Carbon storage potentiality in successional and secondary old growth forests

Abstract

As the capacity of old-growth forests to store carbon until very old ages has been proved, their conservation has become a mitigation strategy to reduce net CO2 emissions and moderate climate warming. We investigated the effect of tree age, competition and climate on aboveground standing biomass and C stocks over a 50-years period in two Spanish forest stands (successional Pinus pinea forests with old-growth attributes, OGFA and secondary Pinus nigra old-growth Forest, SOGF), combining dendroecological methods with forest inventory data, using semiparametric modeling. P. nigra SOGF stored 69.9 t C ha−1 in standing volume, while P. pinea OGFA stored 58.2 t C ha−1. Carbon stored during the last 50 years increased in both forests, with a steeper increase in P. pinea OGFA. The fraction of annual C stored by the oldest trees was 20–25% in P. nigra SOGF and 17–23% in P. pinea OGFA. The different patterns of biomass growth increment in the two forests were explained by different biophysical environments, climate and history effects. The response to contrasted climate events was forest-specific. Results for P.nigra showed a similar response to climate irrespective of tree age, while biomass growth in P. pinea increased in humid periods compared to dry periods in trees older than 100-years. The negative effect of drought is evidenced in P. pinea trees over 100-years old, while P. nigra showed a cumulative negative effect of drought for all ages. A lower effect of competition was recorded in the oldest trees in both forests. The interaction of competition with climate and tree age showed attenuated climate-mediated differences when competition was high.