In the last few years, there has been heartening news, based on new scientific data, about progress in reducing global deforestation. The IPCC, in its Fifth Assessment Report in 2014, reviewed all the previously published evidence and concluded that deforestation and the emissions of global warming pollution that it produces had dropped in recent years. The Global Carbon Project, an annual review of the planet’s carbon cycle and its implications for climate change, found the same trend in its 2014 assessment.
Then last year Francesco Tubiello of the FAO and colleagues, using more recent data than had been available to the IPCC, published a paper in the journal Global Change Biology, showing that emissions from deforestation had fallen in all three datasets they analyzed, while those from agriculture had increased. Also last year Do-Hyung Kim and colleagues from the University of Maryland, using a global tree cover dataset, found that losses of tree cover in the humid tropics had peaked in the 2000-2005 period and declined in the following five years. Other recent pan-tropical and regional studies – e.g. by Frederic Achard and colleagues on the tropics, Mitch Aide and colleagues on Latin America, and Phillipe Mayaux and colleagues on African rainforests – are broadly consistent with this trend.
But there still remained some questions, because one analysis, done by Matt Hansen and colleagues from the University of Maryland and using the same dataset but different methods as Kim et al., had found a 5-8% increase in the rate of loss of global tree cover from 2000 to 2012. Although some of the differences could be explained by differences in dates, areas included, methods, and definitions – forest vs. tree cover, net vs. gross loss – the discrepancy did raise questions about the trend found by the large majority of studies.
One of the nice things about science is that disagreements don’t continue forever. Often they actually do get settled, either by new data or by improvements in our methods of analysis. Both of these things have now happened with respect to the Hansen et al. data, which is made available through the Global Forest Watch 2.0 (GfW) platform of the World Resources Institute. At the start of September GfW released new data for 2014, as well as revisions of tree cover loss figures for earlier years. Taken together, the GfW figures show that global tree cover loss reached a high point of about 23 million hectares in 2012, but then dropped in both the following two years to 19 million hectares in 2014, a reduction of about 20%. This brings it down to a level below that of 2004, a decade earlier.
At nearly the same time, we got a large new set of forest data from the FAO, in the form of its 2015 Global Forest Resources Assessment (FRA 2015). The FRA 2015 data show the same decreasing trend in deforestation as the other analyses, but there is lots of additional information that helps to understand how different kinds of forest (and other types of tree cover) are changing. The FRA 2015 data has been analyzed from many different points of view, in a collection of 14 articles in a special issue of the scientific journal Forest Ecology and Management.
Compared to the last FRA in 2010 and those in previous years, there is a considerably wider range of data — not only country-by-country information on the area of forest (login required for Science Direct links), but also on biomass, carbon, wood production, emissions and removals of CO2, ecosystem services, protected areas, natural disturbances, ownership, income, expenditure, and progress towards sustainable management. The capacity of countries to monitor their forests and the quality of the data is distinguished in three tiers, with the encouraging news that 59% of the world’s forest area is now in the top tier, and only 11% in the lowest tier.
Importantly, FRA 2015 also breaks down types of tree-covered land, in several steps. First, Forests (4 billion hectares, globally) are distinguished from “Other Wooded Land” (1.2 billion hectares), which generally is savanna-like vegetation with less than 10% of its ground area covered by trees. Forests are subdivided into Natural Forests (3.72 billion ha) and Planted Forests (0.28 billion ha). Only about a third (1.28 billion ha) of the area of natural forest is considered to be Primary Forest, defined as “naturally regenerated forests of native species, where there are no clearly visible indications of human activities and the ecological processes are not significantly disturbed.” These distinctions allow us to see the differing trends in different kinds of forests and other tree cover, and to understand not only what is happening, but where and why.
The FRA data also gives us an updated global estimate of the climate impact of deforestation—and for the first time, of forest degradation as well. Deforestation annually produces 2.9 billion tons of global warming pollution (Gt CO2eq), and degradation—more precisely, “partial canopy cover loss”—adds under 1.0 Gt CO2eq. Both of these figures are down from the rates in the 2001-2010 period (4.0 and 1.1 Gt CO2eq, respectively) but are still very significant drivers of climate change.
The new FRA and the 14 Forest Ecology and Management articles also compare the new data to other published studies, particularly recent ones based on different remote sensing approaches, and try to untangle which differences among them are just due to different methods and definitions, as opposed to the data disagreeing about the underlying reality. Encouragingly, many of these articles are written by authors outside the FAO, including some who have been quite critical of the numbers and analysis in past FRAs. We seem to be moving toward a broad consensus on the overall trend among forest experts—but with enough differences remaining to keep us busy debating the details for years to come!
The news that deforestation is dropping is encouraging, but it remains high and continues to be a major source of global warming pollution and a serious threat to biodiversity and the livelihoods of forest peoples. It looks like we reached a peak in the last decade or two; the challenge of the next decade is to continue and accelerate that progress so that the world’s forests are no longer disappearing.