1. Introduction
Bioenergy is widely regarded as a major source of renewable energy with numerous benefits including Greenhouse Gas (GHG) reduction and climate change mitigation [
1,
2] To address the climate change challenge, an ideal approach would be to replace fossil fuels with renewable energy sources combined with a rapid improvement in energy efficiency [
3,
4] Bioenergy was intended to mitigate climate change through lowering GHG emissions, nonetheless, many biofuels nowadays emit as much or even more GHGs than fossil fuels or lead to only small savings, considering their whole lifecycle and taking into account the negative impacts of indirect land-use changes [
5].
Several factors are impeding bioenergy’s sustainability development pathways. The most controversial issue is the trade-off between the cultivation of bioenergy crops and food production (i.e., competition for land) [
6,
7,
8]. In recent years, many fertile agricultural lands have been converted to bioenergy crops, mainly maize, rapeseed, and sugar beet [
9,
10].
The most common biofuel in Germany is biogas [
11]. Maize as a bioenergy crop has been responsible for 70% biogas production input [
12,
13] Maize is usually planted as a monocrop and its cultivation is characterized by high nutrition requirements (i.e., fertilizers and/or good soil fertility properties) [
14]. Biodiversity in maize monoculture farms is very low, and they are often called “grass deserts” [
15]. Monoculture does not permit the reproduction of other species since only one species is planted and weeds are controlled by using pre- and post-emergence herbicides [
16]. In this regard, the environmental effects of maize as a bioenergy crop is still a controversial topic [
17]. Intensification in maize monoculture is recognized to result in soil erosion, groundwater contamination, and biodiversity loss, impacting all organisms that live in agricultural habitats [
18]. In Germany, in almost all regions under intense agricultural practices, high nitrate contamination of groundwater can be expected [
19]. N fertilizers contribute to various environmental issues such as contamination of groundwater and air pollution. Furthermore, nitrous oxide gas (N
2O) emissions, also considered as GHG, contribute to climate change [
20,
21] In this line, the 2030 Biodiversity Strategy of the European Union (EU) [
22] includes specific goals to restore, for example, damaged ecosystems to reduce risks from chemical pesticides, or mitigating the decline in farmland birds and insects.
Maize and other edible common energy crops such as wheat, sugarcane, and rapeseed are considered as the feedstock for the first generation (1G) of biofuels [
23]. The problem regarding the use of these crops for bioenergy production is, first, they are either food or feed crops that directly generate negative effects on food security [
24,
25]. Such crops that could be part of the food cycle are being severely processed to be burnt as a fuel. Secondly, their production is competing with food production as they also require arable land [
26,
27]. While bioenergy production is attracting great attention as a renewable source of energy, the world’s population is rapidly increasing and consequently the demand for food is increasing [
28]. According to the Food and Agriculture Organization of the United Nations (FAO), to feed the growing population by 2050, agricultural production will need to increase by 60% [
29]. This raises the question of how to feed the world, which has become a major problem in facing bioenergy development in a regional decision-making context.
To alleviate these negative impacts on the environment and the competition with food production, one of the solutions suggested by many researchers is the use of marginal land for bioenergy cropping [
30,
31,
32]. Thus, the fertile arable land could still be used for food production. Whereas 1G energy crops, the second generation of biofuels (2G), come from non-edible biomass plant species that contain lignocellulosic compounds [
33],
Miscanthus, black locust, switchgrass, and canary grass are common 2G bioenergy crops [
34,
35]. The other common alternative pathway towards the sustainability of the biofuels is to consider a shift to 2G bioenergy crops [
36,
37].
Miscanthus is a perennial C4 rhizomatous grass native to Southeast Asia, and with lignified stems similar to bamboo [
33,
38,
39,
40]. It has specific features such as large root systems and a dormant ability, resulting in higher stress resistance, higher survival rates, lower growth restrictions, and improved yield [
41].
