Optimizing light availability for forages in silvopastoral systems: Modeled results

Authors: O Neill, Katherine; Feldhake, Charles

Submitted to: National Convention of the Society of American Foresters
Publication Type: Abstract Only
Publication Acceptance Date: 9/30/2007
Publication Date: 10/24/2007
Citation: O Neill, K.P., Feldhake, C.M. 2007. Optimizing light availability for forages in silvopastoral systems: Modeled results. In: Proceedings of the National Society of American Foresters meeting, October 24-26, 2007, Portland, Oregon. 2007 CDROM.

Interpretive Summary:

Technical Abstract: Silvopastoral management optimizes the biophysical interactions between pasture species, trees, and grazing animals to increase the production efficiency and sustainability of the entire system. Synchronizing light availability for forage production with grazing animal production requirements requires detailed knowledge of light capture by the overlying tree canopy. A spatially-explicit, geometric-optimal light capture model (tRAYci) was parameterized for two tree species commonly used in agroforestry systems that have different crown architectures and growth habits: black walnut (Juglans nigra) and white pine (Pinus strobus). Light reaching the ground surface (expressed as a percentage of above canopy radiation [ACR]) was estimated at 2,500 individual points within a simulated 0.5 ha plot and sensitivity analyses conducted to determine the effects of spacing, row orientation, and foliage density on the distribution of light availability for forages. Mean light availability increased as a function of tree spacing, with the percentage of the plot in the range optimal for forage growth (40-70% Above Canopy Radiation) exhibiting a distinct maxima at a spacing of 1.5 to 2.0 x the tree height. For all spacing distances and leaf densities evaluated, a North-South row orientation provided the greatest availability of light in the 40-70% ACR range. Row spacing on the order of 1.5 to 2.0 times the tree height maximized light availability in the range optimal for forage production regardless of row orientation. The model was most sensitive to parameters describing the upper crown shape and leaf area density and relatively insensitive to parameters describing the shape of the lower canopy, the thickness of the foliage shell in the lower canopy, and the height of the crown periphery. Results indicate that individual-based light capture models offer the potential for designing systems that optimize light allocation for tree and forage components by quantifying patchiness resulting from tree distribution patterns.