OOS 18-7 - Anthropogenic constraints to the restoration of old-growth characteristics to younger second-growth stands

Tuesday, August 9, 2011: 3:40 PM
14, Austin Convention Center
Julia I. Burton, Forest Ecosystems and Society, Oregon State University, Corvallis, OR, David J. Mladenoff, Department of Forest & Wildlife Ecology, University of Wisconsin-Madison, Madison, WI, Jodi A. Forrester, Department of Forest & Wildlife Ecology, University of Wisconsin - Madison, Madison, WI and Murray K. Clayton, Statistics, UW-Madison, Madison, WI

Increases in our understanding of the role of structural features in old-growth forests, such as a range of canopy gap sizes, in driving fine-scale patterns of ground-layer plant communities has led to an interest in restoring such characteristics within younger second-growth forest ecosystems.  However, studies have been retrospective and few have examined the role of such structures experimentally and in the modern context of younger second-growth forests and elevated levels of white-tailed deer herbivory.  We examined the roles environmental variation and the effects of a range of canopy gap sizes (50 – 380 m2) and white-tailed deer exclusion on the composition and structure of ground-layer plant communities.  Here we synthesize results from studies spanning the initial pre-treatment phase to the first three years following gap creation (six years).


Prior to treatment implementation, compositional variation in ground-layer plant communities was associated primarily with variation in soil properties.  Fine-scale spatial variation in the relative abundance of spring ephemerals and early-summer species was associated with gradients in soil phosphorus and percent nitrogen and calcium in the O-horizon resulting from litter inputs, respectively.   Furthermore, spatial analyses of residuals suggest patterns of environmental filtering are limited by the migration of species with short-distance seed dispersal mechanisms (i.e., gravity and ballistics).  Canopy gap creation resulted in increases in plant diversity in medium and large gaps that were associated with increases in the richness and abundance of exotic species, and with shifts from forb-dominated to vine, and shrub-dominated communities, respectively.   Changes in the density tree seedlings varied among species that differ in shade tolerance.  In general density increased where density were initially low and decreased where density was initially high, and mid tolerant species were generally more sensitive to environmental variation associated with gap size, herbivory and overstory composition.

In conclusion, results from these studies suggest that the restoration of patterns and processes characterizing old-growth forests to younger second-growth stands via stand structural manipulations may be constrained by a number of contingencies.  These constraints appear to be related to 1) simplification of overstory composition in addition to structure, 2) the role of disturbance in balancing rates of colonization and local extinction, 3) changes in the regional species pool and the invasiveness of non-native species, and  4) the effects white-tailed deer herbivory on rates of canopy gap closure.

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