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OCR for page 139
14
THREATS TO BIOLOGICAL DIVERSITY AS THE EARTH WARS
Robert L. Peters
This paper will describe how global warming I acting synergistically
with habitat destruction and other human-caused threats, is likely to
cause a wave of extinctions over the next 50 or so years.
BIOLOGICAL DIVERSITY
In the last 10 years a new concept has come to organize the thoughts
of those concerned with the conservation of living things (see Soule,
1985~. This concept is that of biological diversity, which means the
variety of biological organisms in the world, including animals, plants,
fungi, and bacteria. Biological diversity includes not only the species
themselves, like tigers, lions, and the greater Antillean nightjar
(Caprimulgus cubanensis), but also the genetic variation within species
that gives apples, for example, both green and red individuals. Addi-
tionally, biological diversity includes the different ecological func-
tions these organisms perform, from fixing nitrogen in the soil to
cleansing the water we drink.
The idea of biodiversity is the crystallization of an evolution in
thought about how to conserve living things. Historically, protection
measures focused on animal or plant species that were recognized as
being important economic or sport resources--a species-focused approach
to conservation. Although species efforts are still appropriate in a
variety of circumstances, this view has since broadened as our under-
standing of the importance of even apparently insignificant organisms has
grown. Conservation now focuses primarily on conserving entire interde-
pendent webs of species--an ecosystem approach. We now know that not
only are all the biological pieces of the planetary jigsaw puzzle inter-
dependent, but also that human society itself, even in an age of gene
splicing, engineered food crops, and modern medicine, is vastly more
dependent than most people realize upon the natural diversity of living
organisms .
The potential gifts hidden in the array of wild species are rich:
There is the genetic variability found in wild strains of common food
crops, essential for constant infusion of disease- and pest-resistant
characteristics into global agriculture. There are hundreds of poten-
tial new food crops, many superior to ones presently in widespread use.
139
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140
There are new medicines, insecticides, and materials for industry. In
the varied fungi and bacteria are blueprints for genetic engineering.
Possibly even more important, the existing natural ecosystems give us
what are called ecosystem services: recycling of nutrients, restoration
of tired soils, production of oxygen, and even the production of rain
(Ehrlich and Mooney, 1983~. These are just some of the necessary func-
tions supplied by the natural world. Their value in any one year is
incalculable: In dollars, a single plant species may be worth billions
to agriculture. In betterment of the human condition, a single obscure
plant like the rosy periwinkle of Madagascar may save thousands of lives
through the gift of medicine.
Although our knowledge of most species is overshadowed by our ignor-
ance--indeed, most of the possibly 30 million species of organisms have
not even been named--by extrapolation from species that have been inves-
tigated we can safely say that a large number are valuable. For
example, of some 1500 previously uninvestigated plant species assayed
for pharmacological activity, at least 15 percent promised medicinal
importance (Caufield, 1985~. Further, although our knowledge of eco-
logical interactions is limited, we do know that species, like symbiotic
fungi, that at first glance seem insignificant may be vital to ecosystem
functioning. Clearly humans would do well to save as many species as
possible. Aldo Leopold said, "If the biota, in the course of aeons, has
built something we like but do not understand, then who but a fool would
discard seemingly useless parts?" (Leopold, 1953~.
Valuable though they are, a large percentage of biological resources
are being destroyed by the increasing demands of growing human popula-
tions and economic development. Throughout the world, populations of
most wild species are being decreased and fragmented, often to the
degree that species of even present economic importance can no longer
support viable industries, often to the degree that extinctions occur.
For example, the blue pike (Stizostedion vitreum glaucum), a dominant
fish of the U.S. Great Lakes, provided over 1 billion pounds of protein
between 1888 and 1962, only to become extinct suddenly around 1965, most
probably due to a combination of overfishing, pollution, and introduced
species (Ono et al., 1983~.
The best estimate of total world extinctions is still the estimate
made by Lovejoy in 1980 for the Global 2000 report. He estimated, based
on deforestation rates, that between 15 and 20 percent of all species on
earth would become extinct by the year 2000 due to destruction of tropi-
cal forests alone (Lovejoy, 1980~. This gives us a rough percentage
rate, but to estimate absolute numbers of extinctions we need to know how
many species exist on earth. Until the 1980s, estimates ranged between
roughly 3 million and 10 million species. However, T. L. Erwin of the
Smithsonian Institute has recently found that there are huge numbers of
arthropod species, particularly beetles, high up in the Amazon rain
forest canopy (1982, 1983~. This has led to an upward revision of the
world total to perhaps 30 million species. If this estimate is correct
and given Lovejoy's projections, it means that between 1.5 million and
6 million species will be lost due to habitat destruction alone by the
end of this century. This estimate is probably somewhat low because
deforestation rates have increased substantially since Lovejoy made his
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141
estimates (see below).
Although population diminution or extinction of any particular
species may hardly be noted, particularly if its contribution to human
society is subtle or potential only, the cumulative effect of the pro-
cesses of biological impoverishment may be easily seen in many parts of
the world, from the arid Sahel region of Africa, where overgrazing and
tree cutting have contributed to desertification and attendant human
misery, to the United States, where a variety of species, including the
California condor (GYmnogyps californianus), the largest bird of prey in
North America, hover on the edge of extinction.
The primary cause of species loss today is habitat destruction. At
least 71,000 km2 Of primary tropical forest were being cleared yearly
throughout the world at the time of the last definitive estimate in 1982
(Lanly, 19829. However this rate is increasing rapidly, as at least
77,000 km2 Of virgin forest were cleared and burned in 1977 in the
Brazilian Amazon alone (Simons, 1988~. The result of such habitat
destruction is to erase some species entirely and to leave others as
remnant populations surviving in habitat fragments surrounded by cleared
and hostile land.
Understanding the effects of this fragmentation is key to under-
standing how climate change will impact wild ecosystems in the disturbed
landscape of the twentieth and twenty-first centuries. Fragmentation by
definition makes populations smaller and isolated from each other, and
small, isolated populations are at much greater risk from climate change
than are larger ones. (Other factors that reduce populations, like pol-
lution and hunting, will also make species more vulnerable to climate
change, but habitat destruction will have the greatest effect.) To-
gether, habitat destruction and global warming will act synergistically
to cause many more extinctions than either will alone, as detailed below
in the section on "Synergy of Habitat Destruction and Climate Change."
THE NATURE OF THE ECOLOGICALLY SIGNIFICANT CAGES
There is widespread consensus that ecologically significant global
warming will occur during the next century. For example, Hansen et al.
