Enhancing the performance of urban storm water management schemes with tree selection: developing a new approach to assessing waterlogging tolerance in temperate trees

2018 | Andrew Hirons, PhD and Co-Investigator Henrik Sjöman, PhD, Myerscough College, UK

The increasing prominence of stormwater management schemes provides excellent opportunities for the integration of trees into new urban developments, however, there is considerable uncertainty over which species will perform best in these schemes. A notable feature of landscapes designed to manage stormwater is that the substrates used are very free draining. This means that the tree species used must be tolerant to periods of both waterlogging and drought (water deficit).

This project aims to develop a new trait that can be used to develop robust recommendations on the tolerance of trees to waterlogging. This will form part of a constellation of traits that can be used to characterise the tolerance of species to a suite of key stressors in urban landscapes.

As sapflow in trees integrates the aerial and underground environments it has significant value in assessing the physiological activity of different species under contrasting environmental conditions. This study will look at the decline in sapfow under waterlogging and use this to quantitatively evaluate a range of species’ waterlogging tolerance. Further data will be collected on the species’ drought tolerance. It is anticipated that this information will transform the confidence of recommendations for stormwater management and provide a model for others in the research community to quantitatively evaluate tolerance to waterlogging. The overall goal of the project is to improve the confidence of tree selection for stormwater management schemes and sites prone to waterlogging.

Study Results

Despite the importance of waterlogging stress, there is very little research on waterlogging tolerance in temperate trees. This knowledge deficit makes it very difficult to make species recommendations for urban scenarios that are subject to periodic waterlogging, such as stormwater management systems.  

Field trials conducted at University Centre Myerscough, Preston, UK evaluated the response of nine temperate tree species (Acer rubrum, Acer platanoides, Alnus glutinosa, Carpinus betulus, Liquidambar styraciflua, Populus alba, Prunus maackii, Salix alba and Tilia cordata) to a short-term (seven days) waterlogging stress. Species response to stress and recovery was assessed using leaf gas exchange (photosynthesis, stomatal conductance and transpiration) and sap flow. 

A considerable difference in response was observed across species. The most sensitive species (Acer platanoides and Prunus maackii) demonstrated rapid declines in sap flow and gas exchange within days of inundation. However, the most tolerant species (Alnus glutinosa and Salix alba) exhibited no deleterious effects during the period of waterlogging. Intermediate responses were also observed and the post-anoxic period following the re-aeration (draining) of the root system can be important for some species. 

The high temporal resolution of sap flow data (measurements occur every 10 mins) makes it an extremely powerful tool to evaluate tree stress and recovery. Such data will help inform guidance on tree selection for urban environments. One important finding was that species that are evaluated in the literature as being sensitive to waterlogging (e.g., Populus alba) do not appear to be significantly impacted by short duration waterlogging stress. Thus, understanding the interaction between species’ response and waterlogging duration will be important for future research.  

An important finding for arboriculturists is that trees subjected to short term waterlogging do not show any visual symptoms yet may exhibit highly significant differences in physiological parameters (e.g., gas exchange and sap flow). Consequently, conducting a visual assessment of trees subjected to waterlogging (soil anoxia) may have little value and should not be relied on as an indicator of tree health. 

Looking forward, the use of sap flow should be considered integral to our evaluation of tree stress and recovery cycles, particularly when combined with other environmental variables from the atmosphere and the soil. Such approaches will be particularly useful when combined with new internet of things (IoT) sensors that can provide real-time feedback of tree performance. 

Year: 2018

Funding Duration: 3-5 years

Grant Program: Hyland R. Johns Grant

Grant Title: Enhancing the performance of urban storm water management schemes with tree selection: developing a new approach to assessing waterlogging tolerance in temperate trees

Researcher: Dr. Andrew Hirons and Dr. Henrik Sjöman

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For more information on this project, contact the researcher via TREE Fund at treefund@treefund.org.