SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.1. Physical and Biological Environment

3.1.1. Forest Ecosystem Health

A. Background

Forest and Vegetation Health Concepts, Definitions and Additions to FEIS

In the SNFPA FEIS, there was scarce or scattered reference to ecosystem conditions and consequences related to some key aspects of forest and ecosystem health. While forest and ecosystem health can be ambiguous and variously defined terms, for this SEIS, we are referring to the response of vegetation to climate change, drought, insects and pathogens, and the composition and structure of vegetation relative to the desired conditions specified in the FEIS (USDA 2001, Volume I, Chapter 2, pages 135-143). The desired conditions, particularly related to canopy density and species composition were designed in part to restore conditions that would provide greater resilience to drought, climate change and related potential for severe insect/pathogen mortality events.

Vegetation composition, structure, fire regimes and insect/pathogen related mortality for a given landscape or bioregion are dependent at least partially on prevailing climate. In addition, human influences of vegetation management and manipulation also influence these ecosystem components and processes. Climate characteristics such as temperature and precipitation are not constant but constantly varying. The rate and direction of climate change can vary as well. The magnitude and degree of climate change depend in part on the scale of time period examined. For example, droughts occur when precipitation changes to lower levels on an annual time scale. An overall climatic regime can vary over thousands or millions of years. This analysis focuses on droughts, either as part of current climatic regime or projected future climate regimes.

Droughts have been common in the past in the planning area. Various analyses of tree-ring data suggest that the more recent drought periods (within the last 100 years) are not anomalies when considered in the long-term context of 1,000 years (Fritts and Gordon, 1980, Graumlich, 1991, Fritts et al. 1979). These studies indicate that California has experienced at least six periods of significant precipitation deficit since 1600. In the perspective of a 360-year reconstruction of precipitation, the period since 1890 has been one of moisture surplus. This surplus in combination with fire suppression as well as selective removal of the more drought tolerant pine species since European settlement has resulted in increased forest densities and changed species composition that make forests and other vegetation communities more susceptible to direct and indirectly related drought induced mortality. Vegetation near the limits of species distributions (particularly low levels of precipitation that can be tolerated) is particularly vulnerable to drought (Dale et al. 2001). This is evidenced by the greater concentrations of high mortality events with droughts in the last century in the eastside and lower elevations of the westside in the project area. Further, large portions of the westside mixed conifer zone, particularly on drier portions (ridgetops, upper slopes, south and west-facing aspects) are also vulnerable to high levels of mortality during droughts, particularly where precipitation levels are lower (<40" average annual precipitation). These areas in mixed conifer, although not as dry as the eastside forests, are more productive, so stand densification from fire suppression and consequently competition for scarce water resources, can be elevated (Franklin, pers. comm.). Reports of drought related insect/pathogen mortality in mixed conifer forests of the Stanislaus in 1924 support the notion of greater vulnerability of these drier portions of the mixed conifer forests (Meinecke 1925).

Projections for climate change in the western U.S. include both increases in mean temperature and increases in precipitation (Dale et al. 2001). However, there is also a trend toward greater fluctuations in precipitation and temperature. The fluctuations, particularly toward low precipitation, are more important than mean trends in interpreting potential consequences of future drought. The extensive vegetation mortality currently being experienced in the San Bernardino National Forest as well as large areas of the southwest in Arizona and New Mexico provide a stark example of the potential consequences of several years of drought in dry ecosystems. In these areas, in addition to extensive mortality in conifer-dominated forests, there are entire hillsides of very drought-tolerant manzanita and live oak that are dead or dying.

