Tree species effects on understory forage productivity and microclimate in a silvopasture of the southeastern USA

Authors: CASTILLO, MIGUEL - North Carolina State University; TIEZZI, FRANCESCO - North Carolina State University; Franzluebbers, Alan

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2020
Publication Date: 6/15/2020
Citation: Castillo, M., Tiezzi, F., Franzluebbers, A.J. 2020. Tree species effects on understory forage productivity and microclimate in a silvopasture of the southeastern USA. Agriculture, Ecosystems and Environment. 295, Article 106917.

Interpretive Summary: Silvopasture systems can be a sustainable management approach for environmental stressful locations in the southeastern US with sandy soils and yet abundant precipitation. Pasture management and livestock well-being are thought to be improved, but limited data exists to make quantitative recommendations to producers. A scientist from USDA-Agricultural Research Service collaborated with scientists from North Carolina State University to quantify the effects of tree species and location within an alley-based silvopasture system on light penetration, forage growth, and nutritive value of forage. Dense tree canopies reduced light penetration, but since lines of trees were alternated with alleys of forage, cattle had access to abundant forage. Air temperature and temperature-humidity index were reduced in shaded positions. Seasonal effects of shade were more evident with deciduous tree canopy than evergreen tree canopy. This research will help support development of more sustainable ruminant livestock production systems in the warm, humid southeastern US region.

Technical Abstract: Ecosystem services provided by silvopastoral systems are mediated by specific management, environmental conditions, and overall design of the system. Using an original alley-cropping design that transitioned to silvopasture, we hypothesized that selection of trees affects understory forage nutritive value and productivity, light/shade environment, and heat-stress mitigation. The silvopastoral system was located at the Center for Environmental Farming Systems in Goldsboro, North Carolina, USA. Three overstory tree-species were Pinus palustris (PP; longleaf pine), Pinus taeda (PT; lobloblly pine), and Quercus pagoda (QP; cherrybark oak). The understory forage component consisted of a four-way mixture of native warm-season grasses [big bluestem (Andropogon gerardii, ‘Eastern’, KY origin), gamagrass (Tripsacum dactyloides, MO origin), indiangrass (Sorghastrum nutants, ‘NC ecotype’), and switchgrass (Panicum virgatum, ‘Alamo’)]. The overall experimental design was a randomized complete block design replicated five times. There was no effect of seedbed preparation (till versus no-till) on forage establishment. Understory dry matter yield, crude protein and total digestible nutrient concentrations of the harvested forage were not affected by tree species. Overstory effects on microclimate variables were not different among tree-species, were more noticeable during the daytime of the summer months, and were at the most 1-degree point for temperature and temperature-humidity index and 3 points for relative humidity. The main feature of the silvopasture design in our study was the provision of year-round shade by the tree-component, with varying levels of shade (ranging from 90 to 6% of incident photosynthetic active radiation) due to geographic position, tree species, and season. Our results describe and highlight the potential of silvopasture design with forage alleys to mitigate heat stress and allow high forage productivity as a function of tree species in the southeastern USA.