Impact of Ecological Succession and Reforestation on Soil Properties and Microbial Dynamics in a Mediterranean Forest

Succession is the gradual change in the composition of a community of organisms over time that causes changes in soil properties. In Mediterranean areas where soils are subjected to erosion, reforestation is often applied, impacting the ecological succession and the soil properties. The main goals of the present research were (i) to evaluate changes in soil abiotic and biotic properties along successional stages and (ii) to verify the impact of reforestation on soil properties of the mature stage. To achieve the aims, the research was performed inside a Mediterranean forest including patches of zones at different successional stages (early: E, intermediate: I and natural-mature: N-M) and reforested zones (reforested-pine: R-P). The soils were analysed for pH, water content, total nitrogen content and organic matter amount. Additionally, soil microbial and fungal biomasses, hydrolase, dehydrogenase and β-glucosidase activities, and phytotoxicity were also evaluated. Along the succession, increases in organic matter, nutrient and water content occurred, with the highest values observed at the N-M stage. Similarly, microbial biomass and activity were from two- to threefold higher at the N-M than at the E stage; by contrast, soil phytotoxicity was twofold higher at the E than at the N-M stage. Organic matter and water contents were the main factors influencing the soil microbial and fungal biomasses as well as the enzymatic activities. At the R-P stage, the contents of soil water, organic matter and N decreased, leading to the reduction of the microbial biomass and activities as compared to I and N-M stages. At the investigated area, reforestation, modifying the soil abiotic properties and decreasing the microbial abundance and activities, interrupted the evolution of the plant community.