Forest conversion to silvopasture and open pasture: effects on soil hydraulic properties

Abstract

Growing demand for local products in the northeastern U.S. may incentivize forest conversion to pasture, degrading critical soil hydrologic properties such as surface infiltration (Kh) and subsurface saturated hydraulic conductivity (Ksat). Silvopasture, combining tree cover and grazing, may mitigate these impacts by maintaining the positive effects of trees on soil hydraulic properties. We tested this hypothesis using an experimental field manipulation to compare effects of forest conversion to open pasture versus silvopasture on Kh and Ksat at the Organic Dairy Research Farm (ODRF) and North Branch Farm (NBF). Measurements of surface Kh and Ksat at two soil depths (15 cm and 30 cm) were taken 1 and 4 years after treatment establishment at ODRF and NBF, respectively. Data were analyzed using a mixed effects modeling framework. Results show 15 cm Ksat was significantly lower in pasture compared to forest across both sites. However, in contrast to our hypothesis, soil hydraulic properties in silvopasture did not differ from other treatments at either site. Notwithstanding, silvopasture 15 cm Ksat at ODRF (9.4 cm h−1) was statistically similar to both the forest (22.6 cm h−1) and pasture (3.4 cm h−1) and exhibited a weak positive correlation with proximity to trees (R2 = 0.219, P = 0.042). In conclusion, our study did not find strong evidence that recently established silvopastures mitigate negative hydrologic impacts of forest conversion. Future research should focus on a broader range of northeastern sites and include greater replication over longer time scales to better elucidate opportunities for silvopasture.