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Global Climate Change and California Oaks

Contents

This paper is born of ideas that emerging global phenomena may prove of overarching importance to the fate of California oaks, and that successful protection of these trees, if indeed it is possible, may require substantial departure from past strategies. Many California oak advocates and resource specialists give only passing thought to climate change. They reason that damage to oak ecosystems from familiar depredations like agriculture and urbanization is enormous and ongoing, while dangers from human impacts on Earth's climate remain ill-defined and may actually prove minimal. They note also that although effective action to counter human-induced climate destabilization seems forbiddingly difficult, we have already reaped visible benefit by altering grazing practices, changing zoning and general plans, and protecting oaks during construction.

For nearly twenty years, the authors have monitored, planted, and cared for native oaks (Quercus agrifolia, Q. douglassii, and Q. lobata) on more than a thousand semi-rural acres on the San Francisco Peninsula. By guarding oaks against unsustainable grazing, urban sprawl, and firewood cutting, and by suppressing competing exotic vegetation, we have conserved the habitat-and perhaps increased the vigor-of many thousands of trees. By planting and nurturing acorns and seedlings among populations that appeared to be failing to regenerate naturally, we have established more than two thousand new saplings.

Despite these gains, we are concerned that our actions may prove inadequate to our objective: self-sustaining oak populations on the land we steward. We perceive that ongoing human-mediated global climate change is a challenge of a new genre, destined possibly to reverse our own and others' achievements to date, and perhaps even to inflict additional losses far greater than any previously endured.

Consider the following contrasts between contemporary anthropogenic climate change and prior threats:

  1. global vs. local scale;
  2. pervasive vs. narrow impacts on ecosystem integrity;
  3. irreversible vs. reversible consequences;
  4. requires action based upon indeterminate vs. proven damage; and, most importantly,
  5. rooted in behaviors central to the lives of large numbers of people around the world vs. directly resulting from the actions of a tiny fraction of humankind.

This paper is less an effort to predict in detail the consequences of climate change for California oaks than an argument that we already have sufficient information to warrant responding vigorously to this threat. To frame the issue, we begin with a summary of recent and projected human alterations to the gaseous composition of the atmosphere, and with an overview of appraisals of resultant effects on climate, and on ecosystem elements like soils and water. Next we review some of the literature examining possible impacts of sudden climate change on oaks and other biota. Then we discuss how we are adapting our own research, advocacy, and field work to the accumulating evidence of anthropogenic global climate change, noting obstacles that we have encountered and offering our thoughts about their underpinnings and ways to surmount them. Finally we suggest how people may husband oaks through what appears likely to be at least a difficult transitional period, and how we may reduce human threats to their longer-term well-being.

Human Impacts on Atmospheric Composition

The gaseous composition of Earth's atmosphere was relatively stable from the end of the last ice age, about ten thousand years ago, until the 1800s. Over the past century or so, people have substantially altered this long-standing balance (Vitousek, 1994). By burning fossil fuels, clearing forests, increasing domesticated livestock populations, and processing industrial materials we have added to the amounts of carbon dioxide, nitrous oxide, and methane in the air, and we have released artificial chemicals such as chlorofluorocarbons (CFCs), which alter atmospheric composition both by their presence, and by their diminution of other components (e.g. stratospheric ozone) (Mitchell, 1989; Rowland, 1989).

Carbon dioxide, nitrous oxide, methane, and CFCs are all termed "greenhouse gases" because they absorb infrared radiation, impeding the escape of heat from Earth into space, and thereby increasing Earth's temperature (Mitchell, 1989). Already we have raised the concentration of atmospheric CO2 to nearly 30% above pre-industrial levels-higher than it's been for at least 150,000 years (Houghton et al, 1996). If we persist in current behaviors, we will likely double pre-industrial levels by mid-21st century. Methane is now at two and a half times its pre-industrial level, and is likely to reach triple that level by 2015. We have elevated the amount of atmospheric chlorine sixfold in this century alone, and we are still increasing it (Rowland, 1991).

