Effect of thinning on above-ground biomass accumulation in a Douglas-fir plantation in southern Italy

We investigated the effects of a long-term thinning experiment on the distribution of above-ground biomass of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii) in a plantation in southern Italy. Allometric equations were used to estimate biomass and partitioning to stem and crown compartments. Variation in biomass stock estimated with allometric equations were evaluated according to seven thinning treatments: geometric-systematic (1 row every 3), selective (light-moderate-heavy), mixed systematic-selective (1 row every 4, 1 row every 5), unthinned (control). Over the experimental period of 13 years, current annual increments of carbon were lower (3.4 Mg ha-1 year-1) in control plots than in treated plots. At age 30, plots subjected to light selective thinning showed higher values of above-ground biomass (249.7 Mg ha-1). The biomass harvested with this treatment was 29.3 Mg ha-1, and the mean annual increment of carbon over 13 years was 4.8 Mg ha-1. Our results showed that light thinning stimulated increase in carbon stock, with a minimal loss of carbon during the treatment and a current annual increment of carbon higher than in control sub-plots and sub-plots thinned using systematic methods. This treatment yielded least carbon emissions and we affirm it has discrete global warming mitigation potential.