Ecosystem multi-functionality in tropical heath forests

Tropical heath forests comprise a unique habitat prevalent in Borneo, covering approximately 10% of the land surface. Heath forests (HFs) are home to many rare species, and have specialised vegetation with high nutrient-use efficiency, suggesting that the highly acidic sandy soils (podzols) that underlie these forests cause vegetation stress. Indeed, the local name, kerangas, meaning ‘land that will not grow rice’ recognises the edaphic stresses posed by this fascinating forest ecosystem (refs 1, 2).

Despite the high conservation value of heath forests, their relative scarcity, and increasing risk of disturbance/degradation, little is known about how these forests form and what factors control their distribution, diversity and ecosystem functioning. The profusion of insectivorous plants in the forest, and the characteristic thick, small leaves of the vegetation, suggest that HFs are strongly limited by soil nutrients, primarily nitrogen (refs 3, 4). If this is correct, the large increases in nitrogen deposition projected for the region (ref 5) may alter the species composition and hence influence multiple ecosystem functions of these tropical heath forests. To understand the relative impact of nitrogen (N) and soil acidity on soil properties, tree growth and performance in heath forest, in 2016, we established a fertilisation/liming (to reduce soil acidity) experiment in the Sepilok forest reserve in Sabah (Malaysian Borneo) (ref 6, 7). Results suggest that while soil acidity is important in explaining tree species distributions in heath forests (ref 6) and influences soil mesofaunal activity (ref 7), N appears to play a greater role in litter decomposition (ref 7) and tree growth (ref 3).

Soil resource availability can affect both above- and below-ground biodiversity, with knock-on effects on multiple ecosystem functions (ref 8). Yet, it is unclear which aspects of forest biodiversity and their associated traits might affect particular ecosystem functions. Capitalising on the established experimental research infrastructure, and support from UK supervisors and Malaysian colleagues, this PhD project will further explore how soil properties influence the functioning of tropical heath forests. The PhD student will be encouraged to develop the project to address research questions in line with their particular interests. Questions will address how long-term (5+ years) N and lime addition affects the biodiversity of different forest-dwelling taxa and their traits, and link these to measurable aspects of forest functioning and ecosystem service delivery. The results will help to predict the impact of N deposition on heath forests’ biodiversity and organismal multi-functional relationships.

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Copyright Dr. Francis Brearley


The student will maintain the already established fertilisation/liming experiment in Malaysia by continuing the treatments of forest plots every six months. They will undertake two fieldwork campaigns of at least six months each, supported by colleagues at the Sabah Forest Research Centre. Field and laboratory work may include assessing tree diversity, understorey plants, soil fauna, and soil micro-organisms within the experimental plots using standard survey techniques or molecular methodologies for soil microbes. Forest productivity and nutrient cycling will be measured by tree growth rates, collecting litterfall, observing reproductive activity, analysing foliar nutrients and measuring fine root production. Soil nutrients will be measured by standard laboratory techniques.

Project Timeline

Year 1

Months 1-6: Review literature to plan research questions and field activities. Apply for visas and research permission. Training as required and attendance at IAPETUS activities.
Months 7-12: Initial field visit and field work in Borneo.

Year 2

Year 2: Analysis of samples collected in year 1. Second field work period of c. six months. Training as required and attendance at IAPETUS activities.

Year 3

Year 3: Completion of sample analysis, data analysis start writing thesis, prepare manuscripts for publication and conference presentation.

Year 3.5

Complete thesis and writing manuscripts.

& Skills

Specific training needs for the PhD will be identified by the student and supervisors and will be provided by the supervisory team institutions, IAPETUS DTP, or specific courses such as the tropical plant identification course run by RBG Kew. Training will cover transferable skills, such as statistics, ecological modelling, soil analysis, plant identification, presenting research and writing papers for publication. As part of the IAPETUS DTP, the student will automatically be registered for a mini MBA at Durham University and a Postgraduate Certificate in Environmental Methods, to recognize the transferable skills developed. The student will gain experience in working overseas in a challenging environment and will develop an international network of colleagues.

References & further reading

(1) Proctor (1999) Botanical Journal of Scotland 51, 1-14.
(2) Vernimmen et al. (2013) Biogeochemistry 113, 385-403.
(3) Dent et al. (2006) Plant and Soil 288, 197-215.
(4) Sellan (2019) PhD Thesis, Manchester Metropolitan University.
(5) Phoenix et al. (2006) Global Change Biology 12, 470-476.
(6) Sellan et al. (2019) Plant and Soil 438:173-185.
(7) Sellan et al. (2020) Pedobiologia 80, 150645.
(8) Yuan et al. (2020) Journal of Ecology 108:2012-2024.

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