Magnolias for tough urban biotopes

The aim of this research is to identify the extent to which Magnolia species are capable of tolerating conditions in urban environments under climate change in the 21st Century.

Due to the high profile nature of urban tree planting, landscape architects are typically more conservative in species selection of trees than in other types of planting, preferring to rely upon a limited palette of proven species than risk selecting species with which they are not familiar. Under climate change, stress in response to changing weather patterns will be exacerbated by new pests and pathogens, making it more difficult to predict what species will be successful, and creating an urgent need to diversify our urban forest. As specifiers, landscape architects are typically both partly responsible for this crisis and also best placed to help resolve it.

However, the urban forest is not just street trees: new techniques (such as the Stockholm Tree System) and situations (such as swales and podium decks) are being increasingly used, creating opportunities to specify species that are typically seen in horticultural, garden or parkland terms.

The study has an emphasis on identifying genotypes at a sub-specific level that are appropriate for large-scale cultivation. This will enable landscape architects to confidently specify a wider diversity of trees, facilitating adaptation to the impacts of climate change.

The IPCC defines adaptation as the “adjustment in natural or human systems to a new or changing environment. Adaptation to climate change refers to adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities (IPCC Glossary).

Research team

The supervisory team will be lead by Professor James Hitchmough, with Ross Cameron as secondary supervisor and Dr Henrik Sjoman from the University of Gothenburg as adjunct supervisor. There will also be advisory support from the Sichuan Forestry Department and specialist international Magnolia groups.

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Research methods and timetable

The principal research question under investigation is “Do sub-specific Magnolia populations associated with different habitat conditions across a species range confer additional tolerance of common urban stresses?“

Our first step combines a literature review with a scoping study of seedling trials and assessments of mature specimens to establish a database of stress tolerance traits, including tolerance of anoxia, shade, heat, and drought. This data will be mapped against the range of conditions found in urban biotopes, and allow us to identify populations of Magnolia species in Sichuan that can be targeted for seed collection. Seedling trials of wild-collected material will be carried out in 2018, looking at a number of characteristics, including optimum temperature for photosynthesis, flowering time, plant architecture, tolerance of low temperatures, tolerance of limestone-derived soils, and tolerance of drought.

These trials  allow systematic and thorough investigation into the potential performance of Magnolia in urban forestry, providing essential information to landscape architects and nurseries in China and the U.K. Appropriate plants can be brought to market in sufficient volume to support landscape adaptation to the effects of climate change. 

Given the wide range of sources required for this study, the research could have impacts in the research into archival material of early plant collectors, urban forestry, conservation and urban ecologies.

This research is lead by Harry Watkins,  PhD Candidate at the Department of Landscape, University of Sheffield

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