Increasing carbon sequestration and storage in city greenspaces
Nicola McHugh, Jill L. Edmondson, Kevin J. Gaston, Jonathan R. Leake
University of Sheffield & University of Exeter
Introduction
The 4M project revealed that in Leicester, a typical UK city, trees account for 97% of the carbon stored in aboveground vegetation (Davies et
al., 2011; Journal of Applied Ecology 48 1125–1134). Here, using a number of spatial models, we report the potential of tree planting in both
residential and non-residential settings to increase aboveground carbon storage in the city. Our modelled tree planting was based on the
existing species mixtures in the city, and the potential carbon sequestration over 25 years compared to an alternative scenario in which short
rotation coppice is used to generate woody biofuel.
Tree Planting and Short Rotation Coppice
Results
Planting trees has long been recognised as a means of carbon storage
increase and as a method of delivering other ecosystem services. We
developed a GIS based model to quantify the extent of tree planting
possible in Leicester, from adding single trees in small gardens to
larger blocks of woodland in greenspaces, excluding playing fields.
We determined the urban area suitable for short rotation coppice
(SRC) planting with fast growing willow (Salix spp.) and poplar
(Populus spp.). Harvesting for biofuel occurs every 3-5 years and the
coppice system is managed over a 15-30 year lifespan. SRC has yet to
be seriously considered in urban areas although the constraints
identified in industry guidance do not preclude such planting and
smaller irregularly shaped plots and the diversity of urban land use
may allow biodiversity benefits of SRC to be achieved. SRC could also
provide an important contribution to the UK Government target for
15% of energy to come from renewable sources by 2020.
Tree sequestration, or SRC carbon capture models
Short Rotation Coppice
Residential / Non-residential
tree planting
Spatial tree planting
SRC sites identified following
UK Energy Crop Scheme
guidance
- Residential gardens can support
70,000 more trees.
- Land in public or mixed
ownership can support220,000
more trees.
- SRC could be planted on over 300
sites across the city with an
average plot size of 2 hectares.
- SRC plots could absorb around
3,000 tonnes carbon yr-1.
- Biomass from SRC could supply
around 1,200 homes or 24 large
municipal buildings with heating.
Modelled additional carbon storage possible after 25 years
Tree mortality and re-planting
SRC yield, biomass and carbon
storage calculation
Land with potential for tree planting and SRC across Leicester
Over 1,100 hectares of greenspace
were identified in which trees
could be planted to increase
carbon storage. This land includes
public, mixed and privately owned
land including residential gardens.
Tree planting and SRC proposals
have
been
developed
conservatively taking account of
published guidance, local tree
species mixes, proximity of
proposed planting to buildings,
roads, paths and existing tree and
shrub locations.
Tree growth
Biomass and carbon storage
calculation
As a result of tree planting, an increase in carbon storage of over 4,000
tonnes could be achieved over 25 years.
If SRC were planted 11,000 tonnes would be temporarily being
sequestered in each four year coppice cycle, amounting to a total of
72,000 tonnes of additional carbon over 25 years, although if used as
fuel this would be returned to the atmosphere but could substitute for
fossil fuel.
Combining tree planting with SRC could increase by 75,000 tonnes the
carbon taken from the atmosphere in 25 years.
Conclusions
Through additional tree planting it is possible to increase the amount of carbon stored in vegetation in Leicester, and produce biomass that
could be used to substitute for fossil fuels. The spatial modelling approach used identifies areas of the city and landcover types with the
greatest potential for increased carbon storage. Combining traditional tree planting with short rotation coppice plots provides the largest
potential to increase carbon sequestration and storage can be achieved.
Acknowledgements
4M is a consortium of five universities, Loughborough, De Montfort, Sheffield, Newcastle and Leeds funded by the Engineering and Physical Sciences Research
Council (EPSRC) under their Sustainable Urban Environment programme. It is supported by a range of stakeholders including Leicester City Council.