Miscanthus, as an energy crop with relatively low maintenance requirements and a high dry matter yield and energy content, may play a major role in the sustainable development of biofuels [
42,
43]. Furthermore, and more importantly,
Miscanthus can enhance soil organic carbon (SOC) accumulation, which improves soil fertility and, consequently, crop yields [
44] and, on the other hand, contributes to mitigating CO
2 emissions to the atmosphere from the soil [
45]. Under unfertilized
Miscanthus, N
2O emissions might be five times lower than annual crops, and up to 100 times lower than conventional pastures. In
Miscanthus plantations, nitrogen (N) fertilizers are not usually required unless the soil is very poor. Herbicides are only needed for the establishment years, after that, due to its canopy closure, weed suppression happens naturally by shading [
46]. Pesticides are also only required in the establishment period when the shoots are young and fragile, in most cases after the establishment period, pesticides can be avoided [
38]. Due to these environmental benefits, it has been suggested to include this crop as a greening measure of the EU’s common agricultural policy (CAP) [
47].
Because
Miscanthus can be planted on marginal land, competition for land with food production can be avoided or significantly reduced [
48]. Therefore, in order to evaluate the possibility of achieving the bioenergy goal of Brandenburg for 2030 and at the same time avoiding competition for land with food production, a backcasting methodology has been applied in the region for the first time.
Thus, the aim of this study is fourfold:
- 1)
Estimate the area required to meet Brandenburg’s bioenergy target for 2030 (58 PJ) by using silage maize and Miscanthus (backcasting process).
- 2)
Estimate the bioenergy potential production from maize and Miscanthus by using only the available area for bioenergy without occupying the estimated land for achieving 100% of food self-sufficiency in the Berlin-Brandenburg foodshed (forecasting process).
- 3)
Select the most suitable pathway by comparing the results from the backcasting and forecasting.
- 4)
Identify and, in some cases roughly measure, other ecosystem services beyond provisioning services that may be positively affected after Miscanthus plantation in degraded lands.
4. Discussion
- a)
The potential of Miscanthus to achieve Brandenburg’s bioenergy goals and avoiding competition for land to secure food self-sufficiency for the Berlin-Brandenburg population.
By allocating 74.4% of agricultural land to food production based on the food self-sufficiency baseline scenario (BAU_30), the state would afford to assign the other 25.6% of its agricultural land for bioenergy crop cultivation. Therefore, by 2030, there would be around 389,690 ha (AAB), which implies that the maximum amount of arable land may be allocated for bioenergy production (
Table 5). To reach the 2030 bioenergy goal with maize as the main energy crop, the state would require 568,627 ha of land, while under
Miscanthus, only 232,000 ha would be needed. Otherwise stated, under the cultivation of
Miscanthus, Brandenburg would require around 2.5 times less the amount of land in comparison with silage maize. Hence, a transition from maize to
Miscanthus could spare about 337,000 ha.
Considering the 2030 AAB as 389,690 ha, in the BAU scenario (BAU_30) of bioenergy production, silage maize as the main energy crop would only be able to provide 40.1 PJ of energy, which is only 69% of the bioenergy target of 2030 (
Table 5). On the other hand, substituting
Miscanthus as the main biomass crop would lead to much higher energy production besides the numerous positive environmental effects that this crop would bring. Because
Miscanthus’ yield is considerably higher than that of maize (almost by 2.5 times) (
Table 3), shifting toward a
Miscanthus plantation could provide nearly twice the 2030 target (117 PJ energy) (
Table 5). This means substituting maize with
Miscanthus as the main energy crop could boost energy production by 245%, which can be relied on marginal land, as opposed to the current system, where almost 52% of biogas-maize cultivation is being planted on fertile land (
Figure 3). Therefore, this shift not only could release productive land for food production while achieving food self-sufficiency, but could also produce double the energy of 2030 bioenergy targets.
Therefore, when keeping the same dietary patterns and considering the population growth until 2030, our results suggest that the selected pathway (BAU_30) would be suitable for achieving Brandenburg’s bioenergy potential goal and at the same time avoid competition for land. However, when shifting to organic and regional diets (ORG_30), the AAB would not be enough to achieve the goal.
