Effects of microsite conditions and early pruning on growth and health status of holm oak plantations in Central-Western Spain

Abstract

The aim of this study was to examine the influences of early pruning and microsite conditions on the growth and health status of holm oak plantations on former agricultural land in Central-Western Spain. With that purpose, we designed a cross-sectional study to examine the effects of topographic position, gravel surface cover and accompanying vegetation cover on holm oak plantations density, growth (height and basal diameter) and health status. We surveyed three technically identical and multi-patched holm oak plantations dating from 1995, 1998 and 2003, aged 15, 12 and 7 respectively, covering an homogeneous climate and soil area of about 500 ha located in Central-Western Spain. Six hundred and seventy-two pruned and unpruned trees were sampled in 107 systematically sampled plots covering a wide range of site conditions in the studied area. At the tree level, two linear mixed effect models were adjusted for each year under study to explore the influence of pruning and microsite factors on height and diameter. Also at a tree level, a linear mixed effect model was fitted in order to analyze the influence of microsite factors and pruning on the health status of trees. At plot level, we performed a Multifactor Analysis of variance model to explore the influence of the microsite predictor variables and of the age of plantations on stocking. The results revealed that both basal diameter and height were increased by early pruning in all plantations under study. The effects on height and basal diameter of the three microsite parameters analysed varied with the age of plantations. The oldest plantations (15 years old), were affected by the surface gravel cover, while vegetation cover was significant in 12 years old plantations. Slope position was near relevant (p < 0.1) only in the youngest plantations. When significant, a high surface gravel cover was directly related to higher trees and larger basal diameters. Plantations density was significantly affected by the topographic position and, in all the plantations studied, pruned trees were associated with a better health status. Overall, our results show that early pruning and microsite conditions significantly influence the growth of holm oak seedlings. These results suggest that the management and growth modelling of holm oak should take into consideration the spatial distribution of the different microsites represented. Moreover, early- pruning should be considered as a positive practice affecting not only final tree form but also the growth and health status of trees. Finally, our results should lead to for further studies and help for improving future projects in areas with similar conditions.