Summary
Plant community composition is tied to regional (climate/soils) and local (aspect) physiography. Changes in initial floristic composition after a disturbance may be severe enough to change the successional trajectory predicted by physiography. Forest Service scientists evaluated understory vegetation of plant communities exposed to four forest management types, including two harvest types, fire, and no disturbance. Study sites were located on northeast and southwest aspects within two different physiographic regions. Understory composition differed by region and aspect; composition differed by disturbance, but with a significant region interaction. Sites with the highest potential for invasion (as determined in an earlier study) retained fewer plant species defined by physiographic characteristics and had more species that were solely defined by disturbance. Though physiography was more important, some species served as disturbance indicators. As disturbance-indicator species replace regional-indicator species, successional trajectories may deviate towards recovery of native species that benefit from low-level disturbance or towards systems vulnerable to invasion by exotics. Healthy forests can still be disturbed but yet be composed primarily of regionally defined species, which may include many early successional species.
