Originally written by Peter Holmgren for Center for International Forestry Research (CIFOR).
As I took up my job at the Center for International Forestry Research (CIFOR) last month, I noted the so-called World Deforestation Clock on the CIFOR homepage, which tells readers “the number of hectares of forest lost since you arrived on this page.” The longer your web browser stays on our homepage, the higher the number ticks up. At the time, I made a mental note to come back to this feature and revisit what it is we communicate and why. Opening this box reveals a whole range of interesting questions, and I will try to address some of them here.
First of all, what is the clock showing? It is important to note that there are both positive and negative area trends, and that the clock only shows the negative trend. That is, there is a considerable area of forest gained over time, and an even larger area lost. In the year 2000 edition of the Global Forest Resources Assessment (FRA), which is produced by my former employer, the Food and Agriculture Organization of the United Nations (FAO), the estimated losses (deforestation) were 14.8 millions hectares per year (Mha/yr) and the gains 5.6 Mha/yr resulting in a net area change of -9.4 Mha/yr. In FRA 2005, the gross and net changes were not analysed, but a deforestation rate of 13 Mha/yr, or 0.41 hectares per second (ha/s), for the period 1990-2005 was provided as the sum of all country reports showing a negative area trend. This is inherently an underestimate as within-country variations are not taken into account, however the current clock uses this number. FRA 2010 figures are now available and show a lower rate of net area change at -5.2 Mha/yr for 2000-2010. The FRA 2010 report also states a deforestation of “close to 16 Mha/yr” for 1990-2010 based on similar analyses as for FRA 2000. This number is said to be “more accurate”, but no reference is made as to how it was calculated.
There are at this point, in my view, no suitable alternatives to the FRA information, based on country reports, for global forest area change. Several scientific attempts to infer changes using global remote sensing data have been made, but typically these illustrate tree cover changes (which is different from forest area changes), and there have been varying approaches and ambitions to field verification. While science in this field is advancing, the official status of the FRA numbers make them more appropriate to use.