Helmer E.H.

The Forest Types and Ages Cleared for Land Development in Puerto Rico

Kennaway, Todd; Helmer, E. H. 2007. The Forest Types and Ages Cleared for Land Development in Puerto Rico.. GIScience & Remote Sensing, 44, No. 4, :356-382.

On the Caribbean island of Puerto Rico, forest, urban/built-up, and pasture lands have replaced most formerly cultivated lands. The extent and age distribution of each forest type that undergoes land development, however, is unknown. This study assembles a time series of four land cover maps for Puerto Rico. The time series includes two digitized paper maps of land cover in 1951 and 1978 that are based on photo interpretation. The other two maps are of forest type and land cover and are based on decision tree classification of Landsat image mosaics dated 1991 and 2000. With the map time series we quantify land-cover changes from 1951 to 2000; map forest age classes in 1991 and 2000; and quantify the forest that undergoes land development (urban development or surface mining) from 1991 to 2000 by forest type and age. This step relies on intersecting a map of land development from 1991 to 2000 (from the same satellite imagery) with the forest age and type maps. Land cover changes from 1991 to 2000 that continue prior trends include urban expansion and transition of sugar cane, pineapple, and other lowland agriculture to pasture. Forest recovery continues, but it has slowed. Emergent and forested wetland area increased between 1977 and 2000. Sun coffee cultivation appears to have increased slightly. Most of the forests cleared for land development, 55%, were young (1–13 yr). Only 13% of the developed forest was older (41–55+ yr). However, older forest on rugged karst lands that long ago reforested is vulnerable to land development if it is close to an urban center and unprotected.

Diversity and composition of tropical secondary forests recovering from large-scale clearing: results from the 1990 inventory in Puerto Rico

Chinea, J. Danilo; Helmer, Eileen H. 2003. Diversity and composition of tropical secondary forests recovering from large-scale clearing: results from the 1990 inventory in Puerto Rico.. Forest Ecology and Management 180 :227-240.

The extensive recovery from agricultural clearing of Puerto Rican forests over the past half-century provides a good opportunity to study tropical forest recovery on a landscape scale. Using ordination and regression techniques, we analyzed forest inventory data from across Puerto Rico’s moist and wet secondary forests to evaluate their species composition and whether the landscape structure of older forest affected tree species composition of recovering forests at this scale. Our results support conclusions from studies conducted in Puerto Rico at smaller scales and temperate forests at larger scales that timing of abandonment and land use history are of overwhelming importance in determining the species composition of recovering forests. Forest recovery is recent enough in Puerto Rico that previous land use is clearly evident in current species composition, and creates new forest communities. As demonstrated in other work, physical factors such as elevation and substrate co-vary with land use history, so that the species composition of the forest landscape results from the interplay between biophysical and socioeconomic forces over time. Our results also indicate that increasing the distance to the largest forest patches occurring in the landscape 12 years previous had a small negative impact on species richness but not species diversity or community composition.We conclude that land use history has as much influence in species composition as biophysical variables and that, at the scale of this study, there is no large influence of forest landscape structure on species diversity or composition.

The Status of Puerto Rico’s Forests, 2003

Brandeis, Thomas J.; Helmer, Eileen H.; Oswalt, Sonja N. 2007. The status of Puerto Rico's forests, 2003. Resour. Bull. SRS-119. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 72 p.

