CHAPTER 1

Sierra Nevada Ecosystems

❆ CRITICAL FINDING

Climate Change During the period of recent human settlement in

the Sierra Nevada, climate was much wetter, warmer, and more stable

than climates of the past two millennia; successful ecosystem evalu-

ations and planning for the future must factor climate change into

analyses.

I N T RO D U C T I O N

The Sierra Nevada evokes images particular to each indi-vidual’s experience of the range. These images take on thequality of immutability, and we expect to find the range basi-cally unchanged from one year to the next. The Sierra Ne-

FIGURE 1.1

Northern Sierra montane aerial view. (Photo by Jerry F.Franklin.)

❆ The SNEP Study Area

The core area boundary for the Sierra Nevada Ecosys-tem Project was the area containing the headwaters oftwenty-four major river basins and extending throughthe foothill zone on the west side and the base of theescarpment on the east side (figure 1.2). No singleboundary adequately defines all the ecological compo-nents, but watersheds are in many ways the most dis-cernible and to many biota the most meaningfulecological units in the Sierra. At the request of Congress,a larger study area for the project included portionsnorth of the physiographic Sierra Nevada and exten-sions beyond the core area to the south and east. Ap-propriate adjustments to these boundaries wereconsidered in SNEP analyses pertinent to the needs ofeach issue.

vada, however, including its rocky foundations and the plantsand animals that inhabit it, changes continually through time.Ecosystems respond to cumulative effects from the past; theold-growth forests in the Sierra today evolved under differ-ent conditions from those of the present. To understand howthe landscapes of the Sierra Nevada are changing, and whatrole humans have in shaping the future, we benefit by know-ing what makes up the current Sierra as well as key factorsinfluencing change. This was the point of departure for theSierra Nevada Ecosystem Project. A brief introduction to theSierra Nevada and the context of the study are presented here;subsequent chapters summarize the study’s findings.

R O C K A N D S O I L

At its foundation, the Sierra Nevada is an enormous depositof granitic rock whose exposed slopes are readily visible atthe crest of the range. The gradual west slope rising from theexpansive Central Valley to the Sierra crest is dissected by deep,west-trending river canyons. At the eastern edge of the uplift,the high peaks dominate the uppermost elevations, formingrolling highlands in the north—with elevations mostly lessthan 9,000 feet (figure 1.1)—and expansive, highly dissectedmountains in the broad southern alpine zones, where MountWhitney (highest peak in the contiguous forty-eight states)rises to 14,495 feet. The range ends abruptly at the eastern es-carpment, dropping with a shallow gradient in the north, butin the south plunging more than 10,000 feet from the Sierrancrest to the floor of the Great Basin.

7Sierra Nevada Ecosystems

FIGURE 1.2

Boundaries of the core Sierra Nevada ecoregion, the study area, and the twenty-four river basins used by SNEP in itsassessments.

8VOLUME I , CHAPTER 1

As a geological feature, the Sierra Nevada is relatively dis-tinct. The western boundary is defined as a contact betweenold, harder rocks of the Sierra Nevada and their eroded andredeposited younger by-products at the edge of the CentralValley. At the north, the older rocks of the Sierra Nevada areoverlain by younger volcanic rocks of the southern Cascadesin the Mount Lassen area. The eastern edge of the range fol-lows the base of the Sierran escarpment. At the south, the geo-logic Sierra Nevada abuts the structurally distinct TehachapiMountains, forming a discernible boundary in southern KernCounty.

The Sierra Nevada’s environmental history has beenshaped over several hundred million years by varying inten-sities and forms of uplift, erosion, volcanism, and glaciation.Plate tectonics and climate variations acting at millennial,decadal, and annual timescales interact to influence the in-tensity of these events and their impacts on the landscape.These diverse geological activities have produced a broadsuite of rock formations in the Sierra Nevada, dominated bygranite but including many types of igneous, sedimentary,and metamorphic rocks, with ages from Cambrian (about 500million years ago) to Quaternary (the past 2 million years).Most evidence suggests that the modern range is about 10million years old, although very recent and controversial evi-dence suggests a much older age.

