Historical range of variability in live and dead wood biomass: a regional-scale simulation study.

摘要

The historical range of variability (HRV) in landscape structure and composition created by natural disturbance can serve as a general guide for evaluating the ecological conditions of managed landscapes. HRV approaches to evaluating landscapes have been based on age-classes or developmental stages, which may obscure variation in live and dead stand structure. Developing the HRV of stand structural characteristics could improve the ecological resolution of this coarse-filter approach to ecosystem assessment. We investigated HRV in live and dead wood biomass in the regional landscape of the Oregon Coast Range (Oregon, USA) by integrating stand-level biomass models and a spatially explicit fire simulation model. We simulated historical landscapes of the region for 1000 years under pre-Euro-American settlement fire regimes and calculated biomass as a function of disturbance history. The simulation showed that live and dead wood biomass historically varied widely in time and space. The majority of the forests historically contained 500-700 t ha-1 (50-70 kg m-2) of live wood and 50-200 t ha-1 (5-20 kg m-2) of dead wood. The current distributions are more concentrated in much smaller amounts for both biomass types. Although restoring the HRV of forest structure is not necessarily a management goal for most landowners and managing agencies, departure from the reference condition can provide relative measure to evaluate habitat conditions for managers seeking to use forest structure as a means to maintain or restore ecosystem and species diversity.