Like elongated oases, they run through many of Europe’s arable landscapes: the traditional hedgerows made of bushes and trees form important refuges for forest plants, a study clarifies. In order to protect them against the more frequent extreme weather conditions in the course of climate change, the strips of vegetation should now be allowed to grow in width, according to the test results.
In the course of history, man has turned the once forested Europe into a cultural landscape in which there are often only a few natural elements. These include wall hedges, especially in northern and western Europe. These strips of vegetation between fields and meadows, characterized by trees and shrubs, have a centuries-old tradition. In some regions they even form an aspect of cultural identity. This is especially true in England and Northern France, but also in Northern Germany – where the wall hedges are also known as “Knicks”. In the beginning, however, the focus was not on nature conservation: the strips of vegetation served as living fences, as a source of wood and food, and as a windbreak. In the meantime, however, the ecological significance of the wall hedges has come into focus. Because it is known that they enable many animal and plant species to survive in the agricultural regions of Europe.
Substitute habitat for forest species
The focus of the international research team led by Kathrin Litza from the University of Bremen was on the herbaceous plant species that also grow in the vegetation strips characterized by woody plants. As part of their study, the scientists collected data from hundreds of hedgerows in southern Sweden, England, Belgium, northern France and Germany. The existing plant species and characteristics of the respective vegetation strips were recorded. In addition, information about the regional climate, the surrounding landscape and hedge maintenance measures was collected.
As the scientists report, their evaluations prove the important role of wall hedges as substitute habitats: “We have shown that a large variety of forest plant species can live in European hedges. The hedges thus form important refuges, especially in areas with little forest,” says Litza. Species such as wood anemone, star chickweed or spotted arum find a habitat in the wall hedges because they have forest-like conditions. “Our overarching project shows that species composition varies by region. However, overriding patterns were still found,” says Litza.
With more breadth against climate impacts
The researchers were also able to show which factors influence the occurrence of forest species in the wall hedges. A well-known basic principle is shown again: the more intensive the agricultural use of the adjacent fields, the fewer species were found. Above all, the study proves the connection between the diversity of species and the width of the vegetation strips, which can range from a few meters to more than ten. The researchers explain that wide wall hedges have a beneficial effect because they are better able to buffer extreme weather conditions than narrower ones. “The inner climate is demonstrably more stable in wide hedges than in narrow ones,” explains Litza. In this context, the Europe-wide study now provides concrete evidence that wider hedges are home to significantly more forest species than narrower ones.
According to the researchers, this is of importance in the context of the expected developments in the course of climate change: Because extreme weather events such as droughts will increase in the future, the preservation of wider wall hedges is important, or an increase makes sense. The results of the study also clearly support this: hedges that have been exposed to extreme drought or heat in recent years are demonstrably less species-poor. “Since such weather events will probably increase due to climate change, we fear that even more hedges could lose species in the future,” says Litza. The researchers therefore demand that care measures and management strategies be adapted at European level. “It is imperative that the width of the hedges is taken into account as a key element for biodiversity,” says the ecologist.
Source: University of Bremen, specialist article: Ecosystems & Environment, doi: 10.1016/j.agee.2021.107809