(1988a) have said, "we can confidently state that major greenhouse
climate changes are a certainty." It is expected that within the next
40 years greenhouse trace gases in the atmosphere, including carbon
dioxide (CO2), chlorofluorocarbons, and methane, will reach a concen-
tration equivalent to double the preindustrial concentration of CO2. The
National Academy of Sciences and others have estimated that this concen-
tration of greenhouse gases will be sufficient to raise the earth's
temperature by 3 + 1.5°C (Hansen et al., 1988b; NRC, 1983, 1987;
Schneider and Londer, 1984; WHO, 1982~. More recent estimates suggest
that warnings as high as 4.2 + 1.2°C (Schlesinger, 1989), or even 8 to
10°C (Lashof, 1989), cannot be ruled out. Because of a time lag caused
by thermal inertia of the oceans, some of this warming will be delayed by
30 to 40 years beyond the time that a doubling equivalent of CO2 is
reached (EPA, 1988), but substantial warming could occur soon--the
Goddard Institute for Space Studies (GISS) model projects a 2°C rise by
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142
2020 A.D. (Rind, 1989). Such general circulation models have many un-
certainties, but they provide the best estimates possible. As discussed
below, this transitional warming would cause profound ecological change
well before 3 or 4°C is reached--warming of less than 1°C would have
substantial ecological effects.
It should be stressed that although projections can be made about
global averages, regional projections are much less certain (Schneider,
1988~. It is known that warming will not be even over the earth, with
warming likely to be greater in the high latitudes, for example, than in
the low latitudes (Hansen et al., 1988a). Regional and local peculiari-
ties of typography and circulation will play a strong role in determin-
ing local climates.
For the purpose of discussion in this paper, I will take average
global warming to be 3°C, since this is a commonly used benchmark, but
it must be recognized that additional warming well beyond 3°C may be
reached during the next century if the production of anthropogenic
greenhouse gases continues. I will also make the conservative assump-
tion that 3°C warming will not be reached until 2070 A.D. Additional
warming or faster warming would cause additional biological disruption
beyond that laid out in this paper.
The threats to natural systems are serious for the following
reasons. First, 3°C of warming would present natural systems with a
warmer world than has been experienced in the past 100,000 years
(Schneider and Lander, 19841. An increase of 4°C would make the earth
its warmest since the Eocene, 40 million years ago (Barron, 1985; see
Webb, 1990~. This warming would not only be large compared to recent
natural fluctuations, but it would also occur very rapidly, perhaps
15 to 40 times faster than past natural changes (Gleick et al., 1990~.
For reasons discussed below, such a rate of change may exceed the ability
of many species to adapt. Even widespread species are likely to have
drastically curtailed ranges, at least in the short term. Moreover,
human encroachment and habitat destruction will make wild populations of
many species small and vulnerable to local climate changes.
Second, ecological stress would not be caused by temperature rise
alone. Changes in global temperature patterns would trigger widespread
alterations in rainfall patterns (Hansen et al., 1981; Kellogg and
Schware, 1981; Manabe et al., 1981), and we know that for many species
precipitation is a more important determinant of survival than is
temperature per se. Indeed, except at the tree line, rainfall is the
primary determinant of vegetation structure, trees occurring only where
annual precipitation is in excess of 300 mm (Woodward, 1990~. Because
of global warming, some regions would see dramatic increases in rain-
fall, and others would lose their present vegetation because of drought.
For example, the U.S. Environmental Protection Agency (EPA, 1988)
concluded, based on several studies, that a long-term drying trend is
likely in the midlatitude, interior continental regions during the
summer. Specifically, based on rainfall patterns during past warming
periods, Kellogg and Schware (1981) projected that substantial decreases
in rainfall in North America's Great Plains are possible--perhaps as
much as 40 percent by the early decades of the next century.
Other environmental factors important in determining vegetation type
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143
and health would change because of global warming: Soil chemistry would
change (Kellison and Weir, 1987), as, for example, changes in storm
patterns alter leaching and erosion rates (Harte et al., 1990~. In-
creased CO2 concentrations may accelerate the growth of some plants at
the expense of others (NRC, 1983; Strain and Bazzaz, 1983), possibly
destabilizing natural ecosystems. And rises in sea level may inundate
coastal biological communities (NRC, 1983; Hansen et al., 1981; Hoffman
et al., 1983; Titus et al., 1984~.
As mentioned, it is generally concluded from a variety of computer
projections that warming will be relatively greater at higher latitudes
(Hansen et al., 19879. This suggests that, although tropical systems
may be more diverse and are currently under great threat because of
habitat destruction, temperate zone and arctic species may ultimately be
in greater jeopardy from climate change. Arctic vegetation would
experience widespread changes (Edlund, 1987~. A recent attempt to map
climate-induced changes in world biotic communities projected that high-
latitude communities would be particularly stressed (Emanuel et al.,
1985), and boreal forest, for example, was projected to decrease by
37 percent in response to global warming of 3°C.
A final point, important in understanding species response to
climate change, is that weather is variable, and extreme events, like
droughts, floods, blizzards, and hot or cold spells, may have greater
effects on species distributions than does average climate per se (e.g.,
Knopf and Sedgwick, 1987~. For example, in northwestern forests global
warming is expected to increase the frequency of fires, leading to rapid
alteration of forest character (Franklin, 1990~.
SPECIES' RANGES SHIFT IN RESPONSE TO CLIMATE CHANGE
We know that when temperature and rainfall patterns change, species'
ranges change. Not surprisingly, species tend to track their climatic
optima, retracting their ranges where conditions become unsuitable while
expanding them where conditions improve (Peters and Darling, 1985; Ford,
19829. Even very small temperature changes of less than 1°C within this
century have been observed to cause substantial range changes. For
example, the white admiral butterfly (Ladoga camilla) and the comma
butterfly (Polygonia c-album) greatly expanded their ranges in the
British Isles during the past century as the climate warmed approxi-
mately 0.5°C (see Ford, 1982~. The birch (Betula pubescens) responded
rapidly to warming during the first half of this century by expanding its
range north into the Swedish tundra (Kullman, 1983~.
On a larger ecological and temporal scale, entire vegetation types
have shifted in response to past temperature changes no larger than
those that may occur during the next 100 years or less (Baker 1983;
Bernabo and Webb, 1977; Butzer, 1980; Flohn, 1979; Muller, 1979; Van
Devender and Spaulding, 1979~. As the earth warms, species tend to
shift to higher latitudes and altitudes. From a simplified point of
view, rising temperatures have caused species to colonize new habitats
toward the poles, often while their ranges contracted away from the
equator as conditions there became unsuitable.
