Surveying in the lesser studied savannas

Research Lead: Dr Jess Rickenback, Lecturer in Physical Geography, School of GeoSciences, University of Edinburgh

CSFL article author: Rachel Orchard, CSFL digital media officer and PhD researcher, School of GeoSciences, University of Edinburgh

Research recently published by Dr Jess Rickenback provides insights on the grass communities of under-researched savanna ecosystems in Southeast Asia. From field sites in Thailand and Cambodia where savannas are facing multiple threats, Jess investigates the communities of grass species that grow amongst different dominant tree species to explore their cohabiting relationship. 

The article, published in Biotropica the journal of the Association for Tropical Biology and Conservation, draws from fieldwork carried out at five locations across Thailand and Cambodia. The findings demonstrate that in the savanna ecosystems of Thailand and Cambodia, four dominant tree species support distinct grass assemblages.

Read on to hear about Jess’s research experience, including what drew her to exploring Southeast Asia’s savannas, or head straight to the full article following this link: https://onlinelibrary.wiley.com/doi/10.1111/btp.70166

Although it is a dominant form of vegetation across mainland Southeast Asia, the colonial perceptions of savannas as degraded forests has resulted in a lack of botanical understanding. These ecosystems are known to be of critical importance socially by supporting the livelihoods of millions and contributing to the provision of ecosystem services. Yet building an understanding of the ecological dynamics of savannas has so far been under-explored. Despite this, it is an urgent task given the mounting pressures by agriculture and afforestation alongside the changing climate.

Savannas in Southeast Asia have near continuous grass cover and are maintained by fire and/ or grazing, but they are also able to support a range of tree cover, including closed canopy. However, research on these ecosystems so far has prioritised investigating the tree level rather than looking beneath them – they fail to see the grass for the trees. 

In this context, Jess was drawn to explore the missing puzzle piece – the ground layer of these grassy biomes, because the functioning of a savanna ecosystem is dependent on its grassy layer which promotes fire and/or herbivory, maintaining the openness of the landscape.

To gather on the ground data about the identity of the ground-dwelling grasses, Jess and her team set out to Thailand and Cambodia in October and November 2018 to catch the flowering grasses just after the rainy season. Surveying with circular plots across 50 sites, the team gathered information on the grass species richness and diversity, in the four main types of savanna based on the dominant tree species that grow alongside the grassy communities. 

The key research questions they asked were:

1. Do grass communities in savannas differ depending on the dominant tree?
2. If grass communities differ, how many grass species are shared between the savanna ecosystems? 

The four savannas each have distinct characters as well as a dominant tree species as seen below:

Over the two months Jess and her team recorded 160 grass species, with species richness found to be highest in Dipterocarpus and Shorea savannas. Although further research is required to fully characterise the species composition of the distinct savannas, this data provides key insights on the diversity between ecosystems.  While some common grasses overlap between savannas, grass composition varies under each of the different dominant tree. This suggests that the dominant tree is influential in the relationship with grass community diversity, as well as abiotic conditions such as soil nutrients and fire. All four savanna types shared at least one of the 25% most common grass species with another savanna, but no grass species was common across all four savanna ecosystems although they were all species that grow from rhizomes, known to be more resilient to changing conditions.

This research contributes to the conversation about valuing the species diversity and ecological role of grasslands and savannas in the face of climate change and pressures from agriculture and afforestation. Let’s not lose sight of the grass!

Interested in reading more? Find the full open-access article by following the link here: https://onlinelibrary.wiley.com/doi/10.1111/btp.70166