Seasonal silvopastoral system with sheep in pine-oak forest: effects on soil and vegetation

An alternative method for sustainable production of natural forage resources is the use of silvopastoral systems. The study evaluated the impact of a seasonal sheep silvopastoral system on soil and vegetation of a pine-oak forest. The experiment was conducted in the municipality of Jilotzingo, in the State of Mexico, Mexico. The study was performed in Sierra de Las Cruces Mountains, part of the Trans-Mexican neo-volcanic belt. Altitudes were between 2756 and 2870 m. Climate is temperate sub-humid C(w) with rainfalls from June through September. Average annual precipitation is 2680 mm. The experimental plot was delimited in the pine-oak forest, and this area was grazed rotationally by Creole sheep (n = 8) during the rainy season. The microclimate was characterized by air temperature and relative humidity. Soil compaction, leaf litter and floristic composition were assessed before and after the silvopastoralism. The microclimate was more homogeneous in mixed forest than in grassland without trees for both temperature (coefficient of variation: 21.5 vs 24.8%) and relative humidity (coefficient of variation: 37.6 vs 39.3%). Soil compaction showed no significant differences between the condition before and after the silvopastoralism (1.05 vs 0.98 kg cm(-2), respectively; P > 0.05). Leaf litter cover and depth were similar before than after the silvopastoralism (85 vs 88% and 7.6 vs 7.4 cm, respectively; P > 0.05). Plant types before silvopastoralism were 10.5% trees, 40.0% shrubs, and 49.5% herbaceous, presenting a balanced relative importance index, although higher values for Cornus excelsa (27.7%), Garrya laurifolia (17.5%), Symphoricarpos microphyllum (17.1%), Bromus carinatus (16.5%), and Smilax moranensis (16.5%). Micro-histological analysis confirmed that sheep selected herbaceous (S. moranensis), shrubs (C. excelsa, Viburnum stenocalyx), and trees (G. laurifolia, Prunus serotina, Crataegus mexican). Results indicate that the pine-oak forest favors the establishment of a sheep seasonal silvopastoral system. The plant diversity of the pine-oak forest provides sheep with a daily diet of herbaceous, shrubs and trees of nutrient quality. Sheep defoliation is selective and stimulates regrowth of some species sheep consume. They also favor and accelerate incorporation of organic matter into the soil due to feces deposition and trampling.