Energy forestry

Energy forestry is a plantation of fast growing trees with the aim of producing wood as a renewable raw material within short rotation times, in which a fast-growing species of tree or woody shrub is grown specifically to provide biomass or biofuel for heating or power generation. If this happens exclusively for the production of energy, it is also referred to as energy wood plantation or energy forest.

The two forms of energy forestry are short rotation coppice and short rotation forestry:

Short rotation coppice may include tree crops of poplar, willow or eucalyptus, grown for two to five years before harvest.
Short rotation forestry are crops of alder, ash, birch, eucalyptus, poplar, and sycamore, grown for eight to 20 years before harvest.

Density effect
These coppices contain about 1,000 to 4,000 stems per hectare or even 10,000 to 20,000 plants per hectare for dense coppice with very short rotation.

A balance is to be found by the agrosilverist between density and desired stem diameter. In general, the biomass harvested per foot and the diameter of the stems (basal area) decrease with the density of the seedling. The big stems favor the woodcut and the fines interest rather the grinding. According to AFOCEL (1993), “A density close to 2,000 cuttings per hectare is currently the ideal density to optimize the production of ridges for the crushing industry”.

Tree species
In a short rotation plantation fast-growing and ausschlagfähige tree species, especially poplars (genus Populus) or pastures (genus Salix) are used. Research and breeding focuses on tree species that are suitable for temperate climates.

Among the poplars are especially the Balsampappeln such as the Western Balsam poplar and Populus maximowiczii and their hybrids and crosses between balsam and black poplar trees suitable. These are distinguished from pure black poplar and other tree species in that they grow very fast, do not need too much light and form a dense root system. Other targets in poplar combination breeding include increasing biomass production, improving pest resistance, accepting higher planting density, high cane rash, and rapid growth in the early years of development to reduce harvest intervals. The fuel quality of the wood is also influenced by breeding by selecting forms with high efficiency of nutrient use and high, but low-nutrient rootstock.

History and Economic Situation
A historic forerunner of the short rotation plantation in the coppice, in the trees in regular intervals u. a. for the production of firewood were put on the stick.

The cultivation of fast-growing tree species for material use for the production of wood-based materials has been successfully practiced in many European countries for many years. In Germany, however, wood fields have not reached beyond the trial cultivation stage since the 1970s, although the first research center for fast-growing tree species was founded in Hessen in 1974. On the one hand, this is due to a hitherto limited market for the end product wood chipsdue. On the other hand, heating oil has been the most economical fuel for heat supply for years. However, this situation changes as prices for fossil fuels increase. Today, short rotation plantations are mainly grown for energy use.

Since about 1990 willow clones grown in large plantations. In Sweden there are many years of experience with the cultivation of pastures in short rotation. As early as 1999, 16,000 hectares were cultivated there, in the 2005/2006 marketing year there were about 15,000 hectares of woodland in cultivation. In the newer varieties, the yield could be massively increased compared to the first wood fields and currently stands at an annual increase of 8 to 12 tonnes dry matter (atro) per hectare. In Germany, according to IACS, 5,968 ha of short rotation plantations were cultivated in 2014. Short rotation plantations are a very labor intensive cultivation method in the field of agricultural production. Most of the work can be done by farmers or foresters with their own machines. Only for planting and harvesting special machines are needed, which are usually provided by service providers.

Economic Vocation
The economic vocation, possibly alternative to agricultural activity, 19 is the most cited issue of energy crops; the TCR can contribute to producing fuelwood (heat or electricity production 7), poles, woodchips, fibers and to create or maintain rural or peri-urban jobs (through maintenance, exploitation, and marginally for monitoring and evaluation, qualitative and quantitative).

The sustainability of the TTCR sector is discussed (like all crops, the intensification of exploitation may lead to the depletion or overexploitation of the substrate by the export of nutrients 20 or the water resource).

It seems possible to create or maintain a renewable resource available for the wood-cellulose sector, or heat networks, with indirect spin-offs from tourism, and the exploitation of all or part of this afforestation.