Rocks of the Sierra Nevada interact with climate, topogra-phy, surface processes, and biota to create Sierra Nevada soils.Because the Sierra Nevada is underlain by mostly graniticrocks, soils that develop from these foundations are thin androcky. Although the nutrient capital (fertility) of the soil in gen-eral over the Sierra Nevada is rather low, the range containssome of the most productive sites for conifers in the world.Soil types form a mosaic across the Sierra, influencing vegeta-tion, erosion, wildlife distribution, water quality, fertility, anda myriad of human uses.

Such a complex geological and soil foundation has dramaticimplications for human uses of Sierra Nevada ecosystems.Mesozoic deposits (more than 100 million years old), alteredthrough pressure and heat and exposed through erosion orburied deep underground, form the gold and silver that at-tracted a rush of miners and began the period of Euro-Ameri-can settlement. Abundant sediments from ancient seafloors,lake beds, and water-carried deposits create the ore and gravelresources that are the contemporary valuable rocks of the Si-erra (plate 1.1). Persistent seismic activities, especially alongvolcanic vents of the eastern escarpment near MammothLakes and Markleeville, are a focus of concern for urban devel-opment in these areas, yet those same vents provide geother-mal power for existing communities. The rich and fertile soilsthat have formed on the western edges of the Sierra Nevadacontinue to support a diverse agriculture that had its originsin the Native American communities that occupied the region.

Volcanic and seismic activity is highly localized but ongo-ing in the Sierra Nevada. New volcanic craters have been built,vents have erupted, hot springs have formed, faults have

slipped, and volcanic-induced mud slides have occurred asrecently as the past hundred years in a few regions. Volcanicevents will undoubtedly persist as agents of change affectinglocal ecological and human elements of Sierran ecosystemsand demanding local attention.

C L I M AT E

Major climate change has occurred at millennial, decadal, andannual scales in the history of the Sierra Nevada (figure 1.3).The regional climate developed from warm, wet, tropical con-ditions about 65 million years ago through a cycle of at leasteight major glacial and interglacial periods of the last millionyears to the winter-wet, summer-dry pattern of the last 10,000years. These climatic periods have greatly influenced vegeta-tion, animals, and human populations; their effects are observ-able today and influence how people manage resources. Forinstance, two extensive droughts, each lasting 100 to 200 years,occurred within the last 1,200 years. During the cold phase ofthe Little Ice Age (about A.D. 1650–1850), glaciers in the SierraNevada advanced to positions they had not occupied sincethe end of the last major ice age more than 10,000 years ago.The period of modern settlement in the Sierra Nevada (aboutthe last 150 years), by contrast, has been relatively warm andwet, containing one of the wettest half-century intervals ofthe past 1,000 years. Many of the forests that stand today wereestablished under different climates—generally wetter ones—from the present regime.

The current Sierran climate is dominated by a “mediter-ranean” pattern of a cool, wet winter followed by a long dryperiod in summer. High yearly variability in temperature andprecipitation is also characteristic. Because of the influence ofthe Pacific Ocean and storm tracks from the west, strong cli-matic gradients develop with elevation from west to east. Atfoothill altitudes, summer hot, dry climates predominate; aselevation increases, so does precipitation. Winter storms aremoisture-laden and release enormous precipitation on thewest slope. In winter, snow covers the landscape to about6,000–8,000 feet. The transition zone of rain to snow is an im-portant determinant of vegetation types, stream dynamics,and human settlement.

The Sierra summits wring water from the winter storms andsummer convection systems, leaving the eastern flank progres-sively drier each mile east (figure 1.4). From moist mountainecosystems at the Sierran crest, the transition to semiarid desertnear Bishop, for example, can occur in less than two horizon-tal miles. The west shore of Mono Lake, at the base of the Sier-ran escarpment, receives an average of 12 inches of rainannually, whereas the eastern edge, lying in Great Basinsteppe, receives only 6 inches. Strong gradients of aridity alsoexist from north to south along the Sierran axis as a result ofthe location of jet stream and subtropical high pressure cells.

PLATE 1.1

Total mineral claim density per section in the SNEP study area. (From volume II, chapter 18.)

