Our study illustrates clear differences between theoretical potentials and factually usable potentials for biogas production from residual grasslands. Competing policy goals resulting in legal restrictions (protection of soils, aquatic resources and biodiversity), actual accessibility of plots and mowings (property and technology factor), and economic considerations cause these distinct differences. In our detailed assessments the technology factor is probably least important for improved recovery of potentials.
According to the administrator-in-charge, in Schwäbisch Hall County, currently only 0.5% of the land under conservation contracts could be available for biogas production. Most of the landscape maintenance sites are grazed under conservation contracts (slopes) or mowed (wetlands). For landscape maintenance sites, significant subtractions for areas theoretically available have to be made to exclude competition for space. Revenue from the grazing operation provides much needed income for livestock keepers that have often cooperated with conservation authorities for a long time. This is particularly true as livestock used for landscape maintenance or derived livestock products often cannot be profitably sold in the market (e.g., sheep products). Apart from competition, from a nature conservation perspective, traditional land use patterns based on traditional species and breeds often provide the best option to deliver desired landscape qualities [22
Even if more landscape maintenance areas were available provided contracts are not renewed, landscape structure (steep slopes) and lack of potentials for intensification (limits to mowing frequency and fertilization) render these sites unattractive for acquisition of substrates to be used in biogas operations under current funding programs.
Surprisingly, we did not encounter any grassland that had recently been abandoned. Studies [23
] estimate the expected average of these areas in the Federal State of Baden-Württemberg at 26% by 2015, and more specifically at 28% of the total grassland area in Schwäbisch Hall County. An important reason for the perceived discrepancy between predictions and actual findings might be the accumulation of milk quota in Schwäbisch Hall County, which in fact has one of the highest livestock densities in the State of Baden-Württemberg. High livestock density results in high demand for fodder and mainly grassland. On the other hand, and primarily as a result of biogas operations, demand for agricultural land in Baden-Württemberg is high and may render predictions with respect to future land abandonment uncertain at best.
In the perspective of biogas operators, materials from roadside edges are unfavorable because of pollutants and waste. Pollutants along roads include metals such as copper or polycyclic aromatic hydrocarbons (PAH) that are often highly toxic [24
]. The concern that use of biomass from roadside edges will spread pollutants on agricultural soils is warranted. This concern is expressed in legislation that prohibits the use of biogas slurries on agricultural fields, if materials from classified road edges have been used as substrates. Waste (plastic, glass, metals) is of particular concern for biogas operators, because it hampers the fermentation process in biogas plants.
Pollutants might not be a problem for substrates recovered near minor roads and paths closed to public traffic. But even if there are no toxicants and little waste, other problems arise. Cuttings from roadside edges are difficult to collect and cannot be recovered with conventional farming machinery. Rather, the collection of cuttings from roadside edges would require investments into specific suction devices. In Schwäbisch Hall County such suction devices have been abandoned due to nature conservation concerns (Head of County Road Administration, personal communication). Collection of the cut is therefore considered expensive and economically unfeasible. This, in combination with the comparatively low biogas yield from the bulky materials and the lack of specific GREA funding, has prevented requests for such cuttings from non-classified roads to be used in biogas plants and paths usually mowed and then mulched by communal work crews or farmers.
Provided grass along roads can be harvested, there is no foreseeable potential to increase yields by conventional intensification (increased number of cuts, use of fertilizer). Such intensification resulting in enhanced growth would either contradict the management goal for visibility (traffic safety) or the management target of least cost. Least cost management in this case mainly implies that edges have to be mown only twice, preferably only once, in each season. Numbers of personnel, machinery and work schedules are adapted to this situation. Available trucks can accomplish two cuts per year to a width of 3.5 m. Hand driven cutter bar mowers are being used for sites that are cut only once (width of roadside edge >3.5 m). Increasing the number of mowings would require more machinery and personnel.
Ownership structure along streams and ditches prevents the effective use of stream-side biomass. Single plots usually border streams with short boundaries. This equates to a maximum number of plots bordering streams and the subsequent need to communicate with numerous land owners in order to access the sites. Since communities are charged with maintaining so called second-order streams (minor streams); there may be a possibility to have easier access via communal ordinances. We did not examine whether communal ordinances may provide means to facilitate this process. It is, however, doubtful that communities would be willing to interact with property rights in the way described. And, even if the sites were accessible by owner consent, the problem remains of effectively collecting the bulky cut from steep edges and stream banks. Not surprisingly, no interest has ever been expressed in Schwäbisch Hall County in harvesting grassy strips along watercourses and to use these clippings for biogas production.
