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Understanding tree rings – how the interplay of climate and seed production controls tree growth


Project Description

Tree rings have a broad range of applications in environmental science including quantifying forest growth, carbon storage, and the reconstruction of Holocene climate. Many of these applications depend on understanding the drivers of variation in tree ring width (TRW). For example, narrow tree rings associated with drought events are used as an indicator of forest vulnerability to climate extremes, and the relationship between temperature and TRW forms the basis of climate reconstructions.

Recently, a number of studies have shown that an important driver of variation in TRW is variable resource allocation – i.e. where a tree “decides” to allocate carbon and nutrients. In particular, allocation to reproduction (flowers and fruits) is a major drain on resources. In many tree species, a bumper seed crop is associated with a narrow tree ring, indicating a growth-reproduction trade-off. A number of recent studies have focused on this phenomenon and its implications in European beech (Fagus sylvatica) (Hacket-Pain et al., 2015, 2017, 2018). However, these conclusions urgently require testing for other species, particularly those used in tree-ring based climate reconstructions. For example, narrow tree rings resulting from bumper seed crops may influence the calibration of TRW-climate relationships used for climate reconstruction.

Project Summary:
This project will develop new tree ring chronologies to complement existing records of annual seed production in the main European tree species. Time-series of annual seed production will be sourced from the MASTREE database (Ascoli et al., 2017a), and from MASTREE+, a new expanded global dataset currently in development as part of the NERC-funded project “MAST-NET: masting responses to climate change and impacts on ecosystems” (https://www.liverpool.ac.uk/geography-and-planning/research/mast-net). The student will be integrated into this network, providing opportunities for collaboration with institutions in North America, Europe and Japan. The student will be responsible for the development of tree ring chronologies from sites represented in MASTREE and MASTREE+. This will require field campaigns across Europe, and potentially further afield (e.g. North America). Field campaigns will be supported by the recently established Liverpool tree ring laboratory, with additional local support from existing collaborators. Field sites will include locations in Sweden, Germany and the Alps (Switzerland, Italy and Austria).
The objectives of the project will be to assess the potential impact of seed production on tree-ring-based climate reconstruction, using both TRW and Blue-Intensity (BI, a novel new proxy for wood density). The candidate will also develop methods to distinguish between masting- and climate-related variability in TRW and BI chronologies (i.e. identifying whether a narrow tree ring has resulted from a bumper seed year – a “mast year”) – or a climate anomaly). Tree ring and seed production datasets will be combined with climate data, obtainable from the KNMI Climate Explorer. For example, monthly gridded CRU data is available at a resolution of ~50km from 1901-present.
There is substantial scope for the student to develop additional objectives. For example, the datasets developed by the student could provide the basis for the development of unique multi-century reconstructions of mast years. Alternatively, as inter-annual and decadal variation in seed production is influenced by climate (Vacchiano et al. 2017; Ascoli et al. 2017b), masting can create an indirect pathway for climate to influence tree growth. This has been tested in European beech (Hacket-Pain et al., 2015, 2018) but remains unexplored in other tree species.

Tree ring chronologies will be developed in Liverpool. In addition to ring width measurements, the student will develop Blue-Intensity chronologies. An opportunity to measure wood anatomical traits also exists with external collaborators. Furthermore, stable isotope analysis could be conducted using local stable isotope facilities (LIFER lab) and/or dendrochemistry using the scanning XRF – for example to conduct the first tests for isotope or elemental signatures associated with mast years. Training in dendrochronology will be provided by the tree ring lab in Liverpool, and through participation in dendrochronology fieldweeks (e.g. http://siberianschool2018.sfu-kras.ru/index.html), external lab visits, and activities organised by the Association of Tree-Ring Research https://tree-ring.org/. The candidate will also have the opportunity to participate in other fieldwork organised by the lab – in the last twelve months this has included trips to Canada (Northwest Territories) and the Italian Alps. The candidate will have opportunities to present research at the ATR TRACE conference, and other conferences and meetings (e.g. EURODENDRO, EGU).

Funding Notes

Full funding (fees, stipend, research support budget) is provided by the University of Liverpool. Formal training is offered through partnership between the Universities of Liverpool and Manchester in both subject specific and transferable skills to the entire PhD cohort and at each University through local Faculty training programmes.

References

Ascoli, D., Maringer, J., Hacket-Pain, A., Conedera, M., Drobyshev, I., Motta, R. et al. (2017a). Two centuries of masting data for European beech and Norway spruce across the European continent. Ecology, 98, 1473

Ascoli, D., Vacchiano, G., Turco, M., Conedera, M., Drobyshev, I., Maringer, J. et al. (2017b). Inter-annual and decadal changes in teleconnections drive continental-scale synchronization of tree reproduction. Nature Communications, 8.

Hacket-Pain, A.J., Friend, A.D., Lageard, J.G.A. & Thomas, P.A. (2015). The influence of masting phenomenon on growth-climate relationships in trees: explaining the influence of previous summers' climate on ring width. Tree Physiology, 35, 319-330

Hacket-Pain, A.J., Lageard, J.G.A. & Thomas, P.A. (2017). Drought and reproductive effort interact to control growth of a temperate broadleaved tree species (Fagus sylvatica). Tree Physiology, 37, 744-754

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