The speed and magnitude of these changes in greenhouse gas concentrations are extraordinary. For example, the current increase in CO2 concentration is approximately equal to the range of the fluctuations which accompanied the advances and retreats of glacial ice over a period of 160,000 years (Vitousek, 1994). While earlier shifts are thought to have occurred over thousands of years, fully half of the current one has occurred in only thirty (Vitousek, 1992).

CFCs warrant close attention both for their efficiency in blocking escape of heat-each molecule has the effect of ~20,000 CO2 molecules-and for their role in destruction of stratospheric ozone which shields Earth from biologically damaging UVb (Rowland, 1991). CFCs and related synthetics have been present in the biosphere only a few decades. Despite international agreements to curtail production, CFCs are predicted to persist at elevated levels well into, and possibly through, the 21st century. Some will persist for centuries after releases halt (Rowland, 1991; Bojkov, 1995).

Stratospheric ozone in northern hemisphere mid-latitude locations like California has declined ~6% as a result of CFC releases (US EPA , 1995b). Further losses are expected as long as atmospheric chlorine loads exceed 3 ppbv (Bojkov, 1995). Wuebbles has estimated a 25% depletion over California by mid-21st century (1989, cited in Knox, 1991). A burgeoning black market in CFCs has drawn into question predictions that ozone recovery to historic levels might occur within a few decades (Arnst and McWilliams, 1997).

Climatological Consequences of Human Changes to the Atmosphere

The changes described above are already measurably affecting temperature, precipitation, insolation, and wind. Because of system momentum, full effects of recent atmospheric changes are yet to be felt. As humans continue to alter the atmosphere, we make even more disruption almost certain.

Temperature

The Intergovernmental Panel on Climate Change (IPCC) recently concluded that human disturbance of the atmosphere will likely cause global average temperatures to rise at an accelerating rate, producing overall warming of 0.9-3.5° C by the end of the 21st century. Even if atmospheric concentrations of CO2 and other greenhouse gases are stabilized by then, as much as half of overall warming will have yet to occur because of thermal inertia of oceans (Houghton et al, 1996). During the last ice age, the Earth was only about 5° C cooler than it is today (Goudie, 1992). Temperature increases are projected to be greater-perhaps twice the mean-at high latitudes, and less near the equator. Greater seasonal and year-to-year variability is likely (Houghton et al, 1996).

In California, because of maritime influences and variations in topography, local results of warming will vary. For example, a strengthened California current-one possible effect of overall warming-may yield increased fog with resultant cooling of the coast during summer. Alternatively, global warming may weaken the California current. Even if this occurs, higher overall temperatures may make coastal California cooler and wetter by inducing greater and more frequent inland movement of the marine layer (Knox, 1991, Botkin et al 1991).

Precipitation

Warming is projected to increase precipitation globally by ~10%, and may significantly alter its form, timing, intensity, and distribution (Knox, 1991). Seasonal shifts are possible, and wider fluctuations from norms are likely (Vaux, 1991). Reports from thousands of U. S weather stations over the past century show a nearly ten percent rise in precipitation since 1910. Most of this can be accounted for by increased intensity in the most extreme daily rainfall events (Schneider, 1997b). An overall increase in California precipitation is expected, but changes for particular locales fall in the range of ±20% (Vaux, 1991). More certain is that rain will replace snow over 100-150 m of elevation for each 1° C of warming (Gleick, 1987).

Sunlight

Ozone absorbs ultraviolet light. By reducing upper atmosphere concentrations of this gas, humans have allowed more biologically damaging high-frequency UVb to reach Earth's surface (de Gruijl, 1994). In 1991, UVb within California was estimated to be 10-20% above levels of mid-20th century (Knox, 1991). UVb is generally thought to be increasing about 2% for each 1% decrease in ozone, suggesting that it may peak at 20-40% above historic levels (Madronich et al, 1994). In 1996, however, researchers in Hawaii described what they perceive to be a chemical and dynamical synergism augmenting effects over at least part of the UV spectrum (Hoffmann et al, 1996).

Some researchers expect that warming will increase cloud cover locally and seasonally, reducing the duration and intensity of sunlight, and further altering the proportions of solar energy of various frequencies which reach the Earth's surface (Westman and Malanson, 1992).

