Bark fissure index: A scalable indicator of bark niche in forests

Background/Question/Methods The importance of bark fissures as a niche for organisms in forest ecosystems is considerable.  A new metric for quantifying bark surface characteristics, a bark fissure index (BFI), was developed to provide a simple to measure and scalable indicator of the niche provided by bark surfaces in forests.  Species-specific changes in the frequency and depth of bark fissures caused by both horizontal and vertical splitting of bark layers were examined and modeled within the stem profile of trees of different sizes.

Results/Conclusions

BFI increases non-linearly with tree stem diameter, with distinctively different patterns for different tree species.  BFI was found to be strongly correlated with the tree species selected by white-breasted nuthatches, a bark foraging bird species.  BFI can be scaled up along the vertical profile of a trees stem to create a three dimensional index of bark structure within a tree.  BFI can also be scaled up via typical forest measurement data to provide a two- or three-dimensional index of potential bark niche that can be used for making comparisons between forests with different structure and species composition.