California

California

Nevada

Oregon

Nevada

Oregon

California

Tom HillmanU.S. Bureau of Mines W.F.O.C.(509) 353-2700

Claim Density data courtesy ofU.S. Bureau of Land ManagementDenver Service Center, CO

1-12 open claims/section

13-24 open claims/section

25+ open claims/section

U.S. Forest Service

National Park Service

Bureau of Land Management

SNEP boundary

SNEP-core boundary

9Sierra Nevada Ecosystems

FIGURE 1.3

Global temperatures (relative changes based on oxygenisotopes) at four time scales. (From volume II, chapter 4.Reprinted by permission of the Society for RangeManagement.)

Climatic and geological forces are the royal architects ofSierra Nevada ecosystems. Water, wildfire, plants, fauna, andhumans are highly dependent on regional climate and localweather. Organisms must adjust (migrate, adapt) or die asclimate changes. The current patterns of vegetation, waterflow and abundance, and animal distribution in the Sierraare determined largely by cumulative effects of past andpresent climates. Human development in the Sierra has pro-ceeded during a temporary period of relatively wet, warmclimate. Patterns of human settlement, perceptions of wild-fire, design of water delivery systems, predictions of wateravailability, future forest and urban planning, and aestheticexpectations about forest condition (size, composition, healthof forests) are based largely on conditions of this anomalousclimate period. One implication of a longer view of climateis, for instance, that the “droughts” of the mid-1970s and mid-1980s were actually not droughts at all, relative to the cen-tury-long dry periods that have been common in recentSierran climate history.

W AT E R

Water is an essential and often limiting factor for life. Givenstrong seasonal mediterranean patterns, high annual variabil-ity of climate, natural aridity of the eastern flanks, and the con-stant thirst of plants, animals, and burgeoning humancommunities adjacent to the Sierra, water remains a subject ofintense competition for all Sierran biota.

Water partitions the Sierra into twenty-four readily discern-ible river basins or watershed units (figure 1.2). The Sierrancrest divides water flow either west to the Pacific Ocean orterminating in the San Joaquin valley, or east into the GreatBasin, where the water evaporates. To the west, the major wa-tersheds are defined by the Feather, Yuba, American,Cosumnes, Mokelumne, Stanislaus, Tuolumne, Merced, SanJoaquin, Kings, Kaweah, and Kern Rivers; to the east, by theTruckee, Carson, Walker, and Owens Rivers. Streams, creeks,and temporary waters define subwatersheds at increasinglysmaller scales within these areas.

Watersheds at each scale are important to creatures that in-habit water. Sierra Nevada waters are home to a diverse aquaticbiota, including fishes, amphibians, invertebrates, and plants.To denizens of rivers, the landscape is defined and limited bylinear connections; the arterial nature of water systems isolatesaquatic populations. Watersheds also isolate aquatic organisms,so that entirely different aquatic biotas may exist from onewatershed to another. Rivers and their watersheds extend be-yond the geologic edges of the Sierra Nevada to their finaldestination in ocean, valley, or basin. Fish and other aquaticlife have evolved to occupy habitat zones within certain ele-vations along the rivers, but they do not have sharp or readilydefined downstream or upstream boundaries (figure 1.5).

10VOLUME I , CHAPTER 1

FIGURE 1.4

Mount Tom and the steep eastern escarpment of the Sierra Nevada, with piñon woodlands at the base. (Photo by Deborah L.Elliott-Fisk.)

At middle and low elevations, the Sierra Nevada once sup-ported a diverse fish population, including anadromous spe-cies such as chinook salmon. Extensive and abundantpopulations of frogs and salamanders inhabited Sierranstreams, lakes, and meadows. The largest numbers of aquaticspecies in the Sierra Nevada are the little-known invertebrates.The many lakes of the high Sierra, once mostly fishless, origi-nally supported a diversity of aquatic amphibian and inver-tebrate species. These groups of aquatic animals have beenextremely vulnerable to changes in their habitat, and the storyof their composition and distribution is now quite differentfrom that of the past.

