The research underscores the importance of understanding how tropical forests' ecological elements respond to both logging and plantation conversion. Such knowledge helps prioritize habitats for conservation and guides decisions on whether to protect, restore, or convert logged forests. Until now, most studies have examined a narrow set of factors, leaving the broader ecosystem impacts poorly understood.
In this study, researchers assessed over 80 metrics representing tropical forest ecosystem structure, biodiversity, and functioning, such as soil nutrient levels, carbon storage, photosynthesis rates, and bird and bat populations. Data were collected from study sites in Sabah, Malaysian Borneo, which included undisturbed old-growth forests, logged forests (moderately and heavily logged), and previously logged forests converted to oil palm plantations.
This comprehensive approach was facilitated by the extensive network of study sites maintained by the South East Asia Rainforest Research Partnership. Logging and plantation conversion were found to affect 60 out of 82 ecosystem metrics, with notable differences between the two practices.
Logging, typically selective in tropical forests, primarily alters forest structure and environmental factors. Selective removal of commercially valuable trees, particularly older and larger specimens, creates canopy gaps. These gaps allow fast-growing species with distinct characteristics, such as less dense wood and thinner leaves, to thrive, making them more vulnerable to herbivores.
Oil palm plantation conversion, on the other hand, has more severe effects on biodiversity compared to logging. Reductions in abundance and diversity were observed across multiple species groups, including birds, bats, dung beetles, trees, vines, and soil microorganisms. This is attributed to shifts in plant food resources and the creation of hotter, drier microclimates under the uniform canopy of oil palm plantations.
"One of the key messages of the study is that selective logging and conversion differ in how they impact the forest ecosystem, meaning that conversion to plantations brings new impacts that add to those of logging alone," said senior author Professor Andrew Hector from the University of Oxford's Department of Biology.
The findings highlight the value of logged forests for biodiversity preservation and argue against their immediate conversion to oil palm plantations. Professor Ed Turner from the University of Cambridge, who co-led the study, added, "Old growth, intact forests are unique, but secondary logged forests are also valuable and important in terms of their biodiversity and ecosystem functioning relative to the much-reduced levels seen in oil palm plantations."
The research team also noted surprising variability in ecosystem responses. Lead author Dr. Charlie Marsh, previously at Oxford and now at the National University of Singapore, remarked, "Our study demonstrates that focusing on any single component of the ecosystem may lead to incomplete understanding of how the ecosystem responds as a whole. We observed increases, decreases, or no change at all in different aspects. When making decisions concerning land management and conservation, we must consider a broad suite of ecological properties."
Research Report:Tropical forest clearance impacts biodiversity and function whereas logging changes structure
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