Assessing the impact of native disturbance regimes in forests managed to control the invasion of an exotic tree

Background/Question/Methods

Many ecosystems depend on regular disturbances, such as seasonal fires, to maintain community structure and function. This is especially true in Florida where many native plant communities depend on seasonal fires to trigger seed release and open canopies. However, many of Florida’s natural areas have been invaded by exotic plants, including the fire-adapted Melaleuca quinquenervia, which have altered native fire patterns. Little work has been done to evaluate the effects of fire on nutrient storage and availability in Florida’s invaded and managed ecosystems. This study investigated two main questions: 1) Does the quantity and availability of nutrients vary between native and melaleuca invaded and managed systems? 2) Does the method of treatment of melaleuca alter the systems ability to store nutrients after a seasonal fire?

In March 2007, seventy-five 1 m² plots were established across three areas in the Collier County, Florida. The areas sampled are: area #1) reproductive melaleuca treated with herbicide, area #2) reproductive melaleuca treated with biological control, and area #3) native forest with no melaleuca. The experiment plots were sampled to characterize pre-fire conditions and plots were revisited and measurements were repeated after a destructive fire in April 2007. Measurements include: quantity and nutrient concentration of litter and pH, bulk density, quantity and nutrient concentration, and nitrogen mineralization of surface soils. 

Results/Conclusions

Results revealed that pre-fire there was no significant difference in the quantity or availability of carbon (C) or nitrogen (N) in the surface soils of the two managed systems (p=0.1 and 0.19 respectively). The invaded-chemically controlled site had 9.5±1 mg cm^-3 C and 0.6±0.1 mg cm^-3 N and the invaded-biologically controlled site had 12.±1.4 mg cm^-3 C and 0.8±0.1 mg cm^-3 N. However the invaded-chemically controlled area stored significantly less nitrogen than the native forest soil (p=0.04, 0.9±0.1 mg cm^-3 N). Post-fire there were significant differences in the quantity of C and N stored in the litter layers of the native and managed sites. 

These results and future biogeochemical and microbial analysis will be used to quantify the changes caused by melaleuca invasion and management. Currently there is a need to develop a better understanding of the ecological consequences of exotic species invasion and methods for countering them, particularly in the context of natural disturbance regimes. Elucidation of the extent, duration, and impact of the changes caused by invasion and management of exotic plants will help in developing more effective restoration and management techniques.