by Alessandra Lagomarsino
Did you know that worldwide forests each year absorb 30% of the CO2 emitted globally by fossil fuels and are huge carbon sinks, thus contributing to climate change mitigation and storing carbon in different pools (i.e., biomass, soil, dead organic matter, or litter)? However, when a forest is degraded with many dead, fallen and damaged trees, it does not remove enough CO2 from the atmosphere to compensate the emissions due to the decomposition of dead trees and soil organic matter.
The large use of pine species for land restoration since the last century allowed colonizing harshly degraded areas and beginning the chain of ecological succession. Nevertheless, benefits were in some cases nullified by the absence or incorrect execution of the necessary cultivation interventions. The decayed forests lose their resilience capacity, productivity, density, canopy cover and regeneration, with reduced standing biomass and increased deadwood. This also implies reducing the potential of these forests to act as a sink or transforming them into a source of CO2 and other greenhouse gases. Moreover, the large amount of deadwood increases the risk of fires and compromises forest fruition for recreational purposes, especially in peri-urban areas.
To make these pine forests more effective for climate change mitigation*, degraded areas need an innovative management strategy aimed to support and facilitate multi-functionalities. With interventions of low intensity directed to the dominated plants alone, the structure and vigor of the forest is not positively affected. In an attempt to reconcile the advantages of thinning with the easiness and replicability of the intervention, improving the ecological stability and climate change mitigation potential of these ecosystems, a method of thinning from above has been developed with the LIFE FoResMit project (Recovery of degraded coniferous Forests for environmental sustainability Restoration and climate change Mitigation – LIFE14 CCM/IT/905, coordinated by CREA – Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria, Italy). This approach is called “selective thinning” and should work as simple and effective as possible. The method favors the productivity of trees that demonstrate vigor. It aims at guaranteeing stability over time and creating small openings in the coverage of the crowns to increase biodiversity of the shrub and herbaceous plans.
The LIFe FoResMit project tested and verified in the field the effectiveness of this thinning treatment in degraded coniferous forests in the Mediterranean environments of Italy and Greece. This included monitoring its impact on vegetation structure, biomass increment, carbon accumulation in all relevant pools of vegetation and soil, CO2 and other greenhouse gas fluxes, thus giving a complete picture of mitigation potential of management practices.
The project proposed an integrated view of ecosystem services offered by the forest and of thinning impact evaluation, developing both a trade-off and a synergies analysis among different ecosystem services. This also included the provision of substantial co-benefits in terms of society’s needs for energy, increasing the use of forest-derived biomass to substitute fossil fuels and finally the improvement of aesthetic attractiveness, accessibility and recreational value.
Un-thinned forest and after traditional and selective thinning.
Overall, LIFE FoResMit project demonstrated the applicability of selective thinning to recover degraded coniferous forests. The project pointed out that a rational and efficient forest management practice is a “win-to-win” approach for the sustainable management of degraded forests. After three years from thinning, the following main objectives were achieved by the FoResMit project:
- demonstration of the three mitigation options of i) reduction of emissions, ii) sequestration – enhancing uptake of C and iii) substitution of fossil fuels for energy production with biological products;
- increased net primary productivity of forest stands, stability, resilience and structure heterogeneity;
- increased soil C sequestration in biomass and soil;
- after an initial pulse, reduction of CO2 emissions and GWP from soil and increased CH4 uptake;
- energy production with removed woody biomass and fossil fuel substitution;
- generation of carbon credits after 5 years since thinning.
Selective thinning has also many qualitative benefits: first of all, it contributes to improving the aesthetic attractiveness and recreational value. It reduces the risk of fire because of the decrease of dead trees and inflammable material in the forest. Furthermore, selective thinning maximizes synergies among ecosystem services and supports maintenance of hydrological protection and soil structure.
The selective thinning seems to be the most rational and sustainable forest management option, because with comparable cost for the forest activity, it assesses better earnings from wood valorization, improvement in recreational attractiveness and comparable C-sequestration capacity.
Sustainability of the silvicultural treatment will be even more evident in the long-term, allowing forest regeneration and vegetation succession towards a more natural ecosystems dominated by broadleaves. Facilitating the introduction of late successional native broadleaves species means to help restoring natural functioning processes (e.g. natural regeneration, or more generally, self-organization), increasing their stability, resilience and self-perpetuating capacity.
*All forests mitigate climate change because absorb CO2 through photosynthesis. The management is needed in case of degradation to increase the effectiveness of CO2 sequestration and climate change mitigation.
Photos by @Alessandra Lagomarsino
