Developing a methodology to improve soil C stock estimates: report

5. Future Work

5.1. Geostatistical analysis of sampling required to estimate total soil C stocks in Scottish peats

The geostatistical analysis of variation in peat depth suggests that more work is needed on the scales of variation in peat. A greater number of peatland types and examples should be examined over a wider geographical area in order to identify and separate regional components of spatial variation, which may be due to regional climatic differences, from local components influenced by topography, such as slope, or other short range factors which influence hydrology.

5.2. Targeted resampling of map polygons containing peat to measure total depth, bulk density and %carbon

Geostatistical analysis should be used to highlight the areas of Scotland and the relevant peat-containing polygons where additional information would be beneficial. This particularly applies to those QM units where peat is a component but where data is lacking. A depthing and sampling strategy should be undertaken on the prescribed areas to enable better estimates of the average depth, bulk density, % C and ultimately the C stocks, both at a local and national level. Use of this data as well as data from the current NSIS_2 resampling programme will allow estimates of C stocks for soil profiles to be improved, so enhancing the national soil datasets.

5.3. Explore the costs and benefits of Ground Penetrating Radar ( GPR) and Light Detection and Ranging ( LIDAR) to measure peat depth and monitor changes in soil C stocks in the peatlands of Scotland

The use of GPR should be tested in the field at sample peatland sites with detailed depth measurements ( e.g. Glensaugh, Smith et al., 2007b).This would indicate whether the results obtained agree with the depth measurements and whether these methods would be likely to significantly enhance the estimates of C stocks of areas where the depth was unknown.

5.4. Use data derived from NSIS_2 to improve accuracy of ECOSSE and its ability to predict the response of Scotland's organic soils to external change

Simulations of the soil C stocks from phase 2 and phase 3 of the NSIS_2 resampling programme should be compared to experimental measurements, when they become available. This will further refine the estimate of uncertainty associated with the national scale simulations. Additional resampling to include more land use change sites would greatly improve the evaluation of the model simulations.

5.5. Use of ECOSSE to address policy questions

There is a degree of uncertainty in the simulations of changes in soil C associated with the level of disturbance occurring on afforestation of Scottish soils. The uncertainties in the simulations would be greatly reduced by coupling the model to national scale data on past, present and alternative afforestation practices in Scotland. Further work is also needed to develop and evaluate the simulations of soil C turnover on land use change and soil disturbance, possibly explicitly including simulation of practices such as clear-felling, brash incorporation. This could be facilitated by linking ECOSSE to existing forestry models. In particular, these evaluations should focus on soil C losses following afforestation of semi-natural land, but could also include simulation of changes in physical protection of soil organic matter following other land use changes. These evaluations may require further measurements to be made at appropriate sites.

The simulations included here report changes in soil C stocks only. Changes in C stocks in vegetation and emissions of other greenhouse gases (methane and nitrous oxide) are not reported here. Simulations of changes in C held in vegetation would require ECOSSE to be coupled to a simple vegetation model such as BIOTA (Wang and Polglase, 1995); this would be a useful advance. ECOSSE already provides simulations of other greenhouse gas emissions (methane, nitrous oxide). The results were not included in this report as the evaluations at the NSIS sites only provided estimates of the uncertainties associated with national scale simulations of total C loss. Analogous national scale evaluations of uncertainty in methane and nitrous oxide emissions should be done to allow the full greenhouse gas balance to be reported.

The future climate simulations presented above used the UKCIP02 climate scenarios. The UKCIP08 scenarios have not yet been published. In early 2009, the revised UKCIP scenarios are expected to be published, providing improved spatial resolution and updated climate scenarios. Simulations should be rerun with and without changes in land use and plant input when the new climate scenarios become available.

Four simple mitigation options to reduce C losses from Scottish soils were identified in the reported work. In future work, more detailed mitigation options should be considered, refined separately for mineral and organic soils. These could include

1. Including biomass and biofuel crops

2. Changing from high disturbance to low disturbance forestry operations

3. Changing from till to no-till arable management

4. Changing the intensity of grazing

5. Peatland restoration and maintenance

Brown et al. (2008a, 2008b) recently produced a revised map of land capability for agriculture in Scotland based on potential future climate. Future work should use this modelled land capability map as a filter for possible land use changes. The impact on national emissions of other potential land use changes, such as siting wind farms on peatlands, could also be considered.