Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Abstract

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year À1 ) than for native ones (15% year À1 ). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.

Invasive Exotic Plants in the Tropical Pacific Islands: Patterns of Diversity

“…Similar typhoon effects have been seen in Tahiti (Meyer 1994) and Florida (Horvitz et al 1998). However, other reviews have found that vegetation on some islands subject to frequent typhoons may regenerate rapidly following wind disturbances with little change in species composition (Brokaw & Walker 1991, Franklin et al 2004, Thompson et al 2007. Our data were not adequate for evaluating the role of typhoon frequency on island ecosystems.…”

“…While the objective was to restore Hawaii's watersheds, the project also provided opportunity for the establishment and spread of invasive exotic species into native forests at an unprecedented scale. Historic afforestation projects have contributed also to the exotic flora of Australia (Lonsdale 1994), but not apparently to that of Hong Kong (Corlett 1999) or Puerto Rico (Thompson et al 2007) where assessments found that few exotic species used for reforestation or plantations in the past had naturalized or posed a threat to native forest.…”

Climate shapes the novel plant communities that form after deforestation in Puerto Rico and the U.S. Virgin Islands

“…Most previous studies of the influence of land-use history on secondary forests communities in Puerto Rico are limited to samples selected along land-use gradients within small landscapes that encompass only one climatic zone and substrate type (García-Montiel and Scatena, 1994;Rivera and Aide, 1998;Pascarella et al, 2000;Thompson et al, 2002Thompson et al, , 2007Molina and Lugo, 2006). These studies find that past land use has an overriding impact on secondary forest species composition.…”

Belowground nitrogen dynamics in relation to hurricane damage along a tropical dry forest chronosequence

“…Samples were collected 1 month before (pre-hurricane), 2 months after, 1 year after, and 2 years after the pass of Hurricane Wilma. Different letters indicate significant (P \ 0.05) differences among sampling dates within each seral stage (means ± SE, N = 6) the recovery of forest canopy after a large, infrequent disturbance is heavily influenced by prior site history (Foster et al 1999;Uriate et al 2004;Chazdon 2003;Thompson et al 2007). We found early-and mid-seral stages to be more resilient to a hurricane disturbance, whereas the taller, late-seral forest (Table 1), with more biomass to lose, appeared more vulnerable.…”