- b)
The importance of allocating bioenergy crops in marginal lands
One of the objectives of this study was to demonstrate the importance of spatial land resource allocation in sustainable development. Even though Brandenburg has a considerable amount of arable land, soil fertility is relatively low (45% classified as poor soil) and therefore, it is crucial to assign land for the best possible use. Our results suggest that with silage maize is the main bioenergy crop, the 2030 Brandenburg energy targets would not be reached unless the 568,627 ha land is allocated for bioenergy production (
Table 5). However, to achieve 100% of food self-sufficiency by 2030 in the Berlin-Brandenburg region 1,132,611 ha arable land would be required (
Table 2). Therefore, considering imposing no further land-use change, the available area for bioenergy production without affecting regional production to achieve 100% food self-sufficiency would be only around 389,690 ha (
Table 5), which is only 68% of the required land for achieving 2030 bioenergy targets under the current silage maize scenario.
According to [
60], defining marginal land is complex due to changes in land use and socio-economic impacts. Marginal land may be include a transitional phase of land resources, which is very susceptible to natural processes and different managements. The authors argue that the allocation of resources and the management practices can play an undeniable role in the productivity of land in which mismanagement of productive land may trigger soil degradation and in the long run, result in low productivity of the land, whereas marginal land can be improved and restored to a better quality level in the case of implementing sustainable management practices. Because
Miscanthus is a perennial crop with a great ability to restore SOC levels, it can be expected that by allocating marginal land to
Miscanthus production, the SOC depletion may be prevented and, in the long term, soil fertility properties would be improved.
Miscanthus is relatively tolerant of several environmental stressors, primarily salinity, drought, and flooding [
57,
61]. This special resilience encourages the growth of this perennial high yielding grass on marginal land [
62].
Miscanthus plantation on suitable marginal land is regarded to have enormous potential to boost energy protection and to reduce GHG emissions. However, there is still a range of restrictions to the utilization of this capacity to the full. The major drawback is the confusion regarding the existence of the required marginal land owing to increased demand from other uses, such as land reclamation for food crops or other bioenergy crops [
63,
64].
Due to the high importance of defining and locating the marginal land in Brandenburg, maps of marginal land were created based on the M-SQR Index (
Figure 2). Based on the assessment of [
51], marginal land could be considered those soils resulting in an M-SQR level lower than 40. Therefore, according to the results and based on the currently available literature, soils under this value should be allocated for
Miscanthus production and they should not be allocated for commercial food production.
To alleviate the land competition between food and energy crop production, cultivating bioenergy crops on marginal land should be considered as a suitable land policy. In the current policy scenario, however, 53% of maize as the main energy crop is being cultivated in fertile soil.
- c)
The importance of regional food production
Recent concerns about climate change have triggered further justification for local and regional food systems [
65,
66]. Such issues have included the externalities of long-distance shipping of food and the vulnerability of centralized food production to climate change. Regional and organic food agricultural systems are continuously being considered as a significant step toward a more sustainable future [
67]. Increased public awareness in linkages between food, safety, and the environment has driven rapid growth in regional and local food system projects. The associated improvement in the relevant scientific research has come alongside local development [
68].
In the beginning of 2020, the COVID-19 has caused a global health and economic crisis, which has also led to an exacerbation in food security and a food crisis in many countries. In fewer than three months, COVID-19 has exposed risks, instabilities, and inequities in global food processes and has brought them to the point of collapse. The COVID-19 pandemic, along with lockdowns, has shown the fragility of the current food system and the dependency on global food supply chains [
69]. In these turbulent times, food self-sufficiency can play an essential role since it has direct benefits for the capacity of a country or region to fulfill the nutritional needs of the people independently, despite the external situations [
70]. Therefore, the concept of self-sufficiency can bring resilience to the food system and should be prioritized over bioenergy production. For this reason, in this study, the starting point of the calculation of the AAB is the remaining area after calculating the area needed to achieve 100% of food self-sufficiency in the Berlin-Brandenburg region.
