Soil Amendment Increases Tree Seedling Growth but Reduces Seedling Survival at a Retired Gravel Mine

摘要

Restoring forest vegetation within denuded settings requires identifying the abiotic factors that limit plant establishment (Bradshaw 1997, Whisenant 1999). In heavily disturbed sites such as quarries and gravel pits that have been denuded of native soils, degraded soil processes may limit planted tree seedling survival or growth (Williamson et al. 2011). To improve vegetation establishment on denuded sites, soil amendments are commonly used to manipulate soil fertility (Biederman and Whisenant 2011a, Hough-Snee et al. 2011a), introduce organic matter, soil microorganisms, or propagules (Sinnett et al. 2008, Hough-Snee et al. 2012), or to create heterogeneous microhabitats (Biederman and Whisenant 2011b, Hough-Snee et al. 2011b) that improve plant survival. In forest restoration, amendments that facilitate soil development can lead to increased plant survival and growth (Ortiz et al. 2011). Specifically, amendments that increase soil carbon and nitrogen have been shown to improve planted tree seedling growth (Wilson-Kokes et al. 2013). Soil amendments for denuded sites are typically designed to increase planted tree growth so that seedlings may outcompete early seral vegetation and survive to maturity (Bradshaw 1997). In this study we examined how soil amendments change soil properties at a highly disturbed site and how these amendments impact the growth and survival of three early successional tree species. We tested two sets of hypotheses: 1. Soil amendment will increase soil carbon and nitrogen, C to N ratio, soil moisture, and decrease soil bulk density. 2. The amendment-driven increase in soil fertility will increase the survival and growth of planted black cottonwood (Populus balsamifera), red alder (Alnus rubra) and Douglas fir (Pseudotsuga menziesii) seedlings relative to unamended seedlings.