Are tropical tree communities shaped by processes in the seed-to-seedling transition?

Summary

This project will examine how seed traits and key processes such as seed production, predation and the microbiome influence seedling establishment, demography and composition in intact and disturbed tropical forests.

Project background

Tropical forests host a vast number of plant species, which has generated substantial scientific enquiry on how such high levels of diversity arise and are maintained, but disturbances may disrupt processes that regulate diversity. A key stage in determining the composition of plant communities is the flower-to-seed-to-seedling transition, which is the key focus of this project. Several important ecological processes play a role at this life stage: reproductive triggers, seed production, viability, dispersal, germination, establishment and interactions with microbes, herbivores and the environment.

Seed production and seedling dynamics are particularly fascinating in Southeast Asian tropical forests. Here, reproduction is dominated by interannual mass flowering and fruiting events where the majority of trees in the forest canopy flower and fruit in synchrony (Brearley et al. 2016). However, some species reproduce more regularly, and these differences may be connected to seed and seedling traits, dispersal modes and interactions with fauna. We still lack understanding of how these differing cycles impact the resulting seedling community.

Survival in the understory is thought to be strongly influenced by positive and negative microbial associations, and their interactions with the availability of key growth resources. For example, the Dipterocarpaceae rely on ectomycorrhizal symbioses, whilst high densities of conspecifics can drive the presence of pathogens and pests, causing higher mortality rates in those species (namely, density-dependent mortality, O’Brien et al. (2022); Liang et al. (2020).

We especially lack a good understanding of how landscape-level disturbances, such as logging, affect reproductive processes, resource availability and dominant plant-soil feedbacks, including interactions with mutualists and pathogens that determine seedling demographics. These processes may have implications for ecosystem recovery and our approach to restoration (Bartholomew et al. 2023; Banin et al. 2023). 

This project will use a unique long-term monitoring set-up in Sabah, Malaysian Borneo, which encompasses both intact forest areas and previously logged and restored forests to unpick the key processes shaping community dynamics and how these may shift under anthropogenic environmental change.

Research questions

1. How does forest disturbance affect phenological, flower and seed functional and dispersal traits within SE Asian plant communities?
2. What is the rate of seed viability and recruitment of species fruiting outside of masting events?
3. How does the microbial community vary according to seedling and adult tree composition and diversity?
4. Are seedling dynamics related to conspecific density via the microbiome?

Further details can be found here: https://e4-dtp.ed.ac.uk/e5-dtp/supervisor-led-projects/project?item=1715

This project is co-supervised by Dr Ashish Malik at University of Edinburgh and Prof David Burslem at University of Aberdeen.