Location: Invasive Plant Research Laboratory
Title: "Melaleuca quinquenervia dominated forests in Florida: analyses of natural-enemy impacts on stand dynamics". Authors
Submitted to: Journal Of Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2006
Publication Date: November 28, 2006
Citation: Rayamajhi, M.B., Van, T.K., Pratt, P.D., Tipping, P.W., Center, T.D. 2006. "Melaleuca quinquenervia dominated forests in Florida: analyses of natural-enemy impacts on stand dynamics".. Journal Of Plant Ecology. Interpretive Summary: Plant feeding insects and pathogens play important role in growth and survival of weedy trees. This kind of information is rare in the literature. Herein, we report changes in melaleuca tree density and size over 4-year-long periods before (1997-2001) and after (2001-2005) the impact of herbivores and disease. We measured melaleuca tree density and diameter at breast height in south Florida natural areas and calculated density and trunk cut-surface coverage per hectare for a total of 8-year (the first 4-year period and the second 4-year) study period. Introduced herbivore and plant pathogen populations and their damage on melaleuca trees was high during the second 4-year period and these may have played important role in reduction of tree densities and cut-surface coverage during the second 4-year study period. This shows that the herbivores and pathogens are effective biological agents in controlling weedy trees in natural areas of south Florida.
Technical Abstract: Reports on stand dynamics of weedy trees before and after impacts of herbivore and plant pathogens are rare. Herein, we present the results from an 8-year demographic study of the invasive tree Melaleuca quinquenervia in Florida, USA. We measured density (DEN), diameter at breast height (DBH), and basal area coverage (BAC) of melaleuca trees and monitored natural enemy’s population and impact on melaleuca trees in large-, intermediate-, and small-tree statures in each of the three sites during 1997 to 2005. We determined DEN, DBH, and BAC both before (1997-2001) and after (2001-2005) the impacts of natural enemies: herbivores (Oxyops vitiosa, Boreioglycaspis melaleucae, Paratachardina lobata lobata), pathogen (Puccinia psidii), and an unknown species of sooty mold. Decreases in absolute (trees of all dimensions) stem density prior to 2001 were highest in small- and least in large-tree stands. During this period, selective (>1.3 m tall trees) stem density increased in small-tree stands due to density-dependent mortality and shift of smaller trees to larger size classes, and decreased in large- and intermediate-tree stands due to mortality of suppressed trees. During 1997-2001, increasing trends in mean DBH and BAC were observed among all three tree-size stands. After 2001, absolute and selective tree-densities, and BAC in all tree statures decreased steeply. The periodic annual rate of changes in 2001-2005 compared to 1997-2001 were 6-, 2.5-, and 13-fold less in large-, intermediate-, and small-tree stands, respectively for selective-stem DEN; 8-, 2.5-, and 0.3-fold greater in large-, intermediate-, and small-tree stands, respectively for DBH increment; and 11-, 9-, and 4-fold less in large-, intermediate-, and small-tree stands, respectively for BAC. These sudden negative changes in stem DEN and BAC during 2001-2005 corroborate with the increased natural enemy populations in 2001-2003 and their possible negative impacts. These impacts were evidenced by foliar damage estimates in leaf-litter over a 7-year period and a destructive harvesting of trees followed by natural-enemy damage assessment during 2003. These findings lend support to a growing body of literature that documents the impact of natural enemies on M. quinquenervia.