P L A N T S A N D V E G E TAT I O N

The Sierra Nevada today is rich in vascular plant diversity,with more than 3,500 native species of plants, making up morethan 50% of the plant diversity of California. Hundreds of

rare species and species growing only in the Sierra Nevada(endemics) occupy scattered and particular niches of therange. The assemblage of plants growing together in an areacreates characteristic vegetation types. Vegetation is a domi-nant element of ecosystems, for plant diversity, for ecologicalfunctions plants engage in (e.g., soil aeration, microclimatealteration), and as habitat and sustenance for other organ-isms. The architecture of each vegetation type creates habitatsuitable for some species and unsuitable for others. The dis-tribution of wildlife is closely associated with the distribu-tion of vegetation, and the same is true for less visible andless familiar forms of life such as fungi, bacteria, and insects.

The major vegetation zones of the Sierra form readily ap-parent large-scale elevational patterns. Unlike aquatic systems,whose dominant Sierran pattern is defined by east-west wa-tersheds, primary vegetation types of the Sierra form north-south bands along the axis of the Sierra. Major east-westtrending watersheds that dissect the Sierra into steep canyonsform a secondary pattern of vegetation in the Sierra. Diver-sity of regional and local plant species as well as vegetationtypes in the Sierra Nevada are highly influenced by climate,

11Sierra Nevada Ecosystems

❆ Ecosystems

Ecosystem refers to the collective entity formed by theinteraction of organisms (e.g., plants and animals) witheach other and with their physical environment (e.g.,soil, water, weather) at a particular location. SNEP con-siders people, when they are present, as part of ecosys-tems. Ecosystems exist at many, potentially overlapping,scales, from a rotting log to the entire Sierra Nevada;they all have three fundamental attributes. Componentsare the kinds and numbers of organisms (biodiversityof genes, individuals, populations, species, and groupsof species) and physical elements (soil, rock, water) thatmake up the ecosystem—the “pieces.” Trees and wild-life are important to Sierran ecosystems but equallyimportant are the myriad less visable or unseen organ-isms, such as insects, fungi, and bacteria. Structures arethe spatial distributions of the components—the waythe ecosystem “pieces” are arranged at a location andtime in the ecosystem. Plant communities, such as themixed conifer forest, and forest structure, such as old-growth stands, are important examples of ecosystemstructure. Processes or functions refer to the flow or cy-cling of energy, materials, and nutrients among the com-ponents over space and through time. Processes are thework of the ecosystem; they contribute to changes inthe components and the structure of the ecosystem.Ecosystems are linked to one another, so that changesin components, structure, and function in one ecosys-tem may have consequences in contiguous and noncon-tiguous ecosystems.

elevation (temperatures), and soil type. From an aerial per-spective, it is obvious that only part of the Sierran landscapeis forested, the rest being meadow, chaparral scrub, wood-land, savanna, canyon land, alpine habitat, bare rock, andwater. As might be expected, the boundaries of the Sierranfloristic province differ from boundaries defined by geology,watersheds, aquatic diversity, or wildlife, especially at thenorthern and southern edges of the range.

At the lowest elevation on the west side, interfingering withthe Central Valley grasslands and chaparrals, are the foothillwoodland vegetation types. These woodlands are unique toCalifornia, although not to the Sierra (they extend around theCentral Valley), and include several deciduous and evergreenoaks as well as foothill pine. Tree cover here ranges from opensavannas to lush riverside forests. Of all the Sierran vegeta-tion types, the foothill plant communities have supported themost native biodiversity and highest human populations dur-ing the last few centuries. Now these are most at risk of lossby conversion to human settlement.

Intermixed with the foothill woodlands are a large groupof dense shrublands called chaparral. Although chaparral veg-

etation looks similar throughout the range, there is great varia-tion in species composition from one location to another. Manyfactors determine the location of chaparral types, but gener-ally they are restricted to rocky soils with low fertility. Themediterranean climate is an overriding environmental factorin the ecology of Sierran chaparrals, including the climate’spromotion of frequent burning in intense wildfire. The bound-ary between chaparral and forest is dynamic and determinedpartly by wildfire. Shrublands on the east side of the SierraNevada are the Great Basin sagebrush steppe and bitterbrushvegetation types, which begin near the base of the easternescarpment and extend across the vast expanse of the GreatBasin. These arid shrublands have much less species diver-sity than west-slope chaparrals.