Related interest
In addition to their interest in energy crops, these wooded elements could – with appropriate management and if they are inserted into the landscape with a concern for ecological coherence – develop other interests for water, soil, air, water landscape, agriculture, health, carbon sink restoration, green and blue weave, etc.

For breeding
The TCR can produce a part of the benefits of the grove (shading, protection against the wind, microclimate) for the breeding of mammals but also of poultry (Label chickens in particular 21).

Possible landscape vocation
If the species used are local species, adapted, varied, harmoniously planted according to the ecopaysager context (and thus hydrological and geopedological), by marrying the forms of the landscapes, and why not in the context of a neobocage semi-agricultural, hiding possibly black spots in the landscape (infrastructures and unsightly buildings), and if they are not exploited according to the principle of clearcuttingbut for example in several bands being rotated differently, so as to always maintain the equivalent of a hedge in the landscape, they can contribute to the restoration efforts or improvement of certain landscapes (A test with a triple cut woodleaf, each band being cut to a different year) was conducted in Belgium with a hedge of 100 m made up of 6 rows of willows, with an energy vocation of the harvest).

By reintroducing possibly elements of more natural appearance in peri-urban areas, or even in industrial zones, they can improve the landscape and connect to a green flow, a wild or “ecological” garden, a biological corridor, a green wall, a vegetated terrace, a landscaped park, etc.).

A secondary benefit in terms of cynegetic and rural tourism could then be expected, thanks to the improvement in terms of landscape.

Vocation to protect water and fight against soil erosion
Some effectiveness is recognized in afforestation and wooded strips in terms of water purification (for phosphates and nitrates in particular, but also in terms of reduction of turbidity). TCRs have been experimented in the tertiary phase of natural lagooning (for example at Lallaing and the wastewater treatment plant (for example in Villeneuve-d’Ascq for a few years), and fast-growing trees evapotranspired a large quantity of water. must be taken into account for their eco-landscape integration.

Usage
In the short rotation plantation so-called cuttings, Sections of annual, well-developed shoots, planted in rows and harvested mechanically or motormanually every 3 to 10 years, depending on species and climate. The rootstock remaining in the soil has the ability to cattle rash, and so after the harvest is a renewed sprouting of the trees, without having to be replanted. Under good conditions, short rotation plantations can produce on average about 10 tons of dry matter per year per hectare, and twice as much under very good conditions. After about 20 years, the production capacity of the plants decreases, and the area should be recreated with further use.

Cultivation
When planting short rotation plantations, deep soil tillage is strongly recommended. by min. 25 cm deep plowing. This allows fast root growth and high wood growth rates. A good establishment success with growth heights of more than 1.5 m in the first growing season usually only sets in when, in addition to the conscientious soil preparation, the culture in the first growing season is kept largely free of weeds. This can usually be ensured by the use of pre-emergence herbicides directly after planting, as well as at least one mechanical care passage. A good culture care in the first year of growth improves the competitive situation of energy cropsas well as the survival rate and the yield potential significantly. At the end of the second growing season, the crop closes already at most sites if the crop was kept free of weeds in the first two years.

As a rule, short rotation plantations are created in spring (end of March to beginning of June). As planting material are either pre-produced 20 cm – 35 cm long cuttings, which are planted by hand or by hand, or about 2.50 meter long rods, which are cut into about 20 centimeters long cuttings during planting in special planters. When planting it is important to ensure that the cuttings are placed as vertically as possible with good bottom closure in the soil. As a rule of thumb, the more difficult the location, the longer the cuttings should be. Short cuttings are planted at ground level, longer cuttings (from 30 cm) can look to about 1/3 from the ground. At very difficult locations it is recommended to plant plant rods> 100 cm in length, as these are much more robust to weeds and easier to care for. For cost reasons, the cultivation of plant rods is recommended only for a longer rotation in quantities of 2,000 – 3. 500 per hectare. Plant rods are planted at least 50 cm deep. The cultivation of short rotation seedlings is not carried out because the seeds of poplars and willows are not storable and are often no longer germinable after a few weeks. A much more expensive alternative to the cuttings derived from high yielding mother plants is the use of tissue culture propagation. However, this is currently not profitable and is used accordingly only in research. Short rotation plantations are usually created with special planting machines. All leading suppliers of planting material also offer the planting performance.