Wind

As additional heat energy is absorbed by the atmosphere, storm winds may increase in strength and frequency. Though much uncertainty remains, meteorologists are accumulating evidence for such a trend. For example, in 1995, the United States had the most active Atlantic hurricane season since the 1930s (Flavin, 1996; Botkin et al, 1991).

Many parts of California are already regularly subjected to powerful winds. If the California current is strengthened by global warming, onshore winds will probably increase. In addition, overall warming may shift storm tracks northward, subjecting California to greater risk from high velocity wind (Knox, 1991).

Effects of Climate Change on Surface Features

Stream and river flows, lake levels and flushing, ocean levels, aquifer recharge, wetland functioning, and soil depth, texture, and nutrient content are all dependent upon climate and are being affected by the changes underway (Vaux, 1991; Botkin, 1991).

Water

Increased precipitation, especially where peak hourly or daily rainfall is higher than it had been, may result in flooding (Watson et al, 1996). Evidence from the geological record of the past 7,000 years shows that changes in mean annual global temperatures of only 1-2° C and increases in mean annual precipitation of only 10-20% can bring frequent floods of a magnitude that previously occurred only once every 500 years (Knox, 1993).

With a 2-4° C warming, California snowlines are expected to rise by 200-600 m vertically, and the snowpack will probably melt earlier (Gleick, 1987; Vaux, 1991). If this occurs, runoff will increase during winter and early spring, and decrease during late spring and summer. These changes may bring more frequent and extensive winter and spring floods; and they may also lessen the summer and autumn availability of surface water. The amount of water stored in snowpack is projected to drop 33% statewide in an average year, with Sacramento Basin losses projected to be at least 40%, and San Joaquin Basin losses about 25% (Knox, 1991; Vaux, 1991).

One researcher suggests that a 4° C rise in temperature will increase evaporative losses from lakes, rivers, streams, and soils enough to reduce overall annual run-off in northern California by 10%, with summer reductions as high as 62% (Gleick, 1988).

Groundwater drawdown and recharge may well be markedly different as a result both of climate change and of human action to compensate for it, and overall drop of groundwater levels is likely (Vaux, 1991).

Sediment burdens may increase as heavier storms augment runoff, as soils previously subjected primarily to snow are scoured by rain, and as those once protected by vegetative cover are left bare by the death of heat- and drought-stressed plants. Accumulation of water-borne sediment in artificial reservoirs and natural lakes and estuaries may further exacerbate flooding during peak flows (Vaux, 1991; Botkin et al, 1991).

Oceans have risen 10-25 cm in this century as warming seawater has expanded and polar ice has melted. If warming continues as projected, cumulative worldwide mean increases in sea levels by the end of the 21st century are predicted by the IPCC to be about 50 cm, with much local variation (Houghton et al, 1996).

In 1989, the National Research Council estimated sea level rises during the next fifty years along California shores on the order of .2-1 meter. Intrusion of brackish water into coastal aquifers and surface waters, particularly in the San Joaquin/Sacramento delta, and flooding of low-lying areas around San Francisco Bay and in the Central Valley are likely (Vaux, 1991). If global warming continues beyond the 0.9-3.5° C projected for the next century, sea levels may continue rising, extending and intensifying the impacts described here.

Wetlands of all kinds-tidal, estuarine, riverine, palustrine, and lacustrine-will be threatened by changes in CO2 concentration, solar energy, temperature, precipitation, runoff, evaporation, and ocean levels (Vaux, 1991).

Soils

Increased temperatures, greater evapotranspirative losses, more severe storms and runoff, increased flooding, and higher winds will probably accelerate weathering and erosion, and may significantly alter soil moisture, aeration, nutrient levels, organic content, and soil organism populations. Loss of plant cover may reinforce these trends, and soil depth may be altered in many places (Botkin et al, 1991).

Impacts of Climate Change on California Oaks

The term "California oaks" is geopolitical as well as ecological. It includes a few species that occur only in small portions of California, several that are widely distributed throughout much of the state, and one whose range extends beyond the state's borders. Some populations are already in decline or at immediate risk; some appear relatively stable. Different subsets of this broad category will likely vary widely in their responses to climate change.

