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

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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.