Basic:
Rangelands
Rangelands comprise nearly 40% of the landmass of the United States. Largely unsuitable for cultivation, rangelands are primarily used for grazing
livestock. Navajo Nation sheepherders, for example, depend on quality rangeland to raise their herds of sheep, a
tradition central to their lives. The value of rangelands, however, extend beyond livestock support.
Rangelands provide habitat for rich biodiversity, clean air and water, and open space for recreation and spiritual
rejuvenation.
Rangelands are defined by the predominance of grasses, shrubs, forbs, and other grass-like plants. They include
grasslands, shrublands, woodlands, savannahs, tundra, most deserts, and riparian and wetland plant communities,
including marshes and wet meadows. Because of the exceptional diversity of habitats and climatic regions that rangelands
encompass, it is difficult to make broad generalizations on how they are impacted by climate change. Nevertheless, some
long-term trends are apparent.
A ubiquitous threat to rangelands is encroachment by non-native, invasive species, some of which benefit from increased
levels of atmospheric CO2. Higher in biomass than most native species, invasives greatly increase the threat of wildfire.
Warmer, drier summers in the western United States will likely intensify this threat. Some regions, such as the Great
Plains, have adapted to regular fire regimes. In the rangelands of the Southwest, however, fires have historically occurred
only once every several decades. Changes to this natural cycle could transform diverse desert scrub, scrub-steppe, and
desert savannah/grasslands to monocultures of invasive grasses and other plant species.
As biodiversity is lost, landscapes will become more susceptible to erosion. In the West, where precipitation is expected
to become less frequent and more intense, heavy rainfall events can wash away nutrient-rich topsoil. Intervening dry
periods cause wind erosion, which can have serious consequences for air quality. Higher amounts of dust settling on
mountain snowpack accelerates snowmelt and exacerbates water shortages during the summer months.
Unfortunately, forests are being rapidly destroyed in many parts of the world. They are cleared for agriculture or pasture,
logged, mined, and degraded by human land-use practices, such as fire suppression. When forests are cleared, the stored
carbon is released back into the atmosphere. Scientists estimate that tropical deforestation alone is responsible for
20% of all anthropogenic carbon dioxide emissions that contribute to global warming.
Forests, indispensable for their role in the carbon cycle, will not themselves endure climate change unchanged. As the
climate warms, ecosystem composition will likely shift. Trees will die and species will change. Such shifts can decrease
or even reverse the carbon uptake of a forest, causing a "carbon flux." Additional carbon in the atmosphere
will then further catalyze climate change, creating a negative loop of intensification.
While warming temperatures are partly to blame, trees must also contend with more-frequent and severe disturbance events
such as droughts, insects, and fires. Trees already stressed by drought are most susceptible. Massive tree die-backs result
from bark beetle infestations, drought, and warmer temperatures; this is already evident in the piñon-juniper woodlands
of the American West and Canada's boreal forests. According to the IPCC, boreal forests-coniferous forests covering parts
of Alaska, Canada, northern Europe, and Russia-are most vulnerable to disturbance events.
As temperatures warm, mountain and other high-altitude habitats will be increasingly encroached upon by adjacent lowland biomes.ii
In turn, boreal forests will likely migrate northward and invade arctic tundra. Some models project that with a doubling of
atmospheric CO2, forests will replace between 11 and 50% of tundra.
One of the most significant elements of climate change impacts associated with changing land composition is the loss of
biodiversity and other ecosystem services, such as water and air filtration. Such risks are especially virulent in
biodiversity "hotspots," such as equatorial and temperate rainforests. According to IPCC research, most species
extinction and extirpation related to climate change will occur in the early 21st century. Climate change will only exacerbate
the worldwide extinction crisis caused by other anthropogenic factors, most notably tropical deforestation. The International
Union for the Conservation of Nature reports that one in four mammals may be at risk.
For some Native peoples, forests are the embodiment of harmony and balance-a complex system working together seamlessly to
create a balanced web of life. Their value lies beyond the price of timber, and thus their destruction is more catastrophic
for Native people. From time immemorial, indigenous cultures have relied on forests for food, shelter, and medicines, as well
as spiritual and mental health. Global warming may disrupt the ability of forests to provide subsistence for those who rely
on them-plants, animals, and humans alike. For example, climate change is impacting Native basket weavers of the American
Northeast who rely on brown ash. Drought and insect infestations have predisposed the tree species to high mortality rates,
which will intensify as climate change progresses. Other tribes are finding medicines and other traditional plants difficult
or impossible to collect as forest composition changes. As climate change disrupts the forest system, traditional life ways
may likewise be thrown into turmoil until Earth once again finds her balance.