Purpose of Review One of the challenges of forest operations is to consider the consequences of different management strategies and to estimate the economic, environmental and social performance of different processes, products, or services. From the methods available to quantify the impact of alternative forest management, we selected the method of Sustainability Impact Assessment (SIA), an iterative process that includes the analysis of the societal, environmental, and economic sustainability pillars and offers a wider assessment framework, which is useful for stakeholders and policy makers. The purpose of this review is to identify the state of the art and trends of SIA in forest operations. Recent Findings There are few studies including all pillars of sustainability and most of the studies consider different aspects of environmental or economic impacts. It is important to determine the system boundaries and select the appropriate indicators in order to have a comprehensive SIA. Different harvesting technologies and their deployment can influence costs, productivity, environment, and safety risk. Some indicators, such as cost and productivity, can vary between countries and different scenarios. Summary Efficient machines, appropriate technical systems, innovative products, and up-to date training of operators can have a positive impact on sustainability. Economic factors can change at a rapid pace, and new machines can play a positive role in forest operations (e.g., lower fuel consumption, higher level of safety and comfort for operators). The inclusion of indicators measuring the extra value of the forest should be considered. We suggest adopting sensitivity analysis during the assessment of key processes to observe the effect on the hot spots.
Several factors influence land availability for the growth of short rotation coppices (SRC) with fast-growing tree species, including the nationwide availability of agricultural land, economic efficiency, ecological impacts, political boundaries and environmental protection regulations. In this study, we analysed the growing potential of poplar and willow SRC for bioenergy purposes in Germany without negative ecological impacts or land use conflicts. The potential biomass production using SRC on agricultural land in Germany was assessed taking into account ecological, ethical, political and technical restrictions. Using a geographic information system (GIS), digital site maps, climate data and a digital terrain model, the SRC biomass production potential on cropland and grassland was estimated using water supply and mean temperature during the growing season as parameters. From this analysis, a yield model for SRC was developed based on the analysed growth data and site information of 62 short rotation plantations in Germany and France. To assess the technical, ethical and ecological potential of SRC, restrictions in protected areas, technical constraints and competition with food and feed production were investigated. Our results revealed that approximately 18% (2.12 Mio. ha) of cropland and 54% (2.5 Mio. ha) of grassland in Germany were highly suitable for SRC plantations, providing favourable water supplies and mean temperatures during the growing season. These identified sites produced an average yield of more than 14 tons of dry matter per hectare per year. Due to local climate and soil conditions, the federal states in northern and eastern Germany had the highest theoretical SRC potential for agricultural land. After considering all ecological, ethical, political and technical restrictions, as well as future climate predictions, 5.7% (680 000 ha) of cropland and 33% (1.5 Mio. ha) of grassland in Germany were classified as suitable for biomass production with fast-growing tree species in SRC.
Short rotation coppice (SRC) harvesting techniques are available in Germany, but broad experience and knowledge about machine performance and the related effective costs of harvesting operations are still missing. This information is crucial, as harvesting costs strongly influence the economic performance of the overall supply chain. Therefore, it was the aim of this study to collect and analyze productivity data of different harvesting systems for SRC. The combined cut and chip system on the one hand and the cut and storage system on the other hand were studied by literature review. Several studies analyze the combined cut and chip systems and the reported machine productivities showed great variations. The average was 30 green tons per scheduled machine hour (gt smh -1 ). Few studies are analysing the cut and storage system. They report that machines still are under development and that further research is needed. Therefore, time studies of harvesting operations using the cut and storage system were carried out. Five trials were performed with the harvesting machine "Stemster MK III" developed by Nordic Biomass. The share of productive working time was 85% and the average productivity was 21 gt smh -1 . These results were compared with values from the literature. Resulting harvesting costs were calculated per oven dry ton (€ odt -1 ). The advantages and disadvantages of both harvesting systems are highlighted.
For avoiding competition with food production, marginal land is economically and environmentally highly attractive for biomass production with short-rotation coppices (SRCs) of fast-growing tree species such as poplars. Herein, we evaluated the environmental impacts of technological, agronomic, and environmental aspects of bioenergy production from hybrid poplar SRC cultivation on marginal land in southern Germany. For this purpose, different management regimes were considered within a 21-year lifetime (combining measurements and modeling approaches) by means of a holistic Life Cycle Assessment (LCA). We analyzed two coppicing rotation lengths (7 9 3 and 3 9 7 years) and seven nitrogen fertilization rates and included all processes starting from site preparation, planting and coppicing, wood chipping, and heat production up to final stump removal. The 7-year rotation cycles clearly resulted in higher biomass yields and reduced environmental impacts such as nitrate (NO 3 ) leaching and soil nitrous oxide (N 2 O) emissions. Fertilization rates were positively related to enhanced biomass accumulation, but these benefits did not counterbalance the negative impacts on the environment due to increased nitrate leaching and N 2 O emissions. Greenhouse gas (GHG) emissions associated with the heat production from poplar SRC on marginal land ranged between 8 and 46 kg CO 2 -eq. GJ À1 (or 11-57 Mg CO 2 -eq. ha
À1). However, if the produced wood chips substitute oil heating, up to 123 Mg CO 2 -eq. ha À1 can be saved, if produced in a 7-year rotation without fertilization. Dissecting the entire bioenergy production chain, our study shows that environmental impacts occurred mainly during combustion and storage of wood chips, while technological aspects of establishment, harvesting, and transportation played a negligible role.
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