The contribution of forests to sustainable mitigation strategies is shaped by external and internal drivers that influence the ecosystem’s net carbon accumulation. Stand age significantly influences the functioning of forest ecosystems, their structure and physiological traits, affecting ultimately forest stability and resilience. Forest age distribution is mainly determined by the interplay of tree mortality and regeneration, influenced by both natural and anthropogenic disturbances. Most ecosystem services offered by forests become uncertain under future changing environmental conditions, such as the carbon uptake capacity. Therefore a deep understanding of the processes affecting the age dependency of CO2 uptake and wood production is essential for devising strategies to enhance forest resilience and stability under climate change.
There are contrasting information on the synergistic effect of elevated atmospheric CO2 levels and climate dynamics on European forest growth in recent decades. Some studies reported a positive response to the so-called “CO2 fertilization effect”, which could accelerate forest growth and carbon sequestration. Other studies question the strength and future persistence of the CO2 fertilization effect on the forest carbon sink due to the emergence of other limiting factors, like water and nutrient availability. Unveiling and disentangling the interplay between forest age and climate change will lead to better forest management and consequently will increase their resilience and stability.
In the recent study by Vangi et al. “Stand age diversity (and more than climate change) affects forests resilience and stability, although unevenly” we explore the direct impact of climate change on forest productivity across three forest stands, characterized by different species in different European regions. The aim was to investigate how forest age might modulate dynamics in response to future climate change and to assess whether age diversity influences the stability and resilience of future forests under changing climatic conditions. To do so, we employed a biogeochemical, process-based model on historically managed forest stands, projecting their future as undisturbed systems under four representative climate scenarios and one baseline scenario (current climate scenario). We used the variability and the temporal autocorrelation at lag 1 of the net primary productivity (NPP) as a proxy for forest resilience and stability, respectively.
Our findings indicate that NPP peaks in the young and middle-aged classes (16- to 50-year-olds), aligning with longstanding ecological theories, regardless of the climate scenario. Under climate change, the beech forest exhibited an increase in NPP and maintained stability across all age classes, while resilience remained constant with rising atmospheric CO2 and temperatures. However, NPP declined under climate change scenarios for the Norway spruce and Scots pine sites. In these coniferous forests, stability and resilience were more influenced. These complex dynamics highlight the need to promote species and age diversity within forests to strengthen their resilience and adaptability to future climate change.
Different stand age development under RCP 8.5 climate change scenarios as modelled by the 3D-CMCC-FEM (v.5.6) at the European beech forests of Soroe (Denmark)