Building interchanges instead of highways: Use of semi-open corridors to simultaneously connect woodland and grassland habitats

Background/Question/Methods

Corridors, commonly used to counteract habitat fragmentation and enhance species dispersal, facilitate movement between isolated habitats and prevent loss of genetic variability. Typically, they are a linear strip of corresponding vegetation connecting two isolated habitats. However, when intersecting habitats, they may fragment them, forming barriers for species in the intersected habitats. Consequently, woodland corridors fragment grasslands and grassland corridors fragment woodlands, causing dispersal problems, especially for stenotopic species. Semi-open landscapes, such as pastures and heathlands, accommodate much of the European biodiversity and, due to existing shrubs and groves, can shelter both woodland and open landscape species. Thus semi-open landscapes may act as corridors for woodland and open landscape species simultaneously. In Germany, we used an experimental and descriptive approach to investigate whether woodland and calcareous grassland plant species from adjacent habitats (i) germinate and establish themselves and (ii) naturally occur in semi-open landscapes. We examined the germination rate of 5 woodland and 5 grassland species, sowing seeds in 16 plots set in (A) shaded/more densely vegetated and (B) brighter/less densely vegetated semi-open areas. We also quantified species composition using vegetation surveys respectively in woodlands, in (A) and (B), and in calcareous grasslands.

Results/Conclusions

Seeds generally had significant higher germination rates in shaded areas, and grassland species germinated better than woodland species. Grassland species germinated better in brighter areas compared to woodland species; the germination rates of both in shaded areas were similar. Likewise, more woodland species germinated in shaded areas and grassland species showed similar germination rates in shaded and brighter areas. This is supported by the species composition of the different habitat types. Eighty-five percent of woodland species were recorded only in woodland; 15% were recorded in the shaded areas. No woodland species were recorded in brighter areas or grasslands. In contrast, 57% of species recorded in grasslands were also recorded in brighter areas; 38% were recorded in brighter and shaded areas. Four percent of grassland species were found only in grasslands.

Grassland species utilized the semi-open areas more than woodland species, possibly due to the low dispersal power of woodland species. Nevertheless, the high presence of species from adjacent areas indicates dispersal through semi-open corridors and species establishment was also possible. Thus, semi-open corridors form a promising tool in connecting isolated habitats by supporting the dispersal of species typical of those habitats. This counteracts the decreasing fitness of isolated populations by increasing genetic exchange.