Imperial College researchers, in collaboration with researchers from Universiti Malaysia Sabah, have found that after logging in the Borneo rainforest ecosystem processes like litter decomposition and seed dispersal are disrupted due to decreased abundance of key invertebrates.
These ecosystem processes do not come to a complete halt – instead, certain small mammals, amphibians, and birds step in to carry out these processes.
To discover the role of invertebrates in seed dispersal in primary (untouched, ancient) forest and logged forests, the researchers excluded invertebrates from access to seeds in both primary and logged forest and then tested dispersal rates. They found that the invertebrate contribution to dispersal is far more important in primary forest than in logged forests.
This is because vertebrates now carry out many of the essential ecosystem functions in logged forest in the absence of the invertebrates. So why are the invertebrates unable to carry out their ecological role of seed dispersal in logged areas, and why do vertebrates take over?
The researchers say the most likely explanation for the invertebrates’ inability to maintain their role is the changed microclimate. Logging opens gaps in the rainforest canopy, increasing the forest’s overall temperature. Soft-bodied invertebrates like earthworms and termites are particularly sensitive to drying out in heat, so their numbers have dropped in logged forests.
Vertebrate groups probably increase in abundance because of increased resource availability. Researchers found that logged forests were twice as likely to contain trees that are fruiting or flowering and the total invertebrate biomass was doubled in logged relative to primary forest, mainly with insects that do not disperse seeds. Thus, the vertebrates have plenty of food.
This study reassures us that certain ecosystem processes in tropical rainforests are considerably resistant to the human disturbance of high-intensity logging, because creatures other than invertebrates are able to perform the same functions.
However, vertebrates are increasingly under pressure from a range of human activities, so these functions are still at risk of disappearing altogether. The conservation value of logged forests is immense, because they will allow us to understand how ecological processes underlying ecosystems are altered upon human intervention.
Stephanie Sammann is studying for a MSc in Science Media Production
Images: Top: Sustainable logging in Sandakan (FSC certified) by Angela Sevin; Bottom: adapted from Logging by Budi Nusyirwan (Flickr, Creative Commons)