In agricultural grassland, high herbage utilisation efficiency (HEFF), which is the proportion of gross live‐green herbage production that is utilised before entering senescence, is ensured by frequent defoliation. The decision upon which defoliation frequency to apply depends on the farming intensity. Assuming a reduced total herbage accumulation near trees in silvopastoral systems, frequent defoliations with high HEFF become less worthwhile—at least in specific spatial configurations. This makes an extensive management near trees an interesting option because it promotes other grassland‐related ecosystem services such as biodiversity. The present study first analysed the interaction between defoliation frequency and position to trees on the total, dead and live herbage accumulation and the HEFF at two silvopastoral sites with short‐rotation coppices in Germany. In addition, the total grassland–tree interface in Germany was assessed from land use and land cover maps of Germany based on satellite data to approximate the potential of grassland extensification near trees. The total herbage accumulation near trees declined by up to 41% but the HEFF was not affected by the position. Consequently, any intensification is not paid‐off by adequate productivity and herbage quality in terms of HEFF and tree‐related losses in herbage accumulation are expected up to a distance of 4.5–6 m. Applying a 4.5 m border on satellite data, we found that up to 4.4% (approximately 2200 km2) of the total grassland area in Germany is at a tree interface and potentially suitable for extensification. These findings indicate substantial potential for biodiversity conservation in grasslands with low trade‐off for high‐quality yield.
In legume-based grassland, legumes supply the sward with nitrogen (N) from biological N2-fixation. Previous studies in silvopastoral systems have emphasized that legume proportions decline near trees which would cause spatial variation of the N supply and the concentration of N in the harvested herbage of grass swards between trees. In natural ecosystems, it was shown that the N resorption efficiency (NRE) increases with nutrient limitation, hence, near trees where legumes are scarce. We, therefore, tested the hypothesis that the NRE increases near trees and compensates for the loss of legumes with respect to N concentration in live herbage. For this, two vegetation compositions consisting of legume-based grass swards were analyzed across positions between tree lines in an alley cropping system established five years prior to this study. Legume proportion declined up to 45% towards the tree line and thus, also N concentration in live and dead herbage but on average only by 15%. As a consequence of a reduced N concentration and also herbage mass close to trees, the N yield decreased by up to 50%. Despite the loss of legumes near trees, the NRE was unaffected by the tree line irrespective of vegetation composition. Further, the results indicate that internal N cycling of managed grass swards in silvopastoral grassland with short defoliation intervals between harvests is of lesser relevance than in unmanaged ecosystems. Legume proportions control the N concentrations of live and dead herbage irrespective of tree shading in silvopastoral systems.
In recent times, silvopastoral systems gain increasing attention due to their various ecological and economic benefits. They have the potential to be a more sustainable alternative to common intensive land-use practices and monocultures and to mitigate climate change effects in agriculture. Interactions between woody and non-woody components in agroforestry can enhance e.g., nutrient and water cycling, microclimatic conditions and raise productivity compared to non-agroforestry systems because of complementary resource capture. Still, silvopastoral systems are economically unproven land-use systems due to, inter alia, limited understanding of tree-grass sward interactions and their development over time. Further, agricultural grassland systems face changing growth conditions like increasing dry summers due to climate change. Hence, alternative grasses need testing for future climate change conditions. The present dissertation comprises three studies of which the first two aimed to reveal interacting effects of trees, cutting frequency and sward botanical composition on herbage production and nitrogen (N) resorption processes of the grass sward in between tree lines in silvopastoral systems. The aim of the third study was to investigate the effects of N availability on growth and N resorption of tall fescue (Festuca arundinacea), a grass known for its drought tolerance, compared to perennial ryegrass (Lolium perenne) as the most widely used grass.The first two studies were carried out as part of the SIGNAL collaborative project as part of the BonaRes (Soil as a Sustainable Resource for the Bioeconomy) funding program at the University of Göttingen, which investigated the sustainable intensification of agriculture through agroforestry. Therefore, silvopastoral systems were studied at two sites in Central Germany in the years 2016 and 2017. Both silvopastoral systems were arranged in the form of alley cropping systems comprising willow stripes under short
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.