Trees on forest edges may grow faster than those inside

Conservationists have noted plantations outside forest don’t capture carbon efficiently or make up for biodiversity losses

Is a tree in a forest the same as one outside it? The belief that it is, allays the conscience of government-backed afforestation programmes where dense forests are often razed for mines, and multiple saplings are commissioned in alternate locations that are usually outside forest boundaries.

Conservationists have on the other hand pointed out that this isn’t the same because a loss of a section of forest means destroying an ecosystem that can’t be easily substituted for. To account for these losses more minutely, Lucy Hutyra, a bio-geochemist and ecologist at the Boston University, Massachusetts, U.S., has been analysing the terrestrial carbon sink.

This is made up of the billions of square kilometres of forest in the world that are major storehouses of carbon. In net, forests store more carbon dioxide than they release and an estimated 30% of carbon emissions from emitting fossil fuels are absorbed by the forest, making them a terrestrial carbon sink.

Trees absorb carbon dioxide (CO 2), release oxygen by way of photosynthesis, and store carbon in their trunks. When they shed, soil microbes work to decompose the leaves and other organic matter that releases the trapped carbon dioxide. A major prong of countries’ climate change strategy, including India’s, is to increase the terrestrial sink area.

Hutyra, who has been researching the consequences of forest loss, examined if the same species of tree had different patterns of carbon dioxide storage when located at a forest edge or further away.

The textbook assumption was that trees at forest edges release and store carbon at similar rates as forest interiors, but Hutyra and her colleagues report this isn’t true.

In two papers published in the peer-reviewed Global Change Biology, and Nature Communications, Hutyra's team found edge trees grew faster than their country cousins deep in the forest, and that soil in urban areas can hoard more carbon dioxide than previously thought.