This supplemental EIS adds information about drought, insect/pathogen related mortality, and composition (particularly with respect to more drought tolerant pine species) to address forest and ecosystem health. In the FEIS, composition of old forest ecosystems was addressed to some degree (USDA 2001, Volume II, Chapter 3, part 3.2, page 150, 157). This section expands the discussion of forest composition, particularly with reference to retention, regeneration, recruitment and restoration of the yellow pines (ponderosa and Jeffrey pine) where they were historically important. Forest density, along with composition is an important factor in determining the degree of vulnerability to severe drought, and insect/pathogen related mortality. Forest density also influences trends in composition, with greater densities favoring perpetuation of shade-intolerant species (e.g. white fir and incense cedar) and lower densities providing more opportunity for regeneration and recruitment of shade-intolerant species (e.g. ponderosa pine). The non-tree, understory component of vegetation can also be influenced by forest or vegetation density as well as the amount of exposed mineral soil surface and direct heat/chemical outputs of fire. Increased shade and reduced mineral soil can lead to reduced vigor, reproduction and survival of understory species that require more light (e.g. Clarkia, Penstemon species) and a mineral seedbed. Some understory species may also be directly stimulated to germinate or flower from the heat or chemical outputs of fire. It is unknown how many understory species in the planning area are fire dependent, let alone enhanced by fire. Given the historic role of fire in the montane and lower elevation portions of the project area, it is likely that there are a number of species that are favored or require fire.

Background on Insects/Pathogens and Abiotic Factors

Insects and diseases have the potential to degrade vegetation in a relatively short time. Whether bark beetle outbreak in combination with drought conditions can cause widespread effects of insects and diseases on the vegetation depends on what their impacts (positive and/or negative) are on ecosystem structure and function and specific management goals and objectives. Management activities that promote tree health and vigor reduce the susceptibility to successful bark beetle attack and also reduce the potential damage from other insects and diseases.

Historically, the most significant widespread, weather-related effect on the vegetation in the Sierra Nevada has been conifer mortality associated with severe moisture stress and bark and engraver beetles. Conifer mortality tends to increase whenever annual precipitation is less than about 80% of normal. Wide fluctuations in annual precipitation are a common occurrence in California and recurrent droughts have been a long-standing feature of the Sierra Nevada climate (Ferrell 1996). In this century, moderate to extreme (on the Palmer Drought Index scale) drought periods in California occurred between 1897-1900, 1923-1925, 1930-1934, 1946-1949, 1958-1962, 1975-1977 and the latest, between 1987-1994.

The key insect pests and pathogens affecting Sierra Nevada forests usually function as members of biotic complexes in which the members are highly interactive. In California's Mediterranean climate, drought is probably the most important predisposing factor to these complexes. (Ferrel 1996). But overly dense stands, fire, logging, urbanization, air pollution, snow breakage, windthrow, and flooding can also weaken trees and predispose, or cause them to become susceptible, to pathogens and insects. Like biotic complexes, environmental factors can be highly interactive.

In the initial years of a drought, a large proportion of the dead trees have some combination of insects and pathogens. As the drought eases, the proportion of dead trees with multiple biotic agents decreases. As this proportion of multiple agents declines, bark beetles become the dominant organisms involved in tree mortality. This occurs because the early mortality is focused on trees weakened as a result of pathogens; in essence removing trees with existing debilitations. After many of these weakened trees are killed, drought and increased insect populations continue to kill trees that are relatively healthy.

Insects

Bark beetles have the largest impact, with sporadic outbreaks causing widespread mortality in virtually all major conifers and forest types. The bark beetles associated with tree mortality include (1) western pine beetle, Dendroctunus brevicomis, in ponderosa pine, (2) Jeffrey pine beetle, Dendroctonus jeffreyi, in Jeffrey pine, (3) mountain pine beetle, Dendroctonus ponderosae, in lodgepole pine, sugar pine and ponderosa pine and (4) fir engraver, Scolytus ventralis, in red fir and white fir. Red turpentine beetle, Dendroctonus valens, often found in association with other pine bark beetles, is commonly seen after prescribed fire, and can contribute to mortality.

Pine engravers such as Ips paraconfusus and Ips pini periodically infest green pine slash. Host material can be created through wind events, snow breakage or harvesting activities. Residual trees can be attacked simultaneously when pine engravers are infesting the slash or later by emergent populations that have developed in the slash. Attacks to pine trees can result in top kill and/or whole tree mortality. In the warmest part of the summer, Ips beetles can complete their lifecycle in 35-40 days. All the above insects are native to the Sierra Nevada, play a diverse role in forest ecosystem dynamics and have evolved in conjunction with the vegetation.

