Decadal recovery of fungal but not termite deadwood decay in tropical rainforest

Deadwood represents ~11% of carbon stocks in tropical rainforest ecosystems and its decay is driven largely by fungi and termites, which contribute to the cycling of carbon and nutrients. Due to land use change, such as forest clearing, secondary growth tropical rainforests are increasingly prevalent around the globe. In secondary growth rainforest, studies found lower decay rates of leaf litter; however, little is known about how deadwood decays in these forests. Here, we tested whether termite and fungal species richness, composition and functions in decaying deadwood were similar in secondary and old-growth tropical rainforests. We assessed termite ability to discover and consume deadwood, as well as fungi community composition and contributions to wood decay. We placed non-native pine blocks, half of which were accessible to termites, in an old-growth rainforest site as a reference and two secondary growth rainforest sites that were restored 4 and 8 years before the start of the experiment. Blocks were harvested every 6 months for 4 years (eight harvests). Using fungal ITS amplicon sequencing of sawdust samples from the decaying deadwood blocks at the seventh harvest, we determined wood-dwelling fungal community composition. We found that termites discovered similar proportions of deadwood across the secondary and old growth rainforest sites, although the decay rates of the discovered deadwood were lower in the secondary growth rainforest. Further, fungal decay was similar to old growth rainforest levels in the older but not younger secondary growth rainforest, where it was slower; although differences among sites were small. Wood-dwelling fungal communities were similar between secondary and old growth rainforests. Synthesis and applications. Contrary to common assumptions, fungal communities and their wood decay functions were resilient and recovered relatively quickly within secondary growth rainforests; however, those of termites did not, which could reduce carbon and nutrient cycling in secondary growth rainforests. Active management methods such as the local transplant of termite- and fungi-occupied logs could accelerate the recovery of these ecosystems.