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Establishing Native Vegetation with the Hay-Mulch and Hay-Threshing-Method - Biodiversity Included

By Jürgen Bender

In dependence on the lecture in the seminar "Restoration Technologies of the Alfred Toepfer Academy for Nature Conservation" in Schneverdingen.

While the nature conservation legislation aims at conserving the natural diversity of plants by means of the German Federal Law for Nature Conservation, the German seed trading act is not in accord with this principle. Every year, some thousand hectares of landscape areas are restored within the compensation of interferences through construction in Germany. To avoid a genetical unification of our phythocenoses caused by applying standardized types of seeds from the North Sea to the Alps, establishing vegetation suitable to site and with regional, indigenous seeds must be promoted urgently.

It is not only consulting engineers and architects, but also responsible hydroseeding and erosion control professionals, who are to attend to the duty of using regional seeds. Which of the revegetation methods is applied, depends on the size and quality of the available donor areas as well as the site conditions of the area to be restored.

For example, a lot depends on the soil organic matter content (topsoil / raw soil), the thickness of the potential rootzone, the soil type, chemical and hydrological values, etc. Climatical and also geological preconditions play a less important role, as with procedures close to nature, reclamation areas and areas to be revegetated are within the same geographic region. However, micro-climatic parameters like altitude or lighting conditions must be considered. If a reliable erosion control is necessary, parameters like slope length, inclination, soil cohesion, wind strength, etc. are to be regarded.

Hay-mulch seeding: Application of seed-bearing, fresh hay from a suitable donor area.

Hay-threshing method: Application of a seed blend, which was gained from a suitable donor area using a special threshing procedure, containing folios, stems and glumes.

Native seeds: Seeds from exactly defined origins; must not mixed with seeds from other origins. Indigenous seed is either collected from natural sources or originates from regionally breeded crops.

Seeds of agriculturally harvested hay: A very old method, which is rather unreliable with regard to restoration techniques, and where seeds are collected from hay stored in barns. This method is not used nowadays.

Grassland topsoil: Application of seed and root bearing grassland topsoil to an area to be revegetated. The "donor soils" are taken from areas with a vegetation adequate to that one of the area to be grassed. The application of only little quantities is called "vaccination".

Sod transplantation: Living grassland sods are taken from suitable donor areas and transferred to the area to be planted with vegetation. With this method, the complete vegetation phythocenosis is transferred, but it is rather laborious, and therefore, cannot be realized in most cases, because it is too expensive. Moreover, the vegetation on the donor areas is destroyed, and this is why only such areas are considered, which are planned to be changed anyway (e.g. replacing of dykes).

Principally, every procedure has advantages and disadvantages, which are to be considered. Then, there is the problem of availability. If you contemplate economical and ecological aspects, the two procedures mentioned first are to be preferred. This is why the hay-mulch and the Heudrusch® - methods meanwhile are very common in establishing autochthonous vegetation. It is conceivable and what we hope, that these procedures will be increasingly applied in future, too.

First of all you have to find out, which region the seed comes from. In close cooperation with the responsible authorities and local farmers, suitable donor areas are selected. The plants are harvested gently and pressed to round bales. For this, crop time and stage of maturity of the plants play an important role. If necessary, the material is dried once more and kept in an intermediate storage. The time schedule is coordinated with the builder.

The hay-mulch is chaffed with a special machine and either blown on to the vegetation areas or applied with a hydroseeder. For applying the Heudrusch®- procedure, the round bales are brought to the threshing center. Here, the seeding material is completely dried, if necessary, before it is threshed with a special procedure and bagged. The such obtained seed product can be stored easily. After passing a quality process (germination test), the Heudrusch®-material is applied by hydroseeding.

The advantage of the hay-mulch procedure is that the grain remains with the parent plant during the storage and thus may afterripen, if necessary. Additionally, also mosses, spores and microorganisms are transferred, which can accelerate the launching of a successful growth of the vegetation on raw soils without humus. However, larger amounts of biomass have to be applied as with the hay-mulch procedure almost the entire aerial biomass is transferred. This ensures immediate erosion control due to the mulch cover. The micro-climate is improved, and the drying up of the rootzone is reduced, what accelerates germination.

With the Heudrusch® - procedure, the time of the harvest is uncoupled from the time of application, as the material can be stored over a longer period; this allows high flexibility in what concerns the construction progress. Moreover, germination tests are carried out and documented, so that the optimal amount of expenditure can be defined precisely. This ensures comprehensive quality assurance and project documentation.

When establishing vegetation using hay-mulch, you have to consider that the seed material is not yet available for applications in spring. If, however, an immediate seeding is necessary as protection against erosion, we recommend to intermediately apply suitable seed blends for a temporary vegetation. The proper sowing of regionally harvested hay-mulch is carried out at a later time.

With raw-soil sites and high demands on erosion control, fast growing and shortly living nurse grasses, like e.g. Bromus secalinus, Secale multicaule, Lolium multiflorum or suitable legumes ought to be sowed first. If required, soil samples have to be taken and analyzed for pH-value and nutrient contents. Appropriate soil-ameliorating components and fertilizers can be added easily in the hydroseeder.

The most common fault when setting restoration measures on raw soils is to apply seed without necessary additives. Even donor areas of extremely poor and dry grassland are functioning ecosystems and a corresponding nutrient cycle. Hence, generally an initial nutrient admixture and soil amelioration is required in vegetation areas with raw soils, so that a dynamic ecosystem with functions corresponding to bioengineering can develop. However, by using autochthonous seeds of optimally adapted plants, the amount of additives can be reduced in most cases.

Establishing native vegetation usually aims at semi-dry or dry grassland rich in species with a root system ensuring reliable erosion control.

With indigenous vegetation, sown with the hay-mulch and hay-threshing method, a larger acceptability of civil engineering construction measures and landscape interferences is achieved, as an increasingly sensitized public observes and appreciates the aesthetical, ecological and economical aspects arising by the biodiversity and floweriness and the considerably reduced maintenance costs. To ensure quality assurance, we recommend the cooperation with renowned organizations. Meanwhile, long-term experience with autochthonic vegetation forms the basis of the described procedures.


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