Pinus radiata is a tree species native from California, USA, and is the main forestry species planted in Chile and other countries from the southern hemisphere. Many studies have assessed the invasion by this species, but none has evaluated the effect of its invasion on native species. In this study I assessed the effect of the invasion by Pinus radiata on recruitment of native woody species from the Mediterranean region of Chile. In this region recruitment of native species is usually facilitated by nurse species mainly through amelioration of microclimate and increasing soil moisture. Then, Pinus radiata may also facilitate the recruitment of native species by shading effects. Nevertheless, soil acidification and litter produced by Pinus may have negative effects on native species, either biochemically or mechanically. Hence, the net effect of Pinus may be neutral or less positive than the effect produced by native trees. I tested these hypotheses by assessing the natural pattern of recruitment under invasive individuals of Pinus, under native trees and in open sites in 12 localities along the chilean Mediterranean region. Additionally, in one locality I performed a field experiment to assess the net effect of Pinus, and another to assess the role of the soil and shade of Pinus on recruitment of 12 woody species experimentally sown. Finally, to evaluate biochemical and mechanical effects of leaf litter from Pinus on the same 12 species, I conducted a glasshouse experiment including treatments with active carbon and leachates of leaf litter.
I found that naturally recruiting species richness was significantly greater under native trees than under Pinus, and under these two cover types greater than in open sites. The net effects of Pinus and native trees on species richness in the recruitment were positive but the effect of native trees was greater. Shading had a positive effect but the soil from Pinus a negative effect on species richness. Results from the glasshouse experiment suggest that the negative soil effect of Pinus is produced by a mechanical impact of leaf litter. These results suggest that Pinus radiata may facilitate the recruitment of native woody species in this semiarid region but this positive effect is weaker than facilitation produced by native species due to its leaf litter. Fondecyt 3100100.