Despite Recovery, Widespread Evidence of Deforestation Remains a Half-Cen. Later

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Dr. Eileen Helmer, Research Ecologist

Phone: 970-498-2644

ehelmer@usda.gov

Río Piedras, Puerto Rico, November 1, 2018 - The patterns of large-scale tropical deforestation endure across landscapes, even after more than a half-century of tropical rainforest expansion and growth back onto former agricultural lands, according to a new study published today in the journal Remote Sensing[External Site: Opens in New Window]

Scientists mapped forest characteristics across Puerto Rico and the Virgin Islands with forest inventories, Landsat satellite imagery from NASA and the US Geological Survey, and maps of climate and geology. Across this diverse region with many different types of tropical rainforest, the spatial patterns of forest characteristics reflected patterns of past forest clearing for farmland and the subsequent sequence of agricultural abandonment that determined forest age.

Exotic tree species, those which humans introduce to a region, are widespread and often dominate forests. Unprotected forests on more accessible and arable lands are younger because of past clearing, have more exotic species, are less diverse, store less carbon in their living biomass, and are more seasonal. They also have a greater ability to fix atmospheric nitrogen, which is thought to enhance growth but may also inhibit growth and release nitrogen oxides, which are highly potent greenhouse gases, to the atmosphere.

The exotic species are less common or rare, however, in the oldest, most remote forests on the least arable lands, though some can still grow in the shade of older forests.

Tree species native to the region are prominent in older forest, which tends to be further from roads and cities. And endemic species, those found nowhere else but these islands, are concentrated in the oldest forests. They are found in the most remote lands that are least suited for agriculture, in isolated and extreme environments where such unique species tend to evolve, including in cloud forest and forests on fast-draining or infertile soils like serpentine soils. In these places, agriculture was quickly abandoned and, in some places, the forest may never have been cleared. Probably not coincidentally, these same places were protected early.

Several of the mapped forest characteristics have links to United Nations Sustainable Development Goals[External Site: Opens in New Window], that among other things set goals for sustainable forest management.

Given that many of the mapped forest characteristics were related to the combination of forest age, climate and geology, and that forest age can now be mapped globally with long time series of satellite imagery, the study results suggest that forest age maps, when combined with maps of climate and underlying geology, would be useful for sustainably managing tropical forest landscapes.

The article appears in a Special Issue, Remote Sensing of Tropical Forest Biodiversity[External Site: Opens in New Window], guest edited by Dr. Gregory P. Asner of the Carnegie Institution for Science and Stanford University. The lead author is Eileen Helmer of the International Institute for Tropical Forestry. Co-authors of the study include Barry Wilson, Humfredo Marcano, Thomas Brandeis and Bonnie Ruefenacht of the USFS Northern and Southern Research Stations and Geospatial Technology Applications Center, Thomas Ruzycki and Michael Lefsky of Colorado State University, Heather Erickson of Consulting Research Ecology, and Kirk Sherrill of the US National Park Service.

Source: Helmer, E.; Ruzycki, T.; Wilson, B.; Sherrill, K.; Lefsky, M.; Marcano-Vega, H.; Brandeis, T.; Erickson, H.; Ruefenacht, B. Tropical Deforestation and Recolonization by Exotic and Native Trees: Spatial Patterns of Tropical Forest Biomass, Functional Groups, and Species Counts and Links to Stand Age, Geoclimate, and Sustainability Goals.[External Site: Opens in New Window] Remote Sensing 2018, 10, doi:10.3390/rs10111724.


The Institute's mission is to develop and disseminate scientifically-based knowledge that contributes to the conservation of forests, wildlife, and watersheds of the American tropics in the context of environmental change.


The mission of the U.S. Forest Service, an agency of the U.S. Department of Agriculture, is to sustain the health, diversity and productivity of the nation's forests and grasslands to meet the needs of present and future generations. The agency manages 193 million acres of public land, provides assistance to state and private landowners, and maintains world-renowned forestry research and wildland fire management organizations. National forests and grasslands contribute more than $30 billion to the American economy annually and support nearly 360,000 jobs. These lands also provide 30 percent of the nation's surface drinking water to cities and rural communities; approximately 60 million Americans rely on drinking water that originated from the National Forest System.


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Page last modified: 11/15/2018





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