Grassland restoration by seed sowing: when, what and how much?

Our aim is to answer these important questions to support the successful implementation of grassland restoration projects. Choosing the proper timing of seed sowing and the optimal amount and species composition of the sown seed mixtures are very important for maximising restoration success and saving costs.

The matrix of seed mixtures are generally the grass seeds, which have an important role in weed suppression (Deák et al. 2011). Usually they sow the grass seeds in a density of 20-40 kg/ha in the restoration projects. Choosing the right density is crucial: if we don’t sow enough seeds, it can lead to weed encroachment, but sowing too many grass seeds results in the formation of a dense canopy which act as a barrier for the germination of target species via microsite limitation. In large-scale restoration projects, it is not always possible to compose and use a diverse seed mixture in the entire area; thus, they often use low diversity grass seed mixtures. On the one hand, seed sowing of grasses leads to a rapid and predictable vegetation development, and we can expect a species-poor grass-dominated vegetation two or three years after seed sowing (Török et al. 2010, Valkó et al. 2016a). On the other hand, increasing the diversity of these species-poor sown grasslands requires novel methods and a lot of extra work in the future (Valkó et al. 2016b, 2018).

In our project we sowed grass (Festuca rupicola) seeds in 2014 and a diverse seed mixture (containing 20 forb species) in different combinations (together with the grass seeds, and 1, 2 and 3 years later). We study the species composition and functional diversity of the developed communities and evaluate which solution is the best in terms of weed suppression.

Our preliminary results clearly show that the best solution is sowing the diverse seed mixture together with the grass seeds. This treatment resulted in the most diverse vegetation, the lowest level of weed encroachment and the highest number of established target species. In large restoration sites, which are embedded in an agricultural landscape, the spontaneous establishment of target species is very unlikely, given their impoverished seed banks and the lack of propagule sources. In such areas, active introduction of target species is inevitable for restoring species-rich grasslands. Our results suggest that it is a much more practical and cost-effective solution to sow the diverse seed mixture together with the grass seeds, at the very first stage of grassland restoration.

Here are some pictures about the experiment in October 2018.

In this plot, the diverse seed mixture and the grass seeds were sown in the same year (2014).

Here we sowed the diverse seed mixtures in 2015, i.e. 1 year after the grass seeds (2014).

Here we sowed the diverse seed mixtures in 2016, i.e. 2 years after the grass seeds (2014).

Here we sowed the diverse seed mixtures in 2017, i.e. 3 years after the grass seeds (2014).

Literature Cited

Deák, B., Valkó, O., Kelemen, A., Török, P. Miglécz, T., Ölvedi, T., Lengyel, Sz., Tóthmérész, B. 2011: Litter and graminoid biomass accumulation suppresses weedy forbs in grassland restoration. Plant Biosystems 145: 730-737.

Török, P., Deák, B., Vida, E., Valkó, O., Lengyel, Sz., Tóthmérész, B. 2010: Restoring grassland biodiversity: Sowing low-diversity seed mixtures can lead to rapid favourable changes. Biological Conservation 143: 806-812.

Valkó, O., Tóth, K., Kelemen, A., Miglécz, T., Radócz, S., Sonkoly, J., Tóthmérész, B., Török, P., Deák, B. (2018): Cultural heritage and biodiversity conservation – Plant introduction and practical restoration on ancient burial mounds. Nature Conservation 24:65-80.

Valkó, O., Deák, B., Török, P., Kelemen, A., Miglécz, T., Tóth, K., Tóthmérész, B. 2016a: Abandonment of croplands: problem or chance for grassland restoration? Case studies from Hungary. Ecosystem Health and Sustainability 2(2): e01208.

Valkó O., Deák B., Török P., Kirmer A., Tishew S., Kelemen A., Tóth K., Miglécz T., Radócz Sz., Sonkoly J., Tóth E., Kiss R., Kapocsi I., Tóthmérész B. 2016b: High-diversity sowing in establishment gaps: a promising new tool for enhancing grassland biodiversity. Tuexenia 36: 359-378.