California vegetation types with substantial oak components-including oak woodland, blue oak-gray pine woodland, inland prairie, and chaparral-are tightly coupled to both temperature and precipitation. Because the ecosystems in which California oaks grow are typically semi-arid, sometimes bordering on desert, they may be particularly sensitive to warming (Watson et al, 1996).

Like all living things, oaks persist by maintaining a match between their internal information and the qualities of their environment. Raven and Axelrod (1978) assert that the pattern of Mediterranean climate characteristic of California oak habitat-cool, wet winters and warm, dry summers-emerged in the Quaternary (1 my bp). Since then co-evolution of oaks and their surroundings has proceeded within well-defined bounds of scale, speed, and quality. Ongoing global climate changes already exceed some of these. Further violations, posing an unprecedented test of oaks' adaptivity, are certain.

As we have discussed alterations of atmospheric composition, climatological consequences, and impacts on soil and water, we have become progressively less certain of our predictions. In assessing how oaks will be affected by global climate change, we take a further step into indeterminacy. Researchers have widely differing views about the degrees to which oaks will expand beyond, persist in, or disappear from their current ranges. Though accumulating evidence will confirm some forecasts and strengthen our confidence in others, the complexity of the ecosystem and the limitations of our modeling ensure that much about the impacts of global climate change on oaks will remain unknowable even after they occur.

Mechanisms for Climatic Impact on Oaks

Oak species differ in sensitivity to CO2, temperature, water, light, soil, and the presence or absence of other species. Their response to each of these may fluctuate with stages in their life cycles, and will vary also with limiting factors at the boundaries of particular habitats. Climate change may affect reproductive success, vigor, and mortality at many ages (Botkin et al, 1991).

Higher CO2 levels may accelerate growth and improve efficiency of water use during photosynthesis. Oaks admit CO2 and emit water vapor and oxygen through stomata in their leaves. As CO2 concentration rises, plant needs can be satisfied without opening stomata as widely, and less water vapor escapes. This is potentially an advantage to oak species that are metabolically active during summer (Woodward, 1992).

Untimely or excessive heat, cold, rain, or drought may impede flower development, pollination, acorn numbers and viability, and seedling establishment. Warmth may stimulate growth, but excessive heat decreases it, and if prolonged or intense enough can be fatal. Low temperatures may suppress insects and other organisms which can damage or kill oaks, but they also limit growing season. Even short periods of extreme heat or cold during critical times may injure or kill. Because temperatures are expected to become more volatile, damage arising from unseasonable or extreme heat and cold will likely become more common. Synergies of unusual temperature and precipitation may amplify familiar effects, and generate wholly unexpected ones.

Reductions in snowpack and late-season run-off may diminish availability of water during the warmest months with the longest days, and may also bring saltwater intrusion into low-lying areas. Both types of change might prove devastating to oaks (Lewis et al, 1991; Botkin et al, 1991).

Increases or decreases in cloudiness and in stratospheric transparency to UVb will alter light energy available, possibly affecting photosynthesis and evapotranspiration. Ultraviolet radiation can damage many important biologically active molecules, including DNA, and current and expected levels are beyond anything oaks and many of their symbionts have previously endured (de Gruijl, 1994). Already ozone depletion and resultant rise in UVb have been implicated in damage to populations as disparate as ocean corals (Vitousek, 1993) and human beings (de Gruijl, 1994).

Die-off of understory plants may result in disruption of beneficial symbioses, reduced percolation-further limiting water availability, and heating of exposed soils to levels fatal to oak seedlings and damaging to mature trees. Colonization by invasive species may pose added obstacles to regeneration. Woodward (1992) has observed an 8% increase in plant family diversity for every 10° C increase in minimum temperatures. Warming is likely to lead to at least temporary increases in biodiversity, with persistence of oaks and their historical symbionts in their current ranges depending upon successful competition with new challengers in unfamiliar conditions.

Stressed oaks and other species may become more vulnerable to pests of all kinds. Standing dead biomass may fuel more frequent, more prolonged, and hotter fires, which kill additional seedlings or even mature trees (Botkin et al, 1991).

