A team of researchers from the University of Oxford has conducted a detailed examination of how logging and transforming forests into oil palm plantations impact tropical ecosystems. Their findings illustrate that logging and conversion lead to distinct and cumulative environmental effects. These results were published today (10 January) in Science.
It is crucial to comprehend how various elements of tropical forests are influenced by logging and their conversion into oil palm plantations. This understanding is vital for pinpointing critical areas for conservation and restoration. Additionally, it can guide land use decisions—for instance, determining whether a logged forest should be conserved, rehabilitated, or turned into a plantation. However, previous studies often focused on a limited range of factors, complicating the overall assessment of the ecosystem’s impact.
In this extensive study, the researchers examined over 80 metrics that describe various aspects of tropical forest ecosystems, including soil nutrients, carbon storage, photosynthesis rates, and the diversity of bird and bat species. These measurements were taken from study sites situated in three areas of Sabah, Malaysian Borneo, which included undisturbed old-growth forests, moderately and heavily logged forests, as well as areas transformed into oil palm plantations.
This groundbreaking research, which evaluated a broad array of indicators for tropical forest ecosystem health in a single study, was facilitated by the extensive network of study sites established and managed by the South East Asia Rainforest Research Partnership. Overall, the impacts of logging and conversion were significant, affecting 60 out of the 82 metrics assessed. However, the researchers observed distinct differences between the two activities.
Generally, logging had a more significant impact on aspects related to forest structure and environment. Selective logging in tropical regions typically targets specific trees with commercial value; thus, even minimal logging disrupts the ecosystem. For example, the removal of older, larger trees creates gaps in the canopy that allow faster-growing species to thrive. These newer species have different characteristics, such as less dense wood and thinner leaves, which make them more susceptible to herbivores.
In contrast, converting logged forests into oil palm plantations results in more pronounced impacts on biodiversity that exceed those caused by logging alone. The populations of birds, bats, dung beetles, trees, vines, and soil microorganisms declined significantly in plantations compared to logged forests. This decline can be attributed partly to the substantial changes in plant food sources and the transition to hotter and drier microclimates under the uniform layer of oil palm that follows the conversion.
Professor Andrew Hector, the senior author from the Department of Biology at the University of Oxford, stated: “A key takeaway from our study is that selective logging and conversion to plantations affect forest ecosystems in notably different ways, signifying that the impacts of conversion are additional to those caused by logging alone.”
The study team emphasized that logged forests can still hold significant value for biodiversity preservation and should not be hastily discarded for conversion into oil palm plantations.
Co-lead of the study, Professor Ed Turner from the University of Cambridge, added: “This research highlights that while old-growth, undisturbed forests are irreplaceable, secondarily logged forests also possess considerable value and play a crucial role in maintaining biodiversity and ecosystem functions compared to the significantly reduced levels seen in oil palm plantations.”
One unexpected finding for the research team was the variability in ecological responses. Dr. Charlie Marsh, the lead author from the University of Oxford at the time of the study and now at the National University of Singapore, remarked: “Our study shows that concentrating on just one part of the ecosystem may not provide a complete picture of how the entire system responds. We were astonished by the wide range of reactions from different facets of the ecosystem to deforestation. Some aspects increased, some decreased, and others showed no change at all. Interestingly, certain traits improved in logged forests but declined in oil palm plantations. Therefore, broad consideration of ecological properties is essential when making decisions about land management and conservation.”
