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

提案#：DEB-9707871 DEB-9708521调查员(S)：Fownes Binkley和Ryan研究所：夏威夷大学科罗拉多州立大学这项研究的目的是评估几种关于成熟森林生产力为什么在相对较年轻的年龄达到峰值后往往下降的相反的假说。替代方案包括(1)与光合作用有关的呼吸作用随树龄增加，(2)养分在有机质库中积累，周转速度较慢，(3)分配远离生物量积累，以及(4)树木水分导度的变化，导致气孔导度下降，从而降低光合作用。从理解森林储存碳的能力来应对全球气候变化，到提高我们管理森林获取木材和其他产品的能力，对这些替代假设的测试从广泛的角度来看都是重要的。这项研究的地点是夏威夷的一个桉树种植园，几年来，人们一直在通过改变树木密度和施肥量来操纵这片种植园。因此，结果可能有助于人工林的管理，也有助于理解森林生产力的更一般的演替变化。

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.