Detailed Information on Energy Trees and Energy Wood as Short-Rotation Planting

In this first stage of their life, the plants grow above-averagely fast. Within a short period, mauch mass will be produced at comparatively low density (weight per volume). We use special tree breedings (clonese), mostly of poplars, willows, and robinia (acacias). Broadleave trees are regularly “stock-settled”, i.e. cut back at the earth level. Harvest material is used. The stocl grows again, forms mass fast, and new harvesting is possible in a couple of years of “rotation period” (2−10 years).

This produces the following benefits: You save your replanting costs, and the yield is about 2-4 times higher than with the conventional wood. The growing force significantly increases after the first rotation period. In 25-30 years, the yield will decrease, and we would recommend start grubbing (using a tiller), as well as replanting or any other applicable uses.

Key words would be: Location, a good choice of clones regarding climate and soil, due care in the year of planting, planting distances, quality of saplings, availability of water (first of all, during vegetation period), soil quality, verage annual temperature, weed abundance, diseases, and damages caused by game.

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Own needs (independence, self provision) or deliveries for wood chips consumers (such as local heat networks), panel/paper industries. More and more farmers decide to act as heat providers rather than just chopped wood suppliers. The Biomass Association of Upper Austria (Biomasseverband Oberoesterreich) actively supports people that build and want to operate such local heat networks.

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You should consider distances from bordering properties. The minimal distances are stipulated by provincial legislation. 3 to maximum 10 m are recommended as turning circles.

The fast-rotation farm should be timely registered (within 10 years upon arrangement thereof) with a community or a district authority and harvested in accordance with §1(5) of the Forest Act (Forstgesetz). Fast-rotation areas are deemed to be agricultural areas provided that the crop was not planted on forest floor and is registered as such with BH within 10 years upon planting. Energy wood should be first harvested within at most 30 years, otherwise the area will be deemed to be a forest.

Please check the applicable provincial acts before ordering!

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Poplars and willows love water. Therefore, the growth of the plants depends on precipitations (at least 300−400 mm during vegetation period), the water holding capacity of the soil and the availability of ground water. Humus/nutrient content is only secondarily important. In particular, the following areas are suitable for planting: Set-aside areas, arable areas, and agricultural marginal lands. Mild loams with good fresh water balances would be an advantage.

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Clone means the entire range of plants having the same genetic material. Cloning is realized thrugh vegetative propagation, i.e. using shoot parts of the mother tree.

In Middle Europe, we usually consider poplars and willows, the latter to be used, first of all, for water-rich soils and for cooler or highly located sites. However, willow is more endangered regarding browsing by game.

Attention: You shouldn’t plant only one clone on larger areas! Instead, you should prefer a locally adapted variety of clone choices or natural material from the region, which has been further developed by breeding. Willows are rather suitable for fast, 2-5-year rotations and provide a yield of 7-15 t of dry mass per hectare annually. Robinia (acacia) has a higher heating value, newly-harvested only about 35 % of water (while poplars and willows about 55 %), good flammability, and grows relatively well in even dry, sandy and hot locations. No larger areas planted with the only clone!
You should prefer a locally adapted variety of clone choices or natural material from the region, which has been further developed by breeding;
Willos are an almost 100% planting and regenerating success; rotation period of max. 4 years; high browsing by roe deer; yield about 8 t/ha/a;
Robinia: high heat value; good flammability; low demands for the soil quality, tolerant of drought;

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Plough the arable land to 25-30 cm in autumn, then harrow immediately before planting in spring. The moment is determined by the preceding crop and the soil characteristics; cohesive soils – autumn or winter furrow (mellowness due to frost), light soils can also be tilled directly before planting.

