Invasibility of a grassland community by native and introduced genotypes of two invasive plant species (Centaurea maculosa Lam. and Senecio inaequidens D.C.)

Background/Question/Methods

Invasion success of plant species depends on the attributes of the invader, the invasiveness, and on the resistance of the community, the invasibility. Most studies in biological invasions have focused on either invasiveness or invasibility, but hardly both together. We present a two-year field experiment that looks at invasiveness and invasibility simultaneously. The establishment success of native and invasive genotypes of two worldwide invasive species (Centaurea maculosa Lam. and Senecio inaequidens D.C.) is quantified considering effects of structure and dynamics of a grassland community under disturbance. To simulate disturbance scenarios, selective and unselective cutting have been applied. 

We aim at identifying characteristics of the immigrant plant and of the resident community, a semi-natural grassland in Switzerland, involved in the establishment success. The effect of invasiveness is measured by comparing the fitness (survival, growth and potential reproduction) of native and invasive genotypes. The effects of the community structure and dynamics is analysed with repeated floristic surveys and plant trait measurements.

Results/Conclusions

Survival of both target species was very low after the first year. Whereas disturbance scenarios did impact survival of Senecio inaequidens, they had only little effect on Centaurea maculosa. Invasive genotypes from the introduced range of Senecio inaequidens were advantaged over native genotypes during the early growth stage, while fitness of Centaurea maculosa was not different among genotypes.

Intrinsic effects of genotypes (i.e. invasiveness) and community effects in establishment and growth success have been differentiated using multivariate analyses. Importance of drivers of community resistance at early and more advanced stages of invasion have been assessed by variance partitioning. Disturbance was the main driver for resistance at early stages of invasion. Community structure and dynamics impacted the later stages of development and the invasion outcome.

Our results provide us a better understanding of invasion process accounting with invasive species intrinsic attributes in a natural community. The identification of the drivers of community resistance at various development stages of the invader will improve our ability to better manage natural communities faced to invasion.