Invasive plants can 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, 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 (lobate-lac scale and a leaf-rust fungus) 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 diameters representing the range (1 to 33 cm diam at 1.3 m height) within study sites were harvested during 1996, prior to the introduction of herbivorous insects, and again during 2003 after extensive tree damage had become apparent. Aboveground biomass, partitioned into several components (woody structures, foliage, fruits, and seeds), was quantified both times in Broward, Miami–Dade, and Palm Beach county sites located in south Florida. The two harvests within each site 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 sites. 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 at the Broward site where both the natural enemy incidence and damage were more abundant compared to other sites. We therefore attribute the reduced foliar biomass and reproductive capability of melaleuca trees to infestations of natural enemies. These findings highlight the role that natural enemies can play in the long-term management of invasive tree species.
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Vol. 56 • No. 3