Disturbance history and dynamics in forest and prairie communities

Abstract

Scope and Method of Study:

The objective of this research was to evaluate the effects and dynamics of disturbance in grassland and forest communities. To accomplish this I performed three studies. The first study reconstructed the long-term history of fire at the Tallgrass Prairie Preserve in Osage County, Oklahoma using fire-scarred post oak trees. The second study evaluated two methods utilized to detect growth releases in tree-ring series for their efficacy in identifying disturbance-induced release events in Cross Timbers forest. The third study examined community response and change 25 years following a catastrophic windstorm at pine and oak forest sites in south-central Minnesota.

Findings and Conclusions:

At the Tallgrass Prairie Preserve, fire was present throughout the whole period of record (1729-2005). Changes in fire frequency were generally coincident with changes in land-use, most markedly the transition from Native American land-use to the establishment of cattle ranching in the region. The two methods used to detect growth-releases in tree-ring series were unable to identify releases resulting from disturbance. The difficulty in identifying releases is primarily attributed to the climatic limitations imposed on post oak growth in the Cross Timbers region. Consequently, observed releases were generally coincident with climatic reversals from drier to wetter conditions. The pine and oak forests in Minnesota exhibited compositional convergence 25 years post disturbance as later successional species become more important in each site. Forest architecture also exhibited marked changes through time, with forest recovery proceeding at slightly different rates. The most recent samplings indicate both sites are approaching an architectural state similar to that of the pre-disturbed forest.