Like Time Capsules, Tropical Tree Rings Reveal Effects of Human Activity

(CN) – Dr. Seuss’ Lorax spoke for the trees, but what can the trees say about us? Research published Thursday in the journal Trends in Plant Science considers the impact of human activity on the growth of tropical trees, particularly in the Amazon.

Trees can live for hundreds of years and each annual ring growth preserves a snapshot of the carbon, water, and minerals taken in through the year, making them excellent living time capsule.

This image shows a Brazil nut tree in Jaú National Park, Amazonas, Brazil. (Victor Caetano-Andrade)

“Trees incorporate these resources into their wood during growth, with input varying from year to year depending on factors like nutrient availability, sunlight intensity, and rainfall amount and seasonality,” explained researchers funded by the Max Planck Institute in their review. “Their incremental growth rings thus reflect their abiotic and biotic environment throughout their lifespan.”

Researchers propose combining dendrochronology data – the study of tree rings – with radiocarbon dating and historical records of local human settlements. Similar methods are used to understand past climates, since trees experience greater growth in warmer years, and less growth in colder years.

Tree ring data is already used to understand some of the environmental pressures faced by past human settlements, including drought. The very types of trees that populate forest can also offer insight into the resources needed by nearby people.

In addition to variations in climate, the researchers argue destructive human activity can also slow tree growth. Lead author Victor Caetano-Andrade advocates that this holistic approach to investigating both tree growth and forest loss offers profound insight into the onset and impacts of the Anthropocene, the current geological age so named because human activity has been the dominant influence on climate and environment.

In addition to adding other benefits of forest preservation – on top of promoting clean water and resource protection – this research also offers insight into how resource managers can better preserve forests. As Caetano-Andrade noted in a statement, “Traditional populations who live on the riverbanks of tropical forests are the great heroes of preservation as they know the importance of keeping the forest standing to guarantee their well-being.”

This figure shows how humans promote or suppress trees, past and present. (Caeteno-Adrade et al. / Trends in Plant Science)

He added: “One example is during the pre-colonial period in the central Amazon, where populations of Brazil nut experienced heavy recruitment and growth. However, when European colonists invaded the tropics, indigenous people abandoned the landscape, leading to Brazil nut trees to stop recruiting for nearly 70 years.”

With tens of thousands of hectares of tropical forests demolished daily, a mere 107 forest sites are protected by the UNESCO World Heritage program globally preserving about 466,000 square miles. Some of these tropical trees are as old as modern man with roots dating back to the Holocene, more than 10,000 years ago.

Luckily, tree ring data can be gathered by boring a small hole into a tree core, allowing them to give to human knowledge today while recording history for years to come.

%d bloggers like this: