Mixedwood boreal forests are traditionally harvested by clear cutting, a process intended to emulate natural disturbance to remove all trees in a large area. This harvesting procedure targets mature aspen trees, but destroys nonmerchantable understory white spruce trees. Protecting the white spruce understory will provide a greater coniferous timber supply on the landscape. In Alberta, Alberta-Pacific Ltd. has begun implementing understory protection harvesting in areas with high understory spruce densities. Understory protection harvests the aspen by reaching in with a feller buncher machine to avoid damaging the understory. The resulting cutblock retains a considerable amount of forest relative to traditional clear cutting procedures. The ecological effects of clear cutting are well understood, but have yet to be studied in understory protection blocks. The purpose of my research is to compare bird communities in understory protection harvested areas against communities in clear cuts and nearby mature forest. I used autonomous recording units (ARUs) to acoustically survey bird communities in cut blocks of various ages. How does the community in an understory protection block compare to a clear cut or to a mature forest, and how do they change as the cutblocks regenerate?
Results/Conclusions
My research shows that bird communities in understory protection blocks are more similar to mature forests than clear cut communities are. In other words, there is evidence that understory protection harvesting is less disruptive to the natural ecosystem than clear cutting. Many of the species in our study that are most strongly associated with the mature forests show higher prevalence in understory protection blocks than clear cuts. Given that many species that rely on old growth forests are facing substantial population declines, this finding provides critical conservation implications. Many species benefit from understory protection harvesting immediately following harvest, but several species show increasing benefits increase as the cutblocks age. We found that in just 12 years post-harvest, understory protection communities were no longer different from mature forest communities. Therefore, the forest in understory protection cut blocks shows accelerated regeneration relative to clear cuts and may provide valuable habitat much sooner to species of concern. The implementation of understory protection harvesting should be expanded to help ameliorate losses of avian populations in North America.