Ecosystem engineering facilitates invasions by exotic plants in high‐Andean ecosystems

Abstract

Summary1 Ecosystem engineers are organisms that change abiotic conditions in ways that affect the performance and distribution of other species, including exotics. Several mechanisms have been proposed for the successful establishment of exotic plants in natural communities, but the positive effects that native engineer species may have on the distribution and performance of exotic plants remain unknown. 2 In this study, we propose that amelioration of extreme abiotic conditions by ecosystem engineers can make stressful habitats invadable by exotic plant species, with larger positive effects on the performance of exotic plants as environmental harshness increases. We tested this hypothesis by assessing the effects of a high-Andean ecosystem engineer, the cushion plant Azorella monantha , which is known to create habitat patches where environmental conditions are less extreme than in the surrounding habitats, on the distribution and the performance of two exotic plant species, field chickweed ( Cerastium arvense ) and common dandelion ( Taraxacum officinale ), along a an elevation gradient in the Andes of central Chile. 3 We measured and compared the abundance, biomass and survival of both exotic species within and outside cushion habitat patches at three elevations (3200 m, 3400 m and 3600 m), and evaluated whether the effects of A. monantha varied across elevations. 4 The results indicated that cushion plants positively impact the performance of both exotics, and have greater facilitative effects at higher elevations. Indeed, at the higher elevation site, C. arvense was only detected within A. monantha patches, suggesting that cushions may expand the distribution range of exotics. These results suggest that ecosystem engineering by native species could promote biological invasions in harsh environments, leading to higher abundances of invaders than those expected in the absence of engineers. 5 Given the conspicuousness of ecosystem engineering in nature, we suggest that exotic species eradication programmes might be less successful by not taking into account the facilitative effects of native engineer species on invaders. Further, we suggest that the recent proposals to use engineer species in ecosystem restoration should be aware of their potential role in promoting invasions.

A systematic review of the recent ecological literature on cushion plants: champions of plant facilitation

“…For instance, Azorella madreporica, a Chilean cushion species, was found to display both positive and negative associations with plant species depending on the plants location outside or inside the cushion vegetation (Fajardo et al 2008). Plant interactions associated with cushions and environmental gradients supports the stress gradient hypothesis (Bertness and Callaway 1994) showing that the frequency of facilitation increases with environmental severity (Smith et al 1995, Badano et al 2007, Cavieres and Badano 2009). Studies on the biology of cushions have also generated a substantial body of literature (32 publications) including research on life history (7), genetics (9), reproduction (10), and evolution (6).…”

Shrubs as foundation species in a high tropical alpine ecosystem: a multi-scale analysis of plant spatial interactions

“…and Cerastium arvense L. (e.g. Cavieres et al 2005Cavieres et al , 2007Badano et al 2007). Probably life-forms of contrasting architectures (i.e.…”

Life history variation and demography of the invasive plant Eschscholzia californica Cham. (Papaveraceae), in two altitudinal extremes, Central Chile

“…Secondly, if cows are efficient vectors, the seeds can be transported beyond the current invasion front of this exotic plants (2200 masl) to the cushion plants zone (Laretia acaulis, Azorella monantha and Azorella madreporica) which range from 2800 to 3400 masl (Armesto et al 1980); this seed movement is plausible as we have observed horses feces above 3000 masl and beyond. It is well documented that cushion plants provide microclimate conditions for exotic plants, which increase growth, survival and reproduction on species such as Taraxacum officinale and Cerastium arvensis , Badano et al 2007, Arredondo et al 2009). Therefore, it is probable that this positive interaction might occur with Eschscholzia californica as well.…”