A team of researchers has conducted the most thorough evaluation so far on the impact of logging and the conversion of land to oil palm plantations on tropical forest ecosystems. Their findings indicate that logging and land conversion pose distinct and cumulative environmental challenges.
A team led by the University of Oxford has conducted the most extensive assessment available of the effects of logging and oil palm plantation conversion on tropical forest ecosystems. The findings reveal that the impacts of logging and land conversion are notably different and cumulative. These results were published today (10 January) in Science.
It is crucial to understand how various elements of tropical forests are influenced by logging and the transformation into oil palm plantations. This knowledge is essential for pinpointing vital habitats that require conservation and restoration. It can also inform land use decisions—such as whether a logged area should be protected, rehabilitated, or cleared for plantation development. Previously, most research has been limited to only a few specific factors, making it challenging to evaluate the overall consequences on the entire ecosystem.
In this comprehensive study, the researchers examined more than 80 indicators that describe numerous aspects of tropical forest ecosystem structure, biodiversity, and functionality. These indicators range from soil nutrients and carbon storage to rates of photosynthesis and populations of bird and bat species. Data were collected from sites in three regions of Sabah, Malaysian Borneo, which included undisturbed old-growth forests, forests that had been moderately or heavily logged, and previously logged areas that had been converted into oil palm plantations.
This research broke new ground by analyzing such a wide array of indicators regarding the health of tropical forest ecosystems in a single study, facilitated by the vast network of research sites set up by the South East Asia Rainforest Research Partnership. Overall, logging and land conversion significantly impacted the vast majority of the measured indicators—60 out of 82 metrics. Nonetheless, the two processes showed distinct differences.
Typically, logging primarily affects factors related to forest structure and environment. Since tropical logging tends to be selective, concentrating on trees with specific commercial value, even minor logging can disrupt the ecosystem. For instance, the removal of larger, older trees creates gaps in the canopy, allowing rapidly growing species to take hold. These new species often have less dense wood and thinner leaves, making them more susceptible to herbivores.
On the other hand, converting logged forests into oil palm plantations has more profound effects on biodiversity compared to logging alone. Populations and diversity of birds, bats, dung beetles, trees, vines, and soil microorganisms showed steeper declines in plantations than in logged forests. This is likely due to significant modifications in plant food resources and the shift to hotter and drier conditions created by the single-layer canopy of oil palm following 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 land conversion affect forest ecosystems in different ways, indicating that plantation conversion introduces unique challenges that compound those posed by logging.”
The researchers emphasized that logged forests can continue to play a vital role in preserving biodiversity and should not be hastily deemed unsuitable for conversion into oil palm plantations.
According to Professor Ed Turner from the University of Cambridge, who co-led the study, “This study highlights that while intact, old-growth forests are irreplaceable, secondary logged forests also possess significant value and contribute meaningfully to biodiversity and ecosystem functioning when compared to the stark declines noted in oil palm plantations.”
One unexpected finding for the research team was the variability in responses among different elements of the ecosystem. Dr. Charlie Marsh from the University of Oxford, the study’s lead author, remarked: “Our study reveals that concentrating on just one aspect of the ecosystem can lead to a partial understanding of the overall ecological response. We were surprised by the significant variability in responses to deforestation, which included increases, decreases, or sometimes no change at all. Certain aspects even thrived in logged forests but declined in oil palm plantations. When making decisions about land management and conservation, it is essential to consider a broad array of ecological factors.”
