Changes of carbon storage as affected by different soil preparation techiques two years after a forest mixed-stand installation

Taking into account the importance of carbon sequestration on forest systems, and its relation to stand management practices, aboveground and belowground biomass (herbaceous vegetation and forest species) was sampled, together with soil, on a mixed stand of Pseudotsuga menziesii (PM) and Castanea sativa (CS), with two years old, in order to evaluate the impact of soil mechanical operations prior to plantation on carbon storage and distribution. The experimental field was established near Macedo de Cavaleiros, Northern Portugal, at 700 m elevation, mean annual temperature 12ºC and mean annual rainfall 678 mm, with a typically Mediterranean seasonal distribution. The experimental layout included 3 blocks in different topographic situations (flat plateau, steep slope and gentle slope) where the different treatments corresponding to different tillage intensities were randomly distributed (high, moderate and light intensity), in plots with an area of 375 m2 each. The results obtained showed that: (i) more than 90% of the total carbon stored in the system is located in the soil, increasing with depth with tillage intensity; (ii) the contribution of herbaceous vegetation and related roots to the carbon storage is very low; (iii) the amount of carbon per tree was higher in CS than in PM; (iv) the global carbon storage was affected by soil tillage, generally decreasing with the increase of tillage intensity