Mortality related to pine bark and fir engraver beetles occurs primarily in small groups or as single trees scattered over several hundred acres. Successful attacks by the pine bark beetles (western, mountain and Jeffrey pine beetles) result in tree mortality. Successful attacks by the fir engraver (in red and white fir) can result in top-kill, branch kill, patch kills along the bole and/or whole tree mortality. In general, mortality occurs in overstocked stands, however during periods of protracted drought, mortality may be expected to occur throughout various stocking levels.

In part because of the biology and host selection behavior of bark and engraver beetles, the condition or vigor of the host tree is critical as to whether attack by beetles will be successful or unsuccessful. Conifer hosts growing under healthy, vigorous conditions are best able to resist attack through their evolved defense mechanisms. Trees that have been weakened by some factor or agent, including drought, diseases, physical injury, lightening, fire, and between-tree competition due to overstocking, are more likely to be successfully attacked. Consequently, regulation of stocking and species composition through vegetation management in combination with the reduction of other predisposing factors, would allow trees to grow as healthy and vigorously as possible and prevent/reduce chances of successful attacks by bark and engraver beetle and subsequent mortality.

Douglas fir tussock moth (DFTM), Orgyia pseudotsugata, is also found in mixed conifer/white fir stands in the Sierra Nevada. Historically, this defoliator has gone into an outbreak about once every 10 years somewhere within the mixed conifer/white fir type in the Southern Cascade and Sierra Nevada ranges. Repeated defoliation by DFTM can cause white fir mortality.

Direct Suppression (tree removal)

Direct suppression of Jeffrey pine beetle infestations in Jeffrey pine by removing infested trees prior to beetle emergence has greatly reduced the number of trees killed in areas where it has been implemented on a site specific basis, specifically on the Truckee RD, Tahoe NF, the Lake Tahoe Basin Management Unit and in Lassen Volcanic National Park. Immediate implementation of infested tree removal activities prior to beetle emergence has resulted in fewer trees attacked the following year and therefore, the maintenance of a Jeffrey pine component in the stand. Conclusions from monitoring studies in outbreaks where no action was taken indicate that trees will continue to die from the original infestation until either hosts are not available or trees are less susceptible to successful attacks due to an increase in growth and vigor or return to normal precipitation levels.

Fire Damaged Trees

Low to moderate intensity fire can damage some residual trees to the extent that they become more susceptible to bark beetle attacks. Trees that sustain cambial and/or foliar damage may be at increased risk to bark and/or engraver beetle attack that would persist until the trees recover their vigor. Red turpentine beetles, Dendroctonus valens, are commonly found attacking conifers in areas that have burned by either prescribed fire or wildfire.

Forest fires of sufficient intensity or residence time to injure cambium and foliage of pine trees make certain trees more attractive to the bark and/or engraver beetles. Many trees that have been only moderately injured by the fire and are capable of recovering may be attacked and killed by beetles after a fire. Fire-injured trees often cause a concentration of beetles within a burned area that lasts for one or two season following a fire. While fire injured trees can attract bark beetles in considerable numbers they do not always afford favorable breeding conditions for new broods. Some of the factors involved in post-fire bark beetle attacks are: level of stress of trees prior to the fire (i.e. drought-stressed), bark beetle populations levels prior to the fire, fire season occurrence, and timing of salvage operations. Fires that result in cambium damage can also create open entry courts for pathogens.

Pathogens and Abiotic Conditions in the Sierra Nevada

White Pine Blister Rust (caused by Cronartium ribicola) -- A non-native fungus that affects white pines (sugar, western white, whitebark, limber, foxtail) and its alternative host, Ribes. The principal effect is mortality of trees that become infected. Smaller trees die rapidly. Mature trees may survive infection, although with sufficient infections, the tree can be predisposed to bark beetle attack.