Depending on latitude, a broad conifer zone begins at el-evations between 1,000 and 3,000 feet on the west and be-tween 3,000 and 5,000 feet on the east side. Ponderosa pine(mixed with hardwoods) dominates the lower western mon-

FIGURE 1.5

Aquatic and riparian ecosystems in healthy conditionprovide critical habitat for Sierra plants and animals. (Photoby Jerry F. Franklin.)

12VOLUME I , CHAPTER 1

FIGURE 1.6

Mixed conifer forest with giant sequoias, Kings Canyon National Park. (Photo by Constance I. Millar.)

tane zones, whereas at lower elevations on the east side, piñonpine and juniper, then Jeffrey and ponderosa pine forests oc-cur. Above these zones on the west side is the commerciallyimportant mixed conifer forest type (figure 1.6), typified byvarying mixtures of Douglas fir, ponderosa pine, white fir,sugar pine, and incense cedar. On the eastern front, this mixedconifer zone is less diverse, and species mixes vary more fromplace to place than on the west side.

With increasing elevation , the mixed conifer zone givesway to a fir belt—first white fir, then predominantly red fir.The location of this shift in forest type depends on the transi-tion from rain to snow, which varies with elevation at a par-ticular latitude, shifting uphill farther south in the range. Thefir zone is less extensive on the east side; south of Lake Tahoe,only a few pockets exist. Trees become shorter and more scat-tered with increasing elevation. The subalpine zone is a mix-ture of vegetation types and distributions, ranging fromclusters of dense hemlock or lodgepole pine to open forestsof limber pine or western white pine, to sparse, mostly rock-slope types containing whitebark pine, foxtail pine, and west-ern juniper. Above this zone is alpine vegetation adapted tothe cold, dry conditions of the highest Sierran elevations; trees

give way to low shrubs and finally cushion-plant communi-ties that grow among rock crevices in a zone of ice and wind.

As one drives or hikes through the Sierra, it is obvious thateach vegetation type is in itself a mosaic. Small changes intopography, differences in soil and rock characteristics, andthe history of disturbance (fire, storm blowdown, insect andpathogen activity, avalanche) contribute to the complex mix-ture of patches that characterizes Sierran forests. Plant pat-terns vary not only from place to place in the Sierra but alsoover time. This complexity at the local scale makes it difficultto map vegetation, to generalize relationships of structure tofunction, and to assess forest conditions.

Characteristic structure and function develop in Sierranforests as they age. Under aboriginal conditions, fires and otherdisturbance events regularly burned entire stands of trees, leav-ing openings that passed through continuous but distinctivephases as they aged. This succession of a forest through timebetween major disturbances is important for plants and ani-mals that use different stages as habitat. Different ecologicalfunctions develop with successional phase in a forest. Fromseedling colonists to mature forest stands, forests develop instructural complexity and species composition until they reach

13Sierra Nevada Ecosystems

a stage known as late successional, or, more popularly, oldgrowth.

We know most about late successional/old-growth at-tributes—and the relationships of structure to ecological func-tion—in middle-elevation conifer forests, specifically mixedconifer, red fir, and east-side pine. A dominant feature inmiddle-elevation forests is the spatial variability that devel-ops as a result of succession in Sierran forests. In these andother vegetation types of the Sierra, wildfire, which was a fre-quent characteristic of presettlement conditions, has been anarchitect and important ecological agent of forest and standstructure. The vagaries of fire, from low to high intensity, smallto large areas, contribute to the great variability that typifiesSierran middle-elevation forests. Each stand passes throughits own history, thus developing a distinctive structure. Vari-ous events (tree fall, windfall, avalanche, fire hot spot, insectoutbreak) create small and large openings in some areas,whereas other areas maintain standing trees (alive and dead)despite disturbance. Patches develop a characteristic structurein their abundances of large, old trees (relicts left after groundfires); multiple age-classes of live trees; mixtures of dominantspecies; snags and downed woody debris of different sizesand degrees of deterioration; closed crown canopy; and lay-ers of vegetation. Collectively the forests containing thesepatches are highly heterogeneous. The image evoked popu-larly by the term old growth, i.e., extensive uniform stands ofeven-aged, old trees, although descriptive of some PacificNorthwest forests, is inappropriate to the complex and het-erogeneous Sierran forests.

