Shrub climate sensitivity across boreal, subarctic and tundra ecosystems

This project will examine the physiological responses of shrubs to environmental changes in tundra, sub-arctic and boreal ecosystems. The research will reveal how sensitive shrubs in these ecosystems are for drought and frost stress.

High-latitude ecosystems are warming twice as fast as the global average and are considered to be especially sensitive to climate warming. Concurrent with warming, the expansion of shrubs and trees across high-latitude ecosystems is one of the most dramatic ecological manifestations of climate change. Yet, the climate sensitivity of shrubs across ecotones from the boreal forest to Arctic tundra and the sensitivity of shrubs to drought and frost is under studied.

Changes in shrub cover influences nutrient cycling, carbon storage, and the reflectance of energy at high latitudes, thus creating climate feedbacks that could affect the planet as a whole. Even in boreal ecosystems, carbon uptake by shrubs (and other ground vegetation) can make up 10 – 20% of the whole ecosystem carbon uptake. In addition to these direct effects, shrubs also provide a buffer between air and soil affecting soil temperature and moisture, which are crucial factors in many ecosystem processes, including decomposition and tree water usage.

Climate warming, winter thaw events and resulting frost damage and changes to soil moisture could be influencing boreal shrub growth. However, our understanding of the varying factors underlying changes in shrub cover and growth in high-latitude ecosystems is still limited. And boreal forest shrubs have suggested to have much lower climate sensitivity of growth relative to tundra shrubs.

Research questions:
- Are tundra shrubs more climate sensitive than boreal shrubs?
- Do tundra shrubs have different morphology and wood anatomy to boreal shrubs?
- Do tundra shrubs have greater drought and freezing tolerance than boreal shrubs?
- Do tundra shrubs have more climate sensitive and asynchronous above- and below-ground phenology than boreal shrubs?


This PhD project will focus on the ecophysiology and structure of boreal and tundra shrub species and their environmental responses, and compare them between three Northern biomes: the boreal forest, the latitudinal treeline ecotone and Arctic tundra. The recruited student will work with existing dendroecology data, conduct field campaigns to collect new data, work in an established common garden experiment and carry out experiments in controlled laboratory conditions. The work will inform Earth system models to improve future projections of climate change impacts in high latitudes particularly from the boreal forest to Arctic tundra.

The study will be conducted across Northern field sites that represent tundra, sub-Arctic and boreal ecosystems (Fig. 1). Weather and ecosystem scale gas exchange data is available from all these sites. The laboratory experiments will be conducted in the University of Edinburgh premises and the Tree ecophysiology laboratory in the University of Helsinki premises. The project is joint between the Universities of Edinburgh and Helsinki. The student will be based in both Edinburgh and Helsinki and will spend summers in Finland undertaking field measurements, interacting closely with research groups in both countries.


Requirements
An undergraduate degree in natural sciences to at least upper second level (or equivalent), with quantitative skills including programming in languages such as R or python. It would be advantageous to have a MSc degree. The applicant should be keen to conduct quantitative analysis, field data collection and laboratory work.