A Multi-scale Spatial Analysis of Native and Exotic Plant Species Richness Within a Mixed-Disturbance Oak Savanna Landscape

Abstract

Impacts of human land use pose an increasing threat to global biodiversity. Resource managers must respond rapidly to this threat by assessing existing natural areas and prioritizing conservation actions across multiple spatial scales. Plant species richness is a useful measure of biodiversity but typically can only be evaluated on small portions of a given landscape. Modeling relationships between spatial heterogeneity and species richness may allow conservation planners to make predictions of species richness patterns within unsampled areas. We utilized a combination of field data, remotely sensed data, and landscape pattern metrics to develop models of native and exotic plant species richness at two spatial extents (60- and 120-m windows) and at four ecological levels for northwestern Ohio’s Oak Openings region. Multiple regression models explained 37–77 % of the variation in plant species richness. These models consistently explained more variation in exotic richness than in native richness. Exotic richness was better explained at the 120-m extent while native richness was better explained at the 60-m extent. Land cover composition of the surrounding landscape was an important component of all models. We found that percentage of human-modified land cover (negatively correlated with native richness and positively correlated with exotic richness) was a particularly useful predictor of plant species richness and that human-caused disturbances exert a strong influence on species richness patterns within a mixed-disturbance oak savanna landscape. Our results emphasize the importance of using a multi-scale approach to examine the complex relationships between spatial heterogeneity and plant species richness.

Scaling Disturbance Instead of Richness to Better Understand Anthropogenic Impacts on Biodiversity

“…The relationship of native to exotic richness has often been observed to depend on spatial scale—both extent and grain [ 65 ]—with natives and exotics positively correlated at large scales and negatively correlated at smaller scales [ 66 – 70 ]. Davies et al [ 71 ] suggested this scale dependence was a result of spatial heterogeneity, a pattern strongly influenced by disturbance.…”

“…Where disturbance was high at either local or landscape scales, native species declined while exotic species richness increased ( Fig 3 ). Schetter et al [ 70 ] similarly found that richness of natives and exotics was best explained at different scales of land cover. A meta-analysis also showed that the impacts of exotics on species richness declined with the study’s spatial scale [ 74 ] and exotic species can also alter species area relationships [ 75 ].…”

Spatiotemporal Patterns and Mechanisms of Chinese Tallowtree (Triadica sebifera) Spread along Edge Habitat in a Coastal Landscape, Mississippi, USA

“…In another study in GBNWR, for instance, we found that the density of T. sebifera decreased significantly with distance to road (the edge effect) and more T. sebifera trees were clumped underneath the range of an overstory slash pine tree's crown and around snags of high-decay classes in forest interiors (the snag effect) (Fan 2018). Other studies also report bird-mediated dispersal limitation and patchy distribution of invasive species at the landscape level (Bartuszevige et al 2006;Schetter et al 2013). Mechanistically, three key processes-seed dispersal, seed germination, and seedling recruitment (growth)are involved in T. sebifera spread in the landscape (Figure 2).…”

Examining Land Use Changes to Evaluate the Effects of Land Management in a Complex, Dynamic Landscape

“…These are examined through the lens of area, density, edge, shape, proximity, interspersion, connectivity and diversity metrics, which include parameters such as number of patches, perimeter-area ratio, patch richness, etc. (Torbick et al 2006;Driezen et al 2007;Schetter et al 2013;Herse et al 2018). These metrics, specifically landscape and class-level, are reliable for assessing natural and/or anthropogenic LULC changes that disrupt abiotic or biotic landscape structure including management activities (Gottgens et al 1998;Lopez et al 2002;Houlahan and Findlay 2004;Johnston and Rejmánková 2005).…”

“…An example of one of these dynamic yet diverse landscapes is Oak Openings Region within southeastern Michigan and northwestern Ohio, USA, described in more detail below. Large conservation efforts have focused on examining the changes within this region (e.g., Schetter et al 2013 ; Abella et al 2017 ), and there have been significant alterations as a result of anthropogenic activities (e.g., development, restoration), natural disturbance (e.g., tornado) and invasive species (e.g., emerald ash borer, Agrillus planipennis , Fairmaire). Traditional approaches towards ecological restoration include the community and ecosystem approach.…”