The Western Amazon is arguably the most world’s biodiverse region and now scientists have found that not only is the forest rich in species, but also in chemical diversity. The chemical signatures of leaves sampled from the canopy of thousands of trees across the region reveal the secret to the tropical rainforest’s evolution.

Trees use a variety of chemicals to capture light, synthesize and store carbon, develop foliage, and even defend themselves. A study published in the Proceedings of the National Academy of Sciences (PNAS) says that chemicals found in the leaves of a tree’s canopy relates to how the tree adapts to pests, pathogens, and changes in environment and climate.

“Variation in this leaf chemical portfolio expresses multiple strategies evolved in plants to maximize fitness through growth and longevity in any given environment,” the scientists write.

“We discovered that this incredible region is a patchwork mosaic of trees with chemical signatures organized into communities to maximize their growth potential given their local soils and elevation—two geological factors they must negotiate as living organisms,” said lead author and Carnegie Institution ecologist Greg Asner, an advisor to Amazon Aid Foundation.

Asner goes on to discuss how communities of trees have radically different chemistries from area to area, including neighboring communities. “So a community on this [area], if you can walk just a few miles away to a new [area], it’s a different chemical makeup in the next canopy.”

“Every time you climb a tree you’re basically getting a completely different chemical portfolio from the last tree that you climbed. In other words, there is an enormous diversification of chemical traits among the different trees that are living together. We thought that the variation would be slower across the Amazon basin, but what we see is that almost every tree has evolved its own chemical traits unique from one another.”
The total sample pool included foliage from the top of 3,560 trees- 2,420 different species- across 19 forest regions from the foothills of the Amazon to the Andean cloud forests. The study five-years in the making is the first foray of Carnegie’s Spectranomics project, which seeks to study the link between biological diversity and ecological function in biological hot spots such as forests in Madagascar, Ecuador and Australia.

Unfortunately, the Amazon Rainforest is currently fighting against a wide array of unprecedented threats including illicit mining, overlogging, and clearing for agriculture and livestock. The study may also help predict how tree species will fare in the future, especially in the looming effects of climate change. Warmer temperatures may favor species that have evolved to invest more in light capture and growth chemicals.

But the findings go beyond helping scientists to predict the Darwinian fate of the forest, they also act as a warning of what’s at stake, according to Asner.

“I view the results as a wake-up call that we are shaking up a special tropical region full of chemically unique forest communities that have undergone millions of years of evolution and biogeographic construction.”