The forests of the Sierra are part of the river of change in themountain range. Many of the current vegetation distributionshave been in place locally for only a few thousand years. Atshorter intervals within that time, changes in individual dis-tribution have occurred. For instance, during the Little Ice Ageof the last centuries, tree lines dropped and forest densitiesand wildfire patterns changed; during the warm centuries ofthe last millennium, many species grew in different locationsfrom their current sites, wildfires burned in different patterns,and water flows and lake levels were very low. During theglacial-interglacial periods, most vegetation zones shiftedaltitudinally up and down by as much as 1,600 feet; through-out the millennia before the ice ages, vegetation types of theregion were vastly different from anything we see in the Si-erra now. Today Sierran forests show the effects of decades offire suppression, which has changed the character of manyforests even in places otherwise minimally influenced byhumans, such as the national parks.

A N I M A L S

About 400 species of terrestrial vertebrates (including mam-mals, birds, reptiles, and amphibians) use the Sierra Nevada,

although only a fraction are restricted to the range. Animalsthat live in the Sierra Nevada depend greatly on the distribu-tion and quality of vegetation for their habitat and food needs.Many native Sierran species are adapted to habitats maintainedby the precontact fire regime (the regime that prevailed beforenon-Indian settlement of the area). Although only a handfulof species require late successional habitats, many more de-pend on the presence of large, old trees, snags, and logs inSierran woodland and forest communities for some part of theirlife cycle. Late successional and riparian forests are importanthabitats to wildlife, as are the low-elevation foothill woodlandtypes. In the latter zone especially, conversion of habitat andloss of ecological function have dramatically altered the suiteof species that flourished in these communities. A commonand important pattern for Sierran birds is their migratorypatterns up and down slopes, following seasons. When a spe-cific habitat needed for completion of a critical life stage (e.g.,foothills for breeding) is disrupted, species may be put at riskeven if they are able to use alternative habitat for other needs.

❆ Insect Species Found Onlyin the Sierra

The following numbers of known endemic terrestrialinsect species are found in each of the major river basinsin the SNEP study area. (From volume II, chapter 26.)

Eagle Lake 0Honey Lake 0Feather 2Upper Sacramento 0Yuba 1Truckee 7American 0Carson 2Cosumnes 0Mokelumne 4Walker 2Stanislaus 0Calaveras 0Mono Basin 6Tuolumne 7Owens 17Merced 0San Joaquin 3Kings 1Kaweah 3Kern 3Tule 1Caliente 2Mojave 0

14VOLUME I , CHAPTER 1

H U M A N S I N T H E S I E R R A

Humans are an integral part of Sierra Nevada ecosystems,having lived and sustained themselves at various elevationsin the region for at least 10,000 years. Indigenous populationswere widely distributed throughout the range at the time ofEuropean immigration. Archaeological evidence indicates thatfor more than 3,000 years Native Americans practiced local-ized land management for utilitarian purposes, including ani-mal hunting, forest burning, seed harvesting, pruning,irrigation, and vegetation thinning. These practices no doubtinfluenced resource abundance and distribution in areas ofearly human settlement. On a longer timescale, humans mayhave played a role in the decline of large vertebrates duringprehistoric times. Extinction of a large and diverse megafaunathroughout western North America, including the Sierra Ne-vada, at the end of the last major ice age (around 10,000 yearsago) coincided with the arrival of humans in North America.Some scientists link these extinctions to overhunting by hu-mans of animals already stressed by changing environments.

Immigration of non-Indian settlers in the early 1800s be-gan a period of increasingly intense resource use and set-tlement. By the late 1800s, parts of the Sierra had beentransformed as a result of intense interest by these immigrantsin Sierran resources. Agriculture, mining, logging, and graz-ing activities were extensively practiced in many regions ofthe Sierra. The need to divert water to support resource ex-traction and settlement led to a major reordering of naturalhydrological processes through a vast network of ditches andflumes. In some areas, impacts from early use of the Sierracreated rapid and irreversible changes from precontact con-ditions.

