Why the latest study on global forest cover must be taken with a pinch of salt
Like the Indian government’s State of Forest report, the study by two US universities also fails to make a distinction between forest cover and tree cover
A new study published in Nature, a multidisciplinary science journal, has said the global tree canopy cover has increased by 2.24 million square kilometres between 1982 and 2016. Using satellite data, researchers from the University of Maryland, State University of New York and NASA Goddard Space Flight Centre found that the gains made in forest area in the temperate, subtropical, and boreal climatic zones are neutralising the decline that is taking place in the tropics. Interestingly, the study adds, forests in mountain regions are expanding as climate-warming enables trees to grow higher up on mountains. The greatest increase in tree canopy has occurred in Europe, including European Russia (35%). A close second was China, where tree canopy gained 34%. In the US, tree canopy increased by 15%. The important finding is that much of the change is nevertheless anthropogenic; climate change induced vegetation growth is a smaller fraction.
The study, however, has the same limitations that exist in the Indian government’s State of Forest reports because it maps “all tree cover” as one category. The Nature study uses three land-cover categories: tree crops; short vegetation cover; and bare ground. The issue with such categorisation is that “tree crops” could be anything: natural forest, teak plantations, eucalyptus plantations or coconut/arecanut/rubber plantations. But tree covers are not forests, and so telling us about “changes in tree cover” is not very useful.
Second, the reported expansion of “tree cover”, according to the new study, is happening in temperate countries, including temperate parts of China but not so much in the tropics or part of the subtropics. While the study published in Nature does not give countrywise figures, the main change reported for south Asia is bare ground becoming short vegetation cover. This is also not new: over the years, the area under agriculture has expanded and intensified in India because of double cropping/irrigated cropping.
Last, but not the least, one must keep in mind what makes a forest. It is not just the number of trees, but the biodiversity that it nurtures, and so one must always be aware of the difference between a forest cover and tree cover. Since 2003, India has lost over 1,000 sq km of dense forest every year, and compensated roughly half of that with plantations. Such additions only look good on paper.
The same is happening in China where the government has launched a massive tree planting exercise in the past two decades. The tree cover is largely single species, not necessarily native to those regions, and coercive in its creation. Unfortunately, these issues or the impact of such single species (which has a cascading effect on the ecosystem), are never captured in global mappings such as the one published recently in Nature.
First Published: Sep 06, 2018 09:01:43