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 CO 2 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.