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Painting by numbers: chemical variation in the Amazon

Trees around the Madre de Dios river exhibit beautiful variations of chemical concentrations Trees around the Madre de Dios river exhibit beautiful variations of chemical concentrations Gregory Asner, Carnegie Institution for Science
01 Jun
2015
Mapping the chemical fingerprint of the Amazon lowlands from the air reveals the secrets of the forest canopy and the soil beneath

For the past two years The Carnegie Airborne Observatory (CAO) at Stanford University has been revealing the secrets of forest biodiversity. Flying hundreds of metres above the trees, the CAO’s Dornier 228 aeroplane is a flying ecological laboratory, collecting chemical data and rendering it to present dazzling maps of forest chemical variation.

The images, made through laser scanning and image spectroscopy, show hard-to-reach ecosystems in a level of detail that would take years to analyse on the ground. Views that are uniformly green to the naked eye give way to the psychedelic variation of chemical activity. The CAO’s most recent breakthrough has revealed the chemical makeup of the Amazon rainforest’s lowland regions and hinted at the unknown topography beneath it.

The images show a sea of red canopy where there is a high density of growth and defence chemicals. ‘These chemicals include both growth-related, such as pigments and nutrients, and defence-related such as polyphenols and lignin,’ explains Gregory Asner, CAO principal investigator and Professor of Environmental Science at Stanford University.

‘We found that species have evolved higher levels of growth chemicals on soils that are locally higher in fertility,’ he says. So the chemical fingerprint of trees reflects the fingerprint of the topography. However, fertility is also closely related to the movements of rivers too, otherwise known as hydrologic variation.

The CAO has picked on varying chemical properties along the flood plains of the Mardre de Dios and Tambopata rivers. ‘These higher fertility soils are those that are replenished by periodic flooding of the forest floor by neighbouring rivers that bring nutrients down from the Andes,’ explains Asner. For this reason, low-lying forest accumulates the most growth and defence chemicals.

CAO-PLSR-CICRA-Peru-tch ligRed coloured communities show areas with plenty of growth chemicals. Oxbow lakes and old meanders are also visible (Image: Gregory Asner, Carnegie Institution for Science)

Analysing the chemical signature of the Amazon rainforest works towards an understanding of how it might change in the future. ‘Growth and defence chemistry in forest canopies is the best possible way to know two things,’ says Asner. ‘One, how fast the forest is soaking up carbon from the atmosphere and two, the impacts of variable and long-term changing climate on both the biological diversity and the amount of carbon taken up in rainforests.’

Earlier this year, the CAO applied spectroscopy to an area of rainforest that was removed for palm oil cultivation. The transition of prime rainforest to a monoculture crop was reflected in the chemical fingerprint of the canopy. In this way, the maps from the CAO can indicate the impact that human activity can have on biodiversity. ‘It is very similar to getting a blood test to find out the general status of your health,’ says Asner.

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