Botanical implementation and validation monitoring of project buffers; second 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. Monitoring stations recorded data from 04/22/2008 to 06/28/2008 for aboveground temperature and relative humidity. Belowground temperature was recorded from 04/22/2008 to 09/25/2008. From the pooled data, we determined which day was the coolest and wettest and hottest and driest aboveground. For each of these dates, we calculated the daily minimum, maximum, average, and variance aboveground temperature, relative humidity, and belowground temperature. We also calculated the variance for each variable over the entire monitoring period.

Our results suggest that there is a small effect of edge on relative humidity, aboveground temperature, and belowground temperature a few years after selective timber harvest, but that a buffer with a radius of 50 – 100’ may be sufficient to minimize changes in microclimate. However, we recommend caution in interpreting these results as we 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. We hypothesize that edge effects would be more apparent if these sites had been clearcut. As it is possible that yearly climatic regime might also affect these results, we will repeat this study in 2009. We also recommend that future studies include data on populations size, plant size, and reproductive output for the species being buffered.