TY - JOUR A1 - Marquart, Arnim A1 - Goldbach, Lars A1 - Blaum, Niels T1 - Soil-texture affects the influence of termite macropores on soil water infiltration in a semi-arid savanna JF - Ecohydrology : ecosystems, land and water process interactions, ecohydrogeomorphology N2 - Subterranean termites create tunnels (macropores) for foraging that can influence water infiltration and may lead to preferential flow to deeper soil layers. This is particularly important in water limited ecosystems such as semi-arid, agriculturally utilized savannas, which are particularly prone to land degradation and shrub-encroachment. Using termite activity has been suggested as a restoration measure, but their impact on hydrology is neither universal nor yet fully understood. Here, we used highly replicated, small-scale (50 x 50 cm) rain-simulation experiments to analyse the interacting effects of either vegetation (grass dominated vs. shrub dominated sites) or soil texture (sand vs. loamy sand) and termite foraging macropores on infiltration patterns. We used Brilliant Blue FCF as colour tracer to make the flow pathways in paired experiments visible, on either termite-disturbed soil or controls without surface macropores in two semi-arid Namibian savannas (with either heterogeneous soil texture or shrub cover). On highly shrub-encroached plots in the savanna site with heterogeneous soil texture, termite macropores increased maximum infiltration depth and total amount of infiltrated water on loamy sand, but not on sandy soil. In the sandy savanna with heterogeneous shrub cover, neither termite activity nor shrub density affected the infiltration. Termite's effect on infiltration depends on the soil's hydraulic conductivity and occurs mostly under ponded conditions, intercepting run-off. In semi-arid savanna soils with a considerable fraction of fine particles, termites are likely an important factor for soil water dynamics. KW - ecosystem functioning KW - infiltration KW - macropores KW - rain-simulation KW - shrub-encroachment KW - soil texture KW - termites Y1 - 2020 U6 - https://doi.org/10.1002/eco.2249 SN - 1936-0584 SN - 1936-0592 VL - 13 IS - 8 PB - Wiley CY - Chichester ER - TY - JOUR A1 - Marquart, Arnim A1 - Eldridge, David J. A1 - Travers, Samantha K. A1 - Val, James A1 - Blaum, Niels T1 - Large shrubs partly compensate negative effects of grazing on hydrological function in a semi-arid savanna JF - Basic and applied ecology : Journal of the Gesellschaft für Ökologie N2 - Semiarid woodlands and savannas are globally important biomes that provide ecosystem goods and services such as habitat for biota and sinks for carbon, support millions of people that rely primarily on pastoralism, and supply livelihoods for about a third of the global human population. Savannas, however, are prone to degradation by overgrazing, and encroachment by woody plants, reducing their capacity to produce forage that pastoral enterprises depend on. We examined the impacts of livestock grazing and woody encroachment on soil hydrological processes, hypothesizing that heavy grazing by livestock would reduce hydrological function, whereas woody plants would increase hydrological function, therefore, partially offsetting any negative effects of overgrazing by livestock. Understanding the major drivers of soil hydrology in savanna ecosystems is important because water is a critical, yet limited resource in savannas. We found that livestock grazing reduced the early (sorptivity) and late (steady-state infiltration) stages of infiltration under both ponding and tension, and attributed this to a reduction in porosity caused by livestock trampling. Steady-state infiltration and sorptivity under ponding were greater under the canopies of woody shrubs than in open areas, partly compensating for any negative effect of grazing. Structural equation modeling revealed a direct positive effect of shrub height on hydrological functions, and an indirect effect via increases in litter cover. Our results suggest that woody plants can play important roles in driving hydrological function in savannas, counteracting the suppressive effect of livestock overgrazing on infiltration processes. Management strategies in semiarid savannas should aim to reduce trampling by livestock and retain large woody plants in order to maintain hydrological function. (C) 2019 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved. KW - Hydrology KW - Soil function KW - Cattle KW - Encroachment KW - Thickening KW - Water flow KW - Invertebrate pores KW - Porosity Y1 - 2019 U6 - https://doi.org/10.1016/j.baae.2019.06.003 SN - 1439-1791 SN - 1618-0089 VL - 38 SP - 58 EP - 68 PB - Elsevier GMBH CY - München ER - TY - JOUR A1 - Hering, Robert A1 - Hauptfleisch, Morgan A1 - Geissler, Katja A1 - Marquart, Arnim A1 - Schoenen, Maria A1 - Blaum, Niels T1 - Shrub encroachment is not always land degradation BT - Insights from ground‐dwelling beetle species niches along a shrub cover gradient in a semi‐arid Namibian savanna JF - Land degradation & development N2 - Shrub encroachment in semi-arid savannas is induced by interacting effects of climate, fire suppression, and unsustainable livestock farming; it carries a severe risk of land degradation and strongly influences natural communities that provide key ecosystem functions. However, species-specific effects of shrub cover on many animal groups that act as indicators of degradation remain largely unknown. We analysed the consequences of shrub encroachment for ground-dwelling beetles in a semi-arid Namibian savanna rangeland, where beetles and vegetation were recorded along a shrub cover gradient (30%). Focusing on species niche breadths and optima, we identified two crucial shrub cover thresholds (2.9% and 10.0%), corresponding to major changes in the beetle communities with implications for savanna ecosystem