8.3. Impacts and Adaptation
8.3.1. Ecosystems: Nonforest Terrestrial
8.3.1.1. Distribution and Sensitivities
Nonforest terrestrial ecosystems are the single largest type of land surface
cover (>51%) in North America. They are extremely diverse and include nontidal
wetlands (bogs, fens, swamps, and marshes), ecosystems of the polar domain (tundra
and taiga), traditional rangeland ecosystems (grasslands, deserts, and savannas),
and improved pastures. These ecosystems are major components of every region
of North America; they constitute about 80% of the land cover of western North
America and nearly 100% of the land cover above the 75th parallel. They provide
forage for 80 million cattle, sheep, and goats and 25 million deer, elk, antelope,
caribou, and buffalo, as well as most of the breeding and feeding grounds for
waterfowl in North America (Child and Frasier, 1992; WRI, 1996). Nonforest ecosystems
are the source of most surface flow and aquifer recharge in the western Great
Plains and the extreme northern regions of North America. Municipal, agricultural,
and industrial sectors in these regions depend on nonforest ecosystems for the
quantity and quality of water required for economic sustainability. The quality
and quantity of water derived from nonforest ecosystems depend on the management
these lands receive and the average annual and extreme climatic events they
encounter.
Nontidal wetlands in North America include a variety of ecosystems such as
bogs, fens, swamps, marshes, and floodplains. Classification systems are many
and varied. These wetlands are distributed throughout North America, principally
in a band extending from the New England states to Alaska. There are additional
significant areas in the Mississippi Valley, the "Prairie Pothole" region, the
many coastal wetlands (e.g., the Mississippi River delta, the Everglades, and
the Okefenokee), the Atlantic coastal marshes and Fraser River estuary, the
former Great Kankakee and Great Blackwater swamps, the Hudson Bay Lowlands,
the Peace-Athabasca-Slave delta, the Mackenzie delta, and the Queen Maud Gulf
on the Arctic Ocean (Mitsch and Gosselink, 1986; Ecological Stratification Working
Group, 1995; IPCC 1996, WG II, Chapter 6). See Section 8.3.3
for a more detailed discussion of wetlands impacts.
Rangelands are characterized by native and introduced vegetation-predominantly
grasses, grasslike plants, forbs, shrubs, and scattered trees. These lands are
extremely varied: They include the tallgrass, mixed, and shortgrass prairie
regions of central North America; tundra and taiga areas in the polar domain;
annual grasslands of California; chaparral regions of Arizona and California;
sagebrush shrub steppe and pinyon-juniper woodlands in the intermountain region
of western North America; and the Chihuahuan, Sonoran, and Mojave deserts in
the southWestern portion of North America. The associated ecosystems are complex
and are affected by many interacting biotic and abiotic components, and their
health depends on the interaction of climate, soils, species competition, fire,
grazing, and management. These ecosystems provide a wide array of goods and
services, including forage, water, and habitat for wildlife and domesticated
livestock and open space for recreational activities, and they are the source
of many of the raw materials needed to sustain our industrial society (i.e.,
pharmaceuticals, precious metals, minerals, construction materials, natural
gas, oil, and coal) (Heady and Child, 1994).
Although some rangelands are fragile and easily disturbed by anthropogenic
activity (Belnap, 1995), others are resistant to change. Semi-arid and arid
ecosystems are considered among the most sensitive because these ecosystems
often are water-limited and have marginal nutrient reserves (OIES, 1991; IPCC
1996, WG II, Chapter 2).
Current levels of uncertainties associated with the functioning and adaptive
capacity of nonforest ecosystems under variable and changing climate and the
possibility of critical thresholds limit our ability to identify the relative
sensitivities of these ecosystems (and the potential impacts of changing climates).
It is understood, however, that these ecosystems are sensitive to climate variability
and that the impacts can vary depending on the resilience and resistance of
the ecosystem to the stresses applied (e.g., changes in precipitation, CO2,
temperature, fire, land use, and land cover and management). Researchers also
believe that the impacts of CO2 enrichment and shifts in temperature and precipitation
regimes are likely to be greatest when they are reinforced by other destabilizing
forces. Lack of information about how these other factors interact with climate
change also limits our understanding of ecosystem response. Also of concern
are the relative sensitivities of species at the ecotones between vegetation
types, such as between grasslands and woodlands and between woodlands and forests
(Polley, 1997).
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