Thursday, August 6, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Min Bahadur Rayamajhi, Agriculture Research Service, Invasive Plant Research Laboratory, United States Department of Agriculture, Fort Lauderdale, FL, Paul D. Pratt, USDA-ARS, Invasive Plant Research Laboratory, United States Department of Agriculture, Fort Lauderdale, FL and Ted D. Center, USDA-ARS, Invasive Plant Research Laboratory, United States Department of Agriculture: Retired, Fort Lauderdale, FL
Background/Question/Methods The invasive tree Melaleuca quinquenervia (melaleuca) occurs in various habitats of southern Florida where it degrades ecologically sensitive areas. The exotic tree displaces other plant species, such as Cladium jamaicense (sawgrass), from many areas, forms monoculture forests with closed canopies, and deposits a thick layer of litter on the forest floor. We hypothesized that this thick layer of melaleuca litter was due largely to the higher amount of annual litterfall coupled with slower turnover rate; which in turn may have impede other plant regeneration. To test this we documented litterfall rates during 1997-2001 and the standing litter crop in 1997 within mature melaleuca stands located in nonflooded sites of southern Florida. We also investigated mass loss trends of freshly senesced melaleuca and sawgrass leaves that were dried, and encased in separate nylon pouches. Pouches were placed on the floors of melaleuca and sawgrass monoculture stands, and periodically monitored for mass loss during 2002-2008 so as to allow complete decomposition of the leaf mass of one of the two species. The rate of mass was determined based on the time it took to incur ca 50% loss of the original amount of leaf tissues encased in pouches.
Results/Conclusions
Results revealed that melaleuca litterfall rate was 8.78 Mg/ha/yr and two-thirds of the total weight was comprised of leaves. Total standing litter was 25.6 Mg/ha of which 15.6 Mg/ha was un-decomposed and over half of this was comprised of melaleuca leaves; melaleuca leaves were therefore the major component of forest floor cover. Melaleuca leaf mass loss in melaleuca stands was relatively faster in organic-soil than in sandy-soil. The loss of melaleuca leaf biomass on organic soils in melaleuca stands was 1.5 times faster than in sawgrass stands. Melaleuca leaves decomposed 1.8 and 2.9 times more slowly than sawgrass leaves under melaleuca and sawgrass stands, respectively. This is an indication that melaleuca leaf-litterfall decomposition is slower than sawgrass regardless of the site. We also determined the role of melaleuca litter in impeding establishment of other plants by comparing germination and establishment of seeds from seed-bank and seed-rain in undisturbed litter-covered and mineral-soil-exposed plots under mature melaleuca stands. Overall, seed germination and seedling establishment was significantly higher on exposed soils than on litter-covered soils. These findings indicate a negative role of the mulching effects of slowly mineralizing melaleuca litter on the recruitment and establishment of other plants under melaleuca canopies.