The planting association depends on the tree species, the planned product (energy or industrial wood) and the The cultivation of short rotation seedlings is not carried out because the seeds of poplars and willows are not storable and are often no longer germinable after a few weeks. A much more expensive alternative to the cuttings derived from high yielding mother plants is the use of tissue culture propagation. However, this is currently not profitable and is used accordingly only in research. Short rotation plantations are usually created with special planting machines.

Plant protection
In short rotation plantations, the same problems as in forestry crops occur. In addition to general dangers, specialized pests play a certain role, especially in individual species.

The problem with the cultivation of short rotation plantations is the low genetic variability of the plants, which results from the vegetative propagation of the cuttings, as well as the crowding of the plants. This makes the entire population susceptible to pests, with so far only the infestation by rust fungi of the genus Melampsora and by poplar leaf beetle (Chrysomela populi) led to greater yield losses. Against insect pests effective insecticides from agriculture and forestry are available, the use of which, however, so far only in rare cases.

In addition to mechanical plant protection methods such as the fencing of cuttings against Wildverbiss herbicides from crops are used against weeds during the establishment phase. For pesticide applications on unindicated crops, a derogation from the competent authorities is required in Germany under § 18b of the Plant Protection Act. This is usually given easily, as woodchips do not get into the food chain.

Under certain conditions, it is necessary to completely or partially dispense with the use of herbicides. For example, this is the case in water protection zones or in organic farming. There are several alternative measures that can be taken: early and multiple mechanical care and mulching films allow the operator to prevent too much accompanying vegetation. Mulch films reduce the care measures and offer the trees protection and clear growth advantages. Pastures as fast-launches are particularly suitable, since unlike poplars they tend to do without care measures. Mice help against mulchingbetween the rows and birds of prey on the surface.

Harvest
Short rotation plantations are permanent crops that can usually be used for up to 20 years with an average of 3 to 6 harvest rotations. The harvest is carried out over several years Umtrieb, the stock has at harvest time reaches a height of 6 to 8 meters. The yields for balsam poplars are between 10 and 15 tons per hectare per year, for pastures 5 to 10 tons per hectare per year. The harvest time is optimally in the winter after the leaf waste, as this can leave a large part of the nutrients in the fields. As harvesters are mostly high-powered, self-propelled with short rotation Forage used with small timber feeder. Harvester and bundlers from the forestry technology can also be used in higher-yielding crops as well as longer rotation times. It is important not to over-compact the soil so that the trees can stand in a well-ventilated soil.

Fresh wood chips usually have a water content of 50 to 60% and must be pre-dried for use. This happens when the chips are stored outdoors or in pressed bales. For firing in smaller and medium sized plants they should have a maximum water content of 30%. Important is a rough hacking of the wood, as fine wood chips are poorly storable. The chips can be stored as rents and burned, gasified or processed into pellets as needed. Short rotation plantations drive off again after the harvest. Depending on the nutrient supply of the soil, a fertilizer of 50 to 70 kg nitrogen may be used after the harvest/ ha makes sense, but usually no fertilization is necessary because hardly any nutrients are removed from the surface via the wood.

Profitability
Compared to established one-year arable crops, KUP require relatively high investment in founding existing crops and a relatively long production period and generate irregular cash flows. At the same time, after a successful establishment, there are no significant additional costs for the management of the plantations, apart from the harvest costs. Finally, at the end of the useful life, the cost of reconversion of the area for arable use (removal of rhizomes) must also be calculated. CUPs therefore represent a greater entrepreneurial risk than one-year crops; cultivation seems to make economic sense only for fixed purchase contracts with binding prices.

