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Monday, April 9 • 3:30pm - 3:45pm
LANDSCAPE PATTERN & PROCESS: Are Ecotones Zones of Intermingling or Interdigitation? Pattern and Scale of Tree Species Co-occurrence in Wisconsin’s Tension Zone

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AUTHORS: Monika Shea*, David Mladenoff, Murray Clayton, Stephen Berg, Hayden Elza – University of Wisconsin-Madison

ABSTRACT: Ecotones are transitional areas between adjacent ecological systems where species from each system occur. Co-occurrence of species from different systems may follow different patterns: intermingling, where species from opposing systems occur near each other on the same sites, and interdigitation, where species from opposing systems occur in separate patches. If interdigitation occurs, patch size might vary across the ecotone, depending on the strength of controlling factors. The pattern of co-occurrence in ecotones reflects the processes driving species occurrence, which can be complex in ecotones as species approach conditions that limit their existence in the opposing system. Here we examine a regional ecotone, Wisconsin’s Tension Zone, and ask: do northern and southern trees follow a pattern of intermingling or interdigitation? We used witness tree records from the pre-Euro-American settlement (mid-1800s) Public Land Survey; this dataset spans the entire state and contains fine-scale spatial information on tree species occurrence. To detect whether patterns vary spatially, we divided the Tension Zone into 18 km grid cells (known as regions). Within each region, we examined spatial pattern by further dividing the region into smaller grid cells and calculating the proportion of northern trees versus southern trees in each grid cell. For each region, we compared the distribution of observed north/south proportion to a distribution of expected north/south proportion based on 1000 random permutations. We repeated this process for multiple grid sizes within each region to measure the scale of the pattern. We found that interdigitation is the primary pattern within the Tension Zone, and that the scale of interdigitation varies across the region. We examine how variable patterns are influenced by species composition and environmental factors. We infer that multiple processes drive vegetation patterns in the Tension Zone, and that these processes vary along and across the ecotone.

Monday April 9, 2018 3:30pm - 3:45pm CDT
Spire Parlor