevada region are privately owned and with continuing increases in land values these landscapes can be worth far more when converted to housing or intensive agriculture such as vineyards.
The clearing of oak woodlands for development has a tremendous ecological impact by degrading water quality and wildlife habitat. These habitats are among the most critical for California’s native species, including some 2,000 plants as well as 5,000 insects, 80 amphibians and reptiles, 160 birds and 80 mammals. Oak woodlands are also key to water quality concerns. As snowmelt flows down watersheds into streams and rivers, oaks help keep the soil in place, preventing erosion and stream sedimentation.
Oaks are most susceptible during the transition from seedling to
sapling, and the main threats include overgrazing by cattle, and competition from the nonnative annual grasses that have replaced native perennial grasses. State researchers have determined that providing enclosures for young oak seedlings to prevent grazing by cattle goes a long way to ensuring their survival.
California's iconic oak woodlands have endured many assaults over the years. They've been cut for fuel, cleared for vineyards and housing developments, and their seedlings face intense grazing pressure and competition from invasive grasses. But the future also brings the new threat of climate change. Researchers have determined that the areas of the state where the climate is suitable for these oak species to grow will shift northward and could shrink to nearly half their current size as a result of global warming.
Scientific Research
Old-growth Forests of the Sierra Nevada
"As we liquidate the ancient forests, we are redesigning the forests of the future. In fact, we are redesigning the entire world, and we are simultaneously throwing away Nature's blueprint." - Chris Maser, forest ecologist
There are a variety of definitions for old-growth forests, but they are generally defined as forests in their later stages of development, usually referred to as late-seral or late successional. Approximately 4 million acres of old-growth are remaining in the Sierra Nevada, however most of the remaining stands have been highly fragmented, with the majority of old growth found only in the highest reaches of the mountains, wilderness reserves in the lower alpine zone, or in steep inaccessible stream canyons.
Trees sizes for old-growth have been variously defined as trees over 24" diameter with medium to high canopy cover, to 30" trees; however age is the most important factor, and some ancient trees may not appear huge in girth. Old growth trees are—at the minimum—150-200 years in age. Tree size and age-related structure are a result of growing conditions, species type, elevation, and climatic conditions resulting from the diversity of ecosystems in the Sierra Nevada.
There has been an alarming decline in old-growth forest acres and structure in the Sierra Nevada since the 1850's. Estimates vary on the amount of old-growth that existed in the pre-settlement era, depending on what time period is considered. The best estimate (SNEP 1996) states that formerly, late-successional habitat occupied roughly 67 percent of the mixed conifer forest landscape. Today, it is estimated that only 12 percent of mixed conifer old-growth forest remains, a staggering loss of approximately 82 percent of the historical acreage of old-growth found in mixed conifer forests.
Much of this loss is from the high-grading (a type of selective cutting where some or all of the biggest and best trees are cut) of large trees, railroad logging, and clear cutting logging practices, which continued up to the early 1990's on Federal land and continue today on industrial timber lands in the Sierra Nevada. During the logging "hey-days" of the 1980's the Forest Service was producing over 1 billion board feet of saw-timber annually from the Sierra Nevada, much of it in large old-growth trees.
Timber industrial giant Sierra Pacific Industries continues to liquidate all of their remaining old growth trees in their ownership, throughout the Sierra Nevada on the western slope. After clearcutting, the industrial practice is to farm the forest, planting trees that will be uniformly managed with herbicides and then cut again after 50 to 80 years, starting the cycle over again. This is called the timber "rotation." These practices make preservation of the remaining old forest stands in public ownership on national forest lands all the more critical.
Old-growth forests can play a significant role in storing carbon and helping to mitigate global warming. Old-growth forests in the Northern Hemisphere sequester ten percent of the world's net ecosystem productivity, or NEP, a measure of carbon sequestered. Their value in maintaining a climate that can sustain life far outweighs the short term economic gain from cutting them down for lumber.
Old-growth trees provide a critical habitat structural component of species like the imperiled California spotted owl. A study of California spotted owl nest locations in the southern Sierra Nevada (North 2000) found the mean age of nest trees to be greater than 225 years. Old trees develop important characteristics such as cavities and broken tops, which provide ideal and integral nest sites. Also, the large canopies often found in old-growth stands provide much needed shade in hot summer weather for the heat sensitive spotted owl.
Other imperiled species in the Sierra Nevada that depend on intact old-growth habitat are the Northern flying squirrel, Pacific fisher, and pileated woodpecker. Continued degradation of the remaining old-growth in the Sierra Nevada will likewise continue to put pressure on these threatened wildlife species.
Many rare plants, fungi, bryophytes and lichens are also associated with old forests. Some may take decades to build up complex symbiotic relationships with their conifer hosts before they become established and reproduce. Some examples include a suite of terrestrial orchids including coral root, lady slipper, and rattlesnake plantain. Very little is known about the life histories or ecology of some of these rarely seen forest species.
The original 2001 Sierra Nevada Framework Plan called for 4.2 million acres of old forest emphasis areas with specific goals of protecting and enhancing old-growth forests. The 2004 revisions to the Framework allow intensive harvesting of 20"-30" trees in 75 percent of the old-growth reserves across the Sierra Nevada.
Learn more about forest management and its effects on old-growth forests in the Fire and Forest Ecology section of the website.
Scientific Research
Aubry, K.B., C.B. Halpern, and C.E. Peterson. In Press 2009. Variable-retention harvests
in the Pacific Northwest: a review of short-term findings from the DEMO study. Forest
Ecology and Management. (595 KB PDF)
Franklin, J.F., and J.A. Fites-Kaufmann. 1996. Assessment of Late-Successional Forests of the Sierra Nevada. Sierra Nevada Ecosystem Project: Final report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildland Resources, 1996. Large file in four parts: Part 1 (3 MB), Part 2 (4.71 MB) Part 3 (1.57 MB) Part 4 (2.95 MB)