Functional Roles of Invasive Non-Indigenous Plants in Hurricane-Affected Subtropical Hardwood Forests

Abstract

Native forest species exhibit a well‐known range of ecological roles with respect to natural disturbance regimes, from pioneer phase to mature phase, and they regenerate from a range of sources, including dormant seeds, seed rain, pre‐established juveniles, and resprouts from damaged adults. In contrast, the ecological roles of invasive, non‐indigenous species in forest communities after natural disturbances are not well understood. Some previous studies of invasive species have emphasized their weedy nature and their ability to colonize anthropogenic disturbances. Tropical hardwood hammock forests in southern Florida experience frequent disturbance by hurricanes. Our studies of forest regeneration during two years following a recent severe hurricane suggest that invasive non‐indigenous forest species exhibit the same range of ecological roles as native forest species and compete with native species for particular kinds of regeneration opportunities. To study ecological roles of non‐indigenous species in regenerating forests after Hurricane Andrew, we set up four large study areas at each of three study sites that had differing amounts of hurricane‐caused canopy disturbance. There were two pairs of 30 × 60 m research plots per site, and in each pair there was one control plot and one restoration plot; restoration areas were subject to an aggressive management program, focused on reducing non‐indigenous vine cover. Within these study areas we subsampled vegetation in small study plots that were regularly spaced, and conducted vegetation censuses in April (the end of the dry season) and October (the end of the rainy season) for 2 yr, beginning in April 1993. We found that the source of regeneration for forest species was dependent upon the amount of canopy disturbance, the time since disturbance, and the autecology of the constituent species. Overall, 28% of the 90 species were non‐indigenous: 34% of the vines (N = 32) and 24% of other life‐forms (N = 58). Non‐indigenous vines seemed to have a special role; not only could they compete with native vines, but they could also negatively affect the regeneration of other natives from a diverse array of sources including pre‐established juveniles and resprouts from damaged adults. Both native and non‐indigenous vine cover in unmanipulated study areas increased following the hurricane. Non‐indigenous vine species had higher cover than native vine species, and many species formed dense “blankets.” Non‐indigenous species in general (not just vines) did not differ significantly from native species in seed mass, nor were they restricted to the pioneer type of life history. Many non‐indigenous species had invaded forests prior to hurricane disturbance and had their own banks of pre‐established juveniles; others recruited from dormant seeds, seed rain, and/or resprouts from pre‐established adults. Based on information on source of regeneration and impact on native species, we propose a classification scheme for functional roles of non‐indigenous invasive species in forests. To i...

Predicting Woody-Plant Species Richness in Tropical Dry Forests: A Case Study From South Florida, Usa

“…Tropical dry forest, often called ''tropical hardwood hammocks'' or ''tropical hammocks'' in Florida (USA), occur on limestone outcrops in extreme southern Florida on islands in the Keys, on elevated coastal ridges along the Atlantic coast, and as tree islands within the more extensive pine savannas and sawgrass wetlands in the Everglades (Myers and Ewel 1990, Ross et al 1992, Horvitz et al 1998. Tropical dry forests in south Florida occur on Pleistocene limestone and coastal ridges with skeletal organic soils containing minor mineral components, and rarely exceed 20 cm in depth Ewel 1990, Ross et al 2000).…”

“…This is because the tropical dry forests in south Florida are at the northern extreme of this vegetation type and the associated colder temperatures limit the distribution of a number of tropical dry-forest plant species (Tomlinson 1980). Hurricane Andrew passed over a majority of these study sites on 24 August 1992 and resulted in significant structural damage to the tropical dry forests in Miami-Dade county and the Upper Keys (Horvitz et al 1998, Ross et al 2000. Horvitz et al (1998) undertook post-hurricane research in Castellow Hammock, Charlie Deering Estate, and Matheson Hammock and noted the invasion of non-indigenous species, especially vines, that filled a number of functional groups or niches of species absent in the native tropical dry forests of Florida.…”

“…Hurricane Andrew passed over a majority of these study sites on 24 August 1992 and resulted in significant structural damage to the tropical dry forests in Miami-Dade county and the Upper Keys (Horvitz et al 1998, Ross et al 2000. Horvitz et al (1998) undertook post-hurricane research in Castellow Hammock, Charlie Deering Estate, and Matheson Hammock and noted the invasion of non-indigenous species, especially vines, that filled a number of functional groups or niches of species absent in the native tropical dry forests of Florida. Seven years after their study, there were low levels of exotics within stands of forest in south Florida, with no exotics in transects at Matheson Hammock or Castellow Hammock and one exotic species in transects at the Charles Deering Estate.…”

Effects of Invasive, Non-Indigenous Plant Species on Ecosystem Processes: Lessons from Florida

“…While some types of habitats are invaded more easily than others (Usher 1988, Rejmánek 1989, few habitats (Johnstone 1986, Crawley 1987, di Castri 1990. Increasing evidence from autecological research on a number of non-indigenous species around the world provides examples of plant species that are able to invade continental and island habitats without clear exogenous disturbances (Bazzaz 1986, Hobbs and Atkins 1988, Usher 1988, Binggeli 1990, Huenneke 1991, Lodge 1993, Horvitz et al 1998. The natural disturbance factors that maintain native species also allow invasion by species that historically have been excluded by biogeographic barriers and ecological constraints, but now are present because of human-mediated transport (di Castri 1990, Roy et al 1991, Hobbs andHuenneke 1992).…”

Predicted impact of exotic vines on an endangered ecological community under future climate change

“…Vines, both native and exotic, lack autonomous support and use host vegetation to position leaves in adequate light for photosynthesis. They can smother surrounding vegetation, reducing light levels on the forest floor and often leading to the breakage of branches (Horvitz et al 1998;Batianoff and Butler 2002;Llorens and Leishman 2008). The ability of exotic vines to change abiotic conditions after invasion has resulted in them being described as ''transformer'' weeds by some authors (Vivian-Smith and Panetta 2002).…”