Abandoned fields turn into forests five times faster than thought

Russian scientists studied abandoned arable land in the European part of Russia where temperate forests grow. The study showed that trees start to grow on the abandoned fields immediately after the land has been withdrawn from agricultural use. This finding contradicts the belief that trees appear on the fields only after grass that was approved earlier. As it turned out, the presence or absence of grass fires in a given area plays a key role in the stages and rate of overgrowth. The results are published in Ecological Processes.

The area of ??abandoned land in the Russian Federation, especially in its European part, is huge. Arable land was massively abandoned in the late 1980s – early 1990s due to the socio-economic changes. For the first two years, such abandoned lands are overgrown with birch, gray alder, and willow trees. Spontaneous overgrowing of forest vegetation occurs even in fields that have been used in agriculture for a long period of time (up to several centuries and longer). However, as many biologists point out, the density of undergrowth on former arable lands varies greatly in the same climatic conditions, up to the complete absence of trees.

Researchers from the Pushchino Science City in Russia suggested that grass fires are the most important factor determining the overgrowth of certain types of vegetation. Generally, a fire is considered a natural and unavoidable danger that plays a fundamental role in maintaining biodiversity of ecosystems. Scientists have reconstructed a 30-year history of grass fires in the south of Moscow region and analyzed the characteristics of the territory using archival satellite images. In addition, the researchers identified several sites for detailed study and assessed plant species diversity, soil quality and the relationship between soil and vegetation for three types of territories: often burning fields, unburned fields overgrown with forests, and for old forests bordering them.

“Our results showed the key role of grass fires in shaping differences in soil and vegetation in restoring abandoned lands. Settlement of forest species without fires occurs very quickly if this field is near a forest rich in different species. Although usually the time required for this is estimated as 100, 200 or even 300 years, we saw that the restoration of forest flora on former arable lands took only 20 years”, notes leader of the study Larisa Khanina.

Scientists analyzed how grass fires spread and found out that several factors increase the ignition chance: the presence of burning landfills among the neighboring ones, the presence of small settlements within a radius of 300 meters, and the type of land. If the area is overgrown with trees of high density, then the chances of ignition are small, the smaller the trees, the greater the chance of ignition. Moreover, fires likelihood seems to depend on climate conditions.

All in all, despite the ecological theory saying that the forest can grow over the abandoned field only after five years after the grass stage, new study suggests that abandoned arable land in the center of the European part of Russia is immediately overgrown with forest if there are no fires.

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