Submitted to: Biological Invasions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/24/2008
Publication Date: 9/1/2009
Citation: Martin, M.R., Tipping, P.W., Sickman, J.O. 2009. Invasion by an exotic tree alters above and belowground ecosystem components. Biological Invasions. 11:1883-1894. Interpretive Summary: Ecosystem invasion by exotic plant species poses a significant threat to community biodiversity, function, and stability. Exotic plants often thrive in new habitats when they leave their natural enemies behind and subsequently experience less top-down regulation from herbivory. In addition, bottom up forces like high or low resource availability may facilitate colonization and allow exotics to out-compete natives and dominate ecosystems. The resultant changes in plant community structure can alter ecosystem function and stability. Species alteration may reduce or eliminate an ecosystem’s ability to provide ecological goods and services, such as waste processing and carbon sequestration. Although this issue is of global concern, the invasion of exotic plants has been a significant problem in the state of Florida, especially South Florida, which is home to Everglades. The Everglades is an extensive forest and graminoid wetland community that once occupied 4,000 square miles of the state’s lower-peninsula, over twice its present day land area. One of the most problematic species in this ecosystem is Melaleuca quinquenervia (Cav.) Blake otherwise known as the paper-bark tree, cajeput, punk tree, or white bottlebrush tree. This evergreen tree grows up to 30 m in height and its home range includes tropical wetland areas along the eastern coast of Australia. It was introduced into southern Florida in 1886, originally for sale as an ornamental, but later was used for erosion control, as a forestry crop, and as an agricultural windrow plant. Melaleuca quinquenervia has readily invaded and dominated most natural areas of South Florida, including bayhead tree islands, sawgrass prairies, pine flatwoods, pastures, and cypress forests. Although much is known of the aboveground alterations caused by M. quinquenervia invasion, virtually nothing is known about the consequences for belowground processes. Plant induced belowground alterations may allow invasives to promote and maintain community dominance and may affect native plant growth and soil and water quality. Elucidation of the extent, duration, and long-term impact of belowground ecosystem alterations following invasions by exotics will help in developing more effective restoration and management techniques.
Technical Abstract: With the widespread introduction and invasion of exotic plants there is a need for studies that quantify alterations of basic ecosystem structure and function. Most studies have focused on the impacts to aboveground communities while little is known of impacts of plant invasions on belowground systems. Ecosystem invasion by Melaleuca quinquenervia significantly altered both above- and belowground ecosystem components in this study. Annual litterfall was 4.3 times higher in the non-invaded sites and contained 1.9 times more phosphorus than invaded sites. Non-invaded plots contained a larger litter layer compared to invaded plots: 2.4 ± 0.5 kg m-2 and 0.62 ± 0.1 kg m-2, respectively. Lower nutrient concentration and quantity of the litter layer in the invaded plots led to changes in the aboveground storage of nutrients. In the invaded plots there was three times less carbon, six times less nitrogen, and seven times less phosphorus stored in the organic litter layer compared to the non-invaded plots. Microbial biomass nutrient pools were consistently lower at both the 0-5 cm and 5-15 cm depth in the invaded soils compared to non-invaded soils, indicating a plant mediated change. Although M. quinquenervia altered microbial community structure, microbial activities were not different between invaded and non-invaded plots at either depth as measured by rates of soil oxygen demand and potentially mineralizable nitrogen. These changes may affect both native plant growth and water quality, and may act to promote and maintain site dominance by M. quinquenervia.