The distribution of a non-native (Rosa multiflora) and native (Kalmia latifolia) shrub in mature closed-canopy forests across soil fertility gradients

A soil fertility gradient, ranging from infertile to highly fertile soils, may define whether or not a plant will establish and spread at a site. We evaluated whether or not such a fertility gradient exists for Rosa multiflora Thunb., a nonnative invasive shrub, and Kalmia latifolia L., a native problem shrub, in closed-canopy forests of the eastern U.S. We sampled soil and vegetation at the regional scale, along four randomly located 1-km transects in 70+ year-old undisturbed forests in each of three national forests in Ohio, Pennsylvania and West Virginia. We also sampled soil, vegetation and leaf tissue at the local scale, from ten individual shrubs of each species in each national forest. Regional analyses showed a significant fertility gradient with Ohio being the most fertile and West Virginia the least. Soil fertility was associated with pH (most acidic in West Virginia and least acidic in Ohio) and elevation (highest in West Virginia and lowest in Ohio). At the local level, R. multiflora was associated with soil Ca:Al ratios greater than 0.5, and K. latifolia was associated with Ca:Al ratios less than 0.3. Rosa multiflora foliage contained higher concentrations of Ca, Mg, and K than K. latifolia, while K. latifolia foliage contained higher concentrations of Mn and Zn. Our research documents the importance of soil fertility as a predictor of the establishment of invasive and expansive shrubs. This study further shows that R. multiflora can establish and spread across a broader range of soil conditions than K. latifolia.