Results of a competition experiment involving 12 threatened tree species endemic to the Mascarene Islands and nine invasive alien plant species

The experiment was conducted from October 2024 to April 2025 in the Mascarin Botanical Garden, Saint-Leu, Reunion Island. Pots were set up following the experimental design of Hart et al. (2018). A total of 2018 seedlings from 21 species, including 12 threatened endemic trees and nine invasive alien plants, were transplanted alone, and with varying conspecific and heterospecific densities. This allows decomposing intrinsic growth rate, reaction to intraspecific competition, and to interspecific competition. Species were associated in 27 endemic-alien pairs according to their co-occurrence in nature. Each treatment was replicated five times. Plant performance was estimated with leaf biomass and stem volume. The dataset “competition_experiment.csv” contains morphological measurements for each individual plant. Due to the high conservation value of endemic species, we did not harvest plants at the end of the experiment. Instead, we measured leaf area from one tenth of the leaves of each plant (with a minimum of two leaves), and estimated the leaf area-leaf dry mass relationship for each species on a representative number of supernumerary plants to be able to allocate leaf biomass values to plants in the experiment (see dataset “leaf_dry_mass_measurements.csv”). Reference: Hart SP, Freckleton RP, Levine JM (2018) How to quantify competitive ability. J Ecol 106:1902–1909. https://doi.org/10.1111/1365-2745.12954