Effect of pruning and soil treatments on stem growth of holm oak in open woodland forests

Abstract

The growth rate of forest trees indicates the rate of wood production and overall tree health. Tree growth also indicates resource distribution and the effect of ecological variables. Silvicultural treatments may improve the growth and resilience of trees growing in dehesas (Mediterranean open-woodland forests). These ecosystems are expected to experience increased temperature and decreased precipitation due to global climate change; hence their management is a key factor contributing to the adaption, and hence the conservation of these systems. In this paper, we analyzed the effect of traditional silvicultural treatments on the intra-annual stem growth of holm oak (Quercus ilex L.) in three dehesa plots in SW Spain: (i) soil treatments (ploughing, or ploughing + fertilization with calcium superphosphate + sowing with the legume yellow lupin, Lupinus luteus) and (ii) pruning intensity (heavy, moderate, or light). The soil treatments had no significant effects on growth, but pruning significantly affected growth patterns. Heavy pruning slightly reduced growth during the spring, and moderate and heavy pruning increased the normal stem contractions (due to water stress during drought) and expansions (due to rehydration after drought) in sites with poorly developed soils or other stress causes. Hence, heavy pruning could affect the vigor and vegetative status of trees in areas where tree survival is already compromised. Light pruning did not affect tree growth, so this treatment may be acceptable if the extraction of firewood or biomass is one of the management objectives.