Drought cuts back regeneration in logged tropical forests

Lan Qie,Andy Hector,Elizabeth M Telford,Mike R Massam,Reuben Nilus,Hamzah Tangki,Robert M Ewers

doi:10.1088/1748-9326/ab0783

Abstract

Logged tropical forests represent a major opportunity for preserving biodiversity and sequestering carbon, playing a large role in meeting global forest restoration targets. Left alone, these ecosystems have been expected to undergo natural regeneration and succession towards old growth forests, but extreme drought events may challenge this process. While old growth forests possess a certain level of resilience, we lack understanding as to how logging may affect forest responses to drought. This study examines the drought–logging interaction in seedling dynamics within a landscape of logged and unlogged forests in Sabah Malaysia, based on 73 plots monitored before and after the 2015–16 El Niño drought. Drought increased seedling mortality in all forests, but the magnitude of this impact was modulated by logging intensity, with forests with lower canopy leaf area index and above-ground biomass experiencing greater drought induced mortality. Moreover, community traits in more heavily logged forests shifted towards being more ruderal after drought, suggesting that the trajectory of forest succession had been reversed. These results indicate that with reoccurring strong droughts under a changing climate, logged forests that have had over half of their biomass removed may suffer permanently arrested succession. Targeted management interventions may therefore be necessary to lift the vulnerable forests above the biomass threshold.

Highlights

More than half of the world’s tropical forests exist in various disturbed states due to historical or ongoing human activities, such as logging and shifting agriculture
The Stability of Altered Forest Ecosystem (SAFE) landscape consists of a broad gradient of forest disturbance from unlogged tropical lowland forest through to severely logged forest and oil palm plantations(Ewers et al, 2011)
Across the study landscape woody seedling mortality rate over the drought interval during 2015-2017 was 26.0 % yr-1, on average 10.3 % yr-1 higher compared to the pre-drought interval 2012-2015 (15.7 % yr-1, CI 13.7-18.1, p

Summary

Introduction

More than half of the world’s tropical forests exist in various disturbed states due to historical or ongoing human activities, such as logging and shifting agriculture. While old growth tropical forests are important in conserving species diversity(Gibson et al, 2011) and helping to take CO2 out of the atmosphere (Qie et al, 2017), logged tropical forests are increasingly recognized as harbouring great potential for providing much of the same benefits, especially if they recover from past disturbance and progress towards older growth states. Regenerating tropical forests have the potential to provide carbon sinks on par with, or even greater than, intact tropical forests (Rutishauser et al, 2015). In which species assembly and ecological processes progress towards predisturbance state through secondary succession, may be the most cost-effective route of forest regeneration (Chazdon and Guariguata, 2016). The forest succession pathways, depend on land-use history, soil conditions, seed pool and dispersal processes often mediated by animals

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Conclusion