Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/16/2008
Publication Date: 5/1/2008
Citation: Rayamajhi, M.B., Pratt, P.D., Center, T.D., Tipping, P.W., Van, T.K. 2008. Aboveground biomass of an invasive tree Melaleuca (Melaleuca quinquenervia) before and after herbivory by adventive and introduced natural enemies: a temporal case-study in Florida. Weed Science. 56:451-456.2008. Interpretive Summary: Natural enemies can alter the amount of woody materials, foliage, fruits, and seeds of an invasive plant. Here we report the effect of natural enemies on the woody materials, foliage, fruit, and seed biomass of invasive tree melaleuca which has invaded large areas of south Florida. We felled melaleuca trees of different diameters in three counties (Broward, Miami-Dade, and Palm Beach) during 1996. Then we introduced natural enemies (leaf chewing and sap-sucking insects called weevil and psyllid) in 1997 and 2003. These and other natural enemies (a rust fungus and a scale insect) inflicted damage to melaleuca trees. We felled additional trees in 2003 in closely matched (with 1996 sites) sites. We sorted woody materials, leaves, fruits and seeds and compared the changes between 1996 and 2003. During this study period, leaf, fruit and seed biomass of melaleuca was reduced drastically in Broward County compared to Miami-Dade and Palm Beach County. This study also determined that the natural enemies were relatively abundant in Broward County. Hence, overall melaleuca seed and foliage production was severely reduced in Broward County due to the natural-enemy inflected injury on the trees. These findings highlight the role that natural enemies can play in the long-term management of invasive tree species.
Technical Abstract: Invasive plants may respond to injury from natural enemies by altering the quantity and distribution of biomass among woody materials, foliage, fruits, and seeds. Melaleuca, an Australian tree that has naturalized in south Florida, USA, has been reunited with two natural enemies: a weevil introduced during 1997 and a psyllid introduced during 2002. We hypothesized that herbivory from these and other adventive organisms would alter the distribution and allocation of biomass on melaleuca trees. This hypothesis was tested by temporally assessing changes in aboveground biomass components in conjunction with the presence of natural enemies and their damage to melaleuca trees. Melaleuca trees of different size classes were harvested during 1996, prior to the introduction of herbivorous insects, and again during 2003 after extensive damage had become apparent. Biomass, partitioned into components (woody structures, foliage, fruits, and seeds), was quantified both times at three sites, one each in Broward County, Miami-Dade County, and Palm Beach County, Florida. The two harvests within each county were performed in closely matched melaleuca stands and changes in biomass components were compared between years. Total biomass and woody portions decreased in Broward, whereas they increased in Miami-Dade and Palm Beach Counties. Reductions in foliage (on all trees) and seed biomass (among seed-bearing trees) were greatest at Broward and least at Miami-Dade County site. Hence, overall seed and foliage production was severely reduced in Broward County where the natural enemy incidence and damage was also more abundant compared to other counties. We therefore attribute the reduced foliar biomass and reproductive capability of melaleuca trees to infestations of natural enemies. These findings elucidate the role that natural enemies can play in the long-term management of invasive tree species.