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Seeing the Forest - and the Trees

Christina Scott

Conservationists can go into the field to try to track the health of the world’s forests.

Edward Mitchard from the University of Edinburgh has done that, canoeing through the Mbam Djerem national park in Cameroon, which has the oldest field plots of any rainforest in the world, dating back to 1937.

Or, they can sit at home and read the radar data for Mozambican regions like N’hambita and Niassa coming off a satellite such as the first Japanese Earth Resources Satellite (JERS-1).

Mitchard, part of the Tropical Biomes in Transition (TROBIT) consortium, has done that, too. Which one does he prefer? "Satellites", he says, are "much better." "It’s very expensive and time consuming to do field measurements," he said.

Mitchard compared the laboriously acquired field data with the ease of receiving detailed information from Japan’s four-ton Advanced Land Observing Satellite (ALOS), launched in 2006 from the Tanegashima Space Center. The benefits of using one of the largest earth-observing satellites ever designed, orbiting nearly 700 kilometres above our heads, were clear.

"It’s difficult, even impossible in some areas, to do forest plots properly and it’s difficult to scale up," Mitchard noted. Methodologies change, if you’re trying to follow up on earlier research. Human error is another problem. Work done in Lope national park in Gabon predated GPS so staff simply used crosses on the maps to mark sites. The result: some forest plots were deep in water, and boxsearch methodology had to be done to work out where the researchers were meant to be. And it’s not just any old satellite that Mitchard prefers. Radar beats optical satellites because radar sees three-dimensional structures, he explained to the audience at the University of Cape Town: "it sees the whole tree; an optical sensor just sees leaves."

Satellites can even help compensate for the lack of historical field data, by using unchanged regions as a kind of proxy and back-calibrating a useful estimation of what the forest was like earlier. Something like the Phased Array type L-band Synthetic Aperture Radar (PALSAR) is an all-weather friend to the conservationist: it can see through clouds and haze, operate at night, and is highly sensitive at lower biomass values.

And you can expect estimating biomass to become increasingly important given the heated debates over global warming and proposals such as the Clean Development Mechanism and the Reducing Emissions from Deforestation (REDD) plank of the Kyoto Protocol against climate change.

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