Climate change: boon to western trees?Climate change: Boon to western trees? Cold, dry forests in the mountainous West would probably weather significant climate warming far better than nearby trout streams and irrigated crops, suggests Steven W. Running of the University of Montana in Missoula. Scientists expect such warming to occur if atmospheric carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. levels are allowed to double during the next century (SN: 4/8/89, p. 216). Running and his colleagues have developed, and are now refining, a regional-scale ecosystem model Ecosystem models, or ecological models, are mathematical representations of ecosystems. Typically they simplify complex foodwebs down to their major components or trophic levels, and quantify these as either numbers of organisms, biomass or the inventory/concentration of to compute daily changes in the water and carbon dynamics of an actual forest. "We're basically simulating a static snapshot of what we imagine the Montana forest landscape might be a century from now," he says. They predicate In programming, a statement that evaluates an expression and provides a true or false answer based on the condition of the data. their latest snapshots of the 1,200-square-kilometer study site on several basic predictions from large-scale climate models: that with a global doubling of atmospheric carbon dioxide, air in this region will warm by 4[deg.]C and precipitation increase by 10 percent. The researchers also factored in important accommodations plants would make--an increase in photosynthesis and a reduced flow of gases through pores on leaves -- which together should improve their water-use efficiency. But what really makes the model innovative, Running says, is its accounting for how such changes might alter a forest's leaf cover -- where evapotranspiration evapotranspiration Loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it. Factors that affect the rate of evapotranspiration include the amount of solar radiation, atmospheric vapor pressure, (water loss) and photosynthesis occur. Running's model indicates tht if carbon dioxide doubles over the next century, western mountain snowpacks -- which water lower-elevation areas as they melt -- will most likely thaw 60 to 80 days earlier in the spring than they do now. "We're talking about cutting in half the period of snowpack snow·pack n. An area of naturally formed, packed snow that usually melts during the warmer months. snowpack 1. ," Running says. Early-thawing snowpacks will not only melt sooner but also parcel out less water. A longer, warmer growing season growing season, period during which plant growth takes place. In temperate climates the growing season is limited by seasonal changes in temperature and is defined as the period between the last killing frost of spring and the first killing frost of autumn, at which and improved water-use efficiency should spur tree growth 20 to 30 percent, he found. But warmer temperatures will also boost evaporation evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity throughout the ecosystem, more than offsetting the precipitation increase. With less water and bigger trees to consume what there is, lower-elevation users of mountain runoff may go thirsty, Running says. |
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