On slopes of the Sierra foothills and the coastal ranges, erosion from the combined effects of understory species losses to drought, fire, and increasingly violent storms may accelerate decline in older trees and make reseeding and seedling survival in situ, as well as migration to other areas, less likely (Botkin et al, 1991).

Once the fabric of life is rent, a cascade of unforeseen-or even difficult to imagine-effects may ensue. For example, extensive loss of northern and temperate boreal forests during the next few decades may release tens of billions of tons of additional carbon into the atmosphere. Warming of tundra, with attendant decay of long-frozen organic detritus, may generate immense quantities of methane and CO2 (Woodwell and Mackenzie, 1995). Both of these processes may further accelerate warming and intensify resulting impacts on oaks and oak habitat.

Migration as an Adaptation to Climate Change

Obstacles to oaks' migration are many. Unsuitability of contiguous or proximate soils and slopes, momentum in existing plant communities, and competition by weedy species well-adapted to disturbance all pose challenges. Moreover, oaks themselves are in several important ways ill-equipped for rapid migration. They require several years to produce their first seed, and decades to reach reproductive maturity. Their seed production is modest by contrast to that of many plants, and often intermittent, and dispersal is limited by the sheer size of acorns (McBride and Mossadegh, 1990; Westman and Malanson, 1992; Woodward, 1992).

Although some may imagine oaks moving northward or upslope in response to warming, California's diverse physiography often bars such migration. For example, there are no geographic equivalents of the Salinas Valley or the Napa Valley anywhere between Santa Rosa and Washington State (Lewis et al, 1991). In addition, humans have fragmented oak populations and habitat, and have blocked many potential migration corridors with urban settlements and agricultural uses.

If warming stops within the limits of current projections, existing and potential future ranges of particular oak species may indeed overlap, and surviving populations may eventually be able to migrate into newly-available zones of favorable climate. Under transitional conditions, squirrels, jays, and other acorn-planting rodents and birds may increase their numbers, and become even more effective seed dispersers. In any event, oaks' genetic variability may afford them some advantage in competing (McBride and Mossadegh, 1990).

If warming continues beyond what is currently predicted, however, there may be no overlap between existing and future habitats. With each increment of distance, successful migration becomes less likely. Colonization of outlier patches is difficult in a landscape as topographically and geographically complex, and as thoroughly fragmented by humans, as California's.

Even where contiguous potential habitat allows for migration, we have posed an unprecedented challenge by the speed of the changes we have set in motion. During the last period of glacial retreat, sustained, globally-averaged warming of a few degrees occurred over thousands of years. We are projected to generate a shift of this magnitude in mere decades. With mid-latitude temperatures varying ~1° C per 100 kilometers of north-south travel, a 2-4° C warming corresponds to a 200-400 km poleward shift of thermal zones (Roberts, 1989). If such a warming occurs in a century, it will entail movement of kilometers each year, a rate which appears well beyond the capability of oaks, given the time they require to reach reproductive maturity, their seed dispersal ranges, and observed patterns of ecological succession.

Margaret Davis and Catherine Zabinski (1992) studied plant migration in response to warming at the end of the last ice age and concluded that individual species moved at different rates and even in different directions. Such migration can result in new, "no-analog" habitats depauperate in pollinators, dispersal agents, or other critical-link species (Schneider, 1997a).

Observed and Predicted Effects

California oaks may already be waning as a result of climate change. In recent decades, blue oak (Q. douglassii), the dominant native low-elevation tree in the state, has been failing to regenerate. While researchers typically attribute blue oaks' decline to grazing, to increases in populations of rodents resulting from extirpation of their predators, or to inability to compete with non-native annual grasses for limited water, Lewis et al (1992) note that "the only [blue] oaks standing today are those that germinated during periods of 2 or 3 consecutive wet years. The last such period occurred about 60 years ago. A drier environment caused by global warming could conceivably bring about the elimination of the blue oak in California." Others have noted local disappearance of valley oak, and conjecture that this might be attributable to falling water tables (Schoenherr, 1992). This may partially be a result of prolonged drought linked to increased climate volatility.