The Wasserverband Brettach is a specific organizational feature unique to the 4 model communities. The Wasserverband is charged with the maintenance of stream banks and mows the grass on the banks using hand pushed mowers. Cuttings are subsequently collected with hand motorized equipment (Bandrechen). The harvested biomass is currently fed to cattle by a crew member, but could also be used for biogas free of charge. Therefore, in the model communities we included the biomass from stream banks with the technical potentials. However, it has to be noted that there are no potentials for intensification along the watercourses, because this would require the use of fertilizer. For reasons of water quality, use of fertilizer in close vicinity to streams is prohibited und undesirable at distances within the legally protected riparian strip (10 m width along streams).
Under current conditions, only cuttings from public green spaces were found to provide a feasible substrate for biogas production from residual areas. The grassy material is well suited for biogas reactors (mechanically and in terms of biogas yield). And, at least some of the clippings are already collected and then usually have to be deposited. Deposition causes cost (at least for transport, likely transport and volume). Thus, there is a potential for cost reduction on the one hand (communities in charge of public green areas) without causing direct cost for acquiring the biomass on the other (biogas plant operator). Lack of possibilities for simple storage limits the use of the clippings from public green areas. Clippings ideally will be picked up and brought to a biogas reactor at the day of mowing and within 72 hours after mowing at the very latest. Otherwise, rotting will considerably diminish biogas yield. Use therefore is restricted to the growing season (April/May–September/October). Whether mixing of cut from lawns with more bulky materials to allow for production of storable silage could be a viable alternative is unclear. However, such mixing would require considerable logistics and additional processes with associated work time.
Even more cut could be obtained from public green spaces by introducing and optimizing fertilization and increasing mowing frequency. However, this would contradict least cost management and require either additional funds to be invested in park maintenance by communities or an attempt to compensate extra cost by selling the grassy materials to biogas operators. Calculations not considering clippings from private lawns indicate that a 150 KW biogas reactor exclusively operated on feed from public green areas might be profitable under current funding conditions [21
]. However, the operation would not be profitable under the provisions of the new 2012 GREA [21
]. Mayors of the model communities were presented with the calculations. Considering risks and uncertainties from an economic perspective, the research group was unable to recommend the model and the mayors therefore did not express interest in such a project potentially requiring continued input of communal funding.
Some of our results do not compare well to the estimates provided in Table 1
for the national scale [5
]. National estimates for roadside cuts appear to be unrealistically high (56% usable), considering the problems discussed. National estimates for habitat maintenance sites apparently ignore competing use (50% usable), but otherwise may be fairly realistic. Finally, it appears doubtful whether, considering the logistical problems, the estimates for private and public green spaces are achievable (73% usable).
We consider the results presented to be rather robust in terms of general conclusions. Average data on biomass and biogas yields from specifically managed areas used for the calculations will not vary significantly between different geographic regions in Germany and beyond. In terms of area available, there may be more region-specific variation with respect to prominence of nature conservation sites. Southern Germany is a hotspot for species-rich grassland and may harbor more of these sites [25
Our research demonstrates that detailed multi-scale investigations are required in order to properly assess bioenergy potentials. We consider a need for the development of standardized protocols to evaluate these potentials. In the absence of such standardized and detailed investigations, a precautionary approach should consider the following categories for subtractions from theoretically available potentials:
land access (ownership and competing use);
legal provisions restricting intensity of use (overriding environmental concerns);
a precautionary approach, generally basing calculations on available technologies;
economic considerations (yield and of cost of collection relative to other substrates) or participation-based indication (willingness to participate).
There are possibilities to use biomass from residual land for energy production. Opportunities to gain energy from sources that are currently considered as waste should be explored and whenever feasible exploited. However, with respect to biogas these possibilities are rather limited and have been estimated at 1.6–3.2% of the total primary energy needs in the state of Baden-Württemberg [26
]. In the Baden-Württemberg Biomasse-Aktionsplan a considerable share (up to 41%) of the bioenergy from agricultural systems is attributed to landscape maintenance materials, cuttings from roadside edges and clippings from public green spaces [26
]. The discrepancy between the actual data recorded in Schwäbisch Hall County and the political targets for use of residual materials suggests that the potentials for these materials to be used in biogas operations have been vastly overestimated – at least under current funding regimes.
