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Ecohydrological effects of forest conversion to pasture and silvopasture in New England

H. Asbjornsen, A. Coble, K. Jennings, M. Vadeboncoeur
in collaboration with Rich Smith, Alix Contasta, and others.

Much of the current land in New England suitable for agriculture is currently under secondary forest cover.  Many farmers in New England are clearing or thinning forested lands to expand existing agricultural fields in order reclaim land that was used for agriculture prior to the early 1900s and to meet the consumer demands for locally produced agricultural goods.  Clear-cutting portions of the forest is one approach to expand existing agricultural lands.  However, there is a growing interest in agroforestry practices such as silvopasture, which is the simultaneous management of livestock grazing and trees on the same land. 

The goal of the study is to identify the effects of forest-to-agriculture conversion (clear-cut and silvopasture) on ecosystems services such as nutrient retention and water regulation and balance, as well as effects on provisioning services such as forage crop yield on farms across three states (MA, NH, and VT) in New England.  We are currently working with farmers across the three states to develop monitoring sites at five farms where forest-to-pasture and forest-to-silvopasture will be implemented.   Forest-to-agriculture conversion plots across the three states were complemented with an experimental conversion study at the UNH Organic Dairy Research Farm (ODRF) in  Lee, NH.    

The UNH ODRF site includes an established pasture, converted open pasture, converted silvopasture, and an intact forest (see aerial image below and photos at left).  To assess the impacts of three treatment types on hydrologic regulating services, we will quantify indicators related to water yield and soil hydraulic properties.  Water yield will be assessed using a water budget approach and is defined as the difference between rainfall (inputs) and evapotranspiration (outputs).  Precipitation and components of evapotranspiration (plant transpiration, rainfall intercepted by canopy, and soil evaporation) can be directly measured or derived from field measurements.

Recent efforts include conversion of the forest to a silvopasture and open pasture that involved tree felling, mulching of coarse woody debris, and planting grass seed.  Measurements are currently underway, and trees are currently being measured for growth with dendrometer bands.  Sap-flow probes are currently being constructed for measurements of water-use during the growing season.  In addition to measurements of tree sapflow and diameter growth, we plan to measure soil hydraulic properties and precipitation throughfall in order to identify the effects of forest-to-agriculture conversions on ecosystem water balance. 

This work is funded by USDA-AFRI.

Spring 2015 aerial photo of experimental area (click to enlarge):