Understanding resilience in garden flora within the context of a changed climate

This project will investigate how different stress factors (water availability, temperature, wind) interact to affect plant performance. There will also be a scoping study to determine what traits plants in natural ecosystems possess that could be linked to enhance stress tolerance.

We are seeking a highly motivated student with honours degree (1st or 2:1) in plant biology, horticulture, ecology, environmental science or similar, and an MSc / MRes in a relevant subject.

How to Apply

Applicants should apply via our PGR Application System by 22 September 2023

1. Applications must include 2 references
2. Applications must include a 2 page CV in the supporting documents
3. Applications must include a covering letter in either the Research Proposal section or in the supporting documents
4. Applications must list Professor Ross Cameron as the potential supervisor

All enquiries to Prof Ross Cameron r.w.cameron@sheffield.ac.uk

Project Title: UNDERSTANDING RESILIENCE IN GARDEN FLORA WITHIN THE CONTEXT OF A CHANGED CLIMATE

Start and End dates: Jan 2024 – December 2028 (4.0yr)

University: Landscape Architecture, University of Sheffield

Supervisors: Prof Ross Cameron (University of Sheffield), Dr Alastair Culham – (University of Reading), Prof Alistair Griffiths (RHS) & Dr John David (RHS)

The Question - What garden flora have resilience to a changed UK climate?

Climate change will radically change UK natural and cultivated flora. Even if global warming is held to an increase of 1.5-2.0oC, the UK climate is likely to shift to that of one currently prevalent 1200 km to the south within the next 30 years (Bastin et al., 2019). Moreover, increased volatility in the climate will mean more variance in climatic patterns, increased frequency of weather extremes and sudden changes in weather (Webster et al., 2017). UK gardeners are attempting to predict what sorts of plants are going to survive these conditions. Rather than this being a guessing game, UK gardeners (and other stakeholders in the horticultural sector) need some guidance on the type of plants that 1/ can remain viable 2/ perform in a garden setting and 3 / continue to provide ecosystem services and support biodiversity within the context of more variable and extreme weather events (Lewis et al., 2019). Thus, the aim of the proposed research is to determine what denotes plant resilience in the face of a changing climate. Through a better understanding of what confers resilience, we should be better able to predict what plants (or types of plants) we need to plant for the future?

The proposed project will address the following questions:

• Are there key plant traits or ecological adaptations that help confer resilience to the multiple abiotic stresses predicted with a changing climate – specifically drought, flooding, high temperature, rapid temperature changes and wind?
• What can be learned by investigating plant distribution and ecophysiology, with respect to surviving predicted weather extremes? Are there certain plant types that have tolerance to multiple stresses – e.g. species that thrive in dry river-beds where there will be periods of extreme dryness, but also periods where the plant experiences inundation with water.
• What trends may already be apparent in identifying ‘winners’ and ‘losers’ within our current garden flora?
• Can we develop simple, effective empirical methods to test for stress resistance (against a single stress or compounded multiple stresses). Tests that could be used across a wider range of plant taxa at the end of this project.

Why is it important and interesting?

Like almost every other aspect of our society, climate change has the potential to radically alter our gardens and the culture around gardens (Cameron, 2023). Gardeners are challenged by the mixed messages that climate impacts imply. On the one hand, warmer temperatures and higher atmospheric CO₂ levels may encourage plant growth and theoretically, enable a wider range of taxa to be grown in the UK. Conversely, shifts in climate patterns and increased variability in the climate, culminating in more extreme weather events may undermine plant cultivation, especially when plants are exposed to a range of stress factors in relatively short time intervals (Lewis et al., 2019). Gardeners are looking to the RHS to give some guidance on what sorts of plants are likely to survive and continue to perform well, as climate change progresses. To do so, we need a better understanding of what resilience means in terms of plant survival within a changed climate, and to match better the predicted stress factors to subsequent plant performance (Lewis et al., 2017; Sari and Karasah, 2020).

Already we are seeing some trends in garden style as people predict the impacts of climate change, with Mediterranean genera becoming more popular and plant designs based around dry steppe / prairie communities being promoted more frequently (Entwhistle et al., 2017; Hoyle 2021; Tomatis et al., 2023). Another ‘school of thought’ though, suggests it really will only be the most robust, existing garden taxa that will remain useful, as these have the greatest array of traits for survival anyway (Lewis et al., 2019). Research is needed to clarify these points and help develop principles for the types of flora we should be considering as climate change accelerates, and what are the implications for garden design and ecology.   

