CLM20-2 full issue-1 - Flipbook - Page 23
A guide to conservation land management and greenhouse gas emissions
emission of GHGs from the
manufacture and use of nitrate
fertilisers, the production of
supplementary feed, together
with significant emissions
of methane from the high
densities of cattle and sheep
supported by it.
The inconvenient truth is
that, compared to leaving
it alone, most conservation
management reduces the
cooling effect of a habitat. This
is because most conservation
management involves removing
vegetation to slow, prevent
Intensive arable farming on organic soils leads to significant emissions
or reverse succession and/or
of GHGs owing to the cultivation of soil, use of machinery, and the use
and manufacture of nitrate fertilisers. Tim Large – Rural Life/Alamy
create the desired vegetation
Stock Photo
structure, thereby reducing the
quantity of carbon that accumulates in vegetation such as alder, increases the quantity of methane
released into the atmosphere. This is because
and soil. Furthermore, this vegetation removal
methane formed in waterlogged soil diffuses into
is usually carried out by grazing with domestic
the atmosphere more easily via air channels in
livestock which emit significant quantities of
these plants’ roots, stems and leaves (e.g. Rusch
methane, use of fossil fuel or biofuel-powered
& Rennenberg 1998; Couwenberg & Fritz 2012),
machinery which releases CO2 or, more rarely,
rather than making a slower journey by diffusion
by burning, which also releases CO2. Because
or as bubbles through the oxygen-rich surface soil
of this, there will often be a trade-off between
and water layers, where it is exposed to oxidising
maintaining the desired early successional
methanotrophic bacteria that convert it to CO2.
stages and/or vegetation structure and allowing
Thus, the GHG flux of freshwater and lowvegetation to grow unhindered in order to
salinity wetlands comprises the uptake of CO2
maximise the rate of removal of carbon from the
which cools the climate, set against the release of
atmosphere. Conservation management decisions
methane which warms it.
may therefore need to balance benefit to climate
As with ‘dry’ habitats, conservation
with more immediate conservation goals.
management of wetlands usually aims to slow,
prevent or reverse vegetation succession and/
Freshwater and brackish wetlands
or create the desired vegetation structure, and
The GHG flux of freshwater and low-salinity
thereby reduces the rate at which the habitat
wetlands is more complex than that of ‘dry’ semiremoves carbon from the atmosphere. Similarly,
natural habitats. Wet habitats also remove CO2
vegetation management itself will also release
from the atmosphere through photosynthesis,
GHGs. Succession in wetlands can also be set
with a proportion of the carbon from this
back by periodically drying areas out, often
accumulating in the vegetation, soil, peat or
followed by grazing and/or cutting. Drying out
buried sediment. However, wetlands with a
results in oxidation of accumulated carbon in the
salinity of less than about half that of sea water
litter, soil and peat, which again releases CO2 into
also release methane (e.g. Poffenbarger et al.
the atmosphere. So, as with ‘dry’ habitats, there
2011) which, as described earlier, produces a
will often be a trade-off between achieving the
strong warming effect. This methane forms in
desired early successional stages and/or vegetation
oxygen-depleted conditions in waterlogged soil.
structure and maximising the amount of cooling
In fact, the presence of common reed and other
produced by the habitat.
emergent plants, and of wet woodland trees
Conservation Land Management Summer 2022 | Vol. 20 No. 2 21
