Measuring human impacts on tropical forest remnants

Man can impact forests in many ways without deforesting them. Measuring these impacts on multiple forest features and at large spatial scales is challenging but feasible for some parts of the world.

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Deforestation is the greatest human impact on forest ecosystems. Half of the world’s forests have already been lost and they continue to be cut down, mainly in the tropics. So, halting deforestation and restoring deforested lands are key for the future of our planet. Not surprisingly, these topics are at the epicentre of the climate change agenda. But what about the fragments of forest that still stand? How well are they coping with the exposure and isolation that follow the deforestation?

We provided answers to these questions for the Atlantic Forest, home to 35% of the South American population and to over 5,000 tree species (45% of them being endemic). This tropical forest lost most of its original cover in the past century and the current state of the Atlantic Forest remnants is not very encouraging. Over 80% of the ca. 1800 forest remnants bear signs of negative human impacts, with average losses in tree diversity and carbon being as high as 42%. Our estimates of these hidden losses of carbon inside forest remnants were equivalent to US$ 2.6 billion in carbon credits alone.

Impacts of cattle grazing on the Atlantic Forest understory (Photo: Renato Lima).

The picture is not pretty indeed. But the current state of what’s left of the Atlantic Forest can be seen as an opportunity. As there is room to increase carbon stocks inside forest remnants, their restoration could attract billions in investments related to markets of carbon credits without competing for space with agricultural lands. So, we hope that degraded fragments will play a more important role in the ongoing pledges of ecosystem restoration.

The situation of the Atlantic Forest may be the present (or the future) of other forests around the world. But not all forests are as well-known as the Atlantic Forest to allow similar assessments across their full extent. Satellites are great to sort out forests from non-forest areas and high-resolution sensors (e.g., LiDAR) can be used to assess human impacts. But ground data is gold when it comes to providing the state of our forests, particularly regarding their biodiversity. Like true gold, ground data is hard to gather, because it takes time and resources, and depends on specialized personnel, whose work is often undervalued. This is one of the reasons why we are still unable to provide a global picture of our impacts on forest ecosystems (and why we must fund and value the ‘green gold miners’ across the globe).

The forest landscape in the Atlantic Forest of São Paulo state.

Our report on the status of Atlantic Forest fragments was only possible due to the work of hundreds of researchers that went to forest remnants and measured millions of trees and identified thousands of tree species. We compiled the data from these studies in the Neotropical Tree Communities database (a.k.a. TreeCo), a continuous effort to support forest research in eastern South America. TreeCo started in 2014, with the publication of a first diagnosis for the Atlantic Forest.

Today, TreeCo stores data from almost 4,500 inventories (over 2 million tree measurements), with the oldest one dating back to 1959. Most of them are Atlantic Forest inventories, but the database also stores data for the Brazilian savannahs and dry forests (Cerrado and Caatinga). TreeCo is not just a compilation of forest inventories. It stores detailed site descriptions and information on morphological traits of tree species occurring in this part of the world. The database also has routines for the validation of geographic coordinates and updates of species identifications based on herbarium vouchers. In times of biodiversity crisis and lack of research funding, using the available forest inventories to provide synthesis is one of the ways to provide the answers society needs to better conserve its natural resources.

Read the full paper: Lima, R.A.F., Oliveira, A.A., Pitta, G.R., Gasper, A.L., Vibrans, A.C., Chave, J., ter Steege, H., Prado, P.I. The erosion of biodiversity and biomass in the Atlantic Forest biodiversity hotspot. Nature Communications 11, 6347 (2020). https://doi.org/10.1038/s41467-020-20217-w

Renato Lima

Associate researcher, Universidade de São Paulo & Naturalis Biodiversity Center

I am broadly interested on the patterns and processes related to the structure of tropical forests and their biodiversity, with a main focus on the Atlantic Forest of South America. More specifically, I am interested in how tropical tree communities organize themselves, what explain their huge diversity and how we can restore them.