Greenland: Mandatory soil tilling (exception: Planting roots or rooted plants); tilling at the depth of about 30 cm followed by milling immediately before planting the crop would usually be enough;
herbicides: In locations with, as past experience shows, strong occurrence of weeds, the running herbicides can achieve the desired effects directly before or after planting and/or total herbicides – already in autumn
Undersown: Sown before planting saplings can suppress accompanying growth and, therefore, reduce cultivation measures. Experiments with grain or legume seeds undersown can be used as fruit or mulch (mostly act as slightly growth-inhibiting -> water/nutrient competition).
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Energy woods, such as poplars, willows or robinia, are planted in spring, from mid-March to at latest mid-May (upland). About 20 cm long saplings, 1-2 m long rods or one-year 1-2 m long rooted saplings are settled or planted down to 20 to max. 50 cm in the ground and pressed down well. Doing so, you should ensure planting them in a single row with 1,500-8,000 pieces or in double rows (40-80 pieces in a row). Between them, a 2.5-3 m long lane should be made (about 13,000 pcs./ha).

Saplings or rods do not demand very much from soil or climate and can (differently, depending on variety) also be planted on marginal soils. However, higher yields can also be achieved on good arable lands. Arable land should be tilled or ploughed in autumn and prepared in fine crumbs in spring. You can still plant manually on the areas under 0.5 hectares, however, it would be reasonable to use a planting machine.* Rods and rooted plants can also be planted directly in greenland without any further care.

*As a services, we offer planting using a planting machine in the area of about 200-300 km.
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In the year of planting, saplings must be held as protected against weeds as possible. We recommend mechanical or chemical weed control. Starting from the 2^nd year till the end of usage period, no more processing is necessary. However, we still recommend controlling the field for possible insects, diseases or weeds. As for now, only small-scale occurences of any significant pests or diseases have been known.

For bio/ecologically oriented companies, mechanical weed regulation is the only possible cultivation measure. So you should mill the planting widths 3-4 times and, depending on weed abundance, chop between rows. Game damages can be avoided on smaller areas (up to max. 1 ha) using Gatterung or Duftzaun products. For the energy wood formed by willows, we recommend to plant as many clones as possible. For dense crops, browsing is limited by the edge of the wood.

Extensive losses can be balanced through replanting saplings or rods. It would not be reasonable to replant for small-area losses, since replanting cannot propagate itself.
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Fertilizers are not necessarily needed; however, they could help slightly increase the yields (up to 100 kg N/ha). First of all, N-fertilizing provides a yield-increasing effect upon willows. In the year of planting, fertilizing would not be recommended, since this can cause bad maturing in autumn. Fertilizing using compost, manure or ash, if applicable, could be reasonable.

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Harvesting is in the vegetation pause between December and March depending on planting distances and varieties every 2-10 years. Willows and robinia re harvested more frequently than poplars. Similarly, smaller distances or fully mechanized harvesting also provide results oftener than larger distances and extensive harvesting methods.

Harvesting can be fully mechanized using re-built maize choppers and custom-built machines, and it can be economically reasonable for not very wide entrances for areas starting from 3 ha. On smaller areas, harvesting would be performed in a partly mechanized method, using a chainsaw or brushcutter and a trailer.

For your own needs or for storage and private selling, it should be dried down to below 30 %. Deliveries to heating stations can also be performed with fresh harvest; however, depending on the delivery contract, you can usually expect to have wet harvest.

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 Energy Wood Yields

Yields make 7-15 air dry tons (absolutely dry = dry mass) per hectare annually. However, there are very significant differences depending on climate, soil valuation and water supply and varieties. For poplars, the yield can make up to 20 dry air tons in optimal conditions.

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Upon the end of the rotation period, the stocks will be removed, and root stocks will be destroyed using a wood mulcher (at the depth of about 35 cm). The driving speed regulates the crushing ratio. Further agricultural use is possible with tillers then-available on the market without any problems. When resettling, the soil must be dry down tot he processing depth (compaction!).

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The times where fast-rotation areas were considered as exotic crops of strongly experimental nature are definitely over. Great increments of cultivated areas in Austria and Germany, but also in South Europe, demonstrate that energy woods will play a significant role in future biomass providing. For a farmer this may mean, on the one hand, independence through self providing and, on the other hand, also an interesting occupation as wood seller or, in the best case, as a heat seller.

Once again, points to be considered:

• Location

• Plant distances, tree variety, rotation period

• Harvesting machines and methods

• Choice of genera and clones

• Soil preparation

• Weed control methods

• Planning of harvest logistics

• Utilization

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Sources: Our own experience, FHP, LKOE

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