Effect of three tree densities on the forage potential of a natural silvopastoral system in the Atlantic Region of Colombia.
The effects of three tree densities were measured on various characteristics of a 15-ha naturally regenerated silvopastoral system at the La Gloria farm, Santa Ana, northern Colombia. The trees were mixed species of Guazuma ulmifolia, Tabebuia chrysea, Enterolobium cyclocarpum and Calliandra calothyrsus, and characteristics assessed were shade, total biomass, forage quality (of trees and guinea grass (Panicum maximum) pasture below them), and nutrients supplied to the soil through recycling of leaves, fruits and branches. For measurement purposes, 9 permanent plots of 70×70 m were used (an area of 4900 m2 per plot). The numbers of trees, species present and the area of shade projection were determined in each plot. Tree densities were low, medium and high (74, 89 and 96 trees/ha, respectively) with 3 repetitions of each treatment in a randomized complete block design. Measurements were made twice yearly during the rainy (winter) and dry (summer) seasons. The greatest pasture biomass availability occurred with the lowest tree density during the dry season. Trees were tallest at the highest density but no differences in stem diameter due to treatments were observed. Crude protein content of the guinea grass forage was low, especially in the dry season. In situ rumen degradability was not affected by tree density during the dry season, but was low and slow. Root biomass of the pasture was not affected by the tree density. The protein contribution of the trees did not vary with tree density but was highest with the leguminous species Calliandra calothyrsus, which had protein contents greater than 15% in the dry season. This woody legume showed the greatest forage potential in the silvopastoral systems.