Huff and puff and blow down: invasive plants traits response to strong winds at the Southern Oceanic Islands

Abstract

Invasions constitute a major driver of biodiversity changes. Insular plant communities are particularly vulnerable to invasions and are relevant models for investigating mechanisms supporting the establishment and spread of introduced plants. Terrestrial flora of sub‐Antarctic islands must often thrive in highly windy habitats, thus imposing strong mechanical constraints on individuals. Many alien plants at the sub‐Antarctic islands are of tropical or temperate origins, where they were exposed to less stringent wind conditions. As wind likely represents a strong environmental filter for the successful establishment and further geographic spread of plants, they should have developed responses to resist and successfully colonize the Iles Kerguelen. We studied responses to wind of three herbaceous species that are invasive at Iles Kerguelen. We sampled plant individuals at different locations, under windy and sheltered conditions. Traits related to wind avoidance and tolerance and to resource acquisition were measured. We additionally assessed individual performance (biomass) to determine the consequences of trait variations. We focused on trait mean and variance, in particular, through the calculation of hypervolumes. This study emphasized that wind has important effects on plant economics spectrum, including traits involved in mechanical avoidance and light acquisition, with varying strategies, which seem to depend on the biological type of the species (grass versus non‐grass). Wind generally reduces individual performance, and this negative effect is not direct but operates through the modification of plant trait values. Furthermore, analyses performed at the hypervolume scale indicate that not only functional trait mean but also its variability account for plant performance. The existence of contrasting growth strategies to cope with local environmental conditions suggests that invaders will be able to occupy different niches, which may ultimately impact local communities. Our results highlight the importance of considering multi‐traits responses to meaningfully capture plant adjustments to stress.

A synthesis of biological invasion hypotheses associated with the introduction–naturalisation–invasion continuum

“…Diverse degrees of trait plasticity do exist among alien species subjected to the same environmental pressures, as reported from plants exposed to windy conditions (Saiz et al 2021). Plasticity should theoretically be highly beneficial at the early stages of invasion, because of the probable costs of maintaining plasticity (van Kleunen and Fischer 2005), and because it may allow for novel genetic variation to arise (Pigliucci et al 2006).…”

Species differ in their responses to wind: the underexplored link between species fine‐scale occurrences and variation in wind stress

“…There are, however, several other aspects that should still be investigated to provide a more complete understanding of the impacts of chronic wind. For example, wind may have impacts on plant functional traits that were not considered here, including specifically stem density and flexibility (Saiz et al, 2021) and root characteristics (Zhang et al, 2021). The dispersal of propagules through wind could also have an impact on species occurrences at the fine scale (as demonstrated at coarser scales; Engler & Guisan, 2009).…”

“…Trait measurements are described in detail in the publications from which they were obtained. Wind stress was hypothesised to have stronger effects on taller compared with short‐statured vegetation (Saiz et al, 2021). Leaf traits were expected to show a correlation with wind stress due to the mechanical damage and desiccating effect that wind could have on leaves (Russell & Grace, 1978), with windier conditions expected to favour smaller leaves (as observed by Niklas, 1996) and leaves with greater structural investment and, therefore, lower specific leaf area, lower leaf nitrogen content and lower phosphorous content (Pérez‐Harguindeguy et al, 2013).…”