Recovery and diversity of the forest shrub community 38 years after biomass harvesting in the northern Rocky Mountains

We investigated the long-term impact of biomass utilization on shrub recovery, species composition, and biodiversity 38 years after harvesting at Coram Experimental Forest in northwestern Montana. Three levels of biomass removal intensity (high, medium, and low) treatments combined with prescribed burning treatment were nested within three regeneration harvest treatments (shelterwood, group selection, and clearcut). Four shrub biomass surveys (pre-treatment, 2, 10, and 38 years after treatment) were conducted. Shrub biomass for all treatment units 38 years after treatment exceeded the pre-treatment level, and biomass utilization intensity did not affect shrub recovery (ratio of dry biomass at time t to pre-treatment biomass). Species composition changed immediately after harvesting (2 years); however, the species composition of treated units did not differ from the untreated control 38 years after harvesting. Biodiversity indices (Shannon's and Pielou's indices) also decreased immediately following harvesting, but recovered 10 years after harvesting. The responses of diversity indices over time differed among biomass utilization levels with the high-utilization level and unburned treatment producing the most even and diverse species assemblages 38 years after harvesting. Our results indicate the shrub community is quite resilient to biomass harvesting in this forest type.