By the early 1920s, a new phase of Sierran history wasemerging, in which resource use was more regulated and for-est and range protection was emphasized. Suppression of firesbecame a primary goal of federal, state, and private efforts,controls were imposed on the timing and locations of graz-ing, and timber harvest was systematized under governmentand industrial forestry programs. Although trends of use havevaried over the last 150 years, increasing population pressureand complex demands on Sierran resources pose serious eco-logical threats in some regions and severe management chal-lenges elsewhere. Similarly, changing values for naturalresources present economic and social challenges to rural com-munities within the Sierra Nevada.

S O C I A L I N S T I T U T I O N S

The web of institutions laid across the Sierra by successivegenerations of Americans is central to an understanding of themountain range and its future management. This web is the

eventual target of the current study, in that the project’s as-sessments and strategies must be absorbed, adapted, andimplemented not by the biology or geology of the mountainrange but rather by the institutions through which humansociety operates.

Institutions are central elements in the ecology of the SierraNevada because they mediate the relationship betwen the la-bor and desires of people and the Sierran ecosystems thosepeople use. In a biological analogy, institutions—the govern-mental and nongovernmental organizations, agreements, andregulations—constitute a key part of the life history strategythat the human species currently uses in the Sierra. Institu-tions are in large measure how people link themselves to otherparts of the ecosystem.

Institutions govern not only what people extract from theecosystem—water, timber, recreation, amenities—but alsohow they reinvest in the natural capital through actions suchas planting trees or restoring habitats. The extent to whichinstitutions and policies “close the loop”—that is, mitigatethe environmental impact of human activities—is a criticalpart of a Sierra Nevada ecosystem assessment.

As institutions regulate the exchanges between people andthe ecosystem, they also link people who reside outside themountain range with the ecosystem within it. Institutions thatclose the loop by extracting water or reinvesting (for instance,in hatcheries to mitigate for habitat loss) are also closing a loopthat passes beyond the Sierra to include urban and agricul-tural water users in the San Francisco Bay Area, southern Cali-fornia, and the Central Valley. Closing the loop, then, includesidentifying and accounting for the values of all stakeholdersin the Sierra Nevada, regardless of their locations within oroutside the range and understanding how benefits and costsflow among coupled ecosystems.

Although institutions are part of the ecology of the Sierra,nothing ensures that those institutions perceive the entire eco-system, much less manage it in a sustainable manner. Here-tofore, institutions have largely focused on portions ofecosystems. For instance, for streams on the east side of theSierra, the Lahontan Regional Water Quality Control Boardhas jurisdiction over the quality of water, the California Wa-ter Resources Control Board over the rights to the water, theCalifornia Department of Fish and Game over the trout in thewater, and the U.S. Forest Service and the state Departmentof Forestry and Fire Protection over the trees that grow nextto the water. Jurisdictions split along geographic as well asresource lines. The U.S. Forest Service and the National ParkService manage the land along the upper reaches of most Si-erran rivers, while private landowners, the federal Bureau ofLand Management, municipal utilities, and local irrigationdistricts manage much of the land along the lower reaches.There are no existing mechanisms to ensure that the sum ofthe management of the parts of the ecosystem adds up to wisemanagement of the whole ecosystem.

Like all other parts of the Sierran ecosystem, the institutionalcomponents change over time in response to larger forces.

15Sierra Nevada Ecosystems

The Sierra Nevada core area includes 20,663,930 acres. Ofthis, 36% is private. About two-thirds of the land area ispublicly owned (figure 1.7). Most of that is national forest(U.S. Forest Service). Bureau of Land Management (BLM)is the second largest category of public land. The NationalPark Service (NPS), the state of California, and local juris-dictions administer smaller pieces within the SNEP studyarea (table 1.1). Most of the high elevations throughout theSierra are public (see back cover), as are large proportionsof the eastern Sierra. Public lands extend to middle eleva-tions on the west side, with large areas of intermixtures ofprivate and public sections (“checkerboard”) in the north-ern half, which track areas of early railroad crossings ofthe Sierra Nevada. Much of the large private forest com-pany land derives from acquisitions originating from theseearly railroad land grants. South of the central western Si-erra Nevada, fewer large blocks or intermixtures of pri-vate land occur at middle elevations. Below about 3,000feet in the western Sierra, private lands predominate.

