Collaborative Research: Why Does Forest Growth Decline with Stand Age? An Experimental Test

摘要：研究人员(S): FOWNES BINKLEY AND RYAN机构：夏威夷大学科罗拉多州立大学本研究的目的是评估关于成熟森林生产力在相对年轻的年龄达到顶峰后经常下降的几个对比假设。其他可能的原因包括：(1)随着树龄的增长，相对于光合作用，呼吸作用增加；(2)养分在有机质池中积累，但周转速度缓慢；(3)生物量积累之外的分配变化；(4)树木的水力导度变化，导致气孔导度降低，从而导致光合作用减少。从了解森林储存碳以应对全球气候变化的能力，到提高我们管理森林获取木材和其他产品的能力，从广泛的角度来看，对这些替代假设的检验都很重要。研究地点是夏威夷的一个桉树种植园，多年来一直通过改变树木密度和施肥来操纵。因此，研究结果可能有助于人工林的管理，也有助于了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.