Assessing the contribution of dead wood to ecosystem respiration at the UMBS forest: lab component.

Abstract

Coarse woody debris is an often overlooked carbon flux pool in the forest carbon budget that has the potential of greatly affecting overall source/sink dynamics. This study investigates coarse woody debris respiration responses to temperature, moisture, and state of decay with the objective of developing a model to quantify annual course woody debris fluxes, and to compail it to other respiration flux pools in the forest ecosystem. The project was done as a collaborative effort incorporating laboratory and field components. This study addresses the laboratory section which aimed to assess the response of course woody debris respiration at 5, 10, 15, 20, and 25C, three levels of moisture, and five decay classes. Both lab and field investigations were preformed at the University of Michigan Biological Station (UMBS) in northern Lower Michigan. The complimentary field study addresses respiration responses to environmental conditions and the relationship between soil and coarse woody debris moisture. The field study was used as a validation of results found in the lab and to aid in scaling results to the ecosystem level. In both laboratory and field studies coarse woody debris respiration was significantly influenced by both temperature and moisture. Respiration increased exponentially with temperature but showed larger increases among higher decay classes. Respiration response to moisture increased following a positive logarithmic function. Temperature and moisture trends were used to create a non-linear multi-regression model that explained about 65% of variance in respiration. Local forests at UMBS, like many world-wide, currently act as a sink, absorbing more carbon out of the atmosphere than they release. Given the current 2.2 Mg C ha-1 coarse woody debris mass in local forests, 0.1722 Mg C ha-1 is now being produced annually. Although small in comparison to other forest carbon fluxes, coarse woody debris still significantly influences the forest carbon budget. Furthermore, in northern Lower Michigan the disturbance-induced, even-aged forests dominated by bigtooth aspen (Populus grandidentata) are entering a successional transition in which many of these aspen will senesce resulting in a 15 fold increase in coaarse woody debris. With expected increase in coarse woody debris mass the flux pool could increase to almost 3 Mg C ha-1 yr-1 which could tip the delicate carbon balance from a net sink to a net source during the successional transition.