- d)
Environmental benefits and ecosystem services provided by Miscanthus
Miscanthus can be a multifunctional crop that not only offers a great amount of energy but also provides and supports other ecosystem services (ES) (
Figure 4). In this section, these will be discussed and estimated values will be given for some of them (underlined ecosystem services in
Figure 4). In this study, we specifically estimated the energy and food production (provisioning ES), C sequestration, and CO
2 mitigation potential of
Miscanthus (regulating ES).
- 1)
Provisioning Services: Energy and Food
According to our results, under
Miscanthus, each hectare of marginal lands in Brandenburg can generate 250 GJ of energy (
Table 3). This would allow the region to allocate more land for food production by up to 100% self-sufficiency (
Table 2). Therefore,
Miscanthus would provide energy, achieving Brandenburg’s bioenergy goal (direct provision of ES) and would avoid competition for land with food production (indirect provision of ES).
- 2)
Supporting Services
The low requirements in agrochemical inputs make
Miscanthus fields more environmentally friendly by reducing the common damage caused by these substances used in conventional farming. For the same reason,
Miscanthus has been reported to reduce the negative impacts of conventional agricultural activities on groundwater resources (by reducing N runoffs). On the other hand, the relatively high above- and below-ground biomass production has led to high incoming organic C in the soil (leaves on the soil surface and rhizodeposition processes), thus increasing the SOC content and leading to an improvement in the soil quality [
71,
72,
73].
Studies have shown the positive effects of
Miscanthus on biodiversity.
Miscanthus can provide structural resources to agricultural landscapes, offer shelter, and improve the temporal variability that is obtained in different seasons by various bird species [
74,
75,
76]. It increases the number and diversity of earthworms in arable land, similar to grasslands. Furthermore, [
77] showed a considerable increase in bird species diversity in
Miscanthus fields as well as a greater abundance of mammals, compared with arable lands, which cannot provide as much shelter as in the case of perennial crops allowing the growth of wild vegetation. These authors also assessed the diversity and abundance of invertebrates and revealed that “ground beetles, butterflies, and arboreal invertebrates were more abundant and diverse in the most floristically diverse
Miscanthus fields” [
78].
The spike in maize production in Brandenburg results in a reduction of the habitat area of bird species, such as corn bunting by 28.2% and Skylark by 21.3%.
Miscanthus cultivation can be a suitable alternative to not only mitigate the loss of biodiversity, but also to foster it by providing shelter for them [
49]. This specific characteristic of
Miscanthus plantations allowing the growth of non-crop plant species could be of critical importance to increase the diversity of insects, birds, and small mammals in Brandenburg.
- 3)
Regulating services: climate regulation
One tone of dry matter biomass through the pyrolysis process can produce 18.5 GJ energy, which is equal to the energy from one tone of coal [
58]. However, the significant contrast is that coal releases 500 kg C to the atmosphere while
Miscanthus only recycles it. According to our results, each hectare of
Miscanthus in the marginal land of Brandenburg has 250 GJ of energy potential production (
Table 3). Therefore,
Miscanthus could save around 6,750 kg C ha
−1 compared to coal.
In this study, we calculated the
Miscanthus potential for SOC accumulation and the associated sequestered CO
2 in soil under the different scenarios selected for the assessment (
Table 6). According to [
59], an average SOC sequestration rate after planting
Miscanthus would be around 1.1 t C ha
−1 yr
−1. Since
Miscanthus is mowed once a year, the effect on SOC sequestration can be compared to the effect of cover crops that are planted in the inter-row area of some woody crops. In this line, this value is very close to the 0.78 and 1.1 t C ha
−1 yr
−1 found by [
79] in a meta-analysis for cover crops/spontaneous plant cover in vineyards and olive orchards, respectively, and the range of the 0.7–2.2 t C ha
−1 yr
−1 estimated by [
74] for
Miscanthus in the UK. An increase of 1.1 t C ha
−1yr
−1 would imply the sequestration of 4.0 t CO
2 ha
−1yr
−1. Considering the cultivation of
Miscanthus in AAB without affecting food production (389,690 ha) (
Table 5), if all this area was planted with
Miscanthus, the CO
2 sequestration rate would be around 1.6 million t CO
2 ha
−1 yr
−1.
