Effects of site preparation for afforestation on soil properties and greenhouse gas emission
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Date
2009Author
Mojeremane, Witness
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Abstract
Forest plantations in the UK are often established on seasonally waterlogged peaty
gley soils which often require site preparation (drainage and mounding) to lower the
water table and prepare planting positions. Substantial changes in the physical
environment of peaty gley soils can accompany site preparation including fluctuations
in soil temperature and soil moisture. These and other changes can all affect soil
properties and decomposition processes and well as the dynamics of CO2, CH4 and
N2O. A field experiment was established at Harwood Forest (NE England) to
investigate the effects of three site management practices (drainage, mounding and
fertilisation) frequently used for afforestation and replanting on peaty gley soils in the
UK on soil properties and various of C and N, environmental variables (soil
temperature, water content and water table height) and emissions of CO2, CH4 and
N2O. The relationship between GHG emissions and environmental variables was also
examined. The experiment was laid out in a factorial split-plot design. Drainage
decreased C and N concentration in the 10 cm soil layer. The soil bulk density in the 0
to 20 cm soil layer was increased by mounding. Drainage and fertilisation increased
soil CO2 efflux, whereas mounding did not affect soil CO2 efflux. All three practices
affected soil CH4 fluxes with drainage reducing the fluxes and mounding and
fertilisation increasing the fluxes. Nitrous oxide emissions were significantly affected
by mounding and fertilisation, with mounding decreasing emissions and fertilisation
increasing emissions. Soil temperature was the main environmental factor controlling
soil respiration in this site.
Over the two years study drainage and fertilisation increased the total greenhouse
budget by 13.1% and 97.9%, while mounding caused a reduction of−17.6%. Drainage
plus mounding reduced the total greenhouse budget by 6.9%, while drainage plus
mounding plus fertilisation increased the total greenhouse budget by 101.8%. There is
a potential for up-scaling GHG emissions from newly drained peaty gley for inclusion
in the UK Land Use Land-Use Change and Forestry (LULUCF) Greenhouse Gas
Inventory. However up-scaling and evaluation of the net emissions requires high
quality data from different sites newly drained for afforestation. More studies are
needed if net fluxes from newly drained sites are to the included in the LULUCF
Greenhouse Gas Inventory.