Objectives

1. To develop effective methods to link climate change scenarios to empirical models that promote practical understanding of what plants will survive / function and those that won’t. I.e. develop methods that allow us to test plant responses to the stress factors outlined above, (both singly, but also in combination). Ideally, simple methods developed here could be adopted elsewhere and support wider trialing after the PhD finishes.
2. To link plant ecophysiology and traits to climate resilience capacity, (e.g. better resilience within a genus linked to smaller leaves, or slower growth rates).
3. To investigate if plant natural distribution (climatic niche?) gives us clues to what might provide resilience. Do taxa that are widely distributed reflect greater abiotic stress tolerance? Do flora associated with specific habitats (halophytes, thermophiles etc.) provide insights on key traits that underpin resilience? Are there existing climates that relate to the climate models for the UK climates, and what adaptations do flora there possess that ensure survival?
4. To determine what trends gardeners are already experiencing – are we seeing certain cultivars within a genus showing more or less resilience than others? This would take the form of an on-line questionnaire with follow-on interviews with e.g. head gardeners.
5. To test plant viability against a range of abiotic stress factors associated with climate change, and to modify plant selection within the research, as information from objectives 2-4 feeds in.
6. To disseminate the results of the research to RHS members and wider.
7. To assess if data collected and methods developed could help initiate a Resilience Index for garden flora (similar to the RHS Hardiness Ratings).

Proposed outline:

Due to climate change, the average projected temperature increase in Europe ranges from 2.1 °C to 4.4 °C over the next 75 years (Alizadeh and Hitchmough, 2019). Southern England will experience drier summers and wetter winters; a drift towards near-Mediterranean conditions (Murphy, 2009). However, climate models also suggest great variance within these climatic changes – namely more rapid oscillations in precipitation and temperature events, as well as considerable uncertainty on wind and storm patterns. These two distinct phenomena associated with climate change are making it difficult to predict what UK landscape flora may look like in future. Building on previous work (e.g. Alizadeh and Hitchmough, 2019; Lewis et al., 2019) the proposed research aims to evaluate how different garden plant types/communities will stand up to the stresses imposed by climate change.  It will give a steer to what principles gardeners and landscape designers need to adopt to ensure a viable plant palette; and that this palette remains fit for purpose (plants still provide effective floral displays, support wildlife etc.; Cameron, 2023).

Plants representing important garden genera will be evaluated against a range of climate change scenarios, namely variations based on temperature extremes, drought episodes, periodic waterlogging and wind factors (strength / desiccation potential). Plant survival, growth and functionality (e.g. capacity to still provide flowers, interesting foliage, pollen for invertebrates etc.) will be measured against a matrix of climate variables. A number of empirical experiments using semi-controlled conditions (glasshouses & cabinets) will be set-up using plants in pots to tests response to climate variables, performance after exposure to stress, and capacity to provide resources for wildlife (pollen/nectar) when under stress. An additional experiment will utilise in vivo garden specimens to determine if any alterations in winter weather patterns over the course of the PhD, result in plant injury (e.g. determine damage when a frost follows a very mild winter period).

A group of model taxa will be selected in the first year – with opportunities for other taxa to be included later, if information from literature and global distribution suggest enhanced resilience with these. The review of literature will seek to determine if plants from certain ecotypes possess capacities to tolerate the relevant multiple stresses (e.g. alpine species on free draining sun-facing slopes [drought and wind], riverine species where rivers run dry temporarily [flooding and drought], desert or Mediterranean species with adaptations to store water or carbohydrates [drought and heat]. The search will also investigate if there are current climates that are analogous to those predicted for the UK (for examples ones that experience rapid temperature transitions over short time intervals, including those with high diurnal variations). Flora adapted to these climates and situations will be explored with the aim to identify potential resilience traits. This literature will be scrutinised for garden relevant species.

Model plants (12-16 taxa) for study in the semi-controlled pot experiments, will be selected initially based on anecdotal evidence of relative robustness and resilience to stress within garden flora. These being grouped into 2 categories based on this (‘presumed more robust’ vs ‘presumed more susceptible’). Consultations with relevant members of RHS Plant/Science Committees and Curatorial Staff will help select this initial list. There will be sub-categories of shrubs, herbaceous perennials, corms/bulbs, annuals and conifers. Early experiments will test our hypotheses that anecdotal information around growth rates, biomass, flower productivity and leaf type may give some indications of resilience, in a crude sense.

