Jussi Baade

The role of biodiversity for element cycling and trophic interactions: an experimental approach in a grassland community

Abstract The focus of a new experiment, set up in Jena in spring 2002, are the effects of biodiversity on element cycles and the interaction of plant diversity with herbivores and soil fauna. The experimental design explicitly addresses criticisms provoked by previous biodiversity experiments. In particular, the choice of functional groups, the statistical separation of sampling versus complementarity effects, and testing for the effects of particular functional groups differ from previous experiments. Based on a species pool of 60 plant species common to the Central European Arrhenatherion grasslands, mixtures of one to 16 (60) species and of one to four plant functional groups were established on 90 plots (20 m × 20 m) with nested experiments. In order to test specific hypotheses 390 additional small-area plots (3.5 m × 3.5 m) were set-up. Exact replicates of all species mixtures serve to assess the variability in ecosystem responses. In a dominance experiment, the effects of interactions among nine selected highly productive species are studied. Each species is grown as monoculture replicated once. Effekte der Biodiversitat auf Elementkreislaufe und Wechselwirkungen der pflanzlichen Artenvielfalt mit Bodenfauna und Herbivoren stehen im Mitttelpunkt eines neuen Experiments, das im Fruhjahr 2002 in Jena eingerichtet wurde. Das Versuchsdesign berucksichtigt ausdrucklich die Kritik, die an den Aufbau fruherer Biodiversitatsversuche gerichtet wurde. Die Auswahl funktioneller Gruppen von Pflanzenarten, die statistischen Moglichkeiten, die Effekte des “Sampling” gegen Komplementaritat zu trennen sowie den Einflus funktioneller Gruppen zu uberprufen, unterscheiden dieses Experiment von fruheren Versuchen. Sechzig typische Pflanzenarten der zentraleuropaischen Frischwiesen (Arrhenatherion) bilden den Artenpool fur den Versuch. Auf 90 Flachen wurden Artenmischungen etabliert, die 1 bis 16 (60) Arten und 1 bis 4 funktionelle Gruppen dieser Pflanzenarten enthalten. Die Versuchsparzellen haben eine Grose von 20 m × 20 m, auf denen in genesteter Anordnung verschiedene Teilexperimente durchgefuhrt werden. Zusatzlich wurden 390 kleine Parzellen (3.5 m × 3.5 m) angelegt, um spezifische Hypothesen zu uberprufen. Alle Arten werden hier mit je einer Wiederholung als Monokulturen kultiviert. Identische Wiederholungen aller Artenmischungen sollen deren Variabilitat untersuchen. In einem Dominanz-Versuch werden die Effekte der Wechselwirkungen zwischen 9 ausgewahlten hochproduktiven Arten untersucht.

Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands

The diversity–stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

How Do Earthworms, Soil Texture and Plant Composition Affect Infiltration along an Experimental Plant Diversity Gradient in Grassland?

Background Infiltration is a key process in determining the water balance, but so far effects of earthworms, soil texture, plant species diversity and their interaction on infiltration capacity have not been studied. Methodology/Principal Findings We measured infiltration capacity in subplots with ambient and reduced earthworm density nested in plots of different plant species (1, 4, and 16 species) and plant functional group richness and composition (1 to 4 groups; legumes, grasses, small herbs, tall herbs). In summer, earthworm presence significantly increased infiltration, whereas in fall effects of grasses and legumes on infiltration were due to plant-mediated changes in earthworm biomass. Effects of grasses and legumes on infiltration even reversed effects of texture. We propose two pathways: (i) direct, probably by modifying the pore spectrum and (ii) indirect, by enhancing or suppressing earthworm biomass, which in turn influenced infiltration capacity due to change in burrowing activity of earthworms. Conclusions/Significance Overall, the results suggest that spatial and temporal variations in soil hydraulic properties can be explained by biotic processes, especially the presence of certain plant functional groups affecting earthworm biomass, while soil texture had no significant effect. Therefore biotic parameters should be taken into account in hydrological applications.