Puerto Rico’s forest cover continues to increase and is now 57 percent for mainland Puerto Rico, 85 percent for Vieques, and 88 percent for Culebra. Subtropical dry forest occupies 50 346 ha, 6832 ha, 2591 ha, and 6217 ha on the islands of Puerto Rico, Vieques, Culebra, and Mona, respectively. Subtropical moist forest, the most prevalent forested life zone on mainland Puerto Rico, had 49 percent forest cover or 258 861 ha of forest. Subtropical wet and rain forest occupies 161 503 ha, lower montane wet and rain forest occupies 11 723 ha at the highest elevations, and mangrove forest occupies 7920 ha in coastal areas. Puerto Rico’s forests were found to have over 1,602,378,689 trees over 2.5 cm in diameter and 10 607 847 m2 of basal area, and to hold 36.6 million Mg of sequestered carbon. There were 3,112 trees, 19.2 m2 of basal area, 68.25 m3 of merchantable stem volume, and 80 Mg of aboveground biomass in an average hectare of forest. The subtropical moist and wet and rain secondary forests inventoried in 1990 are still young and increasing in average basal area, which rose from 13.2 mm2/ha in 1980, to 15.2 m2/ha in 1990, to the current level of 20.9 mm2/ha. The most important tree species were the African tuliptree [Spathodea campanulata] Beauv., American muskwood [<="" i="">] (L.) Sleumer, cabbagebark tree [Andira inermis] (W. Wright) Kunth ex DC., and pumpwood [Cecropia schreberiana] Miq. Few unhealthy, stressed trees werenoted and widespread pest and disease problems were not observed. Only 12.9 percent of live trees had some type of damage or disease. Average per-hectare amounts of down woody material, forest floor duff, and forest floor litter generally increased as the forest environment became more humid. Small-to-medium forest fire fuels were most common in subtropical dry forests, while medium-to-large fuels were most common in more humid forest life zones.


CHRISTOPHER DALY, E.H. HELMER, AND MAYA QUIÑONES 2003. Mapping the Climate of Puerto Rico, Vieques and Culebra.. Int. J. Climatol. 23 :1359-1381 .

Spatially explicit climate data contribute to watershed resource management, mapping vegetation type with satellite imagery, mapping present and hypothetical future ecological zones, and predicting species distributions. The regression based Parameter-elevation Regressions on Independent Slopes Model (PRISM) uses spatial data sets, a knowledge base and expert interaction to generate GIS-compatible grids of climate variables. This study applied PRISM to generate maps of mean monthly and annual precipitation and minimum and maximum temperature for the Caribbean islands of Puerto Rico, Vieques and Culebra over the 1963-1995 averaging period. PRISM was run under alternative parameterizations that simulated simpler interpolation methods as well as the full PRISM model. For temperature, the standard PRISM parameterization was compared to a hypsometric method, in which the temperature/elevation slope was assumed to be -6.5°C/km (HYPS). For precipitation, the standard PRISM parameterization was compared to an inverse-distance weighting interpolation (IDW). Spatial temperature patterns were linked closely to elevation, topographic position, and coastal proximity. Both PRISM and HYPS performed well for July maximum temperature, but HYPS performed relatively poorly for January minimum temperature, due primarily to lack of a spatially varying temperature/elevation slope, vertical atmospheric layer definition, and coastal proximity guidance. Mean monthly precipitation varied significantly throughout the year, reflecting seasonally differing moisture trajectories. Spatial precipitation patterns were associated most strongly with elevation, upslope exposure to predominant moisture-bearing winds, and proximity to the ocean. IDW performed poorly compared to PRISM, due largely to the lack of elevation and moisture availability information. Overall, the full PRISM approach resulted in greatly improved performance over simpler methods for precipitation and January minimum temperature, but only a small improvement for July maximum temperature. Comparisons of PRISM mean annual temperature and precipitation maps to previously-published, hand-drawn maps showed similar overall patterns and magnitudes, but the PRISM maps provided much more spatial detail

Cloud-Free Satellite Image Mosaics with Regression Trees and Histogram Matching

E.H. Helmer and B. Ruefenacht 2005. Cloud-Free Satellite Image Mosaics with Regression Trees and Histogram Matching.. Photogrammetric Engineering & Remote Sensing Vol. 71, No. 9, September 2005, :1079-1089.

Cloud-free optical satellite imagery simplifies remote sensing, but land-cover phenology limits existing solutions to persistent cloudiness to compositing temporally resolute, spatially coarser imagery. Here, a new strategy for developing cloud-free imagery at finer resolution permits simple automatic change detection. The strategy uses regression trees to predict pixel values underneath clouds and cloud shadows in reference scenes from other scene dates. It then applies improved histogram matching to adjacent scenes. In the study area, the islands of Puerto Rico, Vieques, and Culebra, Landsat image mosaics resulting from this strategy permit accurate detection of land development with only spectral data and maximum likelihood classification. Between about 1991 and 2000, urban/built-up lands increased by 7.2 percent in Puerto Rico and 49 percent in Vieques and Culebra. The regression tree modeling and histogram matching require no manual interpretation. Consequently, they can support large volume processing to distribute cloud-free imagery for simple change detections with common classifiers.

