Topography and species composition do not explain landscape- or patch-level patterns of wind damage within an unmanaged forest following a tornado

Background/Question/Methods

                Wind is a major disturbance within temperature forests, affecting hundreds of thousands of hectares yearly.  These strong storms often create a heterogeneous landscape and a wide variety of unique regenerations. While there has been much interest in the biotic and abiotic conditions that affect damage patterns, identifying the relative roles of these factors is difficult since each varies over the landscape.  Here, we use the unique case of an extensive pre-disturbance vegetation survey (2006-2008) to test how damage from a large windstorm relates to topography and species composition within unmanaged forests.  We address this question at both the landscape and individual blowdown scale.  To do this, we identified and delineated seven blowdowns created in a June 2012 windstorm, ranging in size from 0.14 ha to 6 ha across ridges, hillsides and valleys.  We used GIS to calculate blowdown size and compared this to slope and topographic position.  We also compared the composition of the blowdowns to the composition of adjacent undisturbed forest.  Within a subset of these blowdowns, we mapped the location of all trees, recorded their status (intact, leaning, broken, or uprooted), their orientation (if the tree was leaning or uprooted), as well as slope and aspect. 

Results/Conclusions

                Preliminary results indicate that topography and species composition do not explain damage across the landscape or within a blowdown. Root-up trees had the highest average DBH (61.6 cm), followed by broken trees (55.6 cm) and intact trees (49.9 cm), although significance is marginal or low.  Blowdowns were somewhat smaller within the valley and larger near ridge tops.  Across the study area, blow downs showed no bias for species of trees in blowdowns compared to adjacent intact forest (ie, those that are more likely to resist wind and thus blow down, such as oaks, were not diagnostic for blowdowns).  Within blowdowns, tree species and level of damage reflect expectation based on species available rather than a bias according to properties of the species themselves.