Biotic, abiotic, and anthropogenic drivers of demographic performance of non-native Eucalyptus and Pinus species in forested areas of Spain

Non-native trees enhance services that are fundamental for human well-being. Yet, the extensive use of nonnative trees has the potential of causing environmental and socio-economic harm. Eucalyptus and Pinus are the most widely distributed and extensively planted tree genera worldwide, because their rapid growth allows profitable production of timber and pulp. Their naturalization is causing severe effects on the environment, but the relative importance of underlying factors determining their demographic performance is not well known. Thus, our aim was to evaluate the relative importance of biotic, abiotic, and anthropogenic factors driving demographic changes of Eucalyptus and Pinus at the regional scale. We compiled environmental variables and demographic data for Eucalyptus globulus, Eucalyptus camaldulensis, and Pinus radiata across 6388 permanent forestland plots surveyed in the Spanish Forest Inventory (SFI). We used the second (1986-1996), third (1997-2007), and fourth (2008-2017) SFI datasets to quantify annual changes in basal area per plot between consecutive inventories (delta BA; m(2) ha(-1) year(-1)). We also quantified the components of delta BA: tree ingrowth (transitions from juvenile to adult trees), growth, and mortality. We evaluated juvenile recruitment with in-situ regeneration (No. juvenile trees ha-1) within plots already occupied by the focal species in the previous inventory, and with natural colonization of plots where the focal species was absent at the beginning of the time interval. We found that the structure of the biotic community was especially important to explain demographic performance of non-native trees growing in benign environments (E. globulus and P. radiata), whereas abiotic factors were particularly important regulating basal area increments of E. camaldulensis, which occurs in harsher environments. Basal area increments decreased with species and functional richness, heterospecific density, mean annual temperature, and increased with soil capacity to retain nutrients and water. Colonization of new plots increased with propagule availability in the surrounding landscape. Tree cutting was beneficial for P. radiata. Collectively, our results suggest that non-native trees perform better in forests with high propagule pressure, low biotic resistance, favourable abiotic conditions, and human management.

Automated summary

Non-native trees play an important role in providing services for human well-being, but their extensive use can have detrimental effects on the environment and socio-economic aspects. The demographic changes of Eucalyptus and Pinus at a regional scale are influenced by biotic, abiotic, and anthropogenic factors. The structure of the biotic community, abiotic conditions, propagule pressure, and human management practices all contribute to the performance of non-native trees in forests.