In order to compare the economic efficiency of KUP with that of one-year crops, it is advisable to use the dynamic investment calculation instead of the contribution margin ; The irregular cash flows can thus be converted into an annual constant annuity. The calculated annuity can be compared directly with the contribution margin of one-year crops. According to various studies, the annuity of poplars and willows may, under favorable conditions, be around € 250 to € 500 per hectare per year, but in unfavorable conditions also be negative. The higher the number of rotations, with a rotation period of three to four years, the sooner positive annuities are achieved.

A profitability analysis of the cultivation of fast-growing tree species in short rotation plantations published by the University of Halle-Wittenberg, based on current literature and practice data in 2014, shows that it is economically profitable in the majority of cases, and from an average yield level of 11 to 12 tons of absolute dry matter per hectare per year can certainly compete with agricultural crop rotations. Compared with the average yields and prices of a rotation typical for middle axles (winter rape – winter wheat – winter wheat – winter barley) from 2006 to 2010, a farmer with energy wood production generates an average profit of € 45 per ha. Additional economic benefits can be provided by activating short rotation plantations as “ecological priority areas”.

The total cost of establishing a short rotation plantation is around 2,000 to 3,000 euros per hectare. The first harvest of poplar and willow plantations usually yields significantly lower yields than in subsequent years. From the 2nd harvest, the annual growth rates are i. d. R. at least 50% higher compared to the 1st harvest. In order to keep the specific harvest costs low, it is advisable to wait with the first harvest of a short rotation plantation until a total harvest of at least 25-30 tons of dry matter per hectare is expected. However, care must be taken to ensure that the trunk thickness of the trees does not exceed the possibilities of the harvesting technology used.

In the heating market, woodchip firing becomes economical due to the sharp rise in fossil fuel prices, even at higher investment costs for the combustion and charging technology. The average energy content is between 15.5 and 18.5 MJ / kg, while harvesting and comminution consumes about 0.06 MJ / kg, which makes the energy balance very good. It should be noted, however, that fast-growing plants also have a lower specific energy content, so that the volume of raw materials to be processed increases sharply. For example, a room meter of oak firewood supplies approx. 1890 kWh, fast-growing poplar only 1110 kWh. This is not clear in the calorific value, since it refers to the mass and not to the volume.

Short rotation plantations devastated and urban areas
The global increase in food prices in 2007 and 2008 has led to a discussion on whether and to what extent the production of renewable raw materials for energy production has fueled this increase. For this reason too, pilot projects have been started for the plantation of short rotation plantations on land that is not in competition with food production. In this context, experiments in devastated areas of former opencast mines and on inner-city areas deserve special mention. The latter were started in 2007/2008 by Stadtwirtschaft Halle on areas that were previously occupied by residential buildings that were demolished as part of the so-called “Urban Redevelopment East” in Halle (Saale).

Climate protection effect
Bioenergy value chains based on short rotation plantations for electricity, heat and fuel production enable a significantly higher CO2 avoidance compared to traditional bioenergy processes. This is due to the extensive management, which means that the input of energy in the form of fertilizers and pesticides or machine use is extremely low. Also the CO2- Avoidance costs are only a fraction, compared to biofuels from oilseed rape and grain or biogas from maize silage. The Scientific Advisory Council Agriculture Policy at the Ministry of Agriculture writes in the study: Use of biomass for energy – recommendations to the policy: “The policy could (…) by a change of course in the promotion reach (more biogas based on gül and electricity and heat based on wood chips KUP) that, with consistent use of resources and land, the contribution of bioenergy to climate protection would more than triple. ”

In addition, short rotation plantations offer the opportunity to manage arable land, which has a particularly high drainage requirement. When using willow and poplar clones, therefore, an excessive drainage of these surfaces can be dispensed with, which has a clearly positive effect on their CO2 balance. If particularly humid locations are used in this context, a possible negative influence on the local water balance and thus on sensitive ecosystems can be avoided.

