Suivi satellitaire de la perte en forêts de mangroves

SATELLITE DATA

REVEALS STATE OF THE WORLD’S MANGROVE FORESTS

By Asa Strong and Susan Minnemeyer

Mangrove forests play a vital role in erosion and flood control, fisheries support, carbon storage, biodiversity conservation and nutrient cycling. Photo by Klaus Balzano/Flickr.

The word “forest” often calls to mind a dense landscape of towering trees. However, some of the most carbon-rich and productive forests are clustered along coastlines in the tropics and subtropics. Mangrove forests, made up of salt-tolerant trees and shrubs, play a vital role in erosion and flood control, fisheries support, carbon storage, biodiversity conservation and nutrient cycling. Many coastal communities rely on mangroves for food, forest products and tourism revenue, and the forests provide a natural coastline defense to storm surges by reducing wave and wind velocity. New analysis relies on satellite data to survey the state of these important ecosystems. Using Global Forest Watch (GFW), an online forest monitoring platform, we found that the world lost 192,000 hectares (474,000 acres) of mangroves from 2001 to 2012, a total loss of 1.38 percent since 2000 (or 0.13 percent annually). This is a relatively low rate of loss compared to the rate of tropical deforestation, which stands at a total of 4.9 percent from 2000 to 2012 (or 0.41 percent annually). The tropical deforestation rate was calculated using the same tree cover loss data as the GFW analysis, and considered forests with more than 25 percent canopy cover.

Tracking Mangroves with Satellites

Advances in satellite remote sensing of forest cover offer new opportunities to monitor changes in forests with far better consistency and accuracy than ever before. Our analysis relied on the 2001-2012 satellite data of global tree cover loss from University of Maryland and Google, overlaid on mangrove extent data mapped by Chandra Giri and collaborators and distributed by the United Nations Environment Programme. Annual updates to the global tree cover loss data present the opportunity to monitor forest change in mangrove ecosystems on a consistent basis. And mining archives of satellite imagery offer the potential to map historical changes, adding clarity to the state of mangrove loss prior to 2000. While previous studies have estimated mangrove forest loss prior to 2000, we choose not to compare our estimates with these findings due to differences in analytical methods. In addition to quantifying total global loss of mangroves over the last decade, a few trends emerge. Asia Has the Highest Rates of Mangrove Loss.