Connectivity assessment and prioritization of urban grasslands as a helpful tool for effective management of urban ecosystem services

How to successfully improve the biodiversity of city grasslands?

Urban grasslands (UG) are among the most common types of urban green areas. They are usually species poor, and spontaneous plant migration, which can increase biodiversity, is limited. To improve the range of ecosystem services provided by UG, various seed mixtures are applied during the establishment and restoration of UG. These mixtures vary in content, quality, and cost. High-quality seed mixtures are expensive and are usually only available in small amounts. Meanwhile, alternative methods of seed introduction (e.g., fresh hay application, seeds harvested by brush) have not been well studied in UG restoration, and inexpensive commercial mixtures could have low quality and lead to poor restoration outcomes. Here, we tested the effectiveness of different seed sources to create high-quality UG at two study sites. Based on the results, all seed addition methods increased the species richness of restored grasslands. The outcome of seed addition was satisfactory regardless of differences in residual vegetation species composition and soil properties between the sites. The species richness on plots that received a commercial mixture of flower meadow plants dedicated to pollinators decreased after overwintering. The alternative seed sources (fresh hay and seed incidentally collected during mowing) yielded grassland quality that was comparable to that on plots that received high-quality mixtures with known seed origin (a seminatural meadow mixture and a mixture with the addition of grasses).

Genetic structure of Trifolium pratense populations in a cityscape

Urban grasslands provide numerous ecosystem services, and their maintenance should be based on naturally regenerating plant populations. However, the urban environment is challenging for preserving viable populations, mostly because of their high fragmentation and small size, which can lead to genetic drift. We examined red clover (Trifolium pratense) in a medium-size city in Central Europe to test the cityscape effect on within- and among-population genetic diversity. We used eight inter-simple sequence repeat markers to examine the genetic structure of 16 populations, each represented by eight individuals. The isolation by resistance was analysed using a least cost patch approach, focusing on gene flow via pollinators. We found great variation among T. pratense populations, with no discernible geographic pattern in genetic diversity. We linked the diversity to the long history of the city and high stochasticity of land use changes that occurred with city development. In particular, we did not find that the Odra River (ca. 100 m wide) was a strong barrier to gene transfer. However, notable isolation was present due to resistance and distance, indicating that the populations are threatened by genetic drift. Therefore, gene movement between populations should be increased by appropriate management of urban green areas. We also found that small urban grassland (UG) patches with small populations can still hold rare alleles which significantly contribute to the overall genetic variation of T. pratense in the city.

The effect of grassland type and proximity to the city center on urban soil and vegetation coverage

Urban soils with associated vegetation are important components of urban ecosystems, providing multiple regulating and supporting ecosystem services. This study aimed to analyze the differences in the soil chemistry and vegetation of urban grasslands considering urbanization gradient and urban grassland type (UGT). We hypothesized that the chemical properties of soil, such as metal content, as well as vegetation traits, differ according to grassland type (lawns, grasslands in parks, grasslands on river embankments, and roadsides) and the location of grassland patches (city center versus peripheries). Our samples included 94 UGT patches which each patch represented by four square sampling plots sized 1 m². The results showed high differentiation of measured traits unrelated to UGT and location. The exception was K content, with a relatively high concentration in lawns, and some metals (Cd, Cu, Pb, Zn), with higher concentrations in the city center than in the peripheries. We found two grassland patches located in the city center where the concentrations of Pb, Zn, and Cu exceeded the level authorized by Polish standards. In the case of vegetation traits, the variability was not structured considering the UGT and location of the patches, except for bare soil cover, which was higher in lawns in the city center compared to embankments in the peripheries. We observed correlations between vegetation traits and soil chemical properties. The vascular plant species richness decreased when N, P, and C content, along with an increase in grass cover and a decrease in herbs.