An area bigger than the entire Indian landmass is now used for timber production in the tropics. This logging is largely selective and leads to degradation with loss of specialist species and ecosystem services like carbon storage. However, many have also argued that these forests should be considered a priority for protection since they are at danger of conversion to other land-uses such as agriculture. In addition the impact of logging on tropical forest biodiversity appears to be less negative than other human impacts.
However, simply saying that logging is a less damaging option when compared to other way in which humans exploit forests misses a lot of what is going on. Logging operations differ massively from place to place in terms of the volume of trees cut for timber, the area affected by logging, the distance between logged and unlogged areas, I could go on… All of these differences have the potential to influence the the effect of logging on biodiversity.
It was with a mixture of dread and excitement that I saw a recent paper looking at just this (I recently had an article I have produced that looks at similar stuff rejected. For the third time.) Thankfully, the paper by Zuzana Burivalova and colleagues doesn’t quite cover the same ground as my work, allowing me to breath a sigh of relief. Their meta-analysis took data on the species richness of animals from logged forests and compared it to that of nearby primary forest plots to gauge the impact of logging and then then attempted to explain between site differences using a variety of different variables.
The paper shows that species richness of all birds, mammals, amphibians and invertebrates varies with the intensity of logging, but that importantly there are differences in how each group responds. As you can see from the graph above the richness of mammals, amphibians and invertebrates tends to be reduced with increasing intensity, but bird species richness actually shows a gradual increase. However, this increase in bird richness seems to be as a result of an influx of generalist species, with increasing intensity leading to a reduction in specialist species.
This study is the first to indicate the importance of considering variation in logging practices when assessing their impact on biodiversity. Some of my work from my PhD has also suggested that logging intensity is key to predicting impacts on both trees and carbon storage. Both this study and my work suggest that intensity of logging is an important driver of patterns, but relatively few studies attempt to account for the variation in logging impacts (but see the great work of people like Lucas Mazzei et al for an example of this). It is broadly true that many studies that look at land-use change fail to consider that there may be gradients of degradation within sites. I am starting to get really interested in using these gradients of degradation to look at how they relate to biodiversity and ecosystem service provision, so hopefully you will see more about this in the near future.
Getting back to the subject of this post, despite the important role of logging intensity in driving patterns of biodiversity change what to do in order to balance biodiversity and timber production goals is still an extremely difficult question to answer. High logging intensity appears to be bad for biodiversity and carbon storage, but actually seems to be linked to faster population recovery for commercially important species. This obviously presents a trade-off between the two goals that is difficult to fix. Possible options include Reduced Impact Logging (RIL) which attempts to reduce damage to non-timber trees through a variety of methods, reduction in the area of blocks used for logging in order to encourage recolonisation of forest specialists post logging, and retention of features such as old, hollow trees that may be keystone structures in these forests. To answer these questions collaborative networks like the tropical managed forests observatory are key (if someone working there reads this, get in touch I’m always happy to analyse your data for you 😉 ) as are collaborations with logging companies.