Habitat gaps and research gaps

– shedding light on ecosystem services is cities.

When thinking about urban ecosystem services, the city’s trees are high on the list of habitats that contribute directly to human wellbeing.  They are the Swiss Army Knife of urban habitats – a multi-functional feature that needs to be understood, retained and managed over their long potential lifespans.  

 

Urban trees can cool overheated cities, improve air quality, support pollinators, act as wildlife corridors and create pleasant views that can have positive effects on mental wellbeing.  Considerable research effort is underway to further quantify such benefits, to identify the most appropriate planting strategies and to explore how context sensitive they may be.  Entire conferences are now dedicated to this subject.

 

As is the case with most urban habitats, understanding the context dependency of services derived from urban trees requires ecologists to step outside of their comfort zones.  Traditional ecological approaches to understanding how trees meet their basic needs, and how they support the broader ecosystem, now need to encompass a huge variety of human activities.  For example, to understand how urban trees access water it is necessary to question whether the local soil moisture is derived from cracked waste/water pipes - what would happen if the leak were fixed?  Are newly planted trees being watered by a local volunteer group… and what happens if they lose their funding? 

 

Explicitly considering the interaction between urban trees and human activities is vital if we are to avoid accidentally damaging the functions of the urban forest as we re-engineer the city to meet carbon or resource security goals.  Shifts in the built form, to how infrastructure is maintained or to human values and aspirations may all have unintended impacts on the surrounding Green Infrastructure.

 

Recent research by members of the Liveable Cities team has highlighted the need to explicitly state the multiple intended benefits of urban street trees before they are planted, to improve the chances that such benefits are recognised within management strategies and that multi-functionality is preserved.

 

Current work is exploring how the installation and management of urban street trees might be radically changed to improve future ecosystem services.

 

Low-carbon lighting and urban trees

One example of a huge change to urban environments that is taking place in order to reduce carbon emissions is the large-scale roll out of LED street lighting.  Such lighting is more efficient than previous technologies, reducing levels of urban carbon emissions.  However, due to the rebound effect it is likely that rather than illuminating road surfaces to the same level as previous street lamps, the low cost of running the lighting will mean that illumination levels may be much greater.  Little is known about how his step-change in the nocturnal environment could alter urban ecosystem function, but a range of impacts might be expected.  As day-length is a key indicator of season, trees adjacent to street lamps might be tricked into thinking that summer has been extended – potentially making them vulnerable to frost damage.  Nocturnal pollinators might also be deterred, and the predation of insect communities associated with tree leaves and bark might also be increased.

 

A second paper recently published by members of the Liveable Cities team has focused upon how trees create safe dispersal routes for urban bats, allowing them to fly from their roosts to feed in urban areas where populations of mosquitos and other flying insects are high.  We found that whilst individuals of the Common Pipistrelle bat (Pipistrellus pipistrellus) were happy to cross even quite large gaps between trees, as soon as lighting was present they chose a longer route to cross the gap, or avoided crossing it completely.   The implication of this research is that as cities convert to low-carbon lighting, the resulting higher levels of illumination may reduce the permeability of the city for nocturnal species.  As a result, people living in the most densely developed parts of the city will have fewer opportunities for contact with nature, and to benefit from services such as the regulation of insect pests.

 

Bat flight video 1

Bat flight video 2

 

The ecology team has also recently contributed to a review paper on ecological connectivity in cities.  A key finding was that studies of urban species movement could benefit from greater use of cutting-edge tracking techniques and genetic approaches. One example of how new technology can be used to understand species movement is the use of thermal cameras to monitor nocturnal mammals.  This technology was used in our paper on gap crossing to confirm crossing events of bats.  During this work, other mammal behaviour was captured – highlighting the broader potential use of this technology.

 

Fox and cub1 

Fox and cub 2

 

 

Urban trees provide valuable shade on hot summer days
Urban trees provide valuable shade on hot summer days
Model of connected habitats for urban bats, with gaps in tree lines and artificial lighting acting as movement barriers
Model of connected habitats for urban bats, with gaps in tree lines and artificial lighting acting as movement barriers
A frame from a thermal video of bat flight
A frame from a thermal video of bat flight
Urban foxes captured by accident during thermal video surveys
Urban foxes captured by accident during thermal video surveys