Biodiversity and Ecosystem Functioning across Scales in Real-World Landscapes

Abstract

Biodiversity, the variability of life on all levels from genes to ecosystems, is currently declining globally due to human activities. Research has shown that biodiversity is a fundamental promoter of ecosystem functions that support human existence. This reveals the potentially devastating consequences of biodiversity loss for human well-being. However, most biodiversity-ecosystem functioning (B-EF) research was conducted in simplified, experimental settings at small spatial scales, and knowledge on the consequences of biodiversity loss in complex natural or managed landscapes of the “real world” is still very limited.In my thesis, I elucidated the relevance of biodiversity for ecosystem functions at large scales of space, time and ecological organization in real-world landscapes across Switzerland. In chapter 1, I comparatively analyzed effects of tree species and land-cover type diversity on local forest functions and determined their interrelation with environmental context at the local and landscape scale. I found that local tree diversity is an important determinant of forest productivity and growing season length, whereas landscape diversity likely only indirectly influences these ecosystem functions via positive effects on tree diversity. Tree diversity effects were relatively consistent across the large environmental gradients covered by the study. In chapter 2, I studied the effects of ecosystem diversity approximated by land-cover type richness on the satellite-sensed functioning and stability of landscapes with an area of 62‘500 and 250‘000 m2, respectively. I selected these landscapes using geographic information data according to an orthogonal and balanced study design. I found that landscape-level productivity, growing season length and the inter-annual stability of these variables increased with land-cover type richness in the time of 2000-2016. Also the interannual stability of near-infrared surface albedo increased with land-cover type richness. These land-cover type richness effects were consistently higher in landscapes of larger spatial extent. In chapter 3, I investigated effects of regional species diversity on satellite-sensed ecosystem functioning in 1 km2 – landscapes. I found that regional species diversity of plants, birds and butterflies is strongly related to increased vegetation productivity, increased inter-annual stability of productivity, and to an accelerated lengthening of the growing season in the time of 2000-2015. Species diversity effects were independent of environmental context such as altitude and relatively large compared to effects of topography, climate and land cover. Overall, I found empirical evidence supporting the view that biodiversity is of great importance for ecosystem functioning and stability in complex real-world landscapes. The biodiversity effects I found were consistent across environmental gradients and relatively strong compared to effects of other important environmental drivers. Also, these effects were similar or even larger in size than the effects found under experimental conditions. Intriguingly, I found positive diversity effects not only for local and landscape-level species diversity, but also for the spatial diversity of ecosystem types. Finally, I found diversity effects on ecosystem functions beyond primary productivity’s temporal average and stability. I found diversity effects on vegetation phenology and the temporal stability of land surface albedo, which contribute to the adaptive capacity and the climatic stability in complex real-world landscapes. Hence, my findings highlight the generality and the importance of diversity effects across large scales of space, ecological organization and various hitherto underexplored ecosystem functions important for landscape resilience.