Competitive and allelopathic effects of the invasive shrub Schinus terebinthifolius (Brazilian peppertree)

Abstract

Non-native plant invasions can suppress biodiversity and alter ecosystem functions, but often the mechanisms underlying the impacts of invasions are unknown. We used a greenhouse mesocosm experiment and a growth chamber germination experiment to evaluate the competitive and allelopathic effects of Schinus terebinthifolius (Brazilian peppertree) on three tree species and four herbaceous plant species native to Florida’s pine flatwoods communities. Schinus had little effect on the establishment of native species in the mesocosm experiment, except for one native herbaceous species (Solidago fistulosa), which had 75 % fewer seedlings in Schinus-invaded mesocosms. However, Schinus caused significant declines in native plant performance. Tree biomass was reduced by 85 % and herbaceous plant biomass was 83 % lower, on average, in mesocosms with Schinus compared to uninvaded controls. The addition of activated carbon to the soil did not ameliorate the effects of Schinus on native species, indicating that competition for resources, not allelochemicals exuded by Schinus roots, was likely responsible for the suppressive effects of Schinus on native species. Schinus fruit extract reduced seed germination by 39 % on average compared to water controls, suggesting crushed fruit below invasive Schinus stands may limit native species recruitment. Our results demonstrate significant impacts of Schinus competition and fruit extracts on native trees and herbaceous species, providing experimental evidence for ecological impacts of invasions and further support for restoration of invaded habitats.