Regardless of whether climate-induced changes have begun, and of how great they will ultimately prove, initial effects will probably be subtle, and most evident at the margins. Increases and decreases in seed production and seedling survival may be early indicators of climatological impacts where populations of mature trees appear little changed (Davis and Zabinski, 1992). If late-season stream flows diminish as projected, riparian habitat edges may contract inward and downstream. Also, streamside habitat may narrow if higher-volume winter and early spring flows accelerate bank erosion, or if floods prove directly fatal, or deposit intolerable sediment over root zones or crowns. Where saltwater intrusion currently limits oak survival, as it may in low-lying areas adjoining San Francisco Bay, rising ocean levels and wind-borne salt spray may further restrict their range (Botkin et al, 1991).

Oaks may benefit from some aspects of climate change. Increased warmth, and in some areas greater precipitation, may enable them to become more securely established or to expand their range where lack of heat or water are now constraints. McBride and Mossadegh (1990) assessed responses of California oaks to climate change using models developed at the Goddard Institute for Space Studies (GISS), Geophysical Fluid Dynamics Laboratory (GFDL), and Oregon State University (OSU). They concluded that because greater precipitation will offset higher temperatures in northern California, and because more efficient use of water resulting from elevated CO2 and existing adaptations to drought will enable oaks to persist in the San Joaquin drainage, "distributions of arboreal species of oaks will not be significantly impacted."

Research by others suggests that where oak populations are at the threshold of their tolerance for dry conditions, the hotter, drier climate which may accompany global warming over parts of California may eliminate them. When Westman & Malanson (1992) applied the GISS and GFDL models, they found that expected alterations in temperature and precipitation were likely to lead to expansion of chaparral at the expense of southern oak woodland and blue oak-gray pine woodland. Neilson (1993) asserts that under most models, greater evapotranspiration more than offsets benefits from increases in precipitation and water use efficiency. Woodward (1992) notes that because gases besides CO2 contribute to global warming, actual CO2 will only be about 1.5 times historical levels when temperatures reach the level predicted for "doubled CO2," and that as a result, models of plant response to a doubling of CO2 and studies performed at these concentrations underestimate moisture stress.

T. Webb (1986) has proposed that the ratio of plant taxa response time to the rate of climate change, or period of climate forcing, is a guide in assessing the likelihood of successful adaptation. If the ratio is small (e.g. 200 years/20,000 years) dynamic equilibrium can prevail. If it is larger (e.g. 200 years/200 years) then disequilibrium exists. Response times for tree taxa are yet to be determined conclusively, but minimums on the order of 50-200 years have been estimated. These are similar in length to the period of predicted changes now occurring, and imply disequilibria.

S. P. Hamburg and C. V. Cogbill (1988) describe an example of such a disequilibrium when they report that as growing season has lengthened over the last 180 years in mixed boreal conifer and deciduous broadleaved forest of the eastern U.S., canopy dominance by conifers has been gradually decreasing, and red spruce (Picea rubens) has been virtually extinguished.

Joseph Knox, Director of the National Institute for Global Environmental Change at UC Davis, and editor of Global Climate Change and California, described his group's work as "plausible estimates ... which have been made as consistent as possible with the current consensus understanding of the greenhouse effect." He reported that, "The panel estimates that 20-50% of the area occupied by natural ecosystems will no longer be suitable for the communities that exist there now ..." and concluded bluntly that, "Diebacks ... and loss of species could well prevail ..." (Knox, 1991).

McBride and Mossadegh (1990) cited a study conducted a decade ago, which offers a close parallel to our attempts to foresee the impacts of global climate change on oaks. Woodman and Furiness (1988) evaluated the effects of potential climatic change on the major commercial conifer species in California, and concluded that the state was "unlikely to experience significant large-scale reductions ... in the next century." Yet four of the ten largest California wildfires of the past sixty years occurred between 1987 and 1996 (California Department of Forestry and Fire Protection, 1997). Exceptional heat and drought, and insect infestation of stressed trees were factors in these fires. A link to global climate change remains unproven, yet we may fairly ask whether this threat was accurately assessed, and what relation exists between Woodman's and Furiness' sanguine conclusion and ensuing losses.

