20 December 2023

In the Amazon, forest fragmentation changes the shape of trees


A study from the University of Helsinki highlights how trees in forests change their appearance to adapt to changing environmental conditions. Results are relevant on a global scale

by Matteo Cavallito


The fragmentation of forests – that is, the process of dividing forest areas into smaller parts by cutting down plants – affects the shape taken by trees. This is revealed in a research from the University of Helsinki. The investigation, conducted in the Amazon, reveals for the first time a previously ignored dynamic while simultaneously “shedding light on the impact of human activity on the tropical environment and, consequently, on climate change in a new way,” says a statement from the Finnish university.

Deforestation affects the appearance of trees

The study, published in the journal Nature Communications, showed that trees growing at forest edges have a different shape than those growing in interior areas. The edges of deforested areas, in particular, experience higher temperatures (due to a lower mitigation effect of trees) and higher light levels.

In this scenario, trees are able to adapt to changes in their living conditions and environment. Yeah, but how?

To answer this question, Eduardo Maeda, associate professor at the University of Helsinki, coordinated an international project to study tree forms in the tropical rainforest. The investigation was based on the analysis of data collected by terrestrial laser scanning, which led to the 3D representation of trees.

La scansione laser terrestre (TLS) offre nuove prospettive sulla struttura tridimensionale (3D) delle piante, compresa la descrizione di tratti architettonici a scala fine come l'asimmetria degli alberi e la distribuzione verticale dei rami. I ricercatori hanno utilizzato i dati TLS che hanno prodotto una spaziatura dei punti di 1,4 cm a una distanza di 20 m dallo scanner. Immagine: Nunes, M.H., Vaz, M.C., Camargo, J.L.C. et al. Edge effects on tree architecture exacerbate biomass loss of fragmented Amazonian forests. Nat Commun 14, 8129 (2023). https://doi.org/10.1038/s41467-023-44004-5 CC BY 4.0 DEED

Terrestrial laser scanning (TLS) offers new perspectives into the three-dimensional (3D) structure of trees. The scanning allowed descriptions of fine-scale architectural traits such as tree asymmetry and vertical distribution of branches. Researchers used TLS data that resulted in a point spacing of 1.4 cm at a 20 m distance from the scanner. Image: Nunes, M.H., Vaz, M.C., Camargo, J.L.C. et al. Edge effects on tree architecture exacerbate biomass loss of fragmented Amazonian forests. Nat Commun 14, 8129 (2023). CC BY 4.0 DEED Attribution 4.0 International

The study in the forest

The authors, the study says, conducted “ground surveys of terrestrial LiDAR in Central Amazonia to explore the influence of forest edge effects on tree architecture and allometry, as well as forest biomass, 40 years after fragmentation.” In doing so, they found “that young trees colonising the forest fragments have thicker branches and architectural traits that optimise for light capture, which result in 50% more ligneous volume than their counterparts of similar stem size and height in the forest interior.”

However, the authors also simultaneously observed a disproportionate reduction in the height of some large trees, resulting in a 30 percent decrease in their volume.

“Despite the substantial wood production of colonising trees,” the survey continues, on balance, “the lower height of some large trees has resulted in a net loss of 6.0 Mg ha−1 of aboveground biomass – representing 2.3% of the aboveground biomass of edge forests. Our findings indicate a strong influence of edge effects on tree architecture and allometry, and uncover an overlooked factor that likely exacerbates carbon losses in fragmented forests.”


Effects on carbon sequestration

The observed phenomena obviously impact carbon management as well. In the observed area, for example, the amount of biomass that binds carbon dioxide has decreased. Considering that tropical rainforests continue to cover vast areas and are an important carbon sink for the Planet, the researchers note, the observed changes in individual trees make the results globally relevant.

“The effect of human activity on climate change will need to be re-evaluated,” Maeda said in the statement. “This study provides new information on the adaptation of the rainforest to environmental change, as well as tools for researchers and decision-makers who are considering how to mitigate climate change.”