Submitted to: Wetlands Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2008
Publication Date: 11/1/2009
Citation: Rayamajhi, M.B., Pratt, P.D., Center, T.D., Tipping, P.W., Van, T.K. 2009. Decline in exotic tree density facilitates increased plant diversity: the experience from Melaleuca quinquenervia invaded wetlands. Wetlands Ecology and Management. 17:455-467.2009. Interpretive Summary: The invasive plant melaleuca of Australian origin has invaded and developed dense forests in many parts of south Florida. It has done so by eliminating other Florida native plants from the area by creating unsuitable environment for other plants. Natural enemies such as plant feeding weevils and psyllids imported from Australia, as well as other insects and pathogens that migrated to the area, defoliated and killed substantial numbers of melaleuca trees. We assumed that native plant diversity would increase following reductions in density of mature melaleuca stands. The death of large number of melaleuca trees and the loss of leaves from surviving trees did open up the forest canopies and created a lot of space on the forest floor. As a result, many native plants were naturally recruited on the forest floor. The return of native plants in previous melaleuca monocultures helped increase the diversity and abundance of native plants in the area. Increases in plant diversity and abundance were 2 to 4 -fold where melaleuca feeding weevils and psyllids are well established. These findings show that plant feeding insects and disease causing pathogens can be used to help rehabilitate sites by promoting the recruitment of native plants.
Technical Abstract: The Australian tree Melaleuca quinquenervia (melaleuca) formed dense monocultural forests several decades after invading Florida and the Caribbean islands. These dominant forests have displaced native vegetation in sensitive wetland systems. We hypothesized that native plant diversity would increase following recent reductions in density of mature melaleuca stands in south Florida. We therefore examined data on changes in melaleuca densities and plant species diversity derived from permanent plots that were monitored from 1997 to 2005. These plots were located within mature melaleuca stands in nonflooded and seasonally-flooded habitats. Two host-specific biological control agents of melaleuca, Oxyops vitiosa and Boreioglycaspis melaleucae, were introduced during 1997 and 2002, respectively. Also, an adventive rust fungus Puccinia psidii and lobate-lac scale Paratachardina pesudolobata became abundant during the latter part of the study period. Melaleuca density declines coincided with 2- to 4-fold increases in plant species diversity. The greatest declines in melaleuca density as well as the greatest increases in importance values and diversity indices occurred in nonflooded as compared to seasonally-flooded habitats. The rapid reduction in melaleuca density and canopy cover during the study period may be attributed to the impact of natural enemies. Densities of other woody plants, particularly Myrica and Myrsine, which were sparsely represented in the understory by a few suppressed individuals, also declined during the same period possibly due to infestation by the generalist lobate-lac scale. These findings showed natural enemy mediated reduction of melaleuca dominance which positively influenced native plant diversity and facilitated the rehabilitation of degraded habitats.