An agricultural landscape interspersed with hedges not only offers many animals valuable habitat and refuge – it also benefits the climate. As a study has now shown, a hedge newly planted on arable land binds almost as much CO2 per hectare as the forest. If the hedges that were cleared in Germany over the past 60 years were to be replanted, ten million tons of CO2 could be saved.
Agriculture is responsible for around twelve percent of all German greenhouse gas emissions. Methane from the digestive tract of cattle and nitrous oxide from fertilized fields and grassland account for the largest share. In addition, large amounts of carbon dioxide are emitted through the agricultural use of peatland. Because many of the underlying biological processes are difficult to prevent, climate neutrality in the agricultural sector will probably only be achievable if the emissions are offset again elsewhere.
Carbon sequestration as high as in the forest
Sophie Drexler from the Thünen Institute for Agricultural Climate Protection in Braunschweig examined in more detail what contribution hedges can make to this. “For the calculations, we compiled all available data on humus and biomass in hedges – 13 studies and our own data with a total of almost 150 examined hedges,” explains Drexler. On the basis of this data, they determined how much carbon dioxide is bound in the form of organic carbon in the biomass and the soils of the hedges.
The surprising result: 2.1 to 5.2 tons of carbon are bound per hectare in a hedge over the course of 20 to 50 years – almost as much as in forests. This can be explained by the high density of branches and twigs in hedges and the good growing conditions in the agricultural landscape. A particularly large amount of carbon is also bound in the rhizomes of the hedges. However, this contribution only applies to newly planted hedges on agricultural land. This carbon storage effect can therefore only be counted once, even if it takes about 20 years for a hedge to grow. In the soil, it can take even longer for the increased humus stocks to reach a new equilibrium and to stop rising.
A lot of effect in a small area
In concrete terms, this means that if the hedges that were cleared in the last 60 years were to be replanted, only 0.3 percent of the agricultural area would be required, but ten million tons of CO2 could be bound and made climate-friendly. On a smaller scale, a new hedge of 720 meters in length can offset a person’s greenhouse emissions for ten years in the long term. A municipality with 5,000 inhabitants could, for example, offset the greenhouse gas emissions associated with milk consumption over a period of ten years by planting six hectares of hedges and field trees, as the research team explains.
In addition to the climate effect, the hedges have other positive effects on the local climate: They protect the soil from wind erosion and have a cooling effect. A drought summer causes less damage in a hedge-rich agricultural landscape. Many animals and plants, for whom hedges are a habitat and link between biotopes, also benefit from hedges. “The diverse benefits of hedges make them attractive structural elements in the agricultural landscape,” says co-author Axel Don. In addition, it is one of the most profitable investments in order to at least partially compensate for the negative climate impacts of agriculture. “There is hardly a climate protection measure in the agricultural sector that can achieve so much effect on so little space,” says Don.
Some hurdles
Nevertheless, there has hardly been any new hedge planting in the last few decades. The Thünen scientists see several reasons for this. One reason is the jungle of subsidies, which farmers and landowners are often overwhelmed by. In each state there are different programs with different requirements and offers. It is also not enough if only the creation of hedges is encouraged. The care of hedges must also be included in the funding. Hedges have to be put on the hive in sections every eight to twelve years, i.e. they have to be cut back radically in order to maintain their function. Landscape conservation associations can help, some of which already offer “turnkey” hedges. In addition, the hunting associations have long been campaigning for a more structured agricultural landscape.
Another reason could be the relatively low flexibility of these structural elements: hedges are under special protection and, once planted, may not be easily removed again. This has the advantage that the carbon sequestration and the climate protection effect are long-lasting. For farmers, however, this limits their area planning. In addition, there has so far been a lack of sales markets for the resulting shrub pruning – although this could also contribute to the climate protection effect if it were used, for example, in the form of wood chips as a renewable energy source.
Source: Johann Heinrich von Thünen Institute, Federal Research Institute for Rural Areas, Forests and Fisheries; Technical article: Regional Environmental Change, doi: 10.1007 / s10113-021-01798-8