What is it about?

We examined whether logged tropical forests in Malaysian Borneo absorb more carbon than they release, in other words, if they are carbon sinks or sources. While abandoned logs, damaged trees and disturbed soils emit carbon after logging, these emissions are seldom measured, and the general assumption is that the rapid re-growth of trees makes these forests carbon sinks. We monitored the carbon exchange over multiple years (2011-2017), and although we did observe this increase in growth, the emissions from deadwood and soil outpaced the carbon gain by trees. Consequently, these forests were a net source of carbon at least a decade after the logging event. Our research used two different independent methods, namely a network of intensively monitored permanent plots and a flux tower above the canopy, and the results were consistent. Higher logging intensity, i.e. the proportion of the trees removed and damaged, was important: the most heavily logged plots were larger sources of carbon than the moderately logged plots.

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Why is it important?

Logged forests are widespread, covering a larger area than unlogged forests in the tropics, but far less studied. Unlogged tropical forests are carbon sinks, and because trees in recovering logged forests grow fast, we have often assumed them to be equal or larger sinks. In this study, we challenge this assumption and show that logged forests may act as persistent net carbon sources for at least a decade after the logging event. By improving our understanding of logged forests we can better represent them in global carbon budgets and models, understand how they may respond to environmental change and inform conservation policy and forest management. Logged forest have high conservation value and biodiversity compared with tree plantations, but we cannot take their carbon sink function for granted. Sustainable logging practices are important to minimise the damage to the soil and vegetation.


This paper incorporates a huge amount of fieldwork for which we are indebted to the expert, dedicated field teams in Malaysia. Together, we climbed hills, measured trees, took soil samples, dug roots, suffered from leech bites and had fun. Furthermore, this paper would not have been possible without the longstanding collaborations with partners in the Malaysian states of Sabah and Sarawak.

Terhi Riutta

Our research shows the long-lasting impacts of logging and highlights how actions have consequences far into the future when it comes to environmental issues. Our research aims to teach people about those issues, and how we can be better informed to avoid them in future.

Maria Mills
University of Leicester

Read the Original

This page is a summary of: Tropical forests post-logging are a persistent net carbon source to the atmosphere, Proceedings of the National Academy of Sciences, January 2023, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2214462120.
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