Botanical implementation and validation monitoring of project buffers; third year report

Areas selected for timber harvest often contain rare and threatened species that are known to prefer interior and/or old forest habitats. Because of this, areas of uncut forest are frequently left where these species are known to occur in order to provide refuge habitat. However, because these patches are surrounded by cut forest, the may be subject to edge effects that may have negative impacts on the species of concern. The depth to which the edge-effects can penetrate the interior of a forest is dependent on many different variables including forest type, soil composition, and microclimate gradient. Currently, the Medford District of the Bureau of Land Management (BLM) requires a 100ft. buffer around Sensitive Species populations during timber operations on publicly owned lands.

The objective of this study was to repeat sampling to determine the appropriateness of using buffers with a 100 ft. radius to protect Sensitive Species. Monitoring stations were placed at select distances within the cut area, buffer area, and along the edge between the two area. In previous years, climatic variables were sampled more frequently in first (2008) and second (2007) halves of the growing season. In this study, we sampled over the majority of the growing season, but with less frequency. Minimum, maximum, average, and variance in aboveground temperature, relative humidity, and below ground temperature were calculated for the hottest and coldest days during the monitoring period. I also calculated the variance for each variable over the entire monitoring period.

Our results suggest that there is a small, but significant effect of edge on relative humidity, aboveground temperature, and belowground temperature a few years after selective timber harvest in the Medford District of the Bureau of Land Management. A buffer with a radius of 50 ft. (Ashland RA) or 70 ft. (Grants Pass RA) may be sufficient to minimize changes in microclimate. However, these results should be interpreted with caution as I do not know what the edge effects were the first year after harvesting. Even if changes in microclimate are transitory, one year of unsuitable abiotic conditions may cause substantial death in a population. These conclusions are also limited to harvesting methods that maintain some canopy cover. I hypothesize that edge effects would be more apparent if these sites had been clearcut. As there were significant differences in the distance of edge effects between the Ashland and Grants Pass RA’s, I recommend that extreme caution should be used when trying to apply these results to different geographic regions. Finally, I recommend that future studies include data on population size, individual size, and reproductive output for the species being buffered.