A 700‐year record on the effects of climate and human impact on the southern cape coast inferred from lake sediments of eilandvlei, wilderness embayment, south africa

Abstract The southern Cape coast, outh frica, is sensitive to climate fluctuations as it is influenced by different atmospheric and oceanic circulation systems. Palaeoecological evidence of Holocene climate variations in this region is presently limited. Here, we present a lake sediment record spanning approximately the last 670 years from ilandvlei, a brackish coastal lake situated mid‐way between Cape Town and Port lizabeth. The results from geochemical and sedimentological analyses point to an increase in minerogenic sediment input from the catchment starting around ad 1400. Changes in the seasonal distribution of rainfall during the Little Ice Age may have altered river discharge and increased erosion rates and fluvial sediment transport in pre‐colonial times. A rising mean lake level, possibly associated with an altered water balance or relative sea‐level rise, may offer an explanation for the deposition of finer sediments. After ad 1450, reduced burial flux of elements associated with autochthonous sediment formation may have resulted from ecological changes in ilandvlei. Enhanced sedimentation rates, increasing carbon, nitrogen, phosphorous and biogenic silica concentrations, as well as high concentrations of proxies for allochthonous sediment input (e.g. aluminium, titanium, zirconium) point to increasing sediment and nutrient flux into ilandvlei from the late nineteenth century onwards. The most likely factor involved in these recent changes is land‐use change and other forms of human impact.

Interferometric Microrelief Sensing With TerraSAR-X—First Results

The meter-scale ground resolution of TerraSAR-X spotlight images promises for the first time the 3-D detection of landforms and landform changes on the microrelief scale from a satellite-based remote sensing system. Using repeat-pass pairs of high-resolution spotlight images, this paper analyzes the spatial variation of coherence on the micro- and mesorelief scale and demonstrates the high potential as well as some limitations of this approach for digital elevation model generation, geomorphological mapping, and geomorphic-change detection in contrasting landscapes of the coastal desert of southern Peru.

Validation of the TanDEM-X Intermediate Digital Elevation Model With Airborne LiDAR and Differential GNSS in Kruger National Park

The recently released TanDEM-X intermediate digital elevation model (IDEM) product by the German Aerospace Center (DLR) provides elevation models at 12-m spatial resolution and above. It was derived from bistatic synthetic aperture radar (SAR) interferometry using the two TerraSAR-X satellites flying in close constellation. The aim of this study was to validate the vertical accuracy of the IDEM data at study sites in the Kruger National Park, South Africa. Two validation locations are presented: a dried up former reservoir (Nhlanganzwani Dam) characterized by bare soil and grassland and the peninsula between the Sabie and Sand Rivers near Skukuza characterized by dense woody cover. The results show that the IDEM elevation data are affected by residual vegetation canopy height and landform features smaller than the IDEM resolution cell. The scattering phase centers are located in the canopy but at a lower height than the location of the LiDAR first return signal. When only LiDAR ground hits or differential GNSS ground survey points are used for comparison, the IDEM data have an rmse <; 1 m and a small bias of less than 0.25 m in moderate terrain.

Uncertainties of a TanDEM-X derived Digital Surface Model — A case study from the Roda catchment, Germany

This contribution presents the results of a comparison between a TanDEM-X derived Digital Surface Model (DSM) and a high resolution, airborne LIDAR-based Digital Terrain Model (DTM) for a catchment characterized by agricultural areas and forest in Germany. It provides evidence for the overall high quality of the TanDEM-X data and guidelines for uncertainty assessment of TanDEM-X derived DSM in areas where high resolution and high quality data is not available.

High-resolution mapping of fluvial landform change in arid environments using terrasar-X images

The high resolution acquisition mode of TerraSAR-X provides a new dimension in fluvial landform change detection. Here we analyzed high resolution (5 m) coherence images with temporal baselines of up to a year from the Palpa Valley in the hyper-arid coastal desert of southern Peru. The results provide evidence that this sensor is suitable for mapping the land surface changes caused by erosion and sedimentation following rainfall and runoff events in bare desert landscape units.

Landslides and Deserted Places in the Semi-Arid Environment of the Inner Himalaya

Among other geomorphologic hazards, landslides are a common feature in high mountain areas like the Himalayan Range (cf. Shroder 1989). On the southern flanks of the Himalayas, specially the Low and Middle Himalaya, landslides, representing the dominant hillslope process (Whitehouse 1990), are of special concern as they cause permanent loss of agricultural land (Ives & Messerli 1981), block important roads and even destroy housing (cf. Schelling 1988). The dominance of landslides in this region can be attributed to lithology, the tectonic stress applied to the rocks and steep relief In addition the climatic conditions promote deep weathering and provide landslide triggering rainfall events, generally mainly during the monsoon (cf. Kienholz et al. 1982, Bartaiya & Valdiya 1989).

Plant species richness and functional groups have different effects on soil water content in a decade‐long grassland experiment

The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above-ground–below-ground feedbacks. Plant–water relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking. Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long-term grassland biodiversity experiment (The Jena Experiment). Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species-rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species-rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water-use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister. Synthesis. Our decade-long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes.