Research: Forest Gaps

Much of our research at the Holt Research Forest focuses on vegetative response to gaps--both natural and harvest-- in the forest canopy.  Effects of gap size interest many natural resource professionals.  Silviculture defines methods used to regenerate forests in terms of gap size a harvest produces. Foresters debate the size and arrangement of gaps needed to regenerate a given tree species or to achieve a desired age/size distribution. Wildlife biologists debate gap design to manage for a particular wildlife species or to maintain species richness.

After the selective harvest in winter 1987-88, we inventoried and mapped all harvest gaps, plus naturally occurring ledge gaps (caused by the absence of canopy trees due to extremely shallow soils or exposed bedrock) and tree gaps (caused by the natural loss of trees in the canopy). Tree gaps covered only 0.7% and ledge gaps only 3.2% of the uncut forest whereas the harvest-created gaps covered 26.5% of the partially cut forest. After four growing seasons, the forest floor vegetation of the three types of gaps differed significantly with junipers dominating ledge gaps, ferns and tree seedlings dominating tree gaps, and tree seedlings, forbs, and slash (downed woody material left from timber harvest) dominating harvest-created gaps (Kimball et al. 1995).