An evaluation of land use strategies for biodiversity conservation in apple farming landscapes

Throughout history, European landscapes have been strongly influenced by farming practices. As a result, extensively managed farming landscapes provided a habitat to many species and nowadays, semi-natural habitats form the focus of nature conservation in Europe. During the past century, these farming landscapes became increasingly intensified, increasing food production levels throughout the region. However, the intensification of traditional farming landscapes has been identified as the main driver behind the widespread decline of farmland biodiversity, owing to high agrochemical inputs, intense disturbance and overall landscape simplification and homogenization. To address this, a well-thought-through shift to more sustainable forms of agriculture is necessary, though the specific way forward remains debated. Organic farming is often proposed as an environmentally-friendly alternative, as it focuses on the application of ecological principles in farming and bans the use of synthetic agrochemicals. It has indeed been shown to positively affect on-field biodiversity, but effects are inconsistent and may depend on the specific taxa, landscape context and crop system. Research in perennial crops remaining scarce and providing inconsistent results. Furthermore, organic farming is also associated with considerable yield losses compared to higher-yielding farming systems, leading to a higher need for land to attain a specific production target. This raises questions about the effective sustainability of organic farming as compared to higher-yielding farming methods, especially when future cropland expansion is also identified as a major threat to biodiversity. Therefore, it is crucial to understand both the tradeoff between yield and multitaxon biodiversity as well as the status of multitaxon biodiversity in farmland as opposed to (semi-)natural habitat. Another way forward to promote biodiversity in farming landscapes is by improving the hospitability of the landscape itself, both at local and landscape scales. This may be achieved by restoring a complex landscape mosaic of diversified farmland and semi-natural features, enhancing the heterogeneity, composition and configuration of landscapes. The contribution of landscape complexity at local scale and at landscape scale to the conservation of biodiversity, however, remains to be disentangled. More generally, the relative importance of local management and landscape complexity on biodiversity across multiple taxa remains obscured, especially for perennial farming systems in northwestern Europe. In this doctoral thesis, we therefore quantified multitaxon biodiversity, pollination services and yield in organic and integrated pest management (IPM) apple orchards and evaluated how this was affected by local agricultural management and landscape context. We also included a semi-natural grassland reference in order to quantify the impact of farming systems on farmland biodiversity. We finally parametrized the trade-off between biodiversity and agricultural intensification, characterized here as apple yield levels, using density-yield curves. Overall, we found nuanced and complex effects of organic farming on farmland biodiversity, with large variation between taxa and between specific biodiversity measures. Though abundance was generally higher in organic compared to IPM orchards, this did not translate to higher diversity levels for most taxa. Additionally, density-yield curves revealed that any type of farming was associated with declines across taxa, except for some that are adapted to the farmland environment and were generally not of conservation concern. Overall, the species that are able to persist in farmland, be it under organic or IPM management, come from a reduced species pool that is well-adapted to the high disturbance levels in these environments. Of all studied taxa, plants were most clearly positively affected by organic management due to its lack of herbicide use, though plant species in organic orchards could mostly be classified as common and ruderal. While fungal diversity was higher in organic orchards, fungal networks were more complex in IPM orchards, owing to the disturbance caused by mechanical weeding in the former system. In contrast, soil bacterial diversity was unaffected by local management, though its networks were more complex in organic orchards, potentially benefitting from enhanced plant diversity. Arthropod diversity and networks were not discernibly affected by the specific local management, while pollination levels, measured by seed set, were higher in organic farming. However, organic yield levels were reduced by an average of 30% compared to IPM yields. The sampling location within study sites consistently affected biodiversity levels across both management types. The soil microbiome was higher under the permanent vegetation cover of drive rows compared to heavily managed crop rows, while plants and arthropods had a higher biodiversity in orchard edges compared to their centers. This underlines the importance of within-orchard non-productive habitat with minimally disturbed, permanent and diverse vegetation to farmland biodiversity. For the semi-natural reference, biodiversity was generally enhanced in grasslands compared to both orchard types, while density-yield curves indicated that the vast majority of taxa, and especially those of conservation concern, fares best when land for nature conservation is maximized through high-yielding farming elsewhere. Additionally, landscape analyses revealed that plants, bees and grasshoppers all benefitted from either more semi-natural habitat in the landscape or being closer it, while plants and true bugs gained from more landscape diversity. These findings illustrate the great value of complex and diverse landscapes for the conservation of farmland biodiversity. Our research especially highlighted the role semi-natural grasslands might play as essential habitat which can enhance local species pools. Overall, orchards, regardless of the specific management, harbored a lower biodiversity compared to a semi-natural benchmark, even when the farmland is managed organically or relatively extensively at intermediate yields. In combination with the significant yield gaps in organic farming, this implies that, at least when certain apple production targets must be achieved at the landscape level, it seems more promising to concentrate conservation efforts in nature reserves that include a variety of habitat types, such as semi-natural grasslands. Additionally, designing farming landscapes to increase landscape complexity with attention to composition, heterogeneity and configuration seems crucial to boost biodiversity conservation. Achieving this, however, will inevitably put pressure on the regional production output, so that high-yielding farming will remain a necessity. It can be argued that traditional intensive agricultural practices are not the way to achieve this, instead focusing on the application of technological advancements and ecological insights in order to mitigate environmental harm. Overall, there seems to be no silver bullet to achieve a sustainable food system in Europe and many different and coordinated actions are necessary. These ambitions require a transformation of farming landscapes as well as interventions at the demand and production side. They do not only involve farmers, but also policy makers, other landscape actors, such as nature conservation agencies, and the food system as a whole. It transcends food production and intersects with other important sectors such as spatial planning and nature conservation.