Structural properties of woody debris populations in old-growth Central Hardwood Region forests: Twenty years of change

Background/Question/Methods

The twenty-first century has brought with it a new era of forest management on public lands throughout North America; a shift away from the utilitarian principles of yesteryear to one that has embraced principles of ecosystem management, and the restoration and maintenance of ecological processes. Value of public forests is no longer defined only by standing timber, but may also include (among others) the value of ecological services provided by forest structural components (e.g. woody debris). In forests of the Central Hardwood Region (CHR), woody debris may enhance the quality of wildlife habitat, provide refugia for seedling establishment, maintain nutrient cycles, and provide long-term carbon storage reservoirs. A network of permanent fixed-area plots was established in 1991 to describe the structure and composition of remnant old-growth forest remaining in the CHR. During the summer of 2011, after 20 years of unmanaged stand development, these plots were remeasured. Five were located in Indiana and are discussed here.

Results/Conclusions

We found no differences in total coarse woody debris (> 10 cm diameter) among the five Indiana sites based on our 2011 remeasurement  (78.2 - 105.2 m³ ha^-1; P = 0.514). Volume of recently recruited logs (decay categories 1 and 2) was significantly different among sites (P < 0.001) and can likely be attributed to recent disturbances in sites where volume estimates were greatest. The majority of coarse woody debris volume across sites was in decay category 3. Of all sites, total volume of coarse woody debris significantly increased only at the Davis-Purdue Research Forest between 1991 and 2011; all other sites showed no change. Increasing volume of coarse woody debris may reflect the stage of old-growth development at Davis, where much of the initiating cohort of oaks and associated species are reaching age of senescence and are recruiting to the forest floor. When analyzed by decay category, most sites reveal differences in volume between 1991 and 2011, which can be explained by the timing of local disturbance events. These estimates will be combined with results from a larger study to enhance the understanding of long-term ecosystem dynamics in old-growth forests of the CHR and to develop forest carbon budgets for the region.