Collaborative Research: Why Does Forest Growth Decline with Stand Age? Experimental Tests of Carbon Acquisition and Allocation Over Stand Development

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ABSTRACT PROPOSAL # : DEB-9707871 DEB-9708521 INVESTIGATOR(S) : FOWNES BINKLEY AND RYAN INSTITUTION: UNIVERSITY OF HAWAII COLORADO STATE UNIVERSITY The aims of this research are to evaluate several contrasting hypotheses about why productivity of mature forests often declines after a peak at a relatively young age. Alternatives include (1) increased respiration relative to photosynthesis with tree age, (2) accumulation of nutrients in organic matter pools with slow rates of turnover, (3) changes in allocation away from biomass accumulation, and (4) changes in hydraulic conductivity of trees, leading to decreased stomatal conductance and thus decreased photosynthesis. Tests of these alternative hypotheses are important from a wide range of perspectives, from understanding the ability of forests to store C in response to global climate change to improving our ability to manage forests for timber and other products. The location of the study is a Eucalyptus plantation in Hawaii that has been manipulated for several years by varying tree density and by fertilizer application. Results thus may be useful to management of plantation forests as well to understanding of more general successional changes in forest productivity.