EPA researchers have warned that, "Greenhouse warming will spell doom for many forests across the United States. Total forested area in the West could be dramatically reduced. Some species would go locally extinct." Even where they deemed dominant trees possibly able to adapt, they characterized chances of survival for many understory plants as "disappearingly small" (Roberts, 1989).

Though there are many grounds to assert that oaks will survive the next century, there is mounting evidence that they will be sorely tested by human-generated climate change.

Evolving Our Response to Global Climate Change

Nearly twenty years ago one of the authors noted that California native oaks were dying without successors on Stanford University lands. With images of Johnny Appleseed and "The Man Who Planted Trees," we began sowing acorns. Our results were disappointing, so we sought assistance from Stanford and UC Berkeley faculty, and from UC Extension and California Division of Forestry staff. From them we learned that oaks in many parts of the California were apparently failing to regenerate, and with their guidance, we began a series of trials. After forestry and landscape architect consultants to Stanford prepared a vegetation management plan, with special emphasis upon oak preservation and regeneration, we were contracted to implement it.

Both our own initial activities and the vegetation management plan were founded on assumptions that proper local resource management was sufficient for oak regeneration. Our tools were prohibition of tree-cutting and of downed wood removal, modified grazing regimes, low density zoning, rodent suppression, restrictions on road construction, limited vehicular access, clustered building, eradication of exotics, re-establishment of natives, fire management, and regulation of recreational use.

Despite these interventions, we observed disconcerting changes to the land we steward. Fox and coyote became rare. Rodent populations burgeoned. Stands of exotics like mustard became denser and more extensive. Most oaks produced few or no acorns.

Reports from other places also were disquieting. Record forest fires swept across the western United States. Long-established patterns of distribution of populations ranging from Monterey Bay snails (Barry, 1995) to Edith's checkerspot butterflies (Parmesan, 1994) shifted. Record heat, cold, rain, drought, winds, and floods struck around the globe (Flavin, 1996). And a steady stream of scientific research suggested that these and other worrisome ecosystem disruptions were human-driven.

As we have become more aware of the linkages between oaks and global phenomena, our own attitudes and strategies have evolved. We have gradually abandoned thoughts that our tree planting and care will have lasting or significant impacts on the landscape. Promises about "restoring" nature, with which we once motivated ourselves and others, have been supplanted by cautions against such hubris. Dreams of returning to admire our handiwork in forty or fifty years have been tempered by questions about what more we will do if oaks are to persist.

With new volunteers and before community audiences interested in conservation and environmental protection we increasingly emphasize oaks' dependence upon the integrity of the global ecosystem, and we outline the unprecedented ways in which humans are disturbing that system. What once was primarily an oak project is now much more a people project, by which we and others become aware of the laws of nature, the consequences of human choices, and the importance of deeply and persistently questioning what we want, how we can get it, and above all, how we know these things.

This transformation has at times been difficult. Some volunteers and audiences have reacted with anger when we challenged long-cherished notions. Our Stanford operating personnel clients have reminded us that we are funded to produce visible results in the landscape, rather than to teach. Prospective clients and collaborators have sought the services of others when we refused to characterize our activities as "restoration." Donors and influential community members have recoiled from calls for sweeping reform, and have criticized our actions and withdrawn or withheld support.

Why are we and others only slowly acknowledging and rising to the challenge of anthropogenic climate change, one of the greatest threats to our own and our descendents well-being? We offer a few ideas, confident that our list is far from exhaustive. For centuries, Europeans and North Americans have led the way in using the leverage of fossil fuel burning to realize a vision of progress by accelerating conversion of nature to artifact. As we have gained the equivalent of slave labor in the form of fossil fuel energy-and capital plant and equipment converted from it-we have also transformed political economy from a consciously communal enterprise to one much more readily imagined to be individualistic, and we have coerced people around the world to follow suit. Now belief, law, and custom are everywhere increasingly uniform, and are reflections of centuries of apparent success in improving upon nature by manipulating it, and in defining self-interest narrowly.

