Greenhouse Gases from Forest Soils

SNS-120: Anthropogenic Greenhouse Gas emissions from organic forest soils: improved inventories and implications for sustainable management.

Coordinator: Dr. Raija Laiho, LUKE, FI

Funding: 500.000 SEK / year

Duration: 2016 – 2019

Organic soils, particularly at northern latitudes, are critical in the context of climate change, as they act as a key source or sink for all three main greenhouse gases (CO2 , CH4  and N2 O). According to the national GHG inventories (2012), total GHG emissions from organic soils in managed forest land in the EU equalled 17.5 mill. tonnes annually, and 98 % of the emissions from organic forest soils are reported in the Nordic and Baltic countries. The total area of forest land on organic soils in Nordic and Baltic countries reported in the national GHG inventories is 11.6 mill. ha (92 % of organic soil reported in forest land in EU). Only CO2  and N2 O emissions from organic soils were reported until 2015. Countries are reporting these emissions using either Tier 1 methods, i.e., default emission factors (EF) published by the Intergovernmental Panel on Climate Change (IPCC), or Tier 2 methods, i.e., country-specific EFs based on scientific reports. Both approaches are characterized by high uncertainty; e.g., the default EF for CO2  has 90 % uncertainty level, which heavily affects the uncertainty of the whole GHG inventory.

In 2014, IPCC approved new guidelines for the GHG inventory, the so-called Wetlands supplement. Having relatively small impact on the GHG inventories in Central and Southern Europe, these guidelines introduce a significant change in the GHG inventories of the Nordic and Baltic countries due to the implementation of new default EFs for organic soils and introduction of new emission categories, such as CH4  and DOC emissions from soils and drainage systems. For all Nordic and Baltic countries, the emissions calculated based on the new guidelines will be higher than previously, even if the Tier 2 approach is applied. Implementation of the default EFs in the GHG inventory would increase the reported CO2 emissions from organic soil in the Nordic and Baltic region by 57 mill. tonnes, and N2 O emissions by 16 mill. tonnes annually. The new total emissions (CO2 , N2 O, CH4  and DOC), assuming that all countries implement the new default EFs for drained organic soils, are 82 mill. tonnes CO2  eq., which is + 467 % in comparison to 2012.

There are still considerable uncertainties in the climatic response of management of organic soils. Several studies have shown that some drained organic forest soils can be CO2  neutral or even sinks of CO2 . This is also reflected in the confidence limits of the IPCC default EFs that may reach negative values. Also, there are publications proposing considerably smaller EFs for N2 O and CH4 . However, no comprehensive evaluation and synthesis of these seemingly contradictory findings has been published. Yet, there are indications that the nutrient regime of the soil, water-table level, temperature climate and vegetation characteristics are key constraints of the emissions, which suggests that reliable, country-specific EFs could be formulated through data collation and modelling. This would further be important for an objective evaluation of the impacts of land-use changes and land management options on GHG emissions, and for designing guidelines for effective measures to improve the C neutrality of forest management on organic soils.

The aim of the project is to produce

i) a synthesis report of the CO2 , N2 O, CH4  and DOC emissions from organic forest soils in the Nordic and Baltic countries;

ii) Tier 2 EFs for the key sources of GHG emissions in organic forest soils in the Nordic and Baltic countries, based on collated data and modelling;

iii) a catalogue of GHG mitigation measures for forest management on organic soils.

iv) a common research agenda for future research to fill in any identified major data gaps.