• Energy Research

The restoration of degraded arable land to species-rich and functional grasslands by sowing native species has been tested successfully, while studies on restoration considering land use interest and climate change challenges are underrepresented. In this five-year study, we focused on the process of restoring grassland biodiversity and biomass production under different fertilizer levels in the face of several years of under-averaged precipitation. In 2017, we sowed a species and forb-rich native seed mixture to establish a submontane Arrhenatherion grassland. We applied fertilizer treatments (0, 60, 120 kg N ha-1 y-1, combined with and without P and K fertilizing) in order to meet local farmers' demands on biomass for hay production with nature conservation goals that aim to promote a highly species-rich and functional grassland community. Our results show that sowing a high-diverse and forbs-rich mixture not only leads to a high species richness, but also to usable aboveground biomass production for animal feeding, even with below-average precipitation. However, the slight decline in species number and cover of sown forbs following the dry period in the first year after sowing indicates the sensitivity of less drought-resistant forbs. Due to the priority effects of sown species, no undesirable species have invaded the sward. The nitrogen treatments shifted the grass-forb ratio, with grasses dominating in the nitrogen enrichment treatments due to their increased competition ability, while forbs dominating in the non-nitrogen enrichment treatments. Biomass production was higher at the first cut than at the second, and non-nitrogen fertilized treatments had a lower biomass production compared to nitrogen fertilized treatments. Both grasses and forbs contributed to drought resilience related to biomass production, but forbs contributed relatively more in the first cut under moderate or no nitrogen fertilization and in the second cut only without nitrogen application. Biomass production was strongly determined by year, and thus precipitation. Under drought conditions, species-rich stands produced sufficient biomass even without nitrogen fertilization. In order to establish and maintain species and forb-rich grasslands on ex-arable land, nitrogen fertilization should be moderate at most. Six of the 44 sown species, namely Arrhenatherum elatius, Alopecurus pratensis, Dactylis glomerata, Poa pratensis, Centaurea jacea, and Trifolium pratense, contributed significantly to the biomass and could act as matrix species in climate-adapted high-diverse native seed mixtures for our study region.

Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making.

Photovoltaics is one of the key technologies for reducing greenhouse gas emissions and achieving climate neutrality for Europe by 2050, which has led to the promotion of solar parks. These parks can span up to several hundred hectares, and grassland vegetation is usually created between and under the panels. Establishing species-rich grasslands using native seed mixtures can enhance a variety of ecosystem services, including pollination. We present an overall concept for designing native seed mixtures to promote pollinators, especially wild bees, in solar parks. It takes into account the specific site conditions, the small-scale modified conditions caused by the solar panels, and the requirement to avoid panel shading. We highlight the challenges and constraints resulting from the availability of species on the seed market. Furthermore, we provide an easy-to-use index for determining the value of native seed mixtures for wild bee enhancement and apply it as an example to several mixtures specifically designed for solar parks. The increased availability of regional seed would allow a more thorough consideration of pollinator-relevant traits when composing native seed mixtures, thereby enhancing ecosystem services associated with pollinators such as wild bees.