Pinus contorta invasion into treeless steppe reduces species richness and alters species traits of the local community

Abstract

Pinus contorta, one of the most invasive tree species in the world, has been proposed as a model species for improving our understanding of invasion ecology. In this study, we assessed the impact of P. contorta invasions on the species richness, diversity and species traits of a resident treeless steppe community. In a Pinus contorta invasion gradient (Patagonia, Chile), we surveyed vegetation from high canopy closure pine invasion to treeless steppe, and computed species richness, diversity and Sorensen similarity indexes. For all species, we determined functional trait values from the literature, data bases, and personal observations. Species richness and diversity were related to canopy cover (a proxy for invasion intensity) using generalized linear mixed-effects models. Changes in species traits due to canopy cover were analyzed using RLQ ordination analysis and the fourth-corner analysis. We found that Pinus contorta canopy cover significantly reduced the number of native species by 70 %, implying a strong effect on species exclusion. A few native species, however, prevail in the novel conditions (e.g. Baccharis magellanica, Acaena integerrima). Species traits changed significantly with increasing pine canopy cover, where P. contorta promoted the existence of traits related to shade-tolerance and conservative reproductive strategies. We conclude that the negative impacts of Pinus contorta into the treeless steppe, including a reduction in the number of species and the shifting to traits adapted to tolerate shade and associated with conservative reproductive strategies, can have severe implications for the conservation of biodiversity and ecosystem functioning where it invades