Influence on biodiversity
When assessing the impact of short rotation plantations on biodiversity, it is crucial to decide which reference system is used. Most of the studies come to the conclusion that short rotation over intensive agricultural use has a positive effect on (plant) biodiversity, but has low biodiversity compared to near-natural forest. In this assessment it should be noted that the conversion of forest into short rotation plantations is strictly prohibited and cultivation is concentrated exclusively on arable agricultural land. The NABU notes that the system of SRC in agricultural regions contributes to the structuring of the landscape and the creation of habitats and stepping stones for plant species. For a comparison with theGrassland use was still lacking robust investigations. For biodiversity in terms of animal species, on the other hand, CUPs would not be of much importance, since endangered species are scarcely available in intensively used regions. However, SRCs would benefit animal ecology, as animals benefited from a longer period of dormancy, less fertilizer and pesticide use and fewer disturbances compared to one-year crops.

Benefits
The main advantage of using “grown fuels”, as opposed to fossil fuels such as coal, natural gas and oil, is that while they are growing they absorb the near-equivalent in carbon dioxide (an important greenhouse gas) to that which is later released in their burning. In comparison, burning fossil fuels increases atmospheric carbon unsustainably, by using carbon that was added to the Earth’s carbon sink millions of years ago. This is a prime contributor to climate change.

According to the FAO, compared to other energy crops, wood is among the most efficient sources of bioenergy in terms of quantity of energy released by unit of carbon emitted. Other advantages of generating energy from trees, as opposed to agricultural crops, are that trees do not have to be harvested each year, the harvest can be delayed when market prices are down, and the products can fulfil a variety of end-uses.

Yields of some varieties can be as high as 12 oven dry tonnes every year. However, commercial experience on plantations in Scandinavia have shown lower yield rates.

These crops can also be used in bank stabilisation and phytoremediation. In fact, experiments in Sweden with willow plantations have proved to have many beneficial effects on the soil and water quality when compared to conventional agricultural crops (such as cereal).

Ecological impacts
They are still partly discussed. In 2010, there are still few advanced studies on the ecological effects of this coppice on biodiversity (45 references found by Gosselin in 2009). Some TCR and TTCR plantations have been made for research and demonstration purposes since the 1980s, but apart from Gustafsson’s (pioneering) isolated work (1987), it was not until the 1990s (in the United States) and 1995 in Europe to find scientific publications, particularly in Sweden and the United Kingdom, the decline is older (around 30 years in 2015).

Very short, short or medium rotations are currently generally high-density plantations (10,000 to 15,000 stems / ha for TTCR and 1,000 to 4,000 stems / ha for TCR), monospecific in variety. hybrids (more productive, but often more fragile), even monoclonal or genetically little biodiversified or even exotic.

While they can – under certain conditions – help purify water and soils, willow and / or poplar coppices are very water-intensive in Northern Europe (up to 6-7 mm / day), in summer when this resource is the smallest.

A permanent coppice (but can be partly periodically cut) can provide protection to a part of the biodiversity or contribute to ecosystem restoration, but the available studies show that they benefit rather mundane species.

Their uniform appearance (same age class) and the absence of wood-dead stage diminish their ecological interest and sometimes make them ecological pitfalls. They attract birds, insects and mammals that take advantage of them for some time and then die when they are crushed with wood or brutally left without habitat. In addition, in the long run, these crops may require large amounts of inputs and exploitation makes them susceptible to various diseases.

However, a more heterogeneous structure (in age classes) and more diversified (in species and genes, although mixing clones induces in the ” dominated clones ” phenomena of mortality by competition, especially when the plantation is very dense could perhaps reduce the need for chemical and phytosanitary inputs by making the practice of energy culture more flexible (less input costs, less maintenance, better resistance to storms, frost, droughts); a culture of different species, densely planted, would develop roots colonizing different depths and make the crop more resilient and resilient.