Dwarf Mistletoes (Arceuthobium spp.) -- Dwarf mistletoes are parasitic seed plants that attack members of the Pinaceae family. They are relatively host specific and require a living host for survival. These agents cause a reduction in the rate of growth of a tree, the development of deformities (cankers, witches brooms), and increase the susceptibility of trees to bark beetle attack and mortality. Dwarf mistletoes commonly interact with other factors, including stocking, precipitation, and insects, to affect their host.

Black Stain Root Disease (caused by Leptographium wagneri) -- locally important mortality. Infected trees are often attacked by bark beetles. This disease is spread through root-feeding beetles that carry the spores of the pathogen, and through root contact with infected trees.

Annosus Root Disease (caused by Heterobasidion annosum) -- extensively distributed pathogen responsible for high levels of mortality, especially during periods of drought stress when it can weaken trees sufficiently so that successful beetle attacks result in mortality (1987 Forest Pest Conditions, CFPC). Adverse effects include mortality, reduction of vegetative cover, and creation of hazard trees. Two strains are present, one that infects true firs, giant sequoia, spruce, and hemlock, and one that infects pines, incense cedar, western juniper and hardwoods. The strain in true fir results in root and heartwood rot, while the strain in pine often causes mortality through girdling. Spread of the disease is through airborne spores or through root-to-root contact between infected and uninfected trees. Impacts increase with multiple logging entries, generally as a result of residual tree damage or stumps, allowing spore entry.

Sudden Oak Death (caused by Phytophthora ramorum) -- This pathogen has caused localized intensive mortality in tanoaks and coast live oaks within the Coast Range. However, this recently discovered disease is not yet a Sierran forest problem. Host species are found in the Sierra Nevada: Douglas-fir, black oak, bigleaf maple, madrone, tanoak and California laurel. Neither the method of spread of the pathogen, its requirements for successful infection, nor the conditions conducive to tree mortality are clearly understood. For these reasons, its potential impacts in the Sierra Nevada are unknown and the 2002 surveys for signs and symptoms will continue in 2003.

Air Pollution (Ozone injury) -- In studies in Southern California on similar forest species, damage results in chlorotic, sparse foliage and reduced exudation of defensive resin in response to bark beetle attack, and therefore an increased risk to bark beetles (Ferrell 1996).

Vegetation Density, Composition, Insects/Pathogens and Vegetation Management

Active vegetation management, including thinning through hand treatments, mechanical removal or burning are important means of restoring and maintaining forest health, particularly in eastside pine and westside ponderosa pine and mixed conifer forests. Vegetation management can effectively be used to reduce vegetation density, modify species composition; thereby indirectly reducing drought and insect/pathogen mortality and restoring desired conditions. Vegetation management can also be used to directly affect composition and insect/pathogen mortality through reforestation and selective removal of infected trees.

The type of vegetation management that is most effective and appropriate is highly dependent upon the specific management objectives and site conditions. Although both mechanical thinning and prescribed fire can reduce forest density, both of these vegetation management activities have negative as well as positive consequences. Prescribed burning can be relatively inexpensive to implement but can cause air quality degradation and may not always achieve desired structural or compositional objectives. For example, there are situations when the desired thinning is of trees with sufficient bark thickness that only very hot fires can kill them. In this case, a "hot" prescribed fire may damage desirable trees or consume substantial amounts of duff and down logs. In another example, dense understory trees may form a "ladder" to adjacent valuable, large or old trees that may experience extensive crown mortality as the prescribed fire burns through the understory and torches live crowns. Further, burning in situations where there are large, old pines that have a large accumulation of duff and bark slough at the base can result in increased likelihood of cambial damage and potential mortality - although these effects can sometimes be mitigated with firing patterns and other fire behavior modifications. On the other hand, mechanical treatments can result in increased incidence of pathogens and insects through creation of host sites on stumps or in slash - although these effects can also often be mitigated with management practices. Mechanical treatments can cause soil compaction. Both mechanical and fire treatments can expose mineral soil which provides a seedbed for natural tree reproduction and opportunity for herbaceous and shrub growth. There are also different economic and social differences between the two types of vegetation management treatments. On steeper slopes, it may be economically impractical to conduct extensive mechanical thinning. There can be economic benefits to mechanical thinning on less steep ground that can provide a means to treat or restore areas elsewhere.

