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| Global change and temperate forest response |
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F. A. Bazzaz
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA., U.S.A.
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Temperate forests are thought to act as a major sink for atmospheric CO2. In a collaborative effort we investigated this with three methods. We used eddy covariance methods to estimate net ecosystem exchange (NEE) for several years. We examined temporal. variation within and between years to estimate gross ecosystem production (GEP). We also measured leaf level photosynthetic activities of the major species in the system, both at the canopy and subcanopy levels, by using canopy access towers and a mobile construction crane.
In 1993 we also used a ultralight aircraft flying at 300 meters above the canopy at a speed of 55 km/h. The craft was equipped with a spectroradiometer that measured the reflection from the vegetation at the red (655-665 nm) and the near farred (785-795 nm) wavelengths. From these data we calculated the Normalized Difference Vegetation Index (NDVI). A very high linear correlation between chlorophyll concentrations in the upper canopy and the quantum efficiency of the major species (r2 = 0.99) shows that seasonal changes in quantum efficiency for the canopy can be quantified with remotely sensed estimates of chlorophyll. Calculations from the leaf photosynthetic scaling show good correspondence between scaling and eddy correlation measurements. Although there is great year-to-year variation, the forestis estimated to take up some carbon each year. We conclude that remotely sensed data of chlorophyll concentration can be a valuable tool in global change studies.
We also studied the impact of nitrogen deposition on forest biodiversity. We found that with nitrogen deposition there is a reduction in biological diversity.
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