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144
; Orl91nal A t ~
FIGURE 14.1 (a) Initial distribution of two species, A and B. whose
ranges largely overlap. (b) In response to climate changes latitudinal
shifting occurs at species-specific rates, and the ranges disassociate.
During several Pleistocene interglacials the temperature in North
America was apparently 2 to 3°C higher than it is now. Sweet gum trees
(Liquidambar) grew in southern Ontario (Wright, 19J1~; Osage oranges
(Maclura) and papaws (Asimina) grew near Toronto, several hundred
kilometers north-of their present distributions; manatees swam in New
Jersey; and tapirs and peccaries foraged in North;Carolina (Dorf, 1976~.
During the last of these interglacials, which ended more than 100,000
years ago, vegetation in northwestern Europe, which is now boreal, was
predominantly temperate (in Critchfield, 1980~. Other significant
changes in species' ranges have been caused by altered precipitation
accompanying past global warming, including expansion of prairie in the
American Midwest during a global warming episode approximately 7,000
years ago (Bernabo and Webb, 1977~.
It should not be imagined, because species tend to shift in the same
general direction, that existing biological communities move in syn-
chrony. Conversely, because species shift at different rates in
response to climate change, communities often disassociate into their
component species (Figure 14.1~. Recent studies of fossil packrat
(Neotoma spp.) middens in the southwestern United States show that
during the wetter, moderate climate of 22,000 to 12,000 years ago, there
was not a concerted shift of plant communities. Instead, species
responded individually to climatic change, forming stable but, by
present-day standards, unusual assemblages of plants and animals (Van
Devender and Spaulding, 1979~. In eastern North America, too, post-
glacial communities were often ephemeral associations of species,
changing as individual ranges changed (Davis, 1983; Graham, 1986~.
A final aspect of species response is that species may shift
aptitudinally as well as latitudinally. When climate warms, species
shift upward. Generally, a short climb in altitude corresponds to a
major shift in latitude: The 3°C cooling of a 500-m rise in elevation
equals roughly the cooling achieved by a 250-km northward shift in
latitude (MacArthur, 1972~. Thus, during the middle Holocene, when
temperatures in eastern North America were 2°C warmer than they are at
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500m ~B~
\
ton
—~ |
FIGURE 14.2 (a) Present attitudinal distribution of three species, A,
B. and C. (b) Species distribution after a 500-m shift in altitude in
response to a 3°C rise in temperature (based on Hopkin's bioclimatic
law; MacArthur, l972!~ . Species A becomes locally extinct. Species B
shifts upward and the total area it occupies decreases. Species C
becomes fragmented and restricted to a smaller area, while species D
successfully colonizes the lowest-altitude habitats.
present, hemlock (Tsuga canadensis) and white pine (Pinus strobus) were
found 350 m higher on mountains than they are today (Davis, 1983~.
Because mountain peaks are smaller than bases, as species shift
upward in response to warming, they typically occupy smaller and smaller
areas, have smaller populations, and may thus become more w lnerable to
genetic and environmental pressures (see Murphy and Weiss, 1990~.
Species originally situated near mountaintops may have no habitat to
move up to and may be entirely replaced by the relatively thermophilous
species moving up from below (Figure 14.2~. Examples of past extinc-
tions attributed to upward shifting include alpine plants once living on
mountains in Central and South America, where vegetation zones have
shifted upward by 1000 to 1500 m since the last glacial maximum (Flen-
ley, 1979; Heusser, 1974)
MAGNITUDE OF PROJECTED LATITUDINAL SHIFTS
If the proposed CO2-induced warming occurs, species shifts similar
to those in the Pleistocene will occur, and vegetation belts will move
hundreds of kilometers toward the poles (Davis and Zabinski, 1990; Frye,
1983; Peters and Darling, 1985~. A 300-km shift in the temperate zone
is a reasonable minimum estimate for a 3°C warming, based on the
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146
positions of vegetation zones during analogous warming periods in the
past (Dorf, 1976; Furley et al., 1983~.
Additional confirmation that shifts of this magnitude or greater may
occur comes from attempts to project future range shifts for some
species by looking at their ecological requirements. For example, the
forest industry is concerned about the future of commercially valuable
North American species, like the loblolly pine (Pinus taeda Lob. This
species is limited on its southern border by moisture stress on seed-
lings. Based on its physiological requirements for temperature and
moisture, Miller et al. (1987) projected that the southern range limit
of the species would shift approximately 350 km northward in response to
a global warming of 3°C. Davis and Zabinski (1990) have projected
possible northward range withdrawals among several North American tree,
species, including sugar maple (Acer saccharum) and beech (Fagus grandi-
folia), of from 600 km to possibly as much as 2000 km in response to the
warming caused by a doubled CO2 concentration. Beech would be most
responsive, withdrawing from its present southern extent along the Gulf
Coast and retreating into Canada.
MECHANISMS UNDERLYING RANGE SHIFTS
The range shifts described above are the sum of many local processes
of extinction and colonization that occur in response to climate-caused
changes in suitability of habitats. These changes in habitat suitabil-
ity are determined by both direct climate effects on physiology, includ-
ing temperature and precipitation, and indirect effects secondarily
caused by other species, themselves affected by temperature.
There are numerous examples of climate directly influencing survival
and thereby distribution. In animals, the direct range-limiting effects
of excessive warmth include lethality, as in corals (Glynn, 1984), and
interference with reproduction, as in the large blue butterfly, Macu-
linea arion (Ford 1982~. In plants, excessive heat and associated
decreases in soil moisture may decrease survival and reproduction.
Coniferous seedlings, for example, are injured by soil temperatures over
45°C, although other types of plants can tolerate much higher tempera-
tures (see Daubenmire, 1962~. Many plants have their northern limits
determined by minimum temperature isotherms below which some key physio-
logical process does not occur. For instance, the grey hair grass
(Corynephorus canescens) is largely unsuccessful at germinating seeds
below 15°C and is bounded to the north by the 15°C July mean isotherm
(Marshall, 1978~. Moisture extremes exceeding physiological tolerances
also determine species' distributions. Thus, the European range of the
beech tree (Fagus sylvatica) ends to the south where rainfall is less
than 600 mm annually (Seddon, 1971), and dog's mercury (Mercurialis
perennis), an herb restricted to well-drained sites in Britain, cannot
survive in soil where the water table reaches as high as 10 cm below the
soil surface (see Ford, 1982~.
