The relationship between cork oak growth patterns and soil, slope and drainage in a cork oak woodland in Southern Portugal

Abstract The influence of soil type, slope and drainage on tree growth patterns (density, tree size, crown canopy cover and cork yield) was assessed in a cork oak montado, located in Central-western Portugal, based on a GIS approach followed by field survey. Five soil groups, that is, Arenosols, Regosols, Podzols, Luvisols and Gleysols, combined in three slope classes (flat, undulating and steep) under two different hydromorphic conditions (normal or deficient) were compared based on five cork oak stand parameters using ANOVA and PCA tests. The results showed a clear influence of soil type on cork oak growth patterns (cork yield, basal area, number of trees per hectare, crown canopy cover and circumference at breast height). In Arenosols all parameters showed maximum values and, in contrast, in Gleysols were found the minimum values. For instance, the average of the annual cork production for Gleysols (153 kg ha−1 year−1) was only 70% of the expected annual cork production of Arenosols (219 kg ha−1 year−1) and the average exploited tree density decreased from 56 trees ha−1 in Arenosols to 44 trees ha−1 in Gleysols, for an average exploited tree density of 53 trees ha−1 for the study area. Slope also seems to influence the cork oak growth patterns, as significant statistical differences were found for cork oak growth parameters between slope classes: steep slopes decreased the cork production, the tree size (circumference at breast height) and the tree density. An overall PCA test showed that three main soil groups could be identified: (i) Arenosols and Podzols; (ii) Regosols and (iii) Luvisols and Gleysols, showing that the former, which could allow the tree root development, have a positive influence on the cork oak growth. A two-way analysis of variance, for soil type and slope, showed that the cork yield and the exploited tree density are clearly affected by these two factors interaction.

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