Greenhouse gas balance of land use
The Land Use sector records greenhouse gas fluxes that occur in connection with land use (such as forestry and agriculture, settlements or protection areas) or as the result of a change in land use, such as building houses on former cropland. Unlike the other sectors, which only produce emissions, the carbon stock of the soil and vegetation can increase and thus remove carbon dioxide (CO2) from the atmosphere (so-called carbon sinks).
Forest dominates the greenhouse gas balance of Switzerland’s land use. Most years, forest management has resulted in a distinct increase in the total carbon reservoir in trees, dead wood, litter and forest soils (“forest sink”). Salvage logging following severe storms (Vivian in February 1990, Lothar in December 1999) and the rise in volumes harvested in some years (e.g. 2006, 2007, 2014) are clearly recognisable. In terms of climate policy, sustainable forest management can be achieved by using the wood grown in a cascade, firstly for long-lasting harvested wood products and subsequently for energy purposes. In almost all the years since 1990, more wood has been incorporated into new products (such as construction timber or furniture) than has been released (as CO2) in the disposal and/or combustion of end-of-life wood products. The size of the annual sink from harvested wood products has fallen in the past few years.
The agricultural use of cropland and grassland affects the carbon stock of the soil. For example, ploughing promotes the decomposition of humus, whereas spreading farmyard manure or leaving harvest residues on the fields increases their carbon stock. As well as the farming method, the main factors influencing the annual fluctuations are the crops grown and the climatic conditions. The case of drained former peatlands is a special one. When subjected to intense agricultural use, these fertile soils release large amounts of the greenhouse gases CO2 and N2O.
Wetlands now only account for a small part of the land area. As almost all of the remaining peatlands have been impaired by the consequences of previous use (particularly drainage), the build-up of peat has stopped, and many of the former sinks are now sources of greenhouse gases.
The development of new settlements has resulted in comparatively low emissions since 1990. Emissions are mainly produced if trees have to be felled during construction work.
Unproductive land such as rocks, scree and glacier forelands have very little vegetation and only poorly developed soil or none at all. These areas therefore play an insignificant role in the greenhouse gas balance.
With the exception of 2000, Switzerland’s land use resulted in more CO2 equivalents being absorbed from the atmosphere by the soil and vegetation than were emitted. Switzerland thus reduced its annual net emissions of greenhouse gases. Greenhouse gases continue to be released due mainly to the non-sustainable use of primary peaty soils and the use of land for settlement and traffic areas. For this reason, the state is not unreservedly satisfactory. The changes are impossible to evaluate since many factors can influence the total balance (forest and agricultural policies, spatial planning, construction activity, storms).
The greenhouse gas balance of land use can be compared to the data from other countries, given that it is calculated in accordance with the IPCC guidelines.
The data are taken from the inventory of greenhouse gas emissions in Switzerland (Land Use, Land-Use Change and Forestry Sector), which is drawn up annually by the FOEN in accordance with the guidelines of the UN Framework Convention on Climate Change. The methods are consistent with the guidelines of the IPCC (Intergovernmental Panel on Climate Change).
The greenhouse gas fluxes are surveyed for six categories of land use: forest, cropland, grassland, wetlands, settlements and unproductive land (other land). The carbon stock of harvested wood products made from Swiss wood is also recorded. CO2 is the most important greenhouse gas by far in the Land Use sector. Methane (CH4) and nitrous oxide (N2O) from fires, humus depletion, reservoirs and drained peatlands make a minor contribution to the emissions. In addition to the categories listed here, total emissions include low levels of N2O which, under international guidelines, are not allocated to any of these categories. The emissions of CH4 and N2O are converted to CO2 equivalents and added to the CO2 emissions.