Abstract
Aim of the study: To analyse the decline in aged holm oak coppice forests as regards above-ground and below-ground fractions and physiological features.Area of study: Centre of the Iberian Peninsula (Guadalajara province).Material and methods: 26 pairs of holm oak stools with different vigour but with similar site and structural characteristics within each pair were selected. Morphological (basal area, number of stools, maximum height) and physiological traits (leaf water potential, stomatal conductance) of the standing stools were assessed. Their aerial and underground parts were extracted and different size fractions of both their above and below-ground biomass were quantified. Linear mixed models were built to test the effect of ’Stool vigour’ on the mean behaviour of the measured variables. Additionally, for the aerial part, linear regressions between the weights of the different size fractions and the basal area at breast height were performed using ‘Stool vigour’ as a fixed factor.Main results: For the same site, root depth, and number and diameter of shoots than good vigour stools, poor vigour stools displayed: lower predawn water potential, greater leaf mass per unit of area; lower total leaf area; lower above-ground biomass (in total as well as per fractions); lower fine roots biomass; lower proportion of leaf biomass and a greater proportion of biomass of both all roots and those with diameter 2-7 cm.Research highlights: The above-ground physiological and morphological characteristics of declined stools are interpreted as poorer adaptation to site conditions. Root system architecture was found to be relevant to explain this behaviour.
Highlights
Mediterranean coppices of hardwood species generally are natural stands with a simplified structure resulting from their historical management, traditionally aimed at producing firewood and charcoal through clearcutting with short rotations
As reported by various authors (Gracia et al, 1999b; Gracia et al, 1999c; Sabaté et al, 2002; Ogaya & Peñuelas, 2007b), under the current climate change, the decrease in precipitation and the increase in temperatures lead to greater water deficit in Mediterranean forests such as those of holm oak, which in turn results in lower photosynthetic activity; the rise in temperature leads to an increase in the rate of leaf and fine root renewal
This study aims to provide answers to some of these issues through an experimental design for the exhaustive analysis of individual stems including the extraction of root systems within a sample of larger magnitude than that used in previous studies
Summary
Mediterranean coppices of hardwood species generally are natural stands with a simplified structure resulting from their historical management, traditionally aimed at producing firewood and charcoal through clearcutting with short rotations. There are large areas of holm oak coppice with serious silvicultural and ecological problems; namely, high number of trees per hectare with low mean diameters and reduced basal areas; slow growth; scarce acorn production; little or no sexual regeneration; very low biodiversity; and high fire risk (Serrada et al, 1992; Bravo et al, 2008) These poor stand conditions together with the progressive ageing of stools (at least as regards the root systems as they were not renewed through cuttings) may account to some extent for the increasing sensitivity to climate observed in holm oak coppices in recent decades (Camarero et al, 2004; Gea-Izquierdo et al, 2009). When the effects of climate change are combined with the excessive stand density and ageing due to the abandonment of management practices, there is an increased risk of fire, stands decline and some individuals even die from drought, pests and disease (Camarero et al, 2004; Serrada et al, 2011)
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