Long term evolution of tree growth, understorey vegetation and soil properties in a silvopastoral system of northern Greece

摘要

Tree growth, understorey characteristics and soil parameters?were evaluated in a silvopastoral system in northern Greece at seven?and twelve years after its establishment. The experiment was laid out in?1992 and included three understorey treatments (grass, legume and control- unsown), two tree species - sycamore (Acer pseudoplatanus L.) and?Scots pine (Pinus sylvestris L.) and two tree spacings (2.5 x 2.5 m and?3.5 x 3.5 m). Tree height was taller in the control and in the dense stands?while Scots pine had better growth but, higher mortality than sycamore in?the both periods. In 2004, understorey vegetation was uniform under the?three understorey treatments and a significant decrease in sward above?ground biomass was recorded under the dense treatment, compared with?the open stand. In the same year, organic C and N, Mg and K concentrations?as well as arbuscular mycorrhizal fungi spore numbers were found?significantly higher under sycamore than Scots pine plots in the 0-20 cm?soil depth. The results show that, although understorey vegetation became?uniform over time, the initial plant composition of the understorey treatments?continued to affect tree growth, indicating the importance of the understorey?vegetation at the establishment stage of silvopastoral systems.?However, as time passed initial tree spacing started to affect tree growth?and tree species, particularly sycamore to improve soil properties. These?results indicate an evolution of the initial silvopastoral system to a forest.