Ansgar Quinkenstein

Ecological benefits provided by alley cropping systems for production of woody biomass in the temperate region: a review

In temperate Europe alley cropping systems which integrate strips of short rotation coppices into conventional agricultural fields (ACS) are receiving increasing attention. These systems can be used for crops and woody biomass production at the same time, enabling farmers to diversify the provision of market goods. Adding trees into the agricultural land creates various additional benefits for the farmer and society, also known as ecosystem services. However, tree-crop interactions in the temperate region have not been adequately substantiated which is identified as a drawback to the practical implementation of such systems. In order to bridge this gap, the current paper aims to present a comprehensive overview of selected ecosystem services provided by agroforestry with focus on ACS in the temperate region. The literature indicates that compared with conventional agriculture ACS have the potential to increase carbon sequestration, improve soil fertility and generally optimize the utilization of resources. Furthermore, due to their structural flexibility, ACS may help to regulate water quality, enhance biodiversity, and increase the overall productivity. ACS are shown as suitable land use systems especially for marginal sites. Based on the available data collected, we conclude that ACS are advantageous compared to conventional agriculture in many aspects, and therefore suggest that they should be implemented at a larger scale in temperate regions.

Organic Matter Dynamics in Reclaimed Lignite Mine Soils under Robinia pseudoacacia L. Plantations of Different Ages in Germany

In temperate regions, cultivation of Robinia pseudoacacia L. has recently received considerable attention because it is a fast-growing species for biomass and bioenergy production, while acting as a potential carbon (C) sink to counterbalance carbon dioxide (CO2) emissions and an alternative to agricultural crops on marginal sites. The objective of our work was to compare total organic carbon (TOC), total nitrogen (TN), and organic C fractions in postlignite mining soils under different development stages of R. pseudoacacia. Soil samples from three different depths (0–3, 3–10 and 10–30 cm) were taken in plantations 2, 3, 4, and 14 years old (R2, R3, R4, and R14, respectively). The TOC and TN contents increased with increasing tree age in all layers (P < 0.01). In the top 30 cm, TOC and TN stocks ranged from 11.7 to 59.8 Mg C ha−1 and from 0.30 to 2.61 Mg N ha−1 at R2 and R14, respectively. The rate of C sequestration was calculated to be 4.0 Mg C ha−1 year−1. Microbial biomass C and N were strongly correlated to TOC (r2 = 0.96 – 0.81; P < 0.001) and TN contents (r2 = 0.92 – 0.91; P < 0.001). The light fraction C (CLF) accounted for 15–30% and the heavy fraction C for 70% of TOC in all layers. In the 0- to 3-cm layer, CLF increased by 0.5 g kg−1 year−1. The results indicate that plantations of R. pseudoacacia are an attractive alternative to increase soil C contents in reclaimed lignite mining soils. In the short term, microbial biomass C and light fraction C are sensitive and provide an appropriate measure to assess soil C changes caused by cultivation of R. pseudoacacia.

Agroforestry for Mine-Land Reclamation in Germany: Capitalizing on Carbon Sequestration and Bioenergy Production

Surface mining operations generate significant and large-scale landscape disturbances. As a consequence, effective reclamation management is required to ensure the establishment of a sustainably productive, ecologically valuable, and economically attractive post-mining landscape. In the post-surface-mining landscape of Lower Lusatia (northeast Germany), a new land-use option during reclamation is the establishment of alley cropping systems (ACSs) producing food and woody biomass for obtaining bioenergy. The established multi-row tree strips are typically managed as short rotation coppices (SRC), for which black locust (Robinia pseudoacacia L.) is the most frequently used tree species. The alley cropping systems are promising land-use systems for mine-site reclamation because they provide a multitude of ecological and economic benefits; furthermore, within these plantations, significant amounts of carbon (C) can be accumulated in the biomass and the soil. The results of field studies on C sequestration in R. pseudoacacia stands on reclaimed mine sites within the Lusatian region indicate an average shoot dry matter (DM) production of R. pseudoacacia between 3 and 10 Mg DM ha−1 year−1 depending on the plantation age and rotation period. The DM yields for foliage biomass ranged between 12 and 32 % of the shoot biomass for 2- and 4-year-old trees. Estimates of the C storage within the soil are up to 7 Mg C ha−1 year−1 within 0–60 cm depth. In summary, the results support the hypothesis that ACS of R. pseudoacacia may be in many respects a beneficial land-use system for marginal, post-mining landscapes, with a significant C sequestration potential above- and belowground.

