In the last centuries, farming practices lead to the development of structure- and species-rich cultural landscapes. But in recent decades, intensive and large-scale agriculture has become an ongoing and severe threat to biological diversity. This decline in flora and fauna can also be observed in Saxony-Anhalt (Germany).
Within the Common Agricultural Policy (CAP) of the European Union, member states can support biodiversity in implementing specific agri-environmental schemes. In the new funding period (2014-2020), the federal state Sachsen-Anhalt is funding the establishment of perennial flower strips with native herbs.
During former funding periods of the CAP, most perennial flower strips were sown with standard seed mixtures, that contained short-lived cultivars and ornamental plants. Beginning in the second year, the sown sites became more and more dominated by grasses or competitive ruderals, with a steady decline in flowering species.
In 2010, the Anhalt University of Applied Sciences and the State Institute for Agriculture, Forestry and Horticulture Saxony-Anhalt started a cooperation project to test different flower strip mixtures containing native species. The aim was to select seed mixtures and management practices, ensuring a sustainable development of flower strips with high ecological value that flower over the entire growing season. The management should be feasible in terms of farming practice and allowed within the agri-environmental scheme.
A block trial was installed (168 m x 10 m) on arable land in Bernburg-Strenzfeld, Kohlenstraße with seven variants and four repetitions: 3 seed mixtures, containing only native biennial and perennial forbs (25-32 species; H1-3), 3 seed mixtures containing native annual, biennial and perennial forbs and some ornamental plants (22-36 species; F1-F3) and 1 cultivar mixture (9 species; FK). After careful preparation of the seed bed, 3 variants were sown in September 2010 (H1-3) and 4 in April 2011 (F1-3, FK). Because of the low sowing density of 0,7-2 g/m², the seed mixture was diluted with soya grain to 10 g/m². Because seed of most wild plants need light during germination, sowing was done with a drill seeder with the sowing device raised to ensure that the seed were not buried. Afterwards, the site was rolled.
In the first observation year, spontaneously developing species reached a relatively high proportion of the total cover. In all variants sown with native species, this share was decreasing drastically in the second year, whereas in the conventional variant, their cover remained high during the entire observation period. The number of sown native perennial species increased with ongoing time but the number of sown cultivars and ornamental plants as well as annual and biennial native forbs is decreasing, especially the annual plants Papaver rhoeas and Consolida regalis as well as biennial species such as Resedaluteola and Verbascum spp.. In 2014, 87-100 % of the sown native perennials were still present on the sites. From the second year on, cover of the sown species increased to more than 90% of the total.
Variants sown with native species exhibited a varied and long-lasting flowering aspect. In the first observation year, between 9 and 22 of the sown species were already flowering, corresponding to 50 - 90 % of the established sown species. In the following years, this amount increased to 23 - 34 flowering species (depending on the variant), meaning than more than 90 % of the established sown species were flowering. Only three of the sown species in the conventional variant established in the first year. All of them were flowering but their mean cover reached only c. 5 %. In the fourth year, Trifolium pratense was the only remaining flowering species from the conventional mixture, with a very low cover of 1 %. Beginning in the second year, this site was dominated by grasses (Festulolium, Festuca rubra).
Dependent on seed bank content, water availability, soil fertility, and soil type, emerging arable weed can build up dense swards after sowing of flower strip seed mixtures on arable land in the first year. Competitive species such as Chenopodium spp., Atriplex spp., Tripleurospermum maritimum ssp. inodorum, and Conyza canadensis are able to suppress the development of the germinating flower strip species. Therefore, timely management during the bud stage (in May) and prior to flowering it is mandatory. To avoid damage of the juvenile target plants, the cut should be at a height of 10-20 cm. On very productive sites with high weed pressure, a second clearing cut will be necessary in June or July.
For the Kohlenstraße trial, a first cut at c. 15 cm height was made in May 2011 and a second cut in June or July 2011. The biomass was left on the site. Beginning in 2012, the sites were mulched twice: once mid March and once in June or July (one-half of the site in each month with 6-8 weeks between cuttings).
It is very important to manage flower strips in sections, mowing only half of the site in June and the remainder 6-8 weeks later. This guarantees flowering through the entire vegetation period, providing insects with continuous pollen and nectar sources. In addition, the continuous availability of vegetation offers hiding-places for different animals, such as hares and partridges.
Based on our experiences with successful establishment of flower strips, we helped to design five seed mixtures for establishing perennial flower strips within the new agri-environmental schemes in Saxony-Anhalt. The mixtures consist exclusively of native wild forbs from certified propagation. Because of a high probability of spring droughts in Saxony-Anhalt, we recommend sowing in late summer. Because of this, we did not include annual species in the mixture. In addition, most annual ornamental plants are sensitive to mowing. Due to the fact that a clearing cut is mandatory in the first year to suppress noxious weeds, it is not advisable to include annual ornamental plants in the mixture.
For successful establishment and management of perennial flower strips we summarized practical tips to help farmers, bee-keepers, hunters, and other professionals and institutions to develop species-rich plant communities on arable land that exhibit a long-lasting and colorful flowering aspect, and providing important ecosystem services.
Optimal sites are open arable fields as well as the southern side of hedges, tree rows, or woodland edges. Shaded or permanent wet sites are not suitable. The chosen sites should be free from perennial highly-competitive ruderals (e.g. Cirsium arvense, Elymus repens) and neophytic species.
Time of sowing
Late summer between August and mid-September (especially in regions with distinct spring drought); spring sowing until mid-April.
Seed mixture and sowing density
In Saxony-Anhalt, five mixtures for the establishment of flower strips are available within the new agri-environmental scheme. These contain 27-30 wild forbs of certified origin with a recommended seeding rate of 0,4-0,5 g pure seed per m²: (1) loess-loam, fresh, (2) loess-loam, dry, (3) sand, fresh, (4) sand, dry, (5) moist sites.
Seed bed preparation and sowing
Careful seedbed preparation is important. The seed mixture should be diluted with bruised grain (e.g. soya, maize) to provide a seeding rate of 10 g/m². Drill seeding followed by rolling is recommended. Seeds should be dropped on the soil surface and not covered as most wild species require light for germination.
First year management
In case of severe weed pressure, the sites must be mown or mulched in May and, if necessary, again in June /July to a height of 10-20 cm. Timely management during the bud stage and prior to flowering is important. The biomass can be left on the site.
Because stepwise mowing is essential to guarantee continuous flowering during the whole vegetation period, up to half of the site should be mown or mulched early in June and the remainder 6-8 weeks later in July to a cutting height of c. 15-20 cm. On productive sites, a second cut can be necessary in late winter (March). The biomass can remain on the site.