Invasive plants

Melaleuca quinquenervia is an Australian tree, an aggressive invader of South Florida ecosystems, and has impacted over 100,000 acres of wetlands with many documented deleterious effects on native ecosystems. Millions of dollars are spent each year on management. The most rapid and cost-effective approach to date is the delivery of broadcast aerial herbicide application via helicopter, though long-term effects of this indiscriminate approach on native vegetation communities is poorly understood. We experimentally examined the effects of broadcast herbicides on uninvaded sawgrass plots in comparison to clip treatments and controls which showed that while clipped plots quickly recovered toward pre-treatment dominance, herbicide plots remained highly dissimilar and showed little to no recruitment even after 36 weeks. We also examined untreated Melaleuca stands to assess relationships between invasion severity and canopy cover using a generalized linear model with a beta distribution. Basal area, number of stems, and the interaction between basal area and number of stems was significantly related to canopy cover. Finally, we surveyed transects through aerially-treated Melaleuca stands (7 years post-treatment) separated into zones of dense infestation, sparse infestation, and untreated marsh. We compared differences in microtopography, invasion severity, and water quality to quantify changes in the physical environment brought about by both invasion and aerial treatment relative to the surrounding marsh. Additionally, we used percent cover abundance of vascular plant species in plots to compare vegetation communities between zones.

Emerging insights on the role of microbiomes in the sustainability of ecosystems and plant cover are transforming knowledge-driven agro-environmental management practices. For more than a century, the Brazilian pepper tree -BP (Schinus terebinthifolius), a category 1 invasive plant in Florida has defied numerous conventional control measures directed at its well-known ecology. This dissertation is one of the pioneer studies designed to determine whether microorganisms play a role in the aggressive invasion of BP in Florida and examine potential mechanisms with the goal of creating supplemental restoration tools. To test the hypothesis that enhanced mutualism of Brazilian pepper tree with microbes, compounded by relatively low biotic resistance of Florida soils is a critical driver of its invasion, plant biomass indices, metagenomics analysis of microbial community shifts, electron microscopy of endomycorrhizal infection and qPCR of key rhizobacterial taxa were measured. A multifactorial grow-room experiment was conducted simulating invasion with BP and two Florida natives (Pinus elliottii and Bidens alba) in a sterile, bioinoculant supplemented, and non-sterile control soils with various plant combinations.