Association of ecotones with relative elevation and fire in an upland Florida landscape

Question: What are the importance of elevation and fire in maintaining ecotones of Florida scrub assemblages along a gradual topographic gradient?Location: Archbold Biological Station (ABS), 12 km south of Lake Placid, Florida, USA.Methods: Vegetation cover of upland Florida shrublands was quantified using the line-intercept method along 20 transects traversing similar elevation gradients, stratified by time since fire (TSF). We objectively identified shrubland ecotones using a split moving windows boundary analysis (SMW) with three different window widths. Non-metric multidimensional scaling ordination was used to determine relationships among plant assemblages defined by SMW.Results: We located up to four ecotones per transect, the majority of which were wide, highly heterogeneous zones. Relative elevation controlled the distribution of plant assemblages in upland Florida shrublands. Ecotones in shrublands > 30 years TSF had relatively low dissimilarity values in SMW, indicating that previously discrete plant assemblages with longer TSF were becoming more similar with time.Conclusions: Split Moving Windows (SMW) analysis identified ecotones relatively well although patches generated by oak clonal growth were sometimes identified as ecotones. Fire suppression caused ecotones to become more diffuse, suggesting that without fire at least every 30 years, discrete plant assemblages within upland Florida shrublands will be more continuous.Abbreviations: ABS == Archbold Biological Station; SMW == Split moving window; TSF ==Time since fire; NMDS == Non-metric multi-dimensional scaling; OSF == Open Scrubby Flatwoods; RS == Rosemary Scrub; SF == Scrubby Flatwoods; F == Flatwoods; SCB == Squared city block dissimilarities.Nomenclature: Wunderlin (1998); Abrahamson et al. (1984).