Why Does Forest Growth Decline with Stand Age? An Experimental Test of Carbon Acquisition and Allocation Over Stand Development

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9306356 Fownes Why does forest growth decline with stand age? An experimental test of carbon acquisition and allocation over stand development. the overall goal of this research is to understand the production biology of even-aged forests. Biomass accumulation rates of even-aged forests typically increase at first, peak, and then decline. The conventional explanation has been that leaf area index, and thus gross while woody biomass, and thus respiration, continues to increase until relatively little photosynthate remains for new growth. However, this proposition has not been tested directly. Recent evidence, both direct estimates of stand respiration and indirect indices of growth efficiency, suggest that this explanation cannot be correct. We propose an integrated experimental test of three hypotheses: (1) that respiration does account for declining growth rate, (2) that nutrient availability decreases over time, thereby lowering leaf area, photosynthesis, or both, or (3) that the pattern is caused by shifting allocation of net production to infrequently-measured components, particularly roots. %%% The significance of the research lies in answering one of the fundamental questions in forest ecosystem biology. If the respiration hypothesis is refuted, conventional explanations of stand growth dynamics will be overthrown. Understanding the controls of stand growth and carbon allocation will be crucial for predicting the response of tropical forest to changing climate. The practical significance of the research will be in formulating a comprehensive approach to plantation management, and in answering such questions as how to optimize the plant-density/ rotation-length/ harvest-size relationship, and whether late-rotation fertilization is likely to be beneficial. The region around the experimental site is receiving serious consideration for a commercial Eucalyptus plantation industry, and results will be readily adopted into planning and management.