Biomass, Carbon and Nitrogen Distribution in Living Woody Plant Parts of Robinia pseudoacacia L. Growing on Reclamation Sites in the Mining Region of Lower Lusatia (Northeast Germany)

In the lignite mining region of Lower Lusatia (NE-Germany), Robinia pseudoacacia L. is an increasingly popular tree for the biomass production with short rotation coppices (SRCs) on reclamation sites. In order to evaluate biomass production, C and N allocation patterns in R. pseudoacacia stands between shoot, stump, coarse, and fine roots samples were collected from seedlings and three adjacent plantations and plants that were one, two and twelve years old. Results indicated that the summarized average dry matter production (DM) of the woody plant parts increased with plant age up to 7.45 t DM ha−1 yr−1 with a corresponding shoot increment of up to 4.77 t DM ha−1 yr−1 in the twelve-year-old stands. The shoot to root ratio changed from 0.2 for the one-year-old trees to 2.0 in the twelve-year-old plantation, whereby an average amount of 3.4 t C ha−1 yr−1 and 0.1 t N ha−1 yr−1 was annually bound in the living woody plant parts over the period of twelve years. Summing up, the results suggest a high potential for C and N storage of R. pseudoacacia what is also beneficial for land reclamation due to positive implications on soil humus and general site fertility.

Alley Cropping with Short Rotation Coppices in the Temperate Region: A Land-use Strategy for Optimizing Microclimate, Soil Organic Carbon and Ecosystem Service Provision of Agricultural Landscapes

Conventional agricultural practices have been associated with negative effects, such as reduction of soil fertility, pollution of surface and groundwater and loss of biodiversity and ecosystem services (ES). To mitigate these effects, while sustaining high levels of crop production, innovative land-use practices are necessary. A promising land-use approach are alley cropping systems (ACS) with short rotation coppices, which are agroforestry systems, that combine the cultivation of conventional agricultural crops with fast-growing trees to produce biomass for energy purposes at the same time on the same piece of land. In the presented study, the effects of trees planted in ACS on agricultural land in Central Europe on microclimate, on soil organic matter (SOM) and on the provision of ecosystem services (ES) were elaborated, based on a review of relevant literature and results of recent research projects. The outcomes suggest that, due to their structural complexity, ACS can be more efficient regarding main microclimatic factors than either crop or tree monocultural systems. As a main factor, wind protection by the hedgerows in ACS was identified. Other microclimatic factors, such as light, temperature or evaporation, were also clearly influenced by the presence of trees; however, occurring interactions were often complex, and cause-effect relations were difficult to ascertain. A further outcome is that planting trees on agricultural sites potentially increases soil organic carbon (SOC) stocks, which can be considered as a main indicator for soil humus and soil fertility. However, it became evident that, in addition to the depth dimension (30 cm sampling depth can be considered as insufficient), the dimension of time needs to be taken more strongly into account. The authors suggest a division of the lifetime of agricultural trees in an initial (SOC stocks may decrease), a transitional (stocks approach steady state; SOC distribution pattern in the soil may change) and a steady-state phase (no major changes in stocks or distribution patterns) when interpreting effects of trees on SOC. Subsequently, in the attempt to value the effects of ACS on crop productivity and soil, suitable and transferable methods for the assessment of ES were discussed. It was demonstrated that the provision of ES from ACS was higher than from conventional agriculture and that ACS can increase productivity while sustaining high levels of SOC. Summarizing, the results suggested that ACS – if designed and managed appropriately – may function as a practical and diverse tool to mitigate negative effects of agricultural production.