Seasonally Distinctive Growth and Drought Stress Functional Traits Enable Leucaena Leucocephala to Successfully Invade a Chinese Tropical Forest

The nitrogen-fixing mimosid Leucaena leucocephala continues to be used for afforestation in degraded tropical forests. Yet, fast-growth and high drought stress tolerance enables L. leucocephala to outperform native species and L. leucocephala has been identified as one of the 100 most invasive species globally. This warrants development of effective control measures, including bio-controls, to prevent the spread of this species particularly across tropical islands. Here, we compare differences in key functional traits between L. leucocephala and eight dominant native species ( Bridelia tomentosa, Radermachera frondosa, Lepisanthes rubiginosa, Rhaphiolepis indica, Pterospermum heterophyllum, Fissistigma oldhamii, Psychotria rubra and Cudrania cochinchinensis) in L. leucocephala invaded tropical forests of Hainan Island, China. Functional traits related to growth (photosynthesis rate, stomatal conductance and transpiration rate) and drought stress tolerance (leaf turgor loss point) were measured in wet and dry seasons to investigate whether these functional traits differed between L. leucocephala and the eight dominant native species. Our results demonstrate that L. leucocephala has significantly increased growth rates (at least two-fold) in both wet and dry seasons. Additionally, L. leucocephala shows significantly higher drought stress tolerance (lower TLP) in the dry season. These results indicate that L. leucocephala would almost certainly outperform the eight dominant native species and might successfully invade Hainan tropical forests. There is an urgent need to identify native species that have similar growth and drought stress tolerance traits to enable the development of effective strategies to control L. leucocephala on Hainan Island.