Clonal structure influences stem growth in Quercus pyrenaica Willd. coppices: Bigger is less vigorous

Quercus pyrenaica Willd. had been historically subjected to intense coppice management in order to supply firewood, charcoal and cattle forage. Due to the emergence of new energy sources and rural exodus, more than 1,200,000 hectares of coppice stands in Spain have been abandoned since 1970. Stand degradation, stem top drying, low production, scarce acorn yield and absence of sexual regeneration are major problems of these coppices. The need to establish new uses by conversion to high forest has been widely recognized and several attempts by thinning have been tested. We suggest that through a shift in the scale of species knowledge, from stand to clonal individual level, we can achieve a better understanding of Q. pyrenaica dynamics for the purpose of applying more effective silvicultural methods. Our objective in this study was to evaluate the effect of individual stool (clonal clump) characteristics influencing stem growth. We performed genetic analyses to assess clonal membership in a one-hectare plot, and 145 stems belonging to 15 different stools were sampled to model individual stem section growth, considering both stem and clonal stool variables. Principal component and cluster analyses were performed to analyze variability among stools. Results revealed that initial stem diameter explained most of the variability in stem growth (R-adj(2) = 0.61). However, the inclusion of clonal stool variables and clonal membership as a qualitative variable improved every modeling performance criterion, reducing mean square error 11% and 25%, respectively. Stems belonging to large biomass stools (determined by large spatial extent, high number of stems within stool, and a high value of a stump root biomass indicator) had lower growth potential than those belonging to small biomass stools. Based on these results, we suggest that root aging (enlarged root biomass) leads to a root/shoot imbalance increase, which consumes, through root respiration, a great proportion of the resources supplied by photosynthesis, thus limiting stem growth. This work attempts to highlight the importance of multidisciplinary perspectives to successfully face management challenges in these forests. (c) 2013 Elsevier B.V. All rights reserved.