However, these numbers must be taken carefully, since the organic carbon sequestration in soil is limited and is dependent on the soil texture [
80] and the C sequestration rate decreases over time as the SOC content reaches the steady-state (i.e., equilibrium) [
79,
81]. On the other hand, not all the SOC would be really “sequestered” into the soil, since part of the accumulated SOC would be easily accessible to the microorganisms, thus being rapidly and easily mineralized (i.e., released into the atmosphere as CO
2). Although there is a high level of uncertainty, the proportion of this non-protected SOC would range between 20–40% of the total accumulated SOC [
82].
Actual levels of SOC in Brandenburg are relatively low and combine with the sandy texture, resulting in a soil poor quality (
Figure 2B) (i.e., M-SQR < 40). However, precisely this very low SOC content (i.e., high SOC saturation deficit) leads to a high potential for SOC sequestration [
80]. SOC accumulation rate is inversely proportional to the actual SOC content. In other words, the lower the SOC content is, the faster is the accumulation. Therefore, if
Miscanthus is planted in the poor soils of Brandenburg, a rapid increase in the SOC is expected. However, the SOC saturation limit is expected to be lower due to the lower content of clay [
80,
83]. Therefore, during the first years after planting
Miscanthus, the C sequestration rate of 1.1 t C ha
−1 yr
−1 might be reliable. More uncertainty remains over time, as SOC content increases.
- 4)
Other regulating services: Water regulation and pollination
Studies have shown that in comparison to maize fields, N leaching is considerably lower under unfertilized
Miscanthus [
74,
84,
85]. Leaching can be exacerbated in sandy soils due to low water-holding capacity [
86]. In Brandenburg, this is a very common problem where approximately 85% of the lakes are extremely or severely polluted with nutrients, while significant parts of the banks have been damaged in almost all big still water bodies, and around 90% of the existing stocks of grasses have vanished in several lakes [
87]. Therefore,
Miscanthus cultivation instead of maize is expected to alleviate water contamination in the region. Moreover, in terms of water efficiency, if
Miscanthus was planted instead of maize, one-third of the water could be saved [
2]. This is an important issue especially for the next few decades, where climate change is expected to increase water stress in Germany.
Miscanthus is not a preferred source of food for most insects and animals, but for many invertebrates and pollinators, its residues left after harvest and canopy closure shade provide nesting, shelter, and breeding sites [
88]. The increase in biodiversity, especially the diversity of insects, as a consequence of the increase in the wild vegetation, would improve the pollination activity in the crops placed in the surrounding areas of
Miscanthus fields.
- 5)
Cultural and socio-economic services
According to [
89], the attainable gross margins of producing
Miscanthus for combustion would range from 400 to 1600 € ha
−1, whereas these values would be somewhat higher, around 1300–2000 € ha
−1, in the case of using
Miscanthus for biogas production. Another key parameter is the labor requirements (e.g., labor peak seasons) of
Miscanthus compared to other annual crops since it could be expected that farmers will not be dedicated entirely to
Miscanthus cultivation, but also to other arable crops (cereals or maize). Thus, the labor peaks of the green harvest regime do not coincide with those of the other cereals or intermediate crops. However, some activities of the brown harvest regime overlap with those for other crops, but the only labor peak takes place in March, whereas for the rest of the year, the activity is less intensive. The total labor effort is estimated to be low, as between 4 and 15 h ha
−1 for
Miscanthus is already established, whereas the highest efforts take place in the establishing year [
89]. Therefore, the combination of low peak times in the management of
Miscanthus and the low labor requirements lead
Miscanthus to be feasible to be combined with the production of other arable crops.
