Temperature changes can also alter the water cycle and the availability of

Temperature changes can also alter the water cycle

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Temperature changes can also alter the water cycle and the availability of nitrogen and other nutrients. Basically, the temperature variations which are now occurring affect all parts of forest ecosystems, some more than others. These interactions are unimaginably complex. While warming may at first increase net primary productivity (NPP), in the longer run, because plant biomass is increasing, more nitrogen is taken up from the soil and sequestered in the plantbodies. This leaves less nitrogen for the growth of additional plants, so the increase in NPP over time (due to a rise in temperature or CO2 levels) will be limited by nitrogen availability. The same is probably true of other mineral nutrients. The consequences of warming-induced shifts in the distribution of nutrients will not be seen rapidly, but perhaps only over many years. These events may effect changes in species distribution and other ecosystem processes in complex ways. We know little about the reactions of tropical forests, but they may differ from those of temperate forests.In tropical forests, warming may be more important because of its effects on evapotranspiration and soil moisture levels than because of nutrient redistribution or NPP (which is already very high because tropical temperatures are close to the optimum range for photosynthesis and there is so much available light energy). And warming will obviously act in concert with other global or local changes – increases in atmospheric CO2 (which may modify plant chemistry and the water balance of the forest) and land clearing (which changes rainfall and local temperatures), for examples. (For an excellent discussion of these issues, see Shaver, et al., 2000.)Root, et al.(2003) have determined that more than 80%of plant and animal species on which they gathered data had undergone temperature-related shifts in physiology. Highland forests in Costa Rica have suffered losses of amphibian and reptile populations which appear to be due to increased warming of montane forests. The golden toad Bufo periglenes of Costa Rica has become extinct, at least partly because of the decrease in mist frequency in its cloud forest habitat. The changes in mists appear to be a consequence of warming trends. Other suspected causes are alterations in juvenile growth or maturation rates or sex ratios due to temperature shifts. Parmesan and Yohe (2003), in a statistical analysis, determined that climate change had biological effects on the 279 species which they examined.The migratory patterns of some birds which live in both tropical and temperate regions during the year seem to be shifting, which is dangerous for these species, as they may arrive at their breeding or wintering grounds at an inappropriate time. Or they may lose their essential interactions with plants which they pollinate or their insect or plant food supplies. Perhaps for these reasons, many migratory species are in decline, and their inability to coördinate migratory clues
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