Land management practices often result in more homogeneous vegetation structure which can lead to losses of biodiversity at stand or landscape scales. In Southeast Alaska clearcut logging has created large areas of land in the most productive landscapes which now are dominated by dense even-aged forests mostly from 10-50 years of age as contrasted with uneven-aged old growth temperate rainforest which preceeded it. These young dense forests, especially after they develop for 15-25 years shade out important browse species for wildlife and can lead to regionally significant biodiversity losses. Much work has been done previously experimenting with thinning treatments to increase light levels and other resources to promote understory vegetation growth. Here we report a novel approach to restoration which aims to increase the heterogeneity of the forest as well as increasing resources for understory vegetation. Twenty years ago we installed a series of canopy gaps, 12-30 m in diameter throughout large clearcut blocks in four study areas. During the summer of 2008 we remeasured 19 of these canopy gaps, including measurements of plant species diversity, cover, biomass, and structure along with their paired control plots in both thinned and unthinned clearcuts.
Results/Conclusions
We found highly significant increases (P<0.001) in percent cover, biomass, and diversity of understory plants 20 years following treatments. Thinning treatments were less effective in promoting understory growth and species richness due to shading from expanding forest canopies. Surprisingly we found little evidence of aggressive tree invasion into these gaps, suggesting that they may continue to persist and provide ecological benefits to the ecosystem well into the future. We suggest that the creation of artificial canopy gaps following catastrophic disturbance may be an important tool to consider in combination with other techniques such as thinning to promote biodiversity in dense forests such as ours.
