Forest fragments in tropical regions are often skirted by trees dying along the edges as the ecosystem declines. But new research in northeastern forests suggests that a different dynamic is at play along their edges.
Scientists at Boston University, Harvard Forest, and City University of New York analyzed data from more than 48,000 forest plots, established as part of the U.S. Department of Agriculture Forest Inventory and Analysis (FIA) long-term monitoring program. They compared forest structure and growth in plots on forest edges (where forest met a different type of land cover) to those of interior forests across the Northeast.
As reported in the December 2021 issue of the journal Nature Communications, the researchers learned that regardless of what lay on the other side (wetland, lake, river, road, parking lot, farm field, and so on), forest edges in the Northeast showed higher levels of forest growth, tree density, and biomass than forest interiors.
According to the researchers, “the growth response is almost certainly related to greater light availability, which affects tree canopy architecture and can increase forest leaf area index and, in turn, stimulate productivity.” This is in contrast to tropical forests, where wind, higher temperatures, and water stress cause trees to die along edges.
Aware that their findings might lead some to conclude that more edges should be created to increase sequestered carbon, the researchers are quick to dispel the notion. “Actively increasing forest fragmentation is not a conclusion to draw from our research,” said Luca Morreale of Boston University.
“The increased carbon storage along the edges of fragmented remnants does not come close to offsetting the loss of terrestrial carbon stocks and future sequestration capacity associated with forest loss,” the researchers wrote. They also noted that there is evidence that forest edge productivity is hindered in extreme heat, suggesting that heat stress in the future may cause more similarity to tropical forest edge conditions.
Also, said Morreale, “forest edges are already a prominent feature on the northeastern landscape, particularly in developed and agricultural areas.” When they quantified forest fragmentation globally, the researchers found that temperate forests contain 52 percent more edge area than tropical forests. Rather than creating more edges, the researchers advocate for a renewed perspective of existing forest fragments. “These edges are often perceived as degraded remnants that are of little value for conservation or as ecosystems. Our work demonstrates that in reality, at least by metrics of forest growth and density, edges are highly productive systems,” said Morreale.