Researchers find the world’s forests are fragmenting at three times the rate of forest loss as a whole

Desdemona Despair

By Mike Gaworecki
4 February 2016

(mongabay.com) – Recent research by the U.S. Forest Service finds that the world lost interior forest at three times the rate of forest loss as a whole. They write that this fragmentation could severely jeopardize the ability of remaining forests to provide critical wildlife habitat and other ecological functions.

In total, the team found there was a global a net loss of 1.71 million square kilometers of forest cover from 2000 to 2012 — 3.2 percent of total global forest area.

But the Forest Service researchers argue that focusing on forest area loss alone risks ignoring the ecological threats of forest fragmentation. In addition to the direct loss of forest, they found a “widespread shift” in the world’s remaining forests to a more fragmented condition.

They calculated a net loss of 3.76 million square kilometers of interior forest area amounting to 9.9 percent of global interior forest cover, according to their study in the journal Landscape Ecology [pdf].

It may seem counter-intuitive that there can be more interior forest loss than total forest loss, but depending on the spatial distribution of deforestation, it’s entirely possible to have more forest area converted to “edge conditions” — say, when a road is built through a forest that penetrates its interior, converting the former heart of the forest into a new forest edge — than the total amount of forest that was destroyed.

The researchers’ findings indicate that the world’s interior forest cover was lost at a rate three times higher than global forest area as a whole was lost — and this could have important consequences for ecological processes.

Kurt Riitters, a research ecologist at the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center and the lead author of the study, told Mongabay, “Some natural ecological goods and services are provided only by interior conditions, and some are adversely impacted by ecological ‘edge effects’ that occur in non-interior conditions.”

In other words, as forests become fragmented by the building of roads and other human activities as well as natural drivers of deforestation like wildfires, the proportion of interior forest generally decreases and the proportion of edge area increases. And Riitters said that leads to two kinds of risks: the loss of ecosystem functions that require interior conditions, and the degradation of functions that are sensitive to edge conditions. [more]

Researchers find the world’s forests are fragmenting at a quick pace

Research Triangle Park, NC, 28 January 2016 (USDA) – Between 2000 and 2012, the world lost more forest area than it gained, according to U.S. Forest Service researchers and partners who estimated a global net loss of 1.71 million square kilometers of forest—an area about two and a half times the size of Texas. Furthermore, when researchers analyzed patterns of remaining forest, they found a global loss of interior forest—core areas that, when intact, maintain critical habitat and ecological functions.

“In addition to the direct loss of forest, there was a widespread shift of the remaining global forest to a more fragmented condition,” explains Kurt Riitters, a research ecologist and team leader with the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center and the lead author of a study describing the phenomenon, published in the January 2016 issue of Landscape Ecology [pdf]. 

Forest area loss alone underestimates ecological risks from forest fragmentation. The spatial pattern of forest is important because the same area of forest can be arranged in different ways on the landscape with important consequences for ecosystem processes. In contrast to core areas of interior forest, non-interior forest edge areas are subject to impacts from invasive species, pollution, and variation in soil moisture, for example.

To understand where interior forest has been lost and therefore where risks from forest fragmentation might be greatest, the researchers used global tree cover data to map the forests of 2000 and 2012 and examined the patterns of change across ecological regions and biomes. Their analysis revealed a net loss of 3.76 million square kilometers of interior forest area, or about ten percent of interior forest—more than twice the global net loss of forest area. The rate at which interior forest area was lost was more than three times the rate of global forest area loss.

All forest biomes experienced a net loss of interior forest area during the study period. Across the globe, temperate coniferous forests experienced the largest percentage of loss, tropical and subtropical moist broadleaf forests lost the most area of interior forest, and boreal forests and taiga lost interior forest at the highest rate. Researchers note that the reasons for losses, and therefore the consequences, depend on local circumstances. Human activities and land use changes that result in permanent deforestation have a much greater impact than temporary deforestation from natural disturbances, such as a fire. 

Monitoring remains an important tool to provide early warnings of forests at risk of reaching a tipping point, and the results of this study can inform and focus conservation and management decisions in areas of concern. “As forest area is lost and the remainder becomes more fragmented, the remaining forest may no longer function as interior forest,” explains Riitters. “Sustaining forest interior is arguably as important as sustaining forest itself.”

The study’s coauthors include James Wickham, U.S. Environmental Protection Agency; Jennifer Costanza, North Carolina State University/Eastern Threat Center; and Peter Vogt, European Commission Joint Research Centre.

Access the full text of the article at http://www.srs.fs.usda.gov/pubs/49729.

Landscape Pattern Analysis Reveals Global Loss of Interior Forest

ABSTRACT

Context: Published maps of global tree cover derived from Landsat data have indicated substantial changes in forest area from 2000 to 2012. The changes can be arranged in different patterns, with different consequences for forest fragmentation. Thus, the changes in forest area do not necessarily equate to changes in forest sustainability.

Objective: The objective is to assess global and regional changes in forest fragmentation in relation to the change of forest area from 2000 to 2012.

Methods: Using published global tree cover data, forest and forest interior areas were mapped in 2000 and 2012. The locations of forest interior change were compared to the locations of overall forest change to identify the direct (pixel level) and indirect (landscape level) components of forest interior change. The changes of forest interior area were compared to the changes of total forest area in each of 768 ecological regions.

Results: A 1.71 million km2 (3.2 %) net loss of global forest area translated to a net loss of 3.76 million km2 (9.9 %) of forest interior area. The difference in loss rates was consistent in most of the 768 ecological regions. The indirect component accounted for 2.44 million km2 of the net forest interior change, compared to 1.32 million km2 that was attributable to the direct component.

Conclusion: Forest area loss alone from 2000 to 2012 underestimates ecological risks from forest fragmentation. In addition to the direct loss of forest, there was a widespread shift of the remaining global forest to a more fragmented condition.

A global evaluation of forest interior area dynamics using tree cover data from 2000 to 2012