Mechanisms of Patch Maintenance in Old-Growth Hemlock-Hardwood Forests

LE用于工具栏执行显示多页放大缩小模式切换全屏2尝试使文档适合更少的一页移动到下一个表格单元格移动到上一个表格单元格*移动到当前行的第一个单元格)移动9423065帝国铁杉和糖枫的单一优势斑块可能会以稳定的森林马赛克模式持续数千年。这项研究将探讨维持这种斑驳镶嵌的机制，主要侧重于反馈和招聘成功的职能基础。在密歇根州和威斯康星州的中生森林中，这项研究将确定是否可以通过冠层特性、资源可用性、物种生态生理差异和种群动态之间的正反馈来维持稳定的斑块结构。具体地说，这项研究将确定这些因素是否会导致糖枫在糖枫下而不是铁杉树冠下，以及铁杉在铁杉下但不是糖枫下成功地重新生长。本研究还将检验多种资源、光照和氮素情景下群落动态的资源减少/耐受假说。在一系列田间和温室研究中，将检验以下假设：(1)铁杉树冠下的平均光和氮有效性低于糖枫树冠下的光效和氮素有效性。(2)小种子铁杉在适宜的微区铁杉覆盖层下形成，并由于对低光照和低氮水平的高度耐受性而持续存在。相比之下，大粒播种糖枫的幼苗可以在铁杉覆盖层下生长，但由于氮素和光能利用率低，无法保持正增长。(3)落叶较密，缺乏合适的育苗原木，铁杉苗木在糖枫树冠下更新失败。相反，糖枫树冠下较高的氮素有效性使糖枫幼苗在深荫下保持正增长。(4)无论哪种斑块类型，黄桦都不能在深荫下建立，只有在适宜的微型立地上，才能在高资源条件下再生。(5)幼苗存活率是相对生长率的函数，而相对生长率又是光和氮素有效性以及幼苗代谢和分配变化的函数。生存所需的最小光照受氮素有效性的影响，黄桦最多，糖枫次之，铁杉最少。田野观测、田野操作和温室实验的结合将产生一个极好的细节组合，以更全面地了解北方森林的自然动态。这个项目的独特之处在于它极好地尝试了将生态系统过程、生理生态和群落动态联系起来。研究结果还将对糖枫等具有商业价值的树种的生理属性产生直接影响。

le for toolbar execution Show multiple pages Toggle zoom-in zoom-out mode Toggles full screen2Attempts to make the document fit on one less page Moves to the next table cell Moves to the previous tablecell*Moves to the first cell in the current row)Moves 9423065 Reich Mono-dominant patches of eastern hemlock and sugar maple may persist for millennia in a stable forest mosaic pattern. This study will explore the mechanisms underlying the maintenance of this patchy mosaic, focusing primarily on feedbacks and the functional underpinnings for recruitment success. Working in mesic forests in Michigan and Wisconsin, the study will determine whether stable patch structure may be maintained by positive feedbacks between canopy properties, resource availability, differences in species ecophysiology, and population dynamics. Specifically this study will determine if these factors result in success of sugar maple recruitment beneath sugar maple, but not hemlock canopies, and of hemlock recruitment beneath hemlock, but not sugar maple. The study will also test the resource reduction/ tolerance hypothesis of community dynamics under a multiple resource, light and nitrogen scenario. In a series of field and greenhouse studies, the following hypotheses will be tested: (1) light and N availability is lower on average beneath hemlock than sugar maple canopies. (2) Small-seeded hemlock will establish beneath hemlock overstories on suitable microsites and persist due to great tolerance of combined low light and N levels. In contrast, seedlings of large seeded sugar maple can establish beneath hemlock overstories, but fail to maintain positive growth rates due to low N and light availability. (3) Hemlock seedling recruitment will fail beneath sugar maple canopies because of dense leaf litter and lack of suitable nurse logs. In contrast, greater N availability beneath sugar maple canopies enables sugar maple seedlings to maintain positive growth rates under deep shade. (4) Yellow birch will fail to establish in deep shade in either patch type and will regenerate in high resource conditions only on suitable microsites. (5) Seedling survival is a function of relative growth rate, which in turn is a function of light and N availability and of variation in seedling metabolism and allocation. The minimum light needed for survival is influenced by N availability, most in yellow birch, less in sugar maple, and least in hemlock. %%% The combination of field observations, field manipulations, and greenhouse experiments will yield a superb combination of detail to more fully understand the natural dynamics of northern forests. This project is unique in its excellent attempt to link ecosystem processes, physiological ecology and community dynamics. The results also will have direct bearing on the physiological attributes of commercially valuable tree species, such as sugar maple.