What to consider when establishing forest stands?
If a new forest stand is to be established because the previous stand has been harvested or storms or calamities have made this necessary, planning for this must begin as early as possible. In order to be able to create optimal conditions for the new forest generation, it is first necessary to determine which operational goal is to be achieved on this area.
Description of the picture element:
- Which tree species are to grow on the area? Depending on the location, this can be a larger or smaller selection of tree species. If a site mapping is available, it should definitely be used for the answer.
- Should the area be a pure stand or a mixed stand? While pure stands are usually easier to maintain, mixed stands offer much greater security against potential risks. Hardwood admixtures in conifer stands often make better use of the site’s nutrient supply and the stand has a higher overall growth rate. Taking nutrients from deeper in the soil introduces bases into the nutrient cycle, improving humus form and increasing the available nutrient supply in the topsoil.
- Are there risks and restrictions given on the site? This can be just as climatic aspects (wet snow, storm risks) as special characteristics of the site. This also includes the question of whether special risks or at least changed conditions arise for the new forest stand as a result of climate warming, which influence the choice of tree species and the rotation period.
Once the above questions have been answered and operational goals and opportunities have been reconciled, the on-site assessment follows.
Planting, seeding or taking over natural regeneration?
The establishment of new forest stands can be done in different ways – by natural or artificial regeneration, still under the umbrella of the old wood or on the cleared area.
Adopting natural regeneration into the new stand has several advantages, especially lower costs (no planting costs), but also safe growing and good root development. However, the maintenance effort is at least as high, rather even somewhat higher, and the protection against browsing by game must begin in time.
How to evaluate the possibilities of taking over natural regeneration? Important starting points are:
- Is there already natural regeneration on the site?
- How does it spread over the surface?
- Does the old-growth stand allow for good development of natural regeneration? (Caution is advised u. a. in case of frequent occurrence of twining or twisted growth and in case of earlier snow break damage due to broad-crowned habit)
- Does an existing natural regeneration contain the tree species that are targeted as the operational goal here??
- Which tree species are missing from the target stand?
Regeneration under old-growth canopy – the light decides
The advantage of regeneration under the umbrella of old growth is protection of the regeneration from weather extremes (frost, sunlight) that can cause seedling failure in the open area.
Basic requirement for photosynthesis and growth is sunlight. Under densely closed tree canopies, only about one to five percent of the sunlight reaches the forest floor – too little for tree seedlings to grow. Therefore, even small beech and fir trees, which get along with very little light, need at least small "light windows" in the old stand, in order to be able to develop. After a year with good seed yield, natural regeneration can be supported by careful thinning of the stand. Thinning of the old-growth stand should continue in subsequent years, especially in old-growth beech stands, as they quickly close the canopy again. Too much can, however, be detrimental.
If a pure coniferous stand is to become a mixed stand of deciduous and coniferous trees in the next forest generation, a careful "conversion" is advisable at. Since here only conifers can naturally provide for regrowth, hardwoods are planted as part of a pre-planting in order to already have a supply of regeneration on the area after the pre-planting has been utilized. If later preplanting and natural seeding are not sufficient, the gaps are still planted.
An important point in regeneration under canopy is the spatial order, i.e.: in the final use, the regeneration stock must not be destroyed by felling and backing of old trees.
Consider the following factors when planting:
- Selection of tree species suitable for the site
- Choice of the right origin of forest plantsplants of local origin are particularly suitable. The recommendations of the countries should be followed.
- Determination of the plant assortment: seedlings, bolted plants or even large plants are offered for different initial conditions. While small assortments are sufficient for normal planting conditions, large plants can significantly shorten the critical growth phase when there is strong weed competition or very high browsing pressure. However, particularly high quality requirements must be placed on large plants (distance between shoots, shoot/root ratio) in order to avoid growth problems. In addition to the bare-root small assortments, container plants are now also offered, which are transplanted with small soil balls and have an improved growth habit and lower failures.
- Suitable planting methodIt is essential to ensure that the roots are not compressed, twisted or pushed over when planting procedures are used. The roots determine the planting method!
- Planting association: In the last decades, the plantations became wider and wider, the number of plants per hectare decreased accordingly. Today, even for oak in open areas, the recommended number of plants (2-year old, not trained) is up to a maximum of 5000 per hectare; for spruce and fir, the recommendations are between 2000 and slightly more than 3000 plants per hectare (3 to 4-year old, trained). If there is already an approach of driftwood on the regeneration area, the number of plants can be reduced.
- Protection against browsing by game: Except for spruce and pine, deer browsing is still a major problem, especially when planting tree species that are rarely found in nearby areas. Here it must be checked whether an area protection (fence) or an individual protection (z.B. The question of whether protection is to be preferred (e.g. by planting a cover) or whether protection can be dispensed with. Here, it is worthwhile to talk to the hunting leaseholder.
Besides the "pure" Types of procedures: seeding, planting, taking over the natural regeneration there are still a variety of possible combinations – for example, supplementing the natural regeneration by small-scale introduction of plants of the target stand.
Here the growth dynamics of the different tree species is important. If, for example, beech trees are planted in a small gap in a natural regeneration of spruce, they may be very quickly darkened out again by the pre-growing spruce trees. Conversely, planting spruce into patchy natural beech regeneration should always leave out larger areas if beech is still to be represented in the old stand: About 10 x 10 meters per tree in the old-growth stand, since spruce "pushes" from the edge and reduce the book area over time.
Seeding, while rare today, offers important advantages as it is ecologically very similar to natural regeneration. This means that the emerging seedling is in the "right place" from the start, does not suffer any planting shock and does not have to accept any restriction of its root development. However, seeding is more uncertain in terms of emergence success and the risk of browsing by game and weed competition takes longer than planting. Seeding can also take place under the umbrella of the old-growth forest. Seed must also be suitable for the site. As with planting, the following applies: follow the countries’ recommendations for origin!
Mixed stand: provide the necessary area for each tree species
If a mixed stand is to be established by planting, attention must be paid to appropriate area sizes for the individual tree species already in the design of the planting area, otherwise dominant tree species (z.B. Douglas fir) quickly gain the upper hand and lead to a segregation of the stand.
The individual plot sizes for the various tree species should therefore roughly correspond to the space required by a tree in the final stand (z. B. 10 x 10 meters). A smaller-scale mixture makes later maintenance interventions necessary in order to keep less incremental tree species in the stand as well.