The physiological adaptations of most species to climate are conser-
vative, and it is unlikely that most species could evolve significantly
new tolerances in the time allotted to them by the coming warming trend.
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147
Indeed, the evolutionary conservatism in thermal tolerance of many plant
and animal species--beetles, for example (Coope, 1977~--is the underlying
assumption that allows us to infer past climates from faunal and plant
assemblages.
Interspecific interactions altered by climate change will have a
major role in determining new species distributions. Temperature can
influence predation rates (Rand, 1964), parasitism (Aho et al., 1976),
and competitive interactions (Beauchamp and Ullyott, 1932~. Changes in
the ranges of tree pathogens and parasites may be important in determin-
ing future tree distributions (Winget, 1988~. Soil moisture is a criti-
cal factor in mediating competitive interactions among plants, as is the
case where the dog's mercury (Mercurialis perennis) excludes oxlip (Pri-
mula elation) from dry sites (Ford, 1982~.
Given the new associations of species that occur as climate changes,
many species will face ''exotic'' competitors for the first time. Local
extinctions may occur as climate change causes increased frequencies of
droughts and fires, favoring invading species. One species that might
spread, given such conditions, is Melaleuca quinquenervia, a bamboo-like
Australian eucalypt. This species has already invaded the Florida
Everglades, forming dense monotypic stands where drainage and frequent
fires have dried the natural marsh community (Courtenay, 1978; Myers,
1983).
The preceding effects, both direct and indirect, may act in synergy,
as when drought makes a tree more susceptible to insect parasitism.
DISPERSAL RATES AND BARRIERS
The ability of species to adapt to changing conditions will depend
to a large extent on their ability to track shifting climatic optima by
dispersing colonists. In the case of warming, a North American species,
for example, would most likely need to establish colonies to the north
or at higher elevations. Survival of plant and animal species would
therefore depend either on long-distance dispersal of colonists, such as
seeds or migrating animals, or on rapid iterative colonization of nearby
habitat until long-distance shifting results. A plant's intrinsic
ability to colonize will depend on its ecological characteristics,
including fecundity, viability and growth characteristics of seeds,
nature of the dispersal mechanism, and ability to tolerate selfing and
inbreeding upon colonization. If a species' intrinsic colonization
ability is low, or if barriers to dispersal are present, extinction may
result if all of its present habitat becomes unsuitable.
There are many cases where complete or local extinction has occurred
because species were unable to disperse rapidly enough when the climate
changed. For example, a large, diverse group of plant genera, including
water-shield (Brassenia), sweet gum (Liquidambar), tulip tree (Lirioden-
dron), magnolia (Magnolia), moonseed (Menispermum), hemlock (Tsuga),
arbor vitae (ThuJa), and white cedar (Chamaecyparis), had a circumpolar
distribution in the Tertiary (Tralau, 1973~. But during the Pleistocene
ice ages, all became extinct in Europe while surviving in North America.
Presumably, the east-west orientation of such barriers as the Pyrenees,
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148
the Alps, and the Mediterranean, which blocked southward migration, was
partly responsible for their extinction (Tralau, 1973~.
Other species of plants and animals thrived in Europe during the
cold periods but could not survive conditions in postglacial forests.
One such previous! y widespread dung beetle, Aphodius hodereri, is now
extinct throughout the world except in the high Tibetan plateau where
conditions remain cold enough for its survival (Cox and Moore, 198S).
Other species, like the Norwegian mugwort (Artemisia novegica) and the
springtail Tetracanthella arctica, now live primarily in the boreal zone
but also survive in a few cold, mountaintop refugia in temperate Europe
(Cox and Moore, 1985~.
These natural changes were slow compared to changes predicted for
the near future. The change to warmer conditions at the end of the las~-
ice age spanned several thousand years yet is considered rapid by
geologic standards (Davis, 1983~. We can deduce that, if such a slow
change was too fast to allow many species to adapt, the projected
warming--possibly 40 times faster--will have more severe consequences.
For widespread, abundant species, like the loblolly pine (modeled by
Miller et al., 1987), even substantial range retraction might not
threaten extinction; but rare, localized species, whose entire ranges
might become unsuitable, would be threatened unless dispersal and
colonization were successful. Even for widespread species, major loss
of important ecotypes and associated germplasm is likely (see Davis and
Zabinski, 1990~.
A key question is whether the dispersal capabilities of most species
prepare them to cope with the coming rapid warming. If the climatic
optima of temperate zone species do shift hundreds of kilometers toward
the poles within the next 100 years, then these species will have to
colonize new areas rapidly. To survive, a localized species whose
present range becomes unsuitable might have to shift poleward at several
hundred kilometers or faster per century. Although some species, such
as plants propagated by spores or "dust" seeds, may be able to match
these rates (Perring, 1965), many species could not disperse quickly
enough to compensate for the expected climatic change without human
assistance (see Rapoport, 1982), particularly given the presence of
dispersal barriers. Even wind-assisted dispersal may fall short of the
mark for many species. In the case of the Engelmann spruce (Picea
engelmanni~) a tree with light wind-dispersed seeds fewer than 5 per-
, , ,
cent of seeds travel even 200 m downwind, leading to an estimated migra-
tion rate of 1 to 20 km per century (Seddon, 1971~; this reconciles well
with rates derived from fossil evidence for North American trees of
between 10 and 45 km per century (Davis and Zabinski, 1990; Roberts,
19899. As described in the next section, many migration routes will
likely be blocked by the cities, roads, and fields replacing natural
habitat.
Although many animals may be, in theory, highly mobile , the dis -
tribution of some is limited by the distributions of particular plants,
i.e., suitable habitat; their dispersal rates may therefore be deter-
mined largely by those of co-occurring plants. Behavior may also re-
strict dispersal even of animals physically capable of large movements.
Dispersal rates below 2.0 km per year have been measured for several
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149
species of deer (Rapoport, 1982), and many tropical deep-forest birds
simply do not cross even very small unforested areas (Diamond, 1975~.
On the other hand, some highly mobile animals may shift rapidly, as have
some European birds (see Edgell, 1984~.
Even if animals can disperse efficiently, suitable habitat may be
reduced under changing climatic conditions. For example, it has been
suggested that tundra nesting habitat for migratory shore birds might be
reduced by high-arctic warming (Myers, 1988~.
SYNERGY OF HABITAT DESTRUCTION AND CLIMATE CHANGE
We know that even slow, natural climate change caused species to
become extinct. What is likely to happen given the environmental con-
ditions of the coming century?
