Alien plant invasion reduces the reproductive success of a critically endangered endemic tree species

Résumé fourni par la source

Abstract The decline of native plant species associated with alien plant invasion is often assumed to be driven by competitive exclusion. However, invasive alien plant species could also directly or indirectly impact native plants by limiting reproductive success. Here, we tested whether invasive alien plants influence seed production, viability, and germination using the Benjoin [ Terminalia bentzoe (L.) L.f. subsp. bentzoe ], a critically endangered tree endemic to the Mascarene Islands (southwest Indian Ocean), as a model species. Seed production was estimated from seed densities under the canopy of adult individuals from one of the largest remaining subpopulations of the species (in Cirque de Mafate, Reunion Island). Seed viability was determined using a tetrazolium test on the different sets of seeds collected in the field. Densities of seeds and viable seeds were then tested for correlation with the percentage cover of invasive alien plant species in the liana, tree, shrub, and herbaceous forest layers. Seed germination was studied by sowing seeds in soils where three alien invasive plants, three endemics, and T. bentzoe subsp. bentzoe had previously been grown. Seed production and viability decreased with increasing abundance in invasive alien plants in the liana and tree strata but not in the lower vegetation strata. Mechanisms specific to tall-statured invasive alien plants could include competition for resources, interference with pollinator behavior and mechanical constraints. Seed germination was inhibited by the invasive alien succulent Mauritius hemp [ Furcraea foetida (L.) Haw.] and T. bentzoe subsp. bentzoe itself, but enhanced by the endemic tree species Poupartia borbonica J.F.Gmel. These species may differ in their resource use intensity, associated microbial communities, and allelopathic effects. Our findings therefore suggest that plant invasions can significantly contribute to the decline of native plants through reduced reproductive ability and induce an extinction debt due to a lack of regeneration.

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