These ways of thinking are singularly maladapted to our current circumstances. Substantially reducing our impacts on climate entails gross reductions in fossil fuel burning, deforestation, CFC releases, and other activities central to many lives. Many of us are eager to believe that the current order can continue, because we want it to. Even those of us who recognize that an end to recent trends is inevitable, and see benefit in that occurring sooner rather than later, face obstacles to voicing such views. In governmental agencies, private enterprise, non-profit organizations, and informal groups, we encounter many determined to maintain the current order by implicitly or explicitly denying global climate change and pretending that humanity can continue with business as usual. Jobs, funding, promotion, publication, and the collateral rewards they bring have been withheld from those who dare suggest that Nature will not countenance more of the same from us. As we weigh the very evident personal costs of addressing climate change against its indeterminate impacts and the uncertain effects of our own actions to arrest it, we have repeatedly chosen the combination of known present benefit and unknown future loss over that of definite present sacrifice and vague future benefit. Unless we break away from habitual patterns of thought and behavior, we will remain at once committed to action by which we are driving climate disruption and bound to a method of analysis by which we can only preserve that commitment.

If we acknowledge the near certainty that climate change is underway, that each increment of change entails additional risk for oaks and for us, that slowing or stopping it will require broad-based public support extending far beyond our community of special interest, and that addressing root causes embedded deep in our current world-view and in the actions of our own and myriad others' everyday lives will likely be necessary, then we will alter our response to work simultaneously within, with others, and with oaks in the landscape.

Recommendations

The long-term welfare of oaks depends to a great extent upon short-term success in developing and implementing resource management policies to effectively protect existing and potential oak habitats and to conserve and regenerate oak populations. The following recommendations are intended to complement rather than replace such activities, by securing their benefits against loss due to climate disruption.

Each of us can reconsider in the light of the evidence for global climate instability our ideas about what we want and how to obtain it. These are our values, from which we generate our lives. With the fruits of introspection and study, we may reshape our behaviors to better reflect the limits of the possible and our preferences within them. In doing so we will almost certainly sacrifice familiar rewards for more subtle satisfactions we reap by enduring criticism or ostracism as we lead towards common good. Though we have been conditioned to view our professional roles as those in which we exercise greatest influence, important changes requisite to slow or halt climate disruption lie outside this realm. We can enhance our effectiveness by modeling these as well.

We may encourage others to reflect upon their own ends and means, and to adjust their behaviors to match emerging realities. We may bring discourse about climate change and its connection to human values into community and professional forums. We may lobby for adoption and rigorous enforcement of local, state, national, and international policies to reduce human impacts on climate in particular and ecosystem stability in general. Specific ends we might pursue include decreasing release of greenhouse gases generally, balancing carbon budgets in particular, and enforcing a total ban on CFCs. If we are to avoid replacing current maladaptive behaviors with others similarly destructive, we will find ways to more fundamentally alter social contracts so that responsibility and privilege are distributed to reinforce behavior conducive to ecosystem integrity. Among the critical issues we might address are setting limits upon reproduction, narrowing disparities in distribution of wealth, and establishing both qualitative and quantitative limits on human-mediated matterenergy conversion.

We may bring the issue of climate change to our field work with oaks by studying existing habitat with an eye to which portions may prove enduring; assessing potential future habitat; laying plans to establish and/or sustain oaks where they appear more likely to survive a century or more of instability; collecting, storing, and planting seed from oaks in many locales to preserve genetic diversity and to learn which trees may be better suited to emerging conditions; more fully mapping biotic interactions to gain a better understanding of symbiotic and parasitic relationships sensitive to climate shifts; and conserving water and increasing local surface storage and percolation.

Conclusion

Links between global climate change and oaks are difficult to describe specifically. Current global climate models are relatively crude tools, informing only imprecise predictions about future events in particular locales. Researchers have reached divergent conclusions about the extent of the threat climate change poses for oaks. When scientific consensus is absent, especially when the costs of miscalculation may be dire, caution is warranted. We can vigorously address the potential impacts of global climate change on oaks, and bring our lives and work nearer the fore of a movement for ecologically informed and sustainable human culture. ß

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