Some clear implications for conservation follow from the preceding
discussion of dispersal rates. Any factor that would decrease the prob-
ability that a species could successfully colonize new habitat would
increase the probability of extinction. Thus, as previously described,
species are more likely to become extinct if there are physical barriers
to colonization, such as oceans, mountains, and cities. Further, species
are more likely to become extinct if their remaining populations are
small. Smaller populations mean that fewer colonists can be sent out and
that the probability of successful colonization is smaller.
Species are more likely to become extinct if they occupy a small
geographic range, which is less likely than a larger range to offer some
suitable remaining refuge when climate changes. Also, if a species has
lost much of its range because of some other factor, like clearing of
the richer and moister soils for agriculture, it is possible that re-
maining populations are located in poor habitat and are therefore more
susceptible to new stresses.
For many species, all of these conditions will be met by human-
caused habitat destruction, which increasingly confines the natural
biota to small patches of original habitat, patches isolated by vast
areas of human-dominated urban or agricultural lands.
Habitat destruction in conjunction with climate change sets the
stage for an even larger wave of extinction than that previously
imagined, based on consideration of human encroachment alone. Small,
remnant populations of most species, surrounded by cities, roads,
reservoirs, and farmland, will have little chance of reaching new
habitat if climate change makes the old unsuitable. Few animals or
plants would be able to cross Los Angeles on the way to new habitat.
Figure 14.3 illustrates the combined effects of habitat loss and warming
on a hypothetical reserve.
AMELIORATION AND MITIGATION
Because of the difficulty of predicting regional and local changes,
conservationists and reserve managers must deal with increased uncer-
tainty in making long-range plans. However, even given imprecise
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150
Range
Limit
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\ ~RESERVE,, ~
old RL ~—..—I t
—_~_
FIGURE 14.3 Climatic warming may cause species within biological
reserves to disappear. Hatching indicates: (a) species distribution
before either human habitation or climate change (range limit, RL,
indicates southern limit of species range); (b) fragmented species
distribution after human habitation but before climate change; (c)
species distribution after human habitation and climate change.
regional projections ? informed guesses can be made at least about the
general direction of change, specifically that most areas will tend to be
hotter and that continental interiors in particular are likely to
experience decreased soil moisture.
How might the threats posed by climatic change to natural commu-
nities be mitigated? One basic truth is that the less populations are
reduced by development now, the more resilient they will be to climate
change. Thus, sound conservation now, in which we try to conserve more
than just the minimum number of individuals of a species necessary for
present survival, would be an excellent way to start planning for climate
change.
In terms of responses specifically directed at the effects of
climate change, the most environmentally conservative response would be
OCR for page 151
151
to halt or slow global warming by cutting back on production of fossil
fuels, methane, and chlorofluorocarbons. Extensive planting of trees to
capture CO2 could help slow the rise in CO2 concentrations (Sedjo,
1989~. Nonetheless, even were the production of all greenhouse gases
stopped today, it is very likely that there are now high enough concen-
trations in the air to cause ecologically significant warming after a
brief lag period (Rind, 1989~. Therefore, those concerned with the
conservation of biological diversity must begin to plan mitigation
activities.
To make intelligent plans for siting and managing reserves, we need
more knowledge. We must refine our ability to predict future conditions
in reserves. We also need to know more about how temperature, precipi-
tation, CO2 concentrations, and interspecific interactions determine
range limits (e.g., Picton, 1984; Randall, 1982) and, most important, how
they can cause local extinctions.
Reserves that suffer from the stresses of altered climatic regimes
will require carefully planned and increasingly intensive management to
minimize species loss. For example, modifying conditions within re-
serves may be necessary to preserve some species; depending on changes
in moisture patterns, irrigation or drainage may be needed. Because of
changes in interspecific interactions, competitors and predators may
need to be controlled and invading species weeded out. The goal would
be to maintain suitable conditions for desired species or species assem-
blages, much as the habitat of Kirtland's warbler is periodically burned
to maintain pine woods (Leopold, 1978~.
In attempting to understand how climatically stressed communities
may respond and how they might be managed to prevent the gradual depau-
perization of their constituents, restoration studies, or more properly,
"community creation" experiments can help. Communities may be created
outside their normal climatic ranges to mimic the effects of climate
change. One such "out-of-place" community is the Leopold Pines at the
University of Wisconsin Arboretum in Madison, where there is periodi-
cally less rainfall than in the normal pine range several hundred
kilometers to the north (Jordan, 1988~. Researchers have found that,
although the pines themselves do fairly well once established at the
Madison site, many of the other species that would normally occur in a
pine forest, especially the various herbs and small shrubs, have not
flourished, despite several attempts to introduce them (Anderson et al.,
1969~.
If management measures are unsuccessful and old reserves do not
retain necessary thermal or moisture characteristics, individuals of
disappearing species might be transferred to new reserves. For example,
warmth-intolerant ecotypes or subspecies might be transplanted to re-
serves nearer the poles. Other species may have to be periodically
reintroduced in reserves that experience occasional climate extremes
severe enough to cause extinction but where the climate would ordinarily
allow the species to survive with minimal management. Such transplanta-
tions and reintroductions, particularly involving complexes of species,
will often be difficult, but some applicable technologies are being
developed (Botkin, 1977; Lovejoy, 1985~.
OCR for page 152
152
To the extent that we can still establish reserves, pertinent in-
formation about changing climate and subsequent ecological response
should be used in deciding how to design and locate them to minimize the
effects of changing temperature and moisture.
o The existence of multiple reserves for a given species or com-
munity type increases the probability that, if one reserve becomes un-
suitable for climatic reasons, the organisms may still be represented in
another reserve.
o Reserves should be heterogeneous with respect to topography and
soil types, so that even given climatic change, remnant populations may
be able to survive in suitable microclimatic areas. Species may survive
better in reserves with wide variations in altitude, since, from a cli- ,
matic point of view, a small attitudinal shift corresponds to a large
latitudinal one. Thus, to compensate for a 2°C rise in temperature, a
northern hemisphere species can achieve almost the same result by in-
creasing its altitude only some 500 m as it would by moving 300 km to the
north (MacArthur, 1972~.