Furthermore, the facilities to transform
Miscanthus into energy are also important in terms of quality job creation and population fixation [
90,
91]. Brandenburg is one of the least densely populated regions in Germany, and under increasing aging that might lead to an increase in land abandonment [
92]. The integration of bioenergy crops into the landscape may stimulate the economy of rural areas and thus mitigate the negative impacts of land abandonment [
93]. Therefore, to avoid or mitigate this,
Miscanthus could be of high relevance.
- 6)
Limitations of the Study and Future Researches
To examine the sustainability of the current biogas production in Brandenburg on the wider scale of Germany, it is required to have official statistics of the exact amount of each crop, in this case, silage maize, which goes to biogas plants, and the specific locations of these bioenergy farms. However, it must be noted that the total amount of “maize for biogas” planted in Brandenburg is reported as only 34,682 ha, which is expected to be about one-third of the actual area of 110,000 ha, but due to lack of clear official statistics or reports, we only demonstrated and analyzed this amount, which is reported by the official IACS database.
We believe that the application of the backcasting methodology to assess the feasibility of achieving the 2030 bioenergy goal of Brandenburg and integrating it with the food self-sufficiency assessment establishes the first step in the assessment of the regional food–energy nexus and can be the basis for future research focused on some specific issues, like locating potential marginal lands to be planted by Miscanthus or the socio-economic impact of these plantations in the region of Brandenburg.
5. Conclusions
Our study suggests that in order to produce bioenergy while avoiding competition for land with food production, it is important to move toward the 2G bioenergy crops that can be cultivated on marginal land. In Brandenburg, the agricultural land has been massively affected by the cultivation of maize for biogas production (300% increase in the past 10 years), thereby, the scarce productive land of the region has been under maize monoculture production, which has led to negative environmental repercussions (e.g., biodiversity reduction, soil degradation, or land-use change), which would nullify the potential GHG mitigation of bioenergy production. Thus, a shift from maize to Miscanthus as the main bioenergy crop could address almost all the negative environmental externalities caused by maize plantation, due to its perennial character and its low nutrient requirements which allow it to be cultivated on degraded areas.
On the other hand, our findings imply that substituting maize with Miscanthus for bioenergy production can ensure food production by releasing productive land for food production and providing a high yield of dry matter, which results in a reduction of land requirements for bioenergy production and, therefore, achieving the 2030 bioenergy goal of Brandenburg would be possible without negatively affecting the food self-sufficiency and in general the resilience of the food system of the Berlin-Brandenburg area.
Today, the world is experiencing a drastic health and economic crisis due to the emergence of COVID-19. This pandemic has shown the fragility of the world’s food systems, which is dependent upon international and complex food supply chains. This is another reason to highlight the significance of food self-sufficiency for regions and countries, especially in the events that strike food supply chains. Therefore, now more than ever before, food production should be prioritized over bioenergy production, particularly in regards to the allocation of fertile arable land.
Furthermore, the backcasting methodology applied in this study, which is one of the first studies to apply it in a specific study case in Germany, could be valuable to assess the current bioenergy goals and strategies of the state of Brandenburg. This is also reflected in the light of a city-regional food strategy launched by the Berlin Senate, which puts potentially competing pressure on land resources and consequently incentivizes the transformation of the food supply from Brandenburg by, for example, favoring organic and locally grown potatoes and vegetables for public procurement. On a more general level, we consider these trends and observations as indications of a general shift of paradigm, away from standardized global chain-oriented production to regionally tailored quality production oriented to specific individualized demands, or in other words, the transformation from cost competition to quality competition.
The approach and results of our study underline that for such a transition, integrated governance across sectors is required, particularly at state and regional levels, in order to better link bioenergy strategies with agricultural and food sectoral strategies and overarching environmental, climate and innovation strategies (e.g., climate change, biodiversity, agriculture, food production) and to create clear sustainable pathways to be achieved in 2030. Additionally, we believe that coherence between the different European strategies will be needed (e.g., the CAP, Green Deal, From Farm to Fork Strategy, or the 2030 Biodiversity Strategy).