There is strong indication that overestimation of bioenergy potentials has caused passage of unsustainable policies (e.g., biofuel targets). Based on calculations by Rauh and Heißenhuber [27
] meeting the national 15% biofuel goal alone would require 50% of the German farmland (farmed fields). Adding the area allocated to biogas production in 2011 (800,000 ha) and ignoring expected biogas expansion in the years to come, would raise this figure to approximately 57% of the farmed area. These figures are not presently under political or public discussion.
Biofuel policies have added an additional demand on the land and caused further intensification of land use. Agricultural intensification tends to create homogeneity at all scales with associated loss of biodiversity [28
]. Drivers for such loss include planting of set aside areas with energy crops, turning permanent grassland into arable fields, intensification of grassland use leading to the decline of species-rich grasslands, a more monotonous pattern of use (larger patches, reduced diversity in crop rotation). In addition, at least in Baden-Württemberg, take-up of agri-environment programs and interest in conservation contracts has considerably declined, as compensations awarded cannot keep up with the increased cost of leasing and increased opportunities for higher market value conventional farming products.
A proper assessment of potentials has to precede large scale renewable energy policies and the local establishment of renewable energy operations. This is particularly true for renewable energy to be produced on the basis of limited area and biological/ecosystem potentials. Our research indicates that theoretical potentials should not be taken into consideration for assessments, because of an overriding public interest in other environmental qualities (clean water, biodiversity, minimization of the spread of toxicants on agricultural soils). The public interest in the preservation of these overriding environmental qualities is expressed in legislation or ordinances (conservation ordinances, state fertilization ordinance, state water act).
In environmentally-sensitive areas, intensification is not an option, in spite of offering high theoretical potentials for increased yields. Biomass yields (dry mass) vary between 1.5 t/ha∙a from single-cut conservation grassland to 12.6 t/ha∙a from intensively managed grasslands and fertilized public green areas. Similarly, biogas yields from residual grasslands vary between 200 m3/t dry mass from conservation grassland to more than 650 m3/t from public green spaces and intensively used grassland. In terms of multiplicative effects, this amounts to a 25-fold difference in terms of area-specific biogas yields – 300 m3/ha from conservation grasslands and 7,560 m3/ha from intensively managed grasslands, including fertilized public lawns. This difference explains inherent pressures towards intensification, associated with the use of grassland for biogas production. This difference warrants extreme caution when promoting or permitting new biogas operations supposedly founded on primarily using residual materials from conservation sites.
Apart from environmental reasons, intensification on residual areas such as public lawns or roadside edges often faces the obstacle that it is linked to more costly management activities in order to produce more of what is currently considered as waste. This inherent limitation can only be overcome with integrated concepts incorporating “producers” of the substrates (communities and other administrations), potential investors and operators of biogas plants. There is a need to link these parties through long-term contracts. Cooperation may include building facilities specifically suited to handle bulky substrates using dry fermentation techniques that currently do not pose direct competition with less labor-intensive operations, such as liquid fermentation and, if necessary, cover economic shortfalls as compared to more cost-effective operations based on maize from prime agricultural land.
In this context, we also perceive a need for a restructuring of the GREA in order to provide appropriate compensation for increased effort, need for investments and little yield when dealing with substrates from residual areas. There is currently no specific attempt to compensate for effort in the GREA, and compensations for the use of bulky landscape maintenance materials in general have proven to be insufficient as compared to compensations provided for popular liquid fermentation technologies.
We face the problem that putting pressures on ecosystems beyond the effects of climate change may accelerate extinctions and environmental degradation, and thus hamper future ecosystem capacities to adapt to such change. The ability of ecosystems to adapt to environmental change is rooted in biodiversity. In changing environments, biodiversity allows adaptive efficiency of ecosystem services and functions [29
]. Despite national or even EU-wide efforts to reduce CO2
emissions, environmental change appears to be inevitable. There are no signs that efforts at community, state, national or even EU levels can override global trends caused by developed and developing economies to use available fossil fuels as long as these are the cheapest and therefore in the short term the most economic means of producing energy.
Efforts by national governments to positively influence global environmental policies have to be applauded. But, climate change is not the only pressure on ecosystems by far. Other such pressures are under much more direct and fuller control of national, regional and local governments. Such pressures are often linked to land use, and land use intensity in particular [30
]. A strong focus for national and regional policies has to be, at least, on not augmenting, ideally even releasing environmental pressures on ecosystems. Development of renewable energy should be evaluated in this context. There has to be a policy focus on responsibilities that can actually be accounted for.