Finally, according to the available data (Christian et al., 1994, Ranney and Mann, 1994, Weih, 2004), the ecological effects of this coppice vary greatly according to the eco-landscape context and its dominant (agricultural, forest, urban…) and according to the former state of the soil and the environment (former annual agricultural crops, fallow land, grassland, wastelands, possibly polluted, forest).

Post-ecological aspects
If they are not subject to phytosanitary treatments, if they do not substitute for natural environments that are richer and more interesting for biodiversity, and if they have genetically and structurally complex multistrate coppices connected to the local green network could be of some ecological interest:

Remediation of natural environments or natural infrastructures to fight against the fragmentation of natural habitats which we know has become one of the first causes (and probably even the first cause) of regression and disappearance of species, for example if one thinks of integrating ponds or ditches in water, and if one avoids the phytosanitary treatments. Multistrate linear plantations can – to some extent – play an ecological infrastructure role (= biological corridors) which are semi – natural, but which may play a role as an alternative biological corridor.

Regulation and storage of water resources (very favorable impact on flood / drought cycles by inertia and regular supply of groundwater by natural drainage).
Microclimatic regulation (macro and micro) and thermohygrometric regulation in particular.
Absorption of greenhouse gases, carbon sink (in soil), to some extent
Favorable impact on the maintenance of natural balances (for example by increasing ecotones or creation of buffer zones and the increase of semi-natural habitats (if the coppice or crops are not subject to pesticides and excesses) fertilizer).
possible (locally) reduction of the overcrowding of natural environments (often relictual).
Detoxification of some polluted wastelands (eg by nitrates / phosphates or even by some heavy metals), but with a necessary prudence, the toxic ones possibly reappearing in the foliage, the woods, the fumes or the ashes. The wood may need to be burned in installations with efficient filters.
absorption or fixation of certain atmospheric pollution (dust, gas, aerosols)
Adverse ecological aspects
They appear especially when the coppice replaces an environment of higher ecological value (permanent meadow, peat bog, heath, limestone hill, floral fallow, etc.), but in general the TCR and TTCR attracts rather banal species, some of which go die crushed or crushed at harvest.

The species used (Salix sp., Populus sp.) In TTCR are among the most water consuming (up to 6-7 mm / day) and often requires (to be industrially exploitable) tillage, control of competing plants (usually by means of a herbicide) and a stump to cause the floor to the other uses. Pollen, seeds and clones releases can be used to source genetic pollution for wild and native populations near.

Pedagogical vocation
The TCR can be a place for training, awareness, formation of communities, elected officials, technicians, associations, schools and public, a place of demonstration of new methods of reconstitution, maintenance and more “ecological” management of Para-forest or semi-natural ecosystems, a place of “Chantier – école”?

Alternate training plans are relatively easy to implement (given the seasonal nature of the work).

Scientific vocation
The TCR can support the development of research on a new form of ecological engineering (reconstitution of semi-natural or semi-forest ecosystems, soil release of ashes or certain trace elements, sulfur, for example; evolution of these semi-natural environments and the ecosystems that appear in them, evaluation of the different methods, their relevance over time, or depending on the pedological and climatic contexts, ecotoxicology (effects of the TCR on soil purification, migration of toxic, etc.); reintroductionor in situ conservation of “useful” plant and animal species; design of reproducible methodologies and techniques; monitoring of mycorrhizal phenomena in this particular context, etc.

Problems
Although in many areas of the world government funding is still required to support large scale development of energy forestry as an industry, it is seen as a valuable component of the renewable energy network and will be increasingly important in the future.

Growing trees is relatively water intensive.

The system of energy forestry has faced criticism over food vs. fuel, whereby it has become financially profitable to replace food crops with energy crops. It has to be noted, however, that such energy forests do not necessarily compete with food crops for highly productive land as they can be grown on slopes, marginal, or degraded land as well – sometimes even with long-term restoration purposes in mind.

Source from Wikipedia