Biomass accumulation and carbon sequestration after heavy mechanical thinning on post-fire Pinus pinaster seedlings (Monte ‘Fraguas’, Guadalajara, Central Spain)

Abstract

An experience has been conducted on aPinus pinaster stand in Guadalajara (Central Spain) affected by a wildfire in 1992 to evaluate biomass allocation of different seedling fractions and to quantify the differences between two heavy pine seedling mechanical thinnings. Nine permanent plots (20 m 20 m) were installed in the study area, in 2000. After measuring initial seedling density (10,000 seedlings/ha), a completely randomized block design was used. Three plots remained as control, three were treated with a heavy pine seedling thinning and the other three were treated with a very heavy pine seedling thinning. In each plot, a yearly dasonomic inventory and a biomass destructive inventory every two years, removing 10 representative seedlings of each treatment, were carried out. Multiplicative models (y = axb) have been elaborated in order to relate dasometric variables with the biomass obtained through destructive samplings. The highest correlation coefficients (from 0.80 to 0.97) were obtained for the stem groundline diameter. Results show that biomass accumulation of different seedling fractions is significantly different among treatments, being the increment of C higher with the heaviest thinning. These changes were higher the two first years after thinning. Nevertheless, Carbon sequestration of the stand was significantly higher in the control plots. Consequently, heavy thinning on post-fire Pinus pinaster seedlings makes better their vigour, and decreases forest fire hazard, but at the same time, it produces an important extraction of Carbon sequestrated.