The loss of forest habitat is a major concern for the 21st century in all parts of the world. It is the key to biodiversity and the health of our planet. Puerto Rico, a small, very heavily populated island in the Caribbean situated due east of the two islands containing Cuba, Haiti and the Dominican Republic, is home to nearly four million people on a landmass 48 km wide and 160 km long.
The major population centres are on the coast, but small towns and farms dot the slopes of the mountains that run nearly the length of the island. Over the years, while the population has grown, forests have shrunk, pollution has increased, and species have decreased in number and diversity.
The impetus for forest preservation in Puerto Rico has come from two sides: the tremendous crush of a large population of humans on a limited landmass, and con-tinuous attempts to stave off massive deforestation. In fact, since 1940, when 94% of the island was already deforested, there has been improvement. Currently, more than 30% of the land is forested.
However, continued development, including the growth of housing areas and roads, and the promotion of the sun-grown coffee industry, which uses large tracts of open land, continue to threaten gains made since 1940.
Puerto Rican Law 1277 (2000) mandates the establishment of corridors to link some of the forests in an effort to promote conservation of species, and provide sufficient habitat for those species that are endangered. Corridors allow animals to move to different habitats, escape predators and so on.
As a result, the Department of Natural and Environmental Resources in Puerto Rico commissioned a small team from WPI, the third-oldest technological university in the United States, to create a plan for biological corridors linking six of these forests. They are Maricao, Susua, and Gurnica (in the southwestern part of the island) and Toro Negro, Bosque de Adjuntas and Guilarte (in the central region). They are situated in several different climate regions, from dry to wet, and thus span several different types of topography.
Figure 1: Targeted forests
The WPI team was challenged to develop the plan for these corridors while taking into consideration both the economic value of the land and the needs of target species - those species that can act as proxies for the other fauna of the area. Several birds were chosen as the target species. The Puerto Rican nightjar was selected as most suitable for the southwest corridor. For the central corridor region, the team chose the sharp-shinned hawk and the broad-winged hawk as the target species. They were endangered species, but just as important, their ranges were larger than those of the mammals residing in the forests.
The Department of Natural Resources provided a variety of shape files or maps of existing roads and housing, rivers, and soils. Other information, which was gathered by the team, was added to the analysis, taking into account accepted theories of corridor development and weighing the social implications of the implementation of the corridors.
The difficulties inherent in the data analysis are illustrated in Figure 3, which shows a map of a proposed corridor design superimposed upon a land use map for the same area. There was a cluster of nightjar sightings in the area outside the Guánica forest (see Figure 2), in land not yet highly developed, but there was little room for the corridor to be designed so as to avoid development.
Designing the corridors meant that certain compromises had to be made, especially in regard to shape. Often, the cost of acquiring developed lands seemed prohibitive, even if they were the most desirable according to other criteria.
To maximise the composition of the corridor as a unity, and in deference to some of the realities in making choices, the design had to deviate from the ideal. For example, some corridors lacked maximum amounts of completely continuous vegetation or common soil types, and there were some differences in topography within a corridor.
The Susua to Maricao corridor was virtually unsettled, and thus posed few problems. Moreover, it was possible to construct the corridor almost entirely following the serpentine soil favoured by the target species, the nightjar. Figure 5 illustrates the planned corridor superimposed over land use.
The other corridors - Guilarte to Adjuntas and Adjuntas to Toro Negro - were designed in a similar fashion, but they posed different problems.
Figure 6 contains the final design for all of the corridors, superimposed over a satellite map of the area.
The first recommendation from our study was that the DNER proceed at once with a plan to acquire those lands needed to reduce fragmentation and expand the forests. A major goal would be to improve the shape of forests and reduce sharp angles, which create barriers to the movement of animals.
The second major recommendation was that the DNER continue to exercise responsibility for the maintenance and management of the corridors through a corridor manager. His or her responsibilities would include monitoring corridors and forests for fires, as well as ensuring that the corridors do not become permanent habitat for species that should be using the corridors for passage from forest to forest.
Figure 2: Locations of the Puerto Rican nightjar between Susua and Gurnica
Figure 3: Gurnica to Susua corridor layered over land use
Figure 4: Recommended patch within Gurnica and Susua corridor
A third recommendation was that the DNER work towards expanding the network of forests by creating other corridors. The implementation of the specific corridors proposed by the team would result in preservation of watersheds, increased habitat for the targeted species and a stabilisation of the island's ecosystem, yet permit development to continue outside the protected areas. While corridors will not solve all problems of the environment, their implementation can provide an important deterrent to the further degradation of the island.
Figure 5: Susua to Maricao corridor layered over soils
Figure 6: Final corridor delineations for all forests
