Land-use history and abiotic gradients drive abundance of non-native shrubs in Appalachian second-growth forests with histories of mining, agriculture, and logging

Abstract

Invasion by non-native species is a consequence of previous anthropogenic disturbance that can be expected to differ between land-use histories with contrasting impacts on the physical and biotic environment. Mining, agriculture, and logging all alter environmental character in different ways through their different effects on soils and surrounding vegetation. We used second-growth forests with histories of mining, agriculture, logging, and older forest (>120 years) with no recent disturbance history to test the hypotheses that invasion is driven by 1) lasting environmental impacts of land use or 2) colonization following niche opening due to disturbance. We sampled shrub cover, environmental variables, and soils in forests with histories of mining, agriculture, logging, and older second-growth with no recent history of land use in four 10-meter2 plots per site. Our analysis focused on the two most common non-native shrubs, Berberis thunbergii and Rosa multiflora. Cover of B. thunbergii was marginally significantly higher in post-agricultural and mined forests than logged sites or older second growth, whereas R. multiflora was most frequent in mined sites. Both species showed a significant relationship with environmental variables such as soil pH, water-holding capacity, and elevation. Soil texture differed with land-use history: post-agricultural sites were significantly higher in silt and clay, and lower in sand, than the mined, logged, or old forest sites, reflecting the interaction of land-use history with landform. Most environmental variables did not differ between land-use histories. Non-native shrubs were associated with land-use histories involving soil disturbance despite the lack of lasting contrasts in most soil variables, indicating that invasion primarily reflects past opportunities for colonization and environmental gradients that are not impacted by land use. We conclude that the presence of non-native shrubs is a biotic legacy of past disturbance that outlasts altered environmental conditions that may be present at the time of abandonment.