Sowing of low and high diversity seed mixtures in ecological restoration of surface mined-land
What are the differences in speed and pathway of vegetation development on nutrient-poor, unvegetated slopes sown with low-diversity seed mixtures of cultivars and high-diversity seed mixtures of regional species? And how is the susceptibility of the different sowing treatments to immigration events via seed rain? We compared differences in using a low-diversity seed mixture in comparison with a high-diversity seed mixture, both sown on nutrient-deficient raw soil. We assessed differences of speed and pathway of vegetation development of different variants as well as their susceptibility to immigration events via seed rain.
Central German Lignite Mining District.
In December 2004, the trial was established in complete block design with four variants: sowing of a low-diversity seed mixture with three grass cultivars and sowing of a high-diversity seed mixture with 40 herbs and 11 grasses of local provenance, both with and without an additional mulch layer. Vegetation surveys were made between 2005 and 2010. Using generalized linear models (GLM), we tested for treatment effects on species diversity, above-ground biomass, total coverage of vegetation as well as number and coverage of target grassland species. In addition, we estimated Bray-Curtis distances between treatments using non-metric-multidimensional scaling.
Sowing of a high-diversity seed mixture clearly accelerated the vegetation development and led to a significantly higher biomass production in the 1st year. On both variants, the additional mulch layer facilitated the establishment of sown species and led to a higher coverage of the herb layer in the 1st year. After 6 yr, the influence of the mulch layer decreased for the benefit of the seed mixture. Despite species exchange between sites, sites sown with different seed mixtures were still dominated by different sets of species in the final year of our study. Whereas high-diversity mixtures sped up vegetation development in the direction of highly diverse semi-natural grasslands, low-diversity mixtures considerably delayed the successional progress.
In grassland restoration in surface-mined land, high-diversity mixtures performed similar or even better than low-diversity mixtures of grass cultivars with respect to ecosystem services such as biomass production and ground cover (erosion control). An additional mulch layer considerably accelerated the vegetation development in the 1st years on both sowing variants. In contrast to sowing of low-diversity seed mixtures of grass cultivars, the use of high-diversity seed mixtures of local provenance contributes to the enhancement of local biodiversity. Although target grassland species were able to migrate into the low-diversity sites, this process is slow and only possible when appropriate seed sources are nearby.