Conditions vary by with the ecosystem or forest type as well. In general, most of the eastside forests are in a state where mechanical treatment is an important first step in forest health restoration. Dense thickets of pine are difficult to burn and achieve all of the desired structural conditions. In addition, soil nutrient processes are more sensitive and fires intense enough to decrease density may result in unwanted losses of soil productivity. In more productive westside forests, the tradeoffs are different and depend more upon the site-specific stand structure. In upper montane, red fir forests, the changes in forest structure and composition since European settlement have been less severe and therefore, the need to conduct restoration management for forest health less important.

Stands that are managed at or below their site capacity will result in reduced mortality of large diameter trees and an increase in mid-diameter trees available to grow into large diameter classes. Selecting for some diversity of residual tree species during thinning is desired as bark beetles are fairly host-specific and diversity should guarantee that some trees would remain alive during elevated stress periods. Removing competing vegetation from plantations will reduce the susceptibility to various insects that often cause damage to regeneration.

Regeneration

Both alternatives emphasize protecting, increasing and perpetuating old forest ecosystems and associated species. Vegetation management activities are designed to increase the density of large trees, increase structural diversity of vegetation, restore the historic species composition and improve the continuity and distribution of old forest. Therefore most recruitment of new regeneration into stands will be under varying densities of overstory trees, except where stand replacing fire or insect outbreaks cause larger openings.

In general, under residual trees, soil moisture and light are less available to young seedlings than in openings. This generally reduces growth rates of all conifer species but has the greatest adverse impacts on growth and survival of shade intolerant species such as ponderosa pine and black oak. Under residual trees, the environmental regime of relatively cool soil surface temperatures and short intervals of overhead light favor the more tolerant species, allowing white fir, incense cedar, sugar pine and Douglas-fir to become dominant. On a high site, mixed conifer stand in northern California, managed under a single tree selection regime (high level of residual trees), Lilieholm (1990) observed that while the best growing seedlings included all species of the mixed conifer forest type, intolerant pines (were) virtually absent from the small and large sapling classes and white fir and Douglas-fir comprised over 85% of the large sapling class.

Residual overstory trees affect the seedling environment by casting shade which moderates temperature extremes. Summer temperatures may be reduced by as much as 10 degrees F and winter extremes may be warmer by a similar amount (Geiger 1966). However, other than occasional sunflecks, the sun shines in the openings only when directly overhead. Sun loving (shade intolerant) species like ponderosa pine and black oak may establish under shade, but typically do not grow as well as more shade tolerant species. Hence heavier shade from residual trees in untreated and lightly thinned areas will tend to favor survival and growth of more tolerant species over ponderosa and sugar pine.

Despite moderating some microsite conditions, residual trees use water, competing strongly with seedlings for this limiting resource. On a good site in northern California Ziemer (1968) measured soil moisture around an isolated 28 inch diameter sugar pine and found that soil moisture depletion extended outward a distance of slightly over 20 feet from the base of the tree and somewhat deeper than 15 feet under the tree. After thinning or other harvest that creates openings between trees, existing roots of bordering trees expand rapidly and capture additional resources. Ziemer (1964) found that roots of bordering trees extended new roots about 10 feet into newly created openings and about 30 feet into 5-year old openings. Clearly root competition from residual overstory trees reduces availability of moisture for young seedlings, adversely affecting survival and growth.

Residual trees may also favor populations of damaging seedling predators, insects and pathogens. Black tailed deer, known to feed on young natural or planted conifers may be more numerous close to hiding cover provided by residual trees. Pocket gopher populations are often highest in thinned stands where the open the canopy allows development of forbs in the understory. Pocket gophers are capable of decimating entire crops of young confer seedlings and have also been observed to damage much larger trees. Dwarf mistletoe (Arceuthobium spp.) readily spreads from residual trees onto young seedlings and saplings in the understory. Cooler, moist conditions under residual trees may also favor western gall rust and white pine blister rust, diseases that kill or stunt young conifers.

USDA Forest Service · Pacific Southwest Region