Process oriented infrastructure for climate-driven forest migration through cities
Global climate change is expected to shift the geographical distribution of tree species worldwide. Increasing empirical evidence has emerged showing that many tree species are already moving toward higher latitudes to track suitable climatic conditions. Yet, such movement cannot guarantee their survival, especially if the accessibility of suitable climates is highly constrained by species dispersal capabilities and human-created barriers. In order to assist forest migration, many efforts have been made to translocate tree species from their native ranges to locations where the climate is projected to be suitable in the future (known as assisted migration). However, there are concerns that such translocations may not be successful and may lead to unpredictable adverse consequences. This is because uncertainties in species’ distribution projections could cause a risk of moving species too far or not far enough. Within this context, this study develops a process-oriented approach to map and design urban landscapes to facilitate forest migration under climate change. The focus lies on the connectivity of urban landscapes for effective seed dispersal. Since the migration of trees is a continuing process that does not rely on their future distributions, a process-oriented approach could avoid projections of species’ future distributions and thus might be more feasible and manageable, as well as more robust to future climate change, than the current “goal-oriented” strategy of assisted migration. This study is guided by the following three research questions: (1) Why should we consider cities in the process of forest migration and what roles can urban landscapes play in the process? (2) How can forest trees migrate through urban areas, and more specifically, how can urban landscapes, as seed sources or stepping stones, contribute to the process? (3) How to design urban green infrastructure to facilitate forest migration and, more specifically, to promote seed dispersal and species’ range expansion across urban areas? A three-phase research methodology, which includes a transdisciplinary literature review, a mapping-based approach and a research-by-design methodology, is proposed to answer each of the three research questions, respectively. The Greater Manchester area, which is one of the most urbanised regions in the UK, is selected as a case study site. Eurasian jays, Eurasian siskins, and coal tits are selected as the main seed dispersal agents in the study area. The results of this study demonstrate the potential of urban landscapes to facilitate climatedriven forest migration through cities. By collecting and integrating knowledge and II information from multiple disciplines, this study suggests that cities could provide suitable climatic (urban heat islands) and environmental conditions for the persistence of outlier populations at higher latitudes than their native ranges, thereby shortening or even eliminating migration lags in tree species. The proposed process-oriented approach maps potential migration flows between urban woodlands in Greater Manchester, from the perspective of seed dispersal. Furthermore, by testing different afforestation strategies, this study reveals that the processes of forest migration at a metropolitan scale can be facilitated by creating small, distributed but functional-connected green spaces at site scales. The process-oriented approach can be used by designers to re-visualise urban landscapes as a series of interconnected flow channels, which in turn allows for a more piecemeal form of landscape design to improve urban green infrastructure for climate adaptation. Moreover, this study will encourage researchers who currently work in climate-driven species migration to consider taking advantage of urban landscapes and will promote the cooperation between biologists, foresters, designers, and managers in urban planting to cope with the rapidly changing climate.
Forest migration, Climate change, Green infrastructure, Urban afforestation, Range shift
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