Reforestation offers an effective mechanism for climate mitigation, and the global momentum for reforestation has never been stronger . Ambitious goals set by the Bonn Challenge in 2011 aim to reforest 350 million hectares of degraded land by 20301. Reforestation in tropical regions offers the biggest gains in ecosystem services and biodiversity, but active reforestation is costly . However, forests also naturally regenerate with no active management  or economic input on abandoned farmland across the tropics. Today more than 50% of remaining tropical forests are secondary and degraded3. These naturally regenerating secondary forests could be harnessed to meet large-scale reforestation targets. The problem is that natural reforestation rates and trajectories are unpredictable and therefore not integrated into national reforestation strategies .
Theories to explain successional change in tropical forests have focused on how shifting abiotic resources (e.g. light) drive changes in tree communities over time [5,6]. In contrast, the role of biotic factors (e.g. pathogenic and mutualistic fungi) in determining succession has largely been ignored, and yet studies have shown that interactions between plants and soil fungi play a critical role in shaping plant communities in undisturbed tropical forests [7,8]. Plant-soil feedbacks (PSF) can be driven by soil pathogens and/ or mutualistic mycorrhizal fungi [8,9] and may shape regenerating tree communities in a variety of ways. For example, host-specific pathogens may accumulate under host trees over time resulting in greater seedling mortality . In this way, plant-pathogen interactions may drive ecological succession, causing shifts in species composition over time as different plant species rise and fall in abundance due to pathogen pressure. In contrast, mycorrhizal fungal associations may have a protective effect on recruiting tree seedlings; increasing growth and reducing susceptibility to drought and disease . However, the composition and abundance of soil fungal communities can shift following forest disturbance [12,13] and suitable mycorrhizal fungi may be absent or present in insufficient densities to enable seedling establishment limiting recruitment of late successional tree species .
Changes in abiotic environment and tree communities during tropical forest succession are well described but by comparison we know very little about soil microbe communities in secondary forests or their impacts throughout succession. This project will describe microbial communities in secondary forest soils and experimentally test the role of plant soil feedbacks in shaping the composition and rate of change in tree communities over secondary succession. The project will address the following questions:
1. How do microbial communities in forest soils change after disturbance and during succession?
2. How do plant-soil feedbacks shape the speed and trajectory of succession?
3. What are the relative roles of plant-soil feedbacks and abiotic environment in determining successional change?
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DJI_0163.jpg – Danum Valley Conservation Area, Malaysia