Dendroecology of forests in Missouri : disturbance and integration over multiple centuries

Abstract

Disturbances are fundamental components of ecological systems which operate at variable frequencies and magnitudes that affect the structures and processes of the system. Multiple disturbance types have functioned in oak (Quercus)-shortleaf pine (Pinus echinata, Mill.) forests including drought, fire, and canopy disturbances that may be natural (wind, ice, insect defoliation) or anthropogenic (logging). To study historic disturbances, dendroecological methods were used to assess the disturbance dynamics across multiple sites in the Missouri Ozarks in order to better understand multiple disturbances and disturbance integration. Increment cores and remnant wood were collected and ring-widths were measured to analyze the patterns of radial growth, used to identify historic disturbances. Growth release analysis (a proxy for canopy disturbance) indicated that species responded to gap openings (1-4 releases), but some trees did not exhibit a growth release suggesting these trees established in large gaps and reached the canopy without a release. An assessment of canopy accession strategies indicated the two most common strategies to reach the canopy were gap origin-no release and gap origin-major release. While some trees did not release, others established in gaps, were subsequently overtopped by adjacent canopy trees and required additional gap openings to reach the canopy. Significant associations (p<0.05) were detected using superposed epoch analysis between drought and fire, drought and growth release, and fire and growth release. This possibly indicates antecedent effects of disturbance. Further analysis of radial growth following fire years showed significant (p<0.05) increases in growth and release events within three years of a fire. However, there were fire years that resulted in significant (p<0.05) decreasing radial growth and no release events that may indicate a severe fire that injured trees. This research demonstrates that frequent, mixed-severity disturbances functioned in promoting the recruitment an