Effects of fire recurrence and different salvage logging techniques on carbon storage in Pinus pinaster forests from northern Portugal

Pinus pinaster (maritime pine) is widely planted in the Mediterranean Basin. Maritime pine forests’ carbon stocks are dynamic because of the effect of wildfires and timber activities. Management practices offer an opportunity to mitigate climate change via increasing carbon storage in various ecosystems. In this work, we quantified carbon pools in P. pinaster forests in relation to fire occurrence and different post-fire salvage logging techniques. For this, we studied an area in northern Portugal where different parts had burned zero, one and four times during the last three decades. Following the last fire in 2012, two salvage logging treatments were carried out: (1) typical logging where all logs and tree biomass were removed and (2) conservation logging where burned tree branches were left in piles and log extraction was restricted to specific extraction trails. We assessed the carbon stocks for the aboveground and belowground compartments, taking into account their different components (vegetation, litter, roots and soil organic carbon). Our main findings were, firstly, that recurrent fires can be catastrophic in terms of carbon sequestration if the overstory dominated by P. pinaster does not regenerate after fire (2.4 times less). Secondly, soil organic carbon constituted an important carbon pool, being the most important when pines are eliminated due to recurrent fires with short intervals (90–95 %). Finally, the conservation technique applied here, leaving piles of branches on the soil surface, would be a suitable measure to increase carbon storage, at least in the short term, but might interfere with the recruitment of the pine stand.