O Corridors between reserves, important for other conservation
reasons, would allow some natural migration of species to track climate
shifting. Corridors along attitudinal gradients are likely to be most
practical because they can be relatively short compared with the longer
distances necessary to accommodate latitudinal shifting.
o As climatic models become more refined, pertinent information
should be taken into consideration in making decisions about where to
site reserves in order to minimize the effects of temperature and
moisture changes. In the northern hemisphere, for example, where a
northward shift in climatic zones is likely, it makes sense to locate
reserves as near the northern limit of a species' or community's range
as possible, rather than farther south, where conditions are likely to
become unsuitable more rapidly.
o Maximizing the size of reserves will increase long-term
persistence of species by increasing the probability that suitable
microclimates exist, by increasing the probability of attitudinal
variation, and by increasing the latitudinal distance available to
shifting populations.
o Flexible zoning around reserves may allow us to actually move
reserves in the future to track climatic optima, as, for example, by
trading present rangeland for reserve land. The success of this
strategy, however, would depend on a highly developed restoration
technology capable of guaranteeing, in effect, the portability of
species and whole communities.
CONCLUSION
The best solutions to the ecological upheaval resulting from
climatic change are not yet clear. In fact, little attention has been
paid to the problem. What is clear, however, is that these
climatological changes would have tremendous impact on communities and
populations isolated by development and by the middle of the next
OCR for page 153
153
century might dwarf any other consideration in planning for reserve
management. The problem may seem overwhelming. One thing, however, is
worth keeping in mind: The more fragmented and the smaller populations
Of species are, the less resilient they will be to the new stresses
brought about by climate change. Thus, one of the best things that can
be done in the short-term is to minimize further encroachment of
development on existing natural ecosystems. Further, we must refine our
climatological predictions and increase our understanding of how climate
affects species, both individually and in their interactions with each
other. Such studies may allow us to identify those areas where
communities will be most stressed, as well as alternate areas where they
might best be saved. Meanwhile, efforts to improve techniques for
managing communities and ecosystems under stress, and also for restoring
them when necessary, must be carried forward energetically.
ACKNOWLEDGMENTS
The bulk of the text on global warming was previously published as
an article in Forest Ecology and Management, in a special 1989 volume
containing the proceedings of the symposium on Conservation of Diversity
in Forest Ecosystems, University of California at Davis, July 25, 1988.
It draws heavily on other previously published versions, including those
in Endangered Species Update (Vol. 5, No. 7, pp. 1-8) and Preparing for
Climate Change: Proceedings of the First North American Conference on
Preparing for Climate Change: A Cooperative Approach (J.C. Topping, Jr.,
ea., Government Institutes, Washington, D.C.~. Many of the ideas and the
three figures derive from Peters and Darling (1985~; please see that pa-
per also for a complete list of acknowledgments for help with this work.
REFERENCES
Aho, J.M.,
J.W. Gibbons, G.W. Esch. 1976. Relationship between thermal
loading and parasitism in the mosquitofish. Pp. 213-218 in G.W.
Esch and R.W. McFarlane, eds. Thermal Ecology II. Technical
Information Center, Energy Research and Development Administration,
Springfield, Va.
Anderson, R.C., O.L. Loucks, and A.M. Swain. 1969. Herbaceous response
to canopy cover, light intensity and throughfall precipitation in
coniferous forests. Ecology 50:255-263.
Baker, R.G. 1983. Holocene vegetational history of the western United
States. Pp. 109-125 in H.E. Wright, Jr., ed. Late-Quaternary
Environments of the United States. Volume 2. The Holocene.
University of Minnesota Press, Minneapolis.
Barron, E.J. 1985. Explanations of the Tertiary global cooling trend.
Palaeogeography, Palaeoclimatology, Palaeoecology 50:17-40.
Beauchamp, R.S.A., and P. Ullyott. 1932. Competitive relationships
between certain species of fresh-water triclads. J. Ecol.
20:200-208.
OCR for page 154
154
Bernabo, J.C., and T. Webb III. 1977. Changing patterns in the
Holocene pollen record of northeastern North America: a mapped
summary. Quat. Res. 8:64-96.
Botkin, D.B. 1977. Strategies for the reintroduction of species into
damaged ecosystems. Pp. 241-260 in J. Cairns, Jr., K.L. Dickson,
and E.E. Herricks, eds. Recovery and Restoration of Damaged
Ecosystems. University Press of Virginia, Charlottesville.
Butzer, K.W. 1980. Adaptation to global environmental change. Prof.
Geogr. 32:269-278.
Caufield, C. 1985. In the Rainforest. Knopf, New York.
Coope, G.R. 1977. Fossil coleopteran assemblages as sensitive
indicators of climatic changes during the Devensian (Last) cold
stage. Philos. Trans. R. Soc. Lond. B. 280:313-340. -
Courtenay, Jr., W.R. 1978. The introduction of exotic organisms. Pp.
237-252 in H.P. Brokaw, ed. Wildlife and America. Council on
Environmental Quality. U.S. Government Printing Office, Washington,
D.C.
Cox, B.C., and P.D. Moore. 1985. Biogeography: An Ecological and
Evolutionary Approach. Blackwell Scientific Publications, Oxford.
Critchfield, W.B. 1980. Origins of the eastern deciduous forest.
Pp. 1-14 in Proceedings, Dendrology in the Eastern Deciduous Forest
Biome, September 11-13, 1979. Virginia Polytechnic Institute and
State University School of Forestry and Wildlife Resources. Publ.
FWS-2-80.
Daubenmire, R.F. 1962. Plants and Environment: A Textbook of Plant
Autecology. John Wiley & Sons, New York.
Davis, M.B. 1983. Holocene vegetational history of the eastern United
States. Pp. 166-181 in H.E. Wright, Jr., ed. Late-Quaternary
Environments of the United States. Volume 2. The Holocene.
University of Minnesota Press, Minneapolis.
Davis, M.B., and C. Zabinski. 1990. Changes in geographical range
resulting from greenhouse warming effects on biodiversity in
forests. In R.L. Peters and T.E. Lovejoy, eds. Proceedings of
World Wildlife Fund's Conference on Consequences of Global Warming
for Biological Diversity. Yale University Press, New Haven, Conn.,
forthcoming.
Diamond, J.M. 197S. The island dilemma: lessons of modern
biogeographic studies for the design of natural preserves. Biol.
Conserv. 7:129-146.
Dorf, E. 1976. Climatic changes of the past and present. Pp. 384-412
in C.A. Ross, ed. Paleobiogeography: Benchmark Papers in Geology
31. Dowden, Hutchinson, and Ross, Stroudsburg, Pa.
Edgell, M.C.R. 1984. Trans-hemispheric movements of Holarctic
Anatidae: the Eurasian wigeon (Anas penelope L.) in North America.
J. Biogeogr. 11:27-39.
Edlund, S.A. 1987. Effects of climate change on diversity of
vegetation in arctic Canada. Pp. 186-193 in J.C. Topping, Jr., ed.
