ACCE+ DLA programme: Effects of climate extremes on the reproduction of trees: how does drought affect seed production?

Background

Reproduction is key to the resilience of forests, but we know little about its response to climate change. For example, severe summer droughts increase tree mortality and reduce tree growth, but for most species we don’t know how seed production responds. The response is hard to predict and likely varies between species; for example there is evidence that some species maintain seed production at the expense of growth when experiencing drought (“fight or flight” strategies). Furthermore, the regeneration of forests requires seeds to germinate and establish, so multiple stages of the demographic process are potentially vulnerable to drought. This project will leverage existing long-term monitoring datasets, study of archived samples, and new lab- and growth-chamber experiments at Kew to investigate the sensitivity of tree reproduction to severe drought, focusing on key temperate tree species from both hemispheres. Tree seed production is typically highly noisy, with strong variability among years, so the project will draw on >1000 long time-series of seed production available from the MASTREE+ database, incorporating >30 species from four continents. Combining these datasets with climate data, the project will test the response of seed production to severe droughts, and quantify how this varies across species and across climate gradients. Germination success also depends on seed quality which may be sensitive to summer drought during seed development, independent of any effect of seed quantity. Therefore, the project will measure how seed traits change in response to summer drought. This will rely on facilities at Kew, such as X-ray imaging to measure seed fill, damage and infestation. Finally, the project will test for the effect of drought stress on seed germination and establishment in UK trees. Finally, lab-based germination experiments at Kew will assess whether seed dormancy, viability, germination rate, and subsequent seedling development are affected by the occurrence of drought during seed development.

Objectives

1. To quantify the response of tree seed production to summer drought, and how this varies across species and climate gradients
2. To investigate how key seed traits vary in response to summer drought
3. To characterise the sensitivity of tree seed germination and establishment to summer drought

Novelty & Timeliness

Climate change, and other interacting pressures such as pests and pathogens, are applying increased pressure on forest ecosystems. Severe drought is leading to increased forest dieback, elevated mortality and severe declines in tree growth, but the long-term resilience of forests – and their species composition – will ultimately depend on the success of tree establishment. This is the case for forests that naturally regenerate, and planted forests that rely on sufficient seed supply to tree nurseries. Consequently, understanding whether severe drought reduces seed production, and the sensitivity of germination and establishment, have emerged as major priorities if we are to fully understand forest resilience to climate change. 

Training & Research environment

The student will develop field- and laboratory skills, including at the world-leading facilities at Kew. In addition to their primary registration at the University of Liverpool, the student will be registered at Kew, joining a network of >100 Kew-affiliated PhD researchers and providing access to Kew facilities, collections, training and events. The project has been developed in collaboration with Defra, and the student will be mentored by the Defra Plant Health R&D manager, exposing them to the intersection of science and policy. 

How to apply

Please see the ACCE website for all details of how to apply to the programme at each ACCE+ institution: https://accedtp.ac.uk/how-to-apply/. 

All applicants to ACCE+ must complete the ACCE+ personal statement proforma. This is instead of a personal/supporting statement or cover letter. The proforma is designed to standardise this part of the application to minimise the difference between those who are given support and those who are not. Candidates should also submit a CV and the contact details of two referees.

Part-Time Study Options

All ACCE+ PhDs are available as part time or full time, with part time being a minimum of 50% of full time. Please discuss potential part time arrangements with the primary supervisor before applying to the programme. 

Project CASE Status

This project is not a CASE project.