It is likely, that some plant taxa will be augmented or substituted for alternatives in year 2 of the study, as further information is gained from both 1. A review of the literature based on plant origin with respect to habitat and geographical distribution and 2. Information derived from a questionnaire sent out to professional and keen amateur gardeners building on previous work from the RHS/UoR (Webster et al., 2017). This questionnaire will gain anecdotal information on what taxa are doing well, or already struggling with the impacts of climate change. Questions will be designed to capture opinions on why loss of plant viability may be occurring, i.e. attempt to differentiate effects due to high temperature, low temperature, lack of winter chilling, rapid temperature shifts, drought, waterlogging, wind and possible secondary biotic factors associated with climate change (e.g. greater susceptibility to key pathogens). Information on plant genotypes already suffering / showing resilience against recent climatic shifts, will help identify the sorts of traits that may be linked to longer-term resilience. Empirical pot-based experiments will start in year 1, but plant choice will be reviewed as information from points 1 and 2 above, feed into the project.

Plants, well-established in pots, will be exposed to stress factors associated with climate change including drought stress, waterlogging stress, heat and high wind; including some stress factors being combined in some experiments. After stress exposure, plants will be assessed for survival, degree of dieback or chlorosis, chlorophyll fluorescence, re-growth, subsequent flower number and quality; and where appropriate, the presence of pollen (capacity to continue to be a food source for pollinators).

Garden observations on winter climatic patterns and subsequent injury will augment the pot based experiments. Three RHS Gardens will be chosen with contrasting locations / climates and individual taxa (within 12 genera) will be identified, each taxa being common to each garden to allow direct comparisons. The student will use climatic patterns for each garden to assess impact on plant performance. Two visits per garden (early and late spring) are envisaged in each year of the project. Visual observations and photographs of the plants will be linked to any previous “atypical” weather patterns in each garden. Although results of plant injury from this experiment will be less predictable (we can’t guarantee mild periods and frost!) observing plant development in vivo will aid the student by: - providing greater context through the study of real garden situations, and help them differentiate approaches and their relative values when working in vivo or in semi-controlled conditions.

In addition to a formal thesis and published papers, the PhD will deliver refined recommendations to gardeners and garden / landscape designers on the types of plants to consider in future plantings.

References

Alizadeh, B. and Hitchmough, J., 2019. A review of urban landscape adaptation to the challenge of climate change. International Journal of Climate Change Strategies and Management, 11,  178-194.

Bastin, J.F., Clark, E., Elliott, T., Hart, S., Van Den Hoogen, J., Hordijk, I., Ma, H., Majumder, S., Manoli, G., Maschler, J. and Mo, L., 2019. Understanding climate change from a global analysis of city analogues. PloS one, 14, p.e0217592.

Cameron, R., 2023. “Do we need to see gardens in a new light?” Recommendations for policy and practice to improve the ecosystem services derived from domestic gardens. Urban Forestry & Urban Greening, 80, 127820.

Entwisle, T.J., Cole, C. and Symes, P., 2017. Adapting the botanical landscape of Melbourne Gardens (Royal Botanic Gardens Victoria) in response to climate change. Plant diversity, 39, 338-347.

Hoyle, H.E., 2021. Climate-adapted, traditional or cottage-garden planting? Public perceptions, values and socio-cultural drivers in a designed garden setting. Urban Forestry & Urban Greening, 65, 127362.Hunter, M., 2011. Using ecological theory to guide urban planting design an adaptation strategy for climate change. Landscape Journal, 30, 173-193.

Lewis, E., Phoenix, G.K., Alexander, P., David, J. and Cameron, R.W., 2019. Rewilding in the garden: Are garden hybrid plants (cultivars) less resilient to the effects of hydrological extremes than their parent species? A case study with Primula. Urban Ecosystems, 22, 841-854.

Murphy, P., Thackray, D. and Wilson, E., 2009. Coastal heritage and climate change in England: Assessing threats and priorities. Conservation and Management of Archaeological Sites, 11(1), pp.9-15.

Sari, D. and Karaşah, B., 2020. Future adaptability of urban trees due to the effects of climate change: the case of Artvin, Turkey. Journal of Environmental Science and Management, 23.

Tomatis, F., Egerer, M., Correa-Guimaraes, A. and Navas-Gracia, L.M., 2023. Urban gardening in a changing climate: A review of effects, responses and adaptation capacities for cities. Agriculture, 13, 502.

Webster, E., Cameron, R. and Culham, A., 2017. Gardening in a changing climate. RHS Report