Preparing for Climate Change: Proceedings of the First North
American Conference on Preparing for Climate Change: A Cooperative
Approach. Government Institutes, Washington, D.C.
r
OCR for page 155
155
Ehrlich, P.R., and H.A. Mooney. 1983. Extinction, substitution, and
ecosystem services. Bioscience 33~4~:248-254.
Emanuel, W.R., H.H. Shugart, and M.P. Stevenson. 1985. Response to
comment: "Climatic change and the broad-scale distribution of
terrestrial ecosystem complexes." Clim. Change 7:457-460.
Environmental Protection Agency (EPA). 1988. The Potential Effects of
Global Climate Change on the United States: Draft Report to
Congress, Vol. 1. EPA, Washington, D.C.
Erwin, T.L. 1982. Tropical forests: their richness in Coleoptera and
other arthropod species. Coleopt. Bull. 36:74-75.
Erwin, T.L. 1983. Beetles and other insects of tropical forest
canopies at Manaus, Brazil, sampled by insecticidal fogging. Pp.
59-75 in T.C. Whitmore and A.C. Chadwick, eds. Tropical Rain Forest
Ecology and Management. Blackwell Scientific Publishers, Oxford.
Flenley, J.R. 1979. The Equatorial Rain Forest. Butterworths, London.
Flohn, H. 1979. Can climate history repeat itself? Possible climatic
warming and the case of paleoclimatic warm phases. Pp. 15-28 in W.
Bach, J. Pankrath, and W.W. Kellogg, eds. Man's Impact on Climate.
Elsevier Scientific Publishing, Amsterdam.
Ford, M.J. 1982. The Changing Climate. George Allen and Unwin,
London.
Franklin, J.F. 1990. Effects of global climatic change on forests in
North Western North America. In R.L. Peters and T.E. Lovejoy, eds.
Proceedings of the Conference on Consequences of Global Warming for
Biological Diversity. Yale University Press, New Haven, Conn.,
forthcoming.
Frye, R. 1983. Climatic change and fisheries management. Nat. Resour.
J. 23:77-96.
Furley, P.A., W.W. Newey, R.P. Kirby, and J.McG. Hotson. 1983.
Geography of the Biosphere. Butterworths, London.
Gleick, P.H., L. Mearns, and S.H. Schneider. 1990. Climate-change
scenarios for impact assessment. In R.L. Peters and T.E. Lovejoy,
eds. Proceedings of World Wildlife Fund~s Conference on
Consequences of the Greenhouse Effect for Biological Diversity. Yale
University Press, New Haven, Conn., £orthcoming.
Glynn, P. 1984. Widespread coral mortality and the 1982-83 E1 Nino
warming event. Environ. Conserv. 11~2~:133-146.
Graham, R.W. 1986. Plant-animal interactions and Pleistocene
Extinctions. Pp. 131-154 in D.K. Elliott, ed. Dynamics of
Extinction. Wiley & Sons, Somerset, N.J.
Hansen, J., D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, and G.
Russell. 1981. Climate impact of increasing atmospheric carbon
dioxide. Science 213:957-966.
Hansen, J., A. Lacis, D. Rind, G. Russell, I. Fung, and S. Lebedeff.
1987. Evidence for future warming: how large and when. In W.E.
Shands and J.S. Hoffman, eds. The Greenhouse Effect, Climate
Change, and U.S. Forests. Conservation Foundation, Washington, D.C.
Hansen, J., I. Fung, A. Lacis, S. Lebedeff, D. Rind, R. Ruedy, G.
Russell. 1988a. Prediction of near-term climate evolution: what
can we tell decision-makers now? Pp. 35-47 in Preparing for Climate
Change: Proceedings of the First North American Conference on
OCR for page 156
156
Preparing for Climate Change: A Cooperative Approach. Government
Institutes, Washington, D.C.
Hansen, J., I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, and G.
Russell. 1988b. Global climate changes as forecast by Goddard
Institute for Space Studies three-dimensional model. J. Geophys.
Res. 93(D8):9341-9364.
Harte, J., M. Torn, and D. Jensen. 1990. The nature and consequences
Of indirect linkages between climate change and biological
diversity. In R.L. Peters and T.E. Lovejoy, eds. Proceedings of
World Wildlife Fund's Conference on Consequences of Global Warming
for Biological Diversity. Yale University Press, New Haven, Conn.,
forthcoming.
Heusser, C.J. 1974. Vegetation and climate of the southern Chilean
lake district during and since the last interglaciation. Quat. Res.
4:290-315.
Hoffman, J.S., D. Keyes, and J.G. Titus. 1983. Projecting Future Sea
Level Rise. U.S. Environmental Protection Agency, Washington, D.C.
Jordan III, W.R. 1988. Ecological restoration: Reflections on a half
century of experience at the University of Wisconsin-Madison
Arboretum. Pp. 311-316 in E.O. Wilson, ed. Biodiversity. National
Academy Press, Washington, D.C.
Kellison, R.C., and R.J. Weir. 1987. Selection and breeding strategies
in tree improvement programs for elevated atmospheric carbon dioxide
levels. In W.E. Shands and J.S. Hoffman, eds. The Greenhouse
Effect, Climate Change, and U.S. Forests. Conservation Foundation,
Washington, D. C.
Kellogg, W.W., and R. Schware. 1981. Climate Change and Society:
Consequences of Increasing Atmospheric Carbon Dioxide. Westview
Press, Boulder, Colo.
Knopf, F.L., and J.A. Sedgwick. 1987. Latent population responses of
summer birds to a catastrophic, climatological event. The Condor
89:869-873.
Kullman, L. 1983. Past and present tree lines of different species in
the Handolan Valley, Central Sweden. Pp. 25-42 in P. Morisset and
S. Payette, eds. Tree Line Ecology. Centre d'etudes nordiques de
l'Universite Laval, Quebec.
Lanly, J. 1982. Tropical Forest Resources, FAO Forestry Paper Number
30. Food and Agriculture Organization of the United Nations, Rome.
Lashof, D.A. 1989. The dynamic greenhouse: feedback processes that may
influence future concentrations of atmospheric trace gases and
climatic change. Climatic Change 14:213-242.
Leopold, A. 1953. Round River. Oxford University Press, New York.
Leopold, A.S. 1978. Wildlife and forest practice. Pp. 108-120 in H.P.
Brokaw, ed. Wildlife and America. Council on Environmental
Quality, U.S. Government Printing Office, Washington, D.C.
Lovejoy, T.E. 1980. A projection of species extinctions. Pp. 328-331
in The Global 2000 Report to the President: Entering the Twenty-
First Century. Council on Environmental Quality and the Department
of State. U.S. Government Printing Office, Washington, D.C.