Reserve areas account for 21% of the Sierra Nevada, asindicated in table 1.1.

TABLE 1.1

Areas of designated biological reserves in the SNEPcore study area.

Acres AcresPublic/Private Ownership (Subtotal) (Total)

Private Reserves 31,340Nature Conservancy reserves 31,340

State of California 144,675Ecological reserves 2,090State parks and reserves 28,837Wildlife areas 113,748

Federal 4,282,204Bureau of Land ManagementAreas of Critical Environmental

Concern and Wild and 208,550Scenic Rivers

Wilderness Areas 306,535

Fish and Wildlife Service 1,129

National Park ServiceDevils Postpile National Monument 806Lassen Volcanic National Park 37,979Sequoia and

Kings Canyon National Parks 861,077Yosemite National Park 746,121

Forest ServiceResearch Natural Areas 45,617Special Interest Areas 54,916Wild and Scenic Rivers 34,055Wilderness Areas 1,985,419

Total reserve areas 4,458,219

FIGURE 1.7

Sierra Nevada ownership, percentage of land within thecore Sierra Nevada ecoregion, and percentage within thegreater study area. (From volume II, chapter 23.)

❆ Land Ownership and Reserve Allocation in the Sierra Nevada

Core Sierra Nevada

ForestService 41%

BLM 13%NPS 6%

Other Federal1%

Private36%

City, County,Regional 1%

State 1%

Greater Study Area

ForestService 41%

BLM 11%

NPS8%

OtherFederal

<1%

Private37%

City, County,Regional 2%

State1%

16VOLUME I , CHAPTER 1

Population growth and development bring more people intothe region, increasing not only the demand for services butalso the diversity of values and issues influencing manage-ment of the range. The creation of markets for values and ben-efits that heretofore have been allocated by right oradministrative arrangement—water is the preeminent ex-ample—upsets many existing arrangements and creates theneed for different types of institutions. Interagency and inter-governmental cooperation blurs lines of authority and bluntsinstitutional prerogative but may allow movement in arenascurrently stymied by gridlock. Grassroots activism creates newinstitutions, which compete with existing ones for legitimacyand authority. These driving forces interact in different waysin different regions of the Sierra and force the evolution of in-stitutions in the range.

SNEP owes its existence to the desire of Congress to searchfor policies and institutions that can transcend their “ecosys-tem component” status to perceive the Sierra Nevada as a setof ecosystems with links to stakeholders within and outsidethe range, and to manage both extraction and reinvestmentto ensure the long-term persistence of the ecosystem and thepeople who depend upon it.

T H E S I E R R A N E VA DAO F T H E F U T U R E

The images of the Sierra Nevada—snapshots from the past,words and maps from SNEP, mental images of a mountain

range—reveal in sketch the unfolding process that has shapedSierra Nevada ecosystems. Our view of the Sierra is flawed ifwe consider today’s ecological or social environment to bestable: The old-growth forests we study today developed in adifferent environment from our current one and are headedinto a different future. Many of the forests that we now mea-sure and manage originated under an anomalously wet cli-mate. The water systems we have developed are based onpredictions of flow derived from this unusually favorable pe-riod. Snapshots of the present may give us misleading pic-tures of what is needed to support a full range of biotic andhuman systems in the near and distant future.

If there is natural environmental change, does this give li-cense for humans to act however they like in ecosystems? Ifecosystems are always changing, why should it matter if weretain the diversity and function of any specific time and place?It matters because both the rate and the direction of change innatural systems are extremely important to ecosystem sustain-ability. Plants and animals, and the ecosystems they compose,evolve and adapt to the gradual pace of most environmentalchange, that is, they produce the successors who are able tosurvive and prosper. Humans may make conscious decisionsto alter the rate and directions of ecosystem change. The im-portant consideration is that we make these decisions withknowledge of potential consequences. As we consider limitsto change and tease out the practical meaning of sustainability,we are best prepared when we understand the context ofchange in the Sierra Nevada.