Disturbance and recovery of ground cover in a longleaf pine forest following silvicultural treatments

Background/Question/Methods

Ecological forestry is an emerging discipline that integrates characteristics of natural disturbances into silvicultural practices to promote biological diversity and sustain viable forest communities. We designed an experiment to test the effect of several harvest treatments that vary in the amount and spatial pattern of canopy retention on ground cover species richness and composition.  Our objectives are: 1) compare species richness and composition before and after harvest treatments, 2) relate ground cover response to a range of disturbance intensities associated with multiple skidder passes, and 3) identify species that are sensitive to disturbance. The study design was a randomized incomplete block with six blocks and three treatment plots per block. Canopy harvest treatments included: 1) uncut control, 2) single-tree selection, 3) group selection with tree retention in gaps, and 4) group selection. Ground cover species richness was sampled in a grid of 64-66 1 m² subplots per plot prior to timber harvest and one and three years later. We examined vegetation response to disturbance intensity by assessing species richness in paired transects of 10 1 m² disturbed and undisturbed subplots with disturbance levels ranging from exposure to 0-29 skidder passes.

Results/Conclusions

Species richness and composition did not differ among plots prior to silvicultural treatments. In the first year after harvest, retention treatment plots had lower species richness than control and single-tree selection plots, but by three years post-harvest there were no differences in species richness among treatments. Despite this apparent recovery in richness, species composition of disturbed subplots in the years following harvest was associated with the presence of ruderal species. All harvest treatments showed the greatest initial change in species composition in the first year following harvest, with some degree of recovery by year three. Species composition within the paired disturbance transects was arranged along a disturbance gradient, with ruderal species being associated with the most disturbed subplots. A suite of several ground cover species common to longleaf pine forests, including wiregrass and several other native grasses, was identified as being associated with the least disturbed subplots. These preliminary results are part of a long-term project and monitoring over numerous fire cycles will be required to determine lasting effects of silvicultural harvest treatments on ground cover species richness and composition.