Biodiversity Within and Beyond the Native Distribution of Tree Species: The Case of Pinus nigra Forests in Europe

[Aim] Forests dominated by non-native trees are becoming increasingly common. However, their impact on biodiversity remainsuncertain, with a debate on whether they represent ‘green deserts’ or secondary habitats for biodiversity. We addressed this ques-tion by evaluating the patterns and ecological drivers of taxonomic and functional understory diversity between black pine (Pinusnigra) forests within and outside its native distribution range.

[Location] Europe

[Methods] We collected a continental database of vegetation plots with full species composition and related functional traits. Wecompared α- and β-taxonomic (TD) and functional (FD) diversity between understories of P. nigra forests within and outside itsnative distribution range, and modelled the relative effects of climate, soil conditions, and canopy cover.

[Results] We found similar values of α- and β-TD and -FD in forests within and outside the native range. The response to localand large-scale drivers was also similar, with high canopy cover reducing α-TD and α-FD but enhancing β-TD and β-FD in bothforest systems. Soil nutrients enhanced α-TD and α-FD and decreased β-FD only in forests within the native range, while droughtreduced α- and β-diversities only in forests outside the native range.

[Main Conclusions] The same dominant tree species under similar ecological conditions resulted in low diversity differentiationbetween forests both within and outside P. nigra native range. Nevertheless, understory diversity was sensitive to different eco-logical drivers, with stronger effects of soil fertility and moisture on forests within and outside native ranges, respectively. Theseresults suggest that P. nigra forests established beyond the species' native range exhibit similar diversity metrics and ecosystemfunctions as those within its native range. Our findings may be linked to the fact that P. nigra forests outside the native rangewere placed in the same biogeographical region as the corresponding forest stands within the native range.

G.B. was funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.4—Call for tender No. 3138 of 16 December 2021, rectified by Decree n. 3175 of 18 December 2021 of Italian Ministry of University and Research funded by the European Union—NextGenerationEU; Award Number: Project code CN_00000033, Concession Decree No. 1034 of 17 June 2022 adopted by the Italian Ministry of University and Research, CUP B63C22000650007, Project title ‘National Biodiversity Future Center – NBFC’. B.J.A. was supported by the grant ‘Laboratorio de Vegetación y Biodiversidad’ (IDE/2024/000720, Principality of Asturias-Sekuens-EU-FEDER).

Peer reviewed