Background/Question/Methods
The spruce budworm (SBW) is a native defoliator of fir and spruce forests in Canada and the north-eastern United States. It has been suggested that increases in the extent and severity of spruce budworm outbreaks over the last century are due to changes in forest composition and configuration as a result of forest management. The corollary of such a hypothesis is that active manipulations of forest structure through management could be used to reduce future forest susceptibility. However, to what extent historical forest management has influenced current spatial patterns of SBW host species remains uncertain. Using the Border Lakes Landscape (BLL) of northern Minnesota and north-western Ontario as a case study, we investigate whether differences in spatial patterns in SBW host species and host species basal area exist that can be attributed to historical differences in forest management. This region contains three zones of historical management: (1) fine scale management in Minnesota, (2) coarse scale management in Ontario, and (3) no management in the Boundary Waters Canoe Area and adjacent Quetico Provincial Park. Multi-temporal LANDSAT data representing species composition and host species relative basal area were analyzed using spatial pattern metrics and wavelets to better understand how management legacies have affected the scale of host species spatial structure. We used the discrete wavelet transform and a parametric bootstrapping procedure to decompose the LANDSAT-based basal area data into scale specific components and identify: (a) which scales of pattern are significant in the basal area data, and (b) where within the study region those significant scales of host structure are significantly represented.
Results/Conclusions
Forest composition and host species basal area are very finely structured over the entire BLL. Nonetheless, patch metrics indicate larger patches and a larger proportion of mixed wood forest in the unmanaged region between the actively managed regions of Ontario and Minnesota. Additionally, there were smaller patches of deciduous species in both the wilderness and Ontario regions relative to Minnesota. Wavelet analysis revealed fine spatial structure and offered some support to the existence of separate zones of host species spatial structure corresponding with political boundaries of the BLL. These results will be later used in combination with insect surveys, remotely sensed defoliation data, and dendrochronology to further investigate the relationship between management, host structure, and defoliation.