Impacts of exotic plant species Oxalis pes-caprae L. on species diversity of herbaceous vegetation understory of olive groves on Lesbos Island

The relationship between plant invasion and diversity of native plant communities was investigated in Mediterranean olive groves. Species abundances were recorded in close-paired plots with natural herbaceous vegetation understory of olive groves on Lesbos. Each paired plot consists of a control and an invaded plot. The exotic plant species Oxalis pes-caprae was absent from control plots, while it was dominant in invaded plots. The species richness, species diversity and species evenness were estimated per plot. The dominance of the biological invader caused a large reduction in species richness and species diversity of grassland communities. On the other hand the species abundances were found to be similar in reference and invaded plots. In addition the measurements’ year had a clear effect on the variation of species richness, diversity and evenness indices. In conclusion impacts of exotic plant species Oxalis pes-caprae on herbaceous vegetation on Lesbos were expressed as a significant decrease of biodiversity of Mediterranean-type grassland communities.