Effect of forest thinning on the diversity and composition of macrofungal sporocarps in Pinus uncinata stands

Pine forests represent globally distributed conifers growing in a wide range of habitats within the Mediterranean basin. One example are the high-altitude mountain pine (Pinus uncinata) forests in the Pyrenees, which stand out for their high fungal sporocarps richness. Nevertheless, studies on the effects of forest management on sporocarps diversity in mountain pine forests have been lacking, despite their importance for optimizing multiple-use forestry practices. To address this gap, we analysed the impact of different thinning intensities on fungal sporocarp diversity and composition in P. uncinata stands in the Pyrenees. The experimental design involved a BACI approach used to compare annual sporocarp diversity and composition five years before and three years after the thinning intervention in 18 permanent plots (9 thinned and 9 control). The results indicated an absence of a thinning effect in the lighter thinning intensities (< 25 % of basal area removal) for the sporocarp richness, while negative effects emerged steadily when increasing the thinning intensity until a clear negative effect reported when removing more than 70 % of the basal area. Sporocarp evenness and Shannon index revealed a negative effect due to forest thinning, with a dominance of some species that can cope with the new stand conditions. The ECM sporocarp composition was mainly affected by interannual variability, while the saprotrophic sporocarp composition was mainly driven by site conditions. However, in both guilds, we detected a reduction of the sporocarps fructification in the higher thinning intensities. Our results indicate that lighter thinning intensities do not compromise fungal diversity conservation. Finally, forest management practices that balance timber production and fungal diversity could create opportunities to enhance the ecological, social and economic value of these forest stands, which have historically been managed exclusively for timber purposes.