Forests play a key role in the carbon cycle as they store huge quantities of organic carbon, most of which is stored in soils, with a smaller part being held in vegetation. While the carbon storage capacity of forests is influenced by forestry, the long-term impacts of forest managers’ decisions on soil organic carbon (SOC) remain unclear. Using a meta-analysis approach, we showed that conventional biomass harvests preserved the SOC of forests, unlike intensive harvests where logging residues were harvested to produce fuelwood. Conventional harvests caused a decrease in carbon storage in the forest floor, but when the whole soil profile was taken into account, we found that this loss in the forest floor was compensated by an accumulation of SOC in deeper soil layers. Conversely, we found that intensive harvests led to SOC losses in all layers of forest soils. We assessed the potential impact of intensive harvests on the carbon budget, focusing on managed European forests. Estimated carbon losses from forest soils suggested that intensive biomass harvests could constitute an important source of carbon transfer from forests to the atmosphere (142–497 Tg-C), partly neutralizing the role of a carbon sink played by forest soils.

We investigated whether timing and rate of growth are related to the life strategies and fitness of three conifer species. Intra-annual dynamics of wood formation, shoot elongation and needle phenology were monitored over 3 years in five Norway spruces (Picea abies (L.) Karst.), five Scots pines (Pinus sylvestris L.) and five silver firs (Abies alba Mill.) grown intermixed. For the three species, the growing season (delimited by cambial activity onset and cessation) lasted about 4 months, while the whole process of wood formation lasted 5–6 months. Needle unfolding and shoot elongation followed the onset of cambial activity and lasted only one-third of the season. Pines exhibited an ‘extensive strategy’ of cambial activity, with long durations but low growth rates, while firs and spruces adopted an ‘intensive strategy’ with shorter durations but higher growth rates. We estimated that about 75% of the annual radial increment variability was attributable to the rate of cell production, and only 25% to its duration. Cambial activity rates culminated at the same time for the three species, whereas shoot elongation reached its maximal rate earlier in pines. Results show that species-specific life strategies are recognizable through functional traits of intra-annual growth dynamics. The opposition between Scots pine extensive strategy and silver fir and Norway spruce intensive strategy supports the theory that pioneer species are greater resource expenders and develop riskier life strategies to capture resources, while shade-tolerant species utilize resources more efficiently and develop safer life strategies. Despite different strategies, synchronicity of the maximal rates of cambial activity suggests a strong functional convergence between co-existing conifer species, resulting in head-on competition for resources.

Differences between intra- and inter-specific competition strategies in mixed stands account for higher productivity. The mechanisms of competition as they relate to stand structure remain poorly explored. Climatic effects have also been overlooked in most approaches aimed at studying tree growth. These effects were investigated through the case study of beech-oak mixtures in France. A single-tree diameter-increment mixed model was fitted to data gathered from the Laboratoire d'Etude des Ressources Forêt-Bois (LERFoB) network of permanent plots. In order to take stand structure into account, the model was able to distinguish between inter- and intra-specific competition at tree level. Differences in intra- and inter-specific competition are mainly detected in the understorey of oak-dominated stands, where suppressed beech trees performed better than suppressed oak trees. From a climatic point of view, diameter increment was sensitive to the mean temperature of the vegetative period. Concerning competition, our results demonstrate that optimal growth induced by mixtures is not only a matter of species proportion but also depends on stand structure. Regarding climatic effects, they need to be considered in growth predictions, especially given the future climatic conditions predicted for continental Europe. These findings could serve as guidelines for designing strategies to alleviate stress in oak-beech stands.