Forest conservation and land development in Puerto Rico

Helmer, E.H., 2004. Forest conservation and land development in Puerto Rico.
Landscape Ecol. 19, 29–40.

In the Caribbean island of Puerto Rico, rapid land-use changes over the past century have included recent land-cover conversion to urban/built-up lands. Observations of this land development adjacent to reserves or replacing dense forest call into question how the changes relate to forests or reserved lands. Using existing maps, this study first summarizes island-wide land-cover change between 1977-78 and 1991-92. Then, using binomial logit modeling, it seeks evidence that simple forest cover attributes, reserve locations, or existing land cover influence land development locations. Finally, this study quantifies land development, reserve protection and forest cover by ecological zone. Results indicate that 1) pasture is more likely to undergo land development than shrubland plus forest with low canopy density, 2) forest condition and conservation status appear unimportant in that development locations neither distinguish between classes of forest canopy development nor relate to forest patch size or reserve proximity, and 3) most land development occurs in the least-protected ecological zones. Outside the boundaries of strictly protected forest and other reserves, accessibility, proximity to existing urban areas, and perhaps desirable natural settings, serve to increase land development. Over the coming century, opportunities to address ecological zone gaps in the island’s forest reserve system could be lost more rapidly in lowland ecological zones, which are relatively unprotected.

Mapping the Forest Type and Land Cover of Puerto Rico, a Component of the Caribbean Biodiversity Hotspot

ELMER,E. H.; RAMOS, O.; LÓPEZ, T. DEL M.; QUIÑONES, M.; DIAZ, W. 2002. Mapping the Forest Type and Land Cover of Puerto Rico, a Component of the Caribbean Biodiversity Hotspot. Caribbean Journal of Science, Vol. 38, No. 3-4, 165-183, .

The Caribbean is one of the world’s centers of biodiversity and endemism. As in similar regions, many of its islands have complex topography, climate and soils, and ecological zones change over small areas. A segmented, supervised classification approach using Landsat TM imagery enabled us to develop the most detailed island-wide map of Puerto Rico’s extremely complex natural vegetation cover. Many Caribbean forest formations that are not spectrally distinct had distributions approximately separable using climatic zone, geology, elevation, and rainfall. Classification accuracy of 26 land cover and woody vegetation classes was 71 % overall and 83 % after combining forest successional stages within image mapping zones. In 1991-92, Puerto Rico had about 364,000 ha of closed forest, which covered 41.6 % of the main island. Unlike previous island-wide mapping, this map better identifies the spatial distributions of forest formations where certain groups of endemic species occur. Approximately 5 % of Puerto Rico’s forest area is under protection, but the reserve system grossly underrepresents lowland moist, seasonal evergreen forests.

The Ecological Consequences of Socioeconomic and Land-Use Changes in Postagriculture Puerto Rico

Grau, H. Ricardo; Aide, T. Mitchell; Zimmerman, Jess K.; Thomlinson, John R.; Helmer, Eileen; Zou, Xioming 2003. The ecological consequences of socioeconomic and land-use changes in post agriculture Puerto Rico. BioScience. Vol. 53, no. 12 (Dec. 2003): Pages 1159-1168.

Contrary to the general trend in the tropics, forests have recovered in Puerto Rico from less than 10% of the landscape in the late 1940s to more than 40% in the present. The recent Puerto Rican history of forest recovery provides the opportunity to study the ecological consequences of economic globalization, reflected in a shift from agriculture to manufacturing and in human migration from rural to urban areas. Forest structure rapidly recovers through secondary succession, reaching mature forest levels of local biodiversity and biomass in approximately 40 years. Despite the rapid structural recovery, the legacy of pre-abandonment land use, including widespread abundance of exotic species and broadscale floristic homogenization, is likely to persist for centuries.
Syndicate content