The forests they are a changin’

G-16: Forest Health in Changing Landscapes: The Roles of Landscape Pattern


Human activities often fragment forests. Photo by Larry Korhnak.
Human activities often fragment forests. Photo by Larry Korhnak.

Bob Dylan composed his famous song, “The Times They Are a Changing,” in response to social upheaval in the 1960s. He might as well have written it about today’s forests.

Around the world, social and economic changes alter ecosystems at alarming rates (think deforestation resulting from agriculture, home construction in fire-dependent ecosystems, etc.). And even without human impacts, forests are constantly in flux. Some changes occur slowly, like the growth of trees from seedlings to giant behemoths. Some are really slow, such as the evolution of new species, and other changes are rapid, resulting from wildfires and other disturbances.

Quantifying change over space and time is the work of landscape ecologists. Remote imagery is a key tool of the trade (e.g., data collected by satellites and photographs taken from planes). Landscape ecologists classify land use and land cover from these images and then track changes over time. Free software such as GuidosToolbox developed by Peter Vogt and colleagues with Joint Research Centre in Italy, help researchers quantify landscape patterns from remote imagery.

Analyses of remote imagery expose the rapid deforestation that’s occurred over the past several decades. According to Olufunke Olayode (University of Ado-Ekiti, Nigeria), cover of non-plantation forests declined 56 percent in the Gambi Forest Reserve in southwest Nigeria from 1984 to 2000. Annual forest loss of 3.5 percent in Nigeria outpaces 1.5 percent annual losses in parts of Madagascar reported by Harifidy Rakoto (University of Antananarivo, Madagascar). In both countries, poor farmers clear forests for subsistence agriculture. Illegal logging also contributes to deforestation.

The U.S. is also experiencing forest loss. Kurt Riitters (U.S. Forest Service) used a novel approach to analyze forest cover for the 2015 Update of the Resource Planning Act Assessment. Riitters combined the National Land Cover Dataset (developed from satellite images) and data from the Forest Inventory and Analysis program (based on field measurements). Results show a 0.2 percent annual loss of total forest cover across the U.S. from 2000 to 2006. Cover of intact forests, defined as 100 percent canopy closure, declined at an annual rate of 0.7 percent over the same time period.

Landscape ecologists are also concerned by the fragmentation of forested landscapes. Fragmentation occurs when disturbances or land management break forests into smaller patches. Smaller forests separated by other land uses can hinder the movement of wildlife and result in lower biodiversity.

Traditional slash and burn agriculture in Madagascar, known as tavy, fragments lowland tropical rainforests. Farmers progressively clear land from lower to higher elevations as soil fertility declines, forcing them to use land farther from home. Some farming expands the size of previous clearings, but tavy also breaks up intact forests.

Fortunately, research by landscape ecologists isn’t all doom and gloom. Olufunke predicts that cover of non-plantation forests in southwest Nigeria will increase from 2006 to 2016. Reforestation efforts by forestry trust funds are experiencing some success.

David Coyle (University of Georgia) shared encouraging news about southern pine decline in the southeastern U.S. Spatial analysis and on-the-ground fieldwork  suggest that managers can curb pine mortality. Education of landowners can improve forest practices and enhance tree vigor, making pines less susceptible to root feeding beetles and fungi.

Rates of hemlock mortality are slowing in forests across the Appalachian region of the U.S. The Lower Linville River Watershed in North Carolina lost nearly 10,000 hemlock trees to mortality from the hemlock woolly adelgid (a sap-sucking insect from Japan). Death of new trees declined each year from 2009 to 2012. Surviving hemlocks and other tree species are happily extending branches into newly vacated growing space.

Finally, Rosemeri Moro (Ponta Grossa State University, Brazil) reminded us that not all fragmentation is “unnatural.” Vila Velha and Guartelá State Parks represent relatively unharvested landscapes in the high plateaus of Brazil. Both parks are characterized by isolated patches of forests and grassland, a mosaic shaped by geographic features and raging rivers. But although the landscape appears structurally fragmented, it is not functionally fragmented. Mammals and birds can transport seeds from native trees anywhere from 50 to 740 m, distances greater than that separating a majority of forest patches.

Lyrics of “The Times They Are a Changing” allude to the universal nature of change. Societies and ecosystems are constantly in flux. Some changes promote sustainability of human communities and forests; others are more concerning. By researching the extent and cause of change, landscape ecologists make important strides towards appreciating and adapting to our ever-changing world.

Written by: Megan S. Matonis

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