CLM20-2 full issue-1 - Flipbook - Page 21
A guide to conservation land management and greenhouse gas emissions
Intensive arable on organic soil
Intensive grassland on organic soil
Eutrophic/mesotrophic open water
Lowland wet grassland on organic soil
Intensive arable on mineral soil (incl. emissions from farming operations)
Bare peat
Oligotrophic open water
Heather-dominated drained bog
Intensive arable on mineral soil (excl. emissions from farming operations
Lowland and upland heathland
Unimproved low-input grassland (incl. LWG on mineral soil)
Near-natural bog
Improved grassland (excl. emissions from farming/livestock operations)
Near-natural fen
Mudflat
Conifer plantation on mineral soil (managed on a 55-year-rotation)
Saltmarsh
Dry broadleaved woodland (mean over first 100 years)
Wet woodland
Dry broadleaved woodland (mean over first 30 years)
-20
-10
0
10
20
30
40
GWP100 (t CO2e per ha per year)
Figure 1. The typical estimated net greenhouse gas (GHG) flux of different habitats, including their
management, expressed as GWP100. Positive values (red bars) indicate that the habitat produces an overall
warming effect on the climate, and negative values (blue bars) mean that it leads to an overall cooling
effect. For dry broadleaved woodland, figures are the mean annual rates over different lengths of time
since the trees were established. Data are taken from Appendix 2 in Natural England’s review of the carbon
storage and sequestration of different habitats (Gregg et al. 2021), apart from the following habitats that
are not included therein. Coniferous woodland: the mean value per year for lowland conifer woodland
managed on a 55-year rotation in Table 2 in Haw (2017). Wet woodland: figure for alder-dominated
woodland in Huth et al. (2018), excluding emissions from methane due to a period of exceptional summer
flooding during the study. Oligotrophic and eutrophic/mesotrophic open water: means of values in Casper
et al. (2000), Stets et al. (2009) and Finlay et al. (2010). Arable on mineral soil including emissions from
machinery, the production and use of fertilisers, and from other energy used in the production of crops
calculated using a lifecycle analysis for growing bread wheat by Williams et al. (2010). Lowland wet
grassland on organic soil: figure in Huth et al. (2018), excluding emissions from methane due to a period of
exceptional summer flooding during the study.
are expressed in terms of comparison to the
warming potential of CO2 over 100 years,
shown as GWP100. Methane and nitrous
oxide are both very potent GHGs, causing,
respectively, 27 and 273 times more warming
than the same quantity of CO2 over a 100-year
period (Forster et al. 2021).
The GWP of land and its management is
expressed in terms of ‘t CO2e per ha per year’.
It is important to note that the main climate
benefits resulting from conservation management
can be through either reducing the quantity of
GHGs being released into the atmosphere (for
example by way of peatland restoration) or
through removing GHGs from the atmosphere
(i.e. carbon sequestration).
To put some of these figures into perspective,
the average GWP100 currently produced by the
activities of one person in the UK is about +10 t
CO2e per year (e.g. see www.carbonindependent.
org/23.html).
The effects of conservation land
management on GHG flux
There are now many studies that have attempted
to quantify the net GHG flux resulting from
different habitats and their management. In
Figure 1 we set out typical estimated GHG
flux for a range of UK habitats, including
their management, based on these studies.
We need, however, to be cautious in drawing
inferences from these values because, as we
describe later, the GHG flux of some habitats
can vary significantly in relation to their age
and condition. Nevertheless, the values shown
in Figure 1 serve to show which types of
habitat produce significant levels of warming,
which produce significant levels of cooling,
and which lie between these two extremes. We
will now describe the components of the GHG
flux of the main types of habitats managed by
conservationists in Britain, and how conservation
management affects these.
Conservation Land Management Summer 2022 | Vol. 20 No. 2 19