functioning. Niche optima of most species were between the first and second thresholds; beyond the second threshold, saprophagous, coprophagous, and rare predatory beetles declined in numbers and diversity. This is problematic because beetles provide important ecosystem functions, such as decomposition and nutrient cycling. However, we also found that certain species were adapted to high shrub cover, thus providing examples of niche differentiation. Despite the predominantly negative effects of heavy shrub encroachment on beetle communities, shrubs in their early life stages apparently provide essential structures, which enhance habitat quality for ground-dwelling beetles. Our results demonstrate that shrub encroachment can have mixed effects on ground-dwelling beetle communities and hence on savanna ecosystem functioning. We, therefore, conclude that rangeland management and restoration should consider the complex trade-offs between species-specific effects and the level of encroachment for sustainable land use. KW - Coleoptera KW - rangeland KW - semi-arid savanna KW - shrub encroachment KW - species niche KW - threshold Y1 - 2018 U6 - https://doi.org/10.1002/ldr.3197 SN - 1085-3278 SN - 1099-145X VL - 30 IS - 1 SP - 14 EP - 24 PB - Wiley CY - Chichester ER - TY - JOUR A1 - Seifert, Linda I. A1 - de Castro, Francisco A1 - Marquart, Arnim A1 - Gaedke, Ursula A1 - Weithoff, Guntram A1 - Vos, Matthijs T1 - Heated relations: temperature-mediated shifts in consumption across trophic levels JF - PLoS one N2 - A rise in temperature will intensify the feeding links involving ectotherms in food webs. However, it is unclear how the effects will quantitatively differ between the plant-herbivore and herbivore-carnivore interface. To test how warming could differentially affect rates of herbivory and carnivory, we studied trophic interaction strength in a food chain comprised of green algae, herbivorous rotifers and carnivorous rotifers at 10, 15, 20 and 25 degrees C. We found significant warming-induced changes in feeding by both herbivorous and carnivorous rotifers, but these responses occurred at different parts of the entire temperature gradient. The strongest response of the per capita herbivore's ingestion rate occurred due to an increase in temperature from 15 to 20 degrees C (1.9 fold: from 834 to 1611 algal cells per h(-1)) and of the per capita carnivore's ingestion rate from 20 to 25 degrees C (1.6 fold: from 1.5 to 2.5 prey h(-1)). Handling time, an important component of a consumer's functional response, significantly decreased from 15 to 20 degrees C in herbivorous rotifers. In contrast, it decreased from 20 to 25 degrees C in carnivorous rotifers. Attack rates significantly and strongly increased from 10 to 25 degrees C in the herbivorous animals, but not at all in the carnivores. Our results exemplify how the relative forces of top-down control exerted by herbivores and carnivores may strongly shift under global warming. But warming, and its magnitude, are not the only issue: If our results would prove to be representative, shifts in ectotherm interactions will quantitatively differ when a 5 degrees C increase starts out from a low, intermediate or high initial temperature. This would imply that warming could have different effects on the relative forces of carnivory and herbivory in habitats differing in average temperature, as would exist at different altitudes and latitudes. Y1 - 2014 U6 - https://doi.org/10.1371/journal.pone.0095046 SN - 1932-6203 VL - 9 IS - 5 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Marquart, Arnim A1 - Eldridge, David J. A1 - Geissler, Katja A1 - Lobas, Christoph A1 - Blaum, Niels T1 - Interconnected effects of shrubs, invertebrate-derived macropores and soil texture on water infiltration in a semi-arid savanna rangeland JF - Land degradation & development N2 - Many semi arid savannas are prone to degradation, caused for example, by overgrazing or extreme climatic events, which often lead to shrub encroachment. Overgrazing by livestock affects vegetation and infiltration processes by directly altering plant composition (selective grazing) or by impacting soil physical properties (trampling). Water infiltration is controlled by several parameters, such as macropores (created by soil-burrowing animals or plant roots) and soil texture, but their effects have mostly been studied in isolation. Here we report on a study, in which we conducted infiltration experiments to analyze the interconnected effects of invertebrate-created macropores, shrubs and soil texture (sandy soil and loamy sand) on infiltration in two Namibian rangelands. Using structural equation modeling, we found a direct positive effect of shrub size on infiltration and indirectly via invertebrate macropores on both soil types. On loamy sands this effect was even stronger, but additionally, invertebrate-created macropores became relevant as a direct driver of infiltration. Our results provide new insights into the effects of vegetation and invertebrates on infiltration under different soil textures. Pastoralists should use management strategies that maintain a heterogeneous plant community that supports soil fauna to sustain healthy soil water dynamics, particularly on soils with higher loam content. Understanding the fundamental functioning of soil water dynamics in drylands is critical because these ecosystems are water-limited and support the livelihoods of many cultures worldwide. KW - hydrology KW - infiltration KW - invertebrate macropores KW - shrub-encroachment KW - soil function KW - soil texture Y1 - 2020 U6 - https://doi.org/10.1002/ldr.3598 SN - 1085-3278 SN - 1099-145X VL - 31 IS - 16 SP - 2307 EP - 2318 PB - Wiley CY - Chichester, Sussex ER - TY - THES A1 - Marquart, Arnim T1 - Feedbacks between macropores and soil water infiltration in semi-arid savanna systems Y1 - 2019 ER -