Near-natural restoration methods have been successfully executed on different sites for many years (e.g. Kirmer & Tischew 2006, Kirmer et al. 2012, Kirmer 2019). Choosing the right method depends on a variety of factors such as restoration target (e.g. erosion control, establishment of extensively used, near-natural sites, compensation), and given site conditions. As a rule of thumb, the method which will achieve the desired targets with the least effort should be chosen. Availability of machines and material, practicality, possible subsequent use, future maintenance, and costs must also be taken into consideration. Regional seed and plant material should always be used. Due to the species’ specific adaptations to their sites, donor sites need to be chosen carefully and should be comparable to the target site. Only then optimal adaptation to the target site and maximum restoration success can be ensured.
The needed material for restoration can be harvested at near-natural meadows within a defined area of origin via several methods. By applying these methods, the typical composition of plants in this specific natural area can be preserved and established on the target site. A summary of near-natural restoration methods is given below. More information can be found in the Information System of Nature-oriented greening measures (INB).
This method is executed by mowing the donor site and applying either the fresh (green hay) or dried (hay mulch) hay to the receptor site. Using heavy machinery such as tractors and loader wagons is the most cost-effective way to achieve this, however, on very steep slopes only small machinery such as slope tractors, single-axle motor mowers or hand-held brush cutters can be used. The right mowing date is key to achieving seed-rich hay and a long-term establishment of the species on the target site.
On-site threshing uses a harvester to mow and thresh the material of a species-rich meadow in just one step. Species composition and seed abundance is dependent on cutting height and cutting time. The seeds can be directly applied to the target site or dried and stored before application. A mulch layer is suggested on sites which are exposed to strong winds or are prone to droughts. Without a mulch layer sites should be rolled directly after seeding.
Seed strippers or seed brushers, either attached to a tractor or operated by hand, are used to brush out seeds. The vegetation is not mown beforehand, and the seeds are collected from the living plant matter. Species composition is then strongly dependent on the time of harvest, vegetation structure, and working method (Scotton et al. 2009). When the machine is pulled along slowly but with high rotation speed high amounts of seeds can be harvested but the vegetation will also be damaged significantly. Fast operation with a low rotation speed on the other hand equals less seeds but enables multiple harvests.
This method uses seed vacuums (Thormann et al. 2003, Stevenson et al. 1997) or vacuum mulchers (Schubert 2009) to harvest seeds by vacuuming them up. The amount of seeds is usually high and early-flowering or low-standing species can be harvested as well. When done at the right time, a single harvest is enough to transfer most of the existing species. To keep the impact on fauna as low as possible harvesting should be done around noon when most insects are active. To prevent overheating of the densely packed mulch it needs to be dried or spread on the target site immediately.
Rakes or leave rakes are best used to harvest seeds from low-standing vegetation with low biomass growth (Jeschke 2008, Stroh et al. 2007). The collected material contains mosses and lichens, parts of the seed bank as well as seeds and parts of plants. It is also possible to transfer species which cannot (or can hardly) be transferred by other near-natural methods. On a larger scale, material can be harvested by special agricultural machines (e.g. curry combs or a rotary tedder).
This method removes topsoil containing the target vegetation and dumps it on the designated site. Since this method destroys the donor population it should be limited to sites endangered by construction, road building etc. The complete transfer of a plant community to a new site is called community translocation. Bullock (1998) describes four different types:
- Hand turfing involved the cutting and lifting of turves using spades. The turves are smaller and thinner than those lifted using machinery.
- Machine turfing usually involved the use of earth-moving machinery to lift the turves and to lay them at the receptor site after transport in a flat bed truck.
- Macroturfing used specially designed tractor-mounted equipment to cut and lift large (1 mx2 m) and deep turves (up to 50 cm).
- Spreading was the translocation of the community as excavated soil and vegetation rather than as intact turves. Usually this involved close cutting of the vegetation, e.g. with a soil scraper, to a depth of usually 0.2-0.3 m, and spreading and rolling of the soil onto the receptor site.
Sowing of seed mixures of native wild plants from certified propagation
If no suitable donor site can be found within the designated area, individual species can be collected by hand and multiplied at regional manufactures. Additional sowing is also advisable for the other methods if important species are missing or not producing seeds at the donor site. The seeds should be certified regularly by an independent institution (in Germany: VWW-Regiosaaten, Regio-Zert). Complete documentation from seed harvesting to seed reproduction is necessary to ensure a high quality certificate.