Lovejoy, T.E. 1985. Rehabilitation of degraded tropical rainforest
lands. Commission on Ecology Occasional Paper 5. International
OCR for page 157
157
Union for the Conservation of Nature and Natural Resources, Gland,
Switzerland.
MacArthur, R.:H. 1972. Geographical Ecology. Harper & Row, New York.
Manabe, S., R.T. Wetherald, and R.J. Stouffer. 1981. Summer dryness
due to an increase of atmospheric CO2 concentration. Clim. Change
3:347-386.
Marshall, J.K. 1978. Factors limiting the survival of Corynephorus
canescens (L) Beauv. in Great Britain at the northern edge of its
distribution. Oikos 19:206-216.
Miller, W.F., P.M. Dougherty, and G.L. Switzer. 1987. Rising CO2 and
changing climate: major southern forest management implications.
The Greenhouse Effect, Climate Change, and U.S. Forests.
Conservation Foundation, Washington, D.C.
Muller, H. 1979. Climatic changes during the last three interglacials.
Pp. 29-41 in W. Bach, J. Pankrath, and W.W. Kellogg, eds. Man's
Impact on Climate. Elsevier Scientific Publishing, Amsterdam.
Murphy, D.D., and S.B. Weiss. 1990. The effects of climate change on
biological diversity in western North America: species Josses and
mechanisms. In R.L. Peters and T.E. Lovejoy, eds. Proceedings of
World Wildlife Fund's Conference on the Consequences of the
Greenhouse Effect for Biological Diversity. Yale University Press,
New Haven, Conn., forthcoming.
Myers, J.P. 1988. The likely impact of climate change on migratory
birds in the arctic. Presentation at Seminar on Impact of Climate
Change on Wildlife, January 21-22, 1988. Climate Institute,
Washington, D.C.
Myers, R.L. 1983. Site susceptibility to invasion by the exotic tree
Melaleuca quinquenervia in southern Florida. J. Appl. Ecol.
20(2):645-658.
National Research Council (NRC). 1983.
Academy Press, Washington, D.C.
National Research Council (NRC). 1987. Current Issues in Atmospheric
Change. National Academy Press, Washington, D.C.
Ono, R.D, J.D. Williams, and A. Wagner. 1983. Vanishing Fishes of
North America. Stone Wall Press, Washington, D.C.
Perring, F.H. 1965. The advance and retreat of the British flora.
Pp. 51-59 in C.J. Johnson and L.P. Smith, eds. The Biological
Significance of Climatic Changes in Britain. Academic Press,
London.
Peters, R.L., and J.D. Darling. 1985. The greenhouse effect and nature
reserves. BioScience 35~11~:707-717.
Picton, H.D. 1984. Climate and the prediction of reproduction of three
ungulate species. J. Appl. Ecol. 21:869-879.
Rand, A.S. 1964. Inverse relationship between temperature and shyness
in the lizard Anolis lineatopus. Ecology 45:863-864.
Randall, M.G.M. 1982. The dynamics of an insect population throughout
its altitudinal distribution: Coleophora alticolella (Lepidoptera)
in northern England. J. Anim. Ecol. 51:993-1016.
Rapoport, E.H. 1982. Areography: Geographical Strategies of Species.
Pergamon Press, New York.
Changing Climate. National
OCR for page 158
158
Rind, D. 1989. A character sketch of greenhouse. EPA Journal 15~1~:
4-7.
Roberts, L. 1989. How fast can trees migrate? Science 243:735-737.
Schlesinger, M.E. 1989. NATO Conference Proceedings, in press.
Schneider, S.H. 1988. The greenhouse effect: What we can or should do
about it. Pp. 19-34 in Preparing for Climate Change: Proceedings of
the First North American Conference on Preparing for Climate Change:
A Cooperative Approach. Government Institutes, Washington, D.C.
Schneider, S.H., and R. Lander. 1984. The Coevolution of Climate and
Life. Sierra Club Books, San Francisco.
Seddon, B. 1971. Introduction to Biogeography. Barnes and Noble, New
York.
Sedjo, R.A. 1989. Forests: a tool to moderate global warming?
Environment 31~1~:14-20.
Simons, M. 1988. Vast Amazon fires, man-made, linked to global
warming. New York Times, August, 11, 1988.
Soule, M.E. 1985. What is conservation biology? Bioscience
35~11~:727-734.
Strain, B.R., and F.A. Bazzaz. 1983. Terrestrial plant communities.
Pp. 177-222 in E.R. Lemon, ed. CO2 and Plants. Westview Press,
Boulder, Colo.
Titus, J.G., T.R. Henderson, and J.M. Teal. 1984. Sea level rise and
wetlands loss in the United States. National Wetlands Newsletter
6~5~:3-6.
Tralau, H. 1973. Some quaternary plants. Pp. 499-503 in A. Hallam,
ed. Atlas of Palaeobiogeography. Elsevier Scientific Publishing,
Amsterdam.
Van Devender, T.R., and W.G. Spaulding. 1979. Development of
vegetation and climate in the southwestern United States. Science
204:701-710.
Webb III, T. 1990. Past Changes in Vegetation and Climate: Lessons for
the Future. In Peters, R.L. and T.E. Lovejoy, eds. Proceedings of
World Wildlife Fund's Conference on Consequences of the Greenhouse
Effect for Biological Diversity. Yale University Press, New Haven,
Conn., forthcoming.
Winget, C.H. 1988. Forest management strategies to address climate
change. Pp. 328-333 in Preparing for Climate Change: Proceedings of
the First North American Conference on Preparing for Climate Change:
A Cooperative Approach. Government Institutes, Washington, D.C.
Woodward, F.I. 1990. Review of the effects of climate on vegetation:
ranges, competition and composition. In R.L. Peters and T.E.
Lovejoy, eds. Proceedings of World Wildlife Fund's Conference on
Consequences of the Greenhouse Effect for Biological Diversity.
Yale University Press, New Haven, Conn., forthcoming.
World Meteorological Organization (WMO). 1982. Report of the JSC/CAS:
A Meeting of Experts on Detection of Possible Climate Change
(Moscow, October 1982~. Geneva, Switzerland: Rep. WCP29.
Wright, Jr., H.E. 1971. Late Quaternary vegetational history of North
America. Pp. 425-464 in K.K. Turekian, ed. The Late Cenozoic
Glacial Ages. Yale University Press, New Haven, Conn.
Representative terms from entire chapter:
biological diversity
