Effects of Mediterranean cropland afforestation and its management in tree and shrub establishment

Abstract

Lack of silvicultural management in afforested agricultural land in Spain has led to low diversity stands that are vulnerable to environmental risks. We evaluated the establishment of young plantations (28 years old) with Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) in an old agricultural land in Central Mediterranean Spain and its effect on spontaneous recruitment of tree and big shrub species. An experiment with (1) non-afforested control plots in a pasture-shrubland, (2) afforested plots without management, (3) afforested plots with systematic thinning and pruning, and (4) afforested plots with selective thinning and pruning was established and we measured spontaneous recruitment of trees and big shrubs. We also established a sowing experiment to study the emergence, survival, and growth of holm oak seedlings in response to the first three management treatments. Compared to control plots, afforestation increased the spontaneous recruitment of trees and big shrubs (0 vs. 9.7 individuals ha^-1 year^-1). The emergence and growth of sown holm oak seedlings did not vary among treatments, but survival was higher in afforested plots compared to non-afforested plots (22.1 vs. 0%). Thinning enhanced seedling survival (30.8 vs. 12.3%). We conclude that afforestation of Mediterranean set-aside agricultural land facilitates long-term tree establishment and short-term oak seedling survival, especially in thinned stands.