Soil quality and growth of southern pines in silvopastures and woodlands integrated with small ruminants

Southern pines are important tree species in both silvopasture and woodland systems. Information on the dynamics of soil quality and growth of southern pines in these systems, especially when grazing animals are included in the system, is limited. Hypothesis of the study was that the soil quality and growth of southern-pine trees would be better in silvopastures vs. woodlands. The study objective was to evaluate the soil quality and growth of southern pines (loblolly, Pinus taeda and longleaf, Pinus palustris) in silvopastures and woodlands. Studies were conducted in silvopastures and woodlands, with six plots in each system (0.4-ha per plot). Silvopastures were developed from the existing woodlands in 2014 by removing the non-pine vegetation, thinning pine trees, and planting suitable cool- and warm-season forages. Woodlands consisted of longleaf and loblolly pines, hardwood trees, and several understory plant species. Understory vegetation present in both systems was managed with the rotational stocking of meat goats (Kiko) and hair sheep (Katahdin and Katahdin St. Croix cross). Soil bulk density and moisture were evaluated in 2019 and both plus carbon and nitrogen were measured in 2020. Tree height and diameter at breast height (DBH) were measured from 2018 to 2020. Soil carbon and nitrogen were greater in silvopastures versus woodlands (p < 0.05). Both loblolly and longleaf pines grew better in silvopastures versus woodlands, with a greater DBH (16–35%) and basal area (35–78%) in the former system (p < 0.0001). Tree species showed a significant effect (p < 0.001) on all growth parameters within each system, with loblolly pines having the greater height (6–9%), DBH (27–43%), and basal area (62–107) than longleaf pines. Results show that silvopastures offer a better environment for a faster growth of southern pine trees versus woodlands, when the understory vegetation present in both systems is managed with small ruminants.