Composite low thinning and slash burning treatment enhances initial Spanish black pine seedling recruitment

Abstract

Global change threatens the persistence of native forest ecosystems mainly by limiting the conditions for natural regeneration but also inducing tree mortality and increasing the risk of large wildfires. In this context, understanding the biotic and biotic factors that ultimately determine tree recruitment is of pivotal importance to implement adaptive forest management strategies. In this study we assess how multipurpose management strategies, including combinations of thinning intensities and prescribed burning, affect the seed emergence and seedling survival of Pinus nigra Arn. subsp. salzmannii in two different forest sites in NE Spain. We tested four overstorey and fuel treatments that combined heavy and light intensity thinnings from below with understorey clearing and two different treatments of the resulting slash: prescribed burning and lop and scatter. The results showed: (1) a lack of regeneration in control units, probably caused by the high density of canopy and understorey; (2) greater seedling recruitment in units treated with slash burning than in units treated with slash lop and scatter, probably due to the effects of prescribed burning on the herbaceous layer, soil organic layer, nutrient pools, and understorey; and (3) a different regeneration response between sites for treatments that included prescribed burning, probably due to microclimatic conditions during the experiment and differences in the characteristics of the prescribed burns. These findings indicate the potential effectiveness of combined treatments of thinning and slash burning in the context of the implementation of multipurpose management actions in endangered ecosystems adapted to low intensity fires.