CARIBBEAN LANDSCAPES IN TURMOIL

Caribbean island landscapes--formed by volcanism and other tectonic forces--evolved initially under the influence of climatic events such as hurricanes. Native vegetation formed ecosystems with structural, physiognomic, and functioning characteristics attributed to a disturbance regime dominated by hurricanes, regardless of geoclimatic zone. Hurricane responses include forest canopies shaped by wind in terms of their physiognomy, volume, and height along with rapid succession and biomass turnover. Forested watersheds are effective in retaining nutrients and sediments during hurricane events. Human activity introduced a new disturbance regime to the islands, which resulted in almost 100 percent deforestation for agricultural activity followed by land abandonment, and subsequent urbanization and recovery of forest cover over large areas (up to 40 percent in Puerto Rico). The new disturbance regime resulted in watersheds with more suspended sediment yield, landslides, and sheetwash than forested watersheds. Landscape attributes such as land cover, fragment size, and fragmentation index changed due to human influence. Humans also introduced new species to the Caribbean, which formed new ecosystems that maintained the hurricane-response attributes of native forests. While hurricanes allow for forest recovery between events, human disturbance is chronic and leads to faster changes in land cover, land form, and ecosystem types. However, humans change their use of the landscape and this leads to reversal of trends in measures of landscape structure. For example, forest and urban expansion at the turn of the century in Puerto Rico resulted in a reduction of landscape fragmentation and an increase the size of fragments. The chronic effects of humans on Caribbean landscapes appear to be durable and unlikely to reverse, but topography and elevation might limit--with some exceptions--these effects. It appears that geoclimatic conditions influence land use and cover, sediment yield, landslides, sheetwash, ecosystem productivity, and distribution of endemic species, while humans change the structure of the landscape, accelerate sediment production and movement, and change ecosystem types. However, the resulting new ecosystems must still cope with the natural disturbance regime.