High resistance of plant biodiversity to moderate native woody encroachment in loess steppe grassland fragments

By Balázs Teleki, Judit Sonkoly, László Erdős, Béla Tóthmérész, Mátyás Prommer & Péter Török

Loess grassland richly decorated with Adonis vernalis. Photo credit: Balázs Teleki

Loess grasslands are among the most species-rich habitat types in the world, often containing up to 40-60 species on a single square meter. Loess grasslands are found in the steppe and forest-steppe zones of Eurasia, especially in Russia and Ukraine. The westernmost outposts are found in the Carpathian Basin and the Morva Basin. Several species have the western and/or northern edge of their distribution range here. We have only a moderate knowledge of this vegetation type because it is very rare in Europe and has a low presence in English scientific literature. The richness of flowers that bloom from spring to autumn makes loess grasslands especially charming.

Loess grasslands are among the most threatened habitats in the world. They developed on highly productive chernozem soils and, as a consequence, have mostly been transformed into croplands in Europe. The decline of loess grassland area exceeds 90% in many countries. Especially in lowland areas, only small fragments of this vegetation type have survived in the form of small isolated midfield islets, road verges or burial mounds.

Although the most important threatening factor is ploughing, woody encroachment also represents a significant threat. However, this process has barely been studied. When a grassland becomes abandoned (i.e. grazing or mowing ceases), many woody species, both natives and invasives, can appear in the area.

In our research, we aimed at analysing the effect of native woody encroachment on grassland plant biodiversity by examining the vegetation composition of grasslands subjected to different levels of shrub encroachment. We compared ancient and restored grasslands. The study region is situated in the South-Eastern part of Transdanubia, Hungary. We sampled 63 sites: 35 of them were ancient grasslands, and 28 were restored grasslands. We analysed our data with several statistical methods, searching for a connection between woody encroachment and the age of the grassland, biological diversity, and the number of dry-grassland species.

Sampling area. (a) Map of Europe with the location of Hungary (in black); (b) map of Hungary showing Lake Balaton (in black) and the study area (in grey); and (c) study area with the sampled ancient grasslands (triangles) and restored grasslands (crosses). (Figure 1 from the AVS paper.)

We found that the species richness and composition of loess grasslands displayed high resistance to woody encroachment; a significant species-loss and plant diversity decline was detected only at high levels of this process (higher than 70%). It turned out that some rare loess grassland species can tolerate moderate encroachment of native shrub and tree species. A low cover of woody species is both structurally and compositionally a natural part of these ecosystems. Some rare, shade-tolerant forest-steppe species can survive the encroachment process. However, the species richness was significantly lower in restored grasslands than in ancient ones; some rare loess grassland species are absent in restored sites (e.g. Inula germanica, Nepeta parviflora).

Our results suggest that low to moderate woody encroachment cannot necessarily be regarded as degradation. Moderately-encroached loess grasslands can be easily restored by the suppression of woody species, as their species pool still contains many dry-grassland species targeted for restoration.

This is a plain language summary for the paper of Teleki et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12474). The post was prepared by László Erdős, Péter Török, Judit Sonkoly, Balázs Teleki and Bálint Bajomi.