Drought responses of an exotic tree (Eriobotrya japonica) in a tropical cloud forest suggest the potential to become an invasive species

Eriobotrya japonica is a non-native tree expanding in secondary forests and threatening the tropical montane cloud forest of central Veracruz, Mexico. Our objective was to investigate whether E. japonica has invasive potential by examining morphological and physiological functional traits in response to drought events. We did field surveys in a cloud forest reserve, and determined responses to experimental drought on germination, growth, morphological (leaf area, specific leaf area, thickness, and chlorophyll content) and physiological (hydraulic conductivity, maximum photosynthesis, and stomatal conductance) functional traits. Eriobotrya japonica adults, saplings, and seedlings were dominant in secondary forest, but scarce in mature forest. In lab, cumulative germination curves were similar across treatments (low–high temperatures; drought, water) while in the forest there was a delayed germination in drought treatment, though ultimately total germination was similarly high in the lab and field. Growth of seedlings was higher in light gaps than in the understory. However, leaf area was similar across treatments, SLA was lower, and thickness and chlorophyll content were higher in the gap-drought treatment. Physiological traits reinforced that E. japonica is highly drought resistant as demonstrated by avoidance of losses in hydraulic conductivity and high levels of carbon fixation. In a drought experiment, it took over 2 months to reach injurious losses in hydraulic conductivity. This study demonstrated that germination, growth, and physiological maintenance will all be unaffected in drought conditions and we concluded that E. japonica has potential to become an invasive alien species.