A Non-native Perennial Invades a Native Forest

Disturbance is frequently a requirement for non-indigenous plant invasions, but plants that invade in the absence of significant disturbance pose special problems for conservationists and land stewards, as the invasion rates and effects are difficult to predict. Knowledge of the invader's population ecology is essential for the preservation of native plant communities. A sub-shrub native to South America, Tibouchina herbacea (Melastomataceae) is invading intact, wet forests and open, disturbed sites on the islands of Hawaii and Maui. Experimental tests of the importance of disturbance for reproductive rates showed that absence of canopy cover produced the highest rates of germination, survival and seed dispersal distance. Ground cover was less important, but had a positive effect on germination and a negative effect on survival. Results of these experiments suggest that T. herbacea will probably spread more quickly in open, disturbed areas, but is very capable of establishment in natural forests. If spread is arrested in the early stages, manual control may be effective, otherwise landscape-level control efforts, such as biological control, will be needed. Prevention of dispersal and control of T. herbacea in forested areas should be a priority for land managers in Hawaii.