Spatial variation of tree growth and site factors in a silvopastoral system in northeast Scotland
The spatial variation of tree growth and site factors was studied in a silvopastoral system at Glensaugh in Northeast Scotland. Sycamore (Acer pseudoplatanus L). Hybrid larch (Larix x eruolepsis Henry) and Scots pine (Pinus sylvestris L) were planted at 5 m x 5 m, 7.1 m x 7.1 m and 10 m x 10 m spacings on plots replicated over three blocks in a Randomised Complete Block design on a rye grass (Lolium perenne L) pasture which was grazed by sheep yearly from April to October. Included in the design were an agricultural control, forestry control and mowed plots. The agricultural control had no trees but grazed pasture and the mowed plots had trees but the pasture was not grazed, instead it was cut at intervals and left to decompose on site. The forestry control plots had no pasture and as such were not given fertiliser treatments and soil samples were not collected from them, in these the trees were planted at the standard 2 m x 2 m spacings and fenced off from the animals. Pastures received 160 kg N/ha-1 annum-1 in four equal applications. The objective of this work is to study at tree-scale the spatial variation of tree growth and site factors in grazed and ungrazed silvopastoral system plots. Total soil N, available Mg and Ca, as well as organic matter (OM), %C, pH in water and Calcium chloride increased significantly with distance from the tree while P decreased significantly with distance from the tree in grazed plots. The presence of trees or animals alone in a treatment did not significantly influence soil nutrient redistribution in a silvopastoral system. Therefore it takes the combined presence of trees and animals in a silvopastoral treatment for a significant redistribution of soil nutrients around the tree to occur.