Logging affects many of the world’s tropical forests, this new study examines whether the ecological health and functionality of these ecosystems.
Tropical forests, after logging, are often considered degraded because they have lost vegetation structure, biomass and carbon stocks. But there has rarely been analysis of whether the ecological health and functionality of these ecosystems are similarly degraded.
A new study by Dr Matthew Struebig study published in Nature tackles this issue through the perspective of ecosystem energetics – the cascade of energy from plants to mammals and birds through the food they consume. The research team, including SAC conservationists with conservationists from Oxford University, combined more than 36,000 tree, root, and canopy measurements with population data on 248 vertebrate species from old-growth forests through logged forests to oil palm plantations in Borneo. The study suggests that this ecological energy flow can be a holistic measure of the ecological vibrancy of the ecosystem.
Remarkably, the study found that the ecological energy flow through the logged forest was 2.5 times greater than in the old-growth forest, before collapsing in the oil palm plantations. The logged forest supported similar or greater densities of almost all bird and mammal species. The main reason for this is probably because logged forest vegetation is more palatable or ‘tastier’. Old-growth forests tend to be slow-growing, and plants defend themselves from herbivores (especially insects) through complex chemical defences, but logged forests are flooded with light, and plants prioritise rapid growth rather than chemical defence, so their leaves are less toxic and more nutritious. These tastier leaves support a high population of herbivores (especially insects), which in turn support more predators such as many birds. The flood of light also means there is more vegetation near the ground, where it is more accessible by large herbivores like elephants or deer.
The study required meticulous counting of almost all bird and mammal species in the remote study sites, as well as measuring the growth rates of trees and their leaves and roots.
Professor Yadvinder Malhi (Lead author), University of Oxford, said: ‘We were very surprised by how much more energy was flowing through the logged forests compared to the old-growth forest, and that it was flowing through the same diverse range of species found in the old-growth forest. We had not expected the logged forest to be so ecologically vibrant.’
Dr Matthew Struebig, joined DICE in 2010, initially as a Leverhulme Trust Research Fellow. He now leads the Tropical Defaunation Hub, launched in 2020 with a ~£1 million investment from the Leverhulme Trust to study the socio-ecological drivers of wildlife population change in Indonesia. The interdisciplinary team comprises specialists in biodiversity, spatial statistics, remote sensing and poverty assessment.
‘In the early morning, ornithologists listened out for birds, while evenings were spent catching bats in special traps. Meanwhile, trail cameras and cage traps over 77,000 combined nights provided much-needed information on secretive and elusive mammals, from tree shrews, sun bears and elephants.’
The authors emphasise that old-growth forests still hold immense ecological value and high carbon stocks, and need to be left intact where possible. But this study questions the labelling of logged forests as ‘degraded’ when they are so ecologically vibrant. Such labelling can mean these logged forest landscapes are seen as lower priorities for protection and are cleared to make way for agriculture such as oil palm.
The study was conducted in the forest landscapes of Malaysian Borneo. Co-author Robert Ewers highlighted: ‘Ecologists often just study one aspect of an ecosystem, like its trees or its birds. This study shows how meticulous and joined-up research across a wide range of species can yield surprising and important new insights into the nature of ecosystems in a human-dominated world.’