Browsing by Author "Farwig, Nina"

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    Area-Wide Prediction of Vertebrate and Invertebrate Hole Density and Depth across a Climate Gradient in Chile Based on UAV and Machine Learning
    (MDPI, 2021) Grigusova, Paulina; Larsen, Annegret; Achilles, Sebastian; Klug, Alexander; Fischer, Robin; Kraus, Diana; Uebernickel, Kirstin; Paulino, Leandro; Pliscoff, Patricio; Brandl, Roland; Farwig, Nina; Bendix, Joerg
    Burrowing animals are important ecosystem engineers affecting soil properties, as their burrowing activity leads to the redistribution of nutrients and soil carbon sequestration. The magnitude of these effects depends on the spatial density and depth of such burrows, but a method to derive this type of spatially explicit data is still lacking. In this study, we test the potential of using consumer-oriented UAV RGB imagery to determine the density and depth of holes created by burrowing animals at four study sites along a climate gradient in Chile, by combining UAV data with empirical field plot observations and machine learning techniques. To enhance the limited spectral information in RGB imagery, we derived spatial layers representing vegetation type and height and used landscape textures and diversity to predict hole parameters. Across-site models for hole density generally performed better than those for depth, where the best-performing model was for the invertebrate hole density (R-2 = 0.62). The best models at individual study sites were obtained for hole density in the arid climate zone (R-2 = 0.75 and 0.68 for invertebrates and vertebrates, respectively). Hole depth models only showed good to fair performance. Regarding predictor importance, the models heavily relied on vegetation height, texture metrics, and diversity indices.
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    Bioturbation 1 enhances C and N contents on near-surface 2 soils in resource-deficient arid climate regions but shows 3 adverse effects in more temperate climates
    Pliscoff, Patricio; Kraus, Diana; Brandl, Roland; Bendix, Jörg; Grigusova, Paulina; Köhler, Sabrina; Larsen, Annegret; Übernickel, Kirstin; Farwig, Nina
    Bioturbating animals can affect physical and chemical soil properties on near-surface soil by either foraging for food or constructing suitable habitats. Thereby, bioturbation can influence the soil texture either sorting or mixing the different grain sizes clay, silt and sand during burrowing. Additionally, bioturbating animals can increase the macronutrients carbon (C), nitrogen (N) and phosphorus (P) through the transport of nutrients by vertically mixing the soil column and the addition of the bioturbators’ feces to the soil surface. To date, it is not clear how the effects of bioturbation on soil properties vary along an ecological gradient. Therefore, we compared the physical properties clay, silt and sand and the chemical contents of the macronutrients C, N and P for soil samples from mounds and the surrounding area as controls in three different climatic regions (arid, semi-arid and Mediterranean) of coastal Chile. To do so, we calculated the difference between the concentrations of paired mound and control samples. When comparing soil texture, we did not find significant differences between mound and control soil samples. For the macronutrient contents, the difference between mound and control C and N contents increased in the arid site and decreased in the two other research sites with increasing vegetation cover. Since we aimed to cover bioturbation patterns on a broader scale, we additionally compared our findings to other bioturbation studies performed in different biomes. Thereby, we found that other studies also show small differences in soil properties caused by bioturbation which are already sufficient to increase soil fertility.
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    Higher sediment redistribution rates related to burrowing animals than previously assumed as revealed by time-of-flight-based monitoring
    (Copernicus Publications, 2022) Grigusova, Paulina; Larsen, Annegret; Achilles, Sebastian; Brandl, Roland; Río López, Camilo Del; Farwig, Nina; Kraus, Diana; Paulino, Leandro; Pliscoff Varas, Patricio Andrés; Übernickel, Kirstin; Bendix, Jörg
    Burrowing animals influence surface microtopography and hillslope sediment redistribution, but changes often remain undetected due to a lack of automated high-resolution field monitoring techniques. In this study, we present a new approach to quantify microtopographic variations and surface changes caused by burrowing animals and rainfall-driven erosional processes applied to remote field plots in arid and Mediterranean climate regions in Chile. We compared the mass balance of redistributed sediment between burrow and burrow-embedded area, quantified the cumulative sediment redistribution caused by animals and rainfall, and upscaled the results to a hillslope scale. The newly developed instrument, a time-of-flight camera, showed a very good detection accuracy. The animal-caused cumulative sediment excavation was 14.6 cm3 cm-2 yr-1 in the Mediterranean climate zone and 16.4 cm3 cm-2 yr-1 in the arid climate zone. The rainfall-related cumulative sediment erosion within burrows was higher (10.4 cm3 cm-2 yr-1) in the Mediterranean climate zone than the arid climate zone (1.4 cm3 cm-2 yr-1). Daily sediment redistribution during rainfall within burrow areas was up to 350 %(40 %) higher in the Mediterranean (arid) zone compared to burrow-embedded areas and much higher than previously reported in studies that were not based on continuous microtopographic monitoring. A total of 38 % of the sediment eroding from burrows accumulated within the burrow entrance, while 62 % was incorporated into hillslope sediment flux, which exceeds previous estimations 2-fold. On average, animals burrowed between 1.2-2.3 times a month, and the burrowing intensity increased after rainfall. This revealed a newly detected feedback mechanism between rainfall, erosion, and animal burrowing activity, likely leading to an underestimation of animal-triggered hillslope sediment flux in wetter climates. Our findings hence show that the rate of sediment redistribution due to animal burrowing is dependent on climate and that animal burrowing plays a larger than previously expected role in hillslope sediment redistribution. Subsequently, animal burrowing activity should be incorporated into soil erosion and landscape evolution models that rely on soil processes but do not yet include animal-induced surface processes on microtopographical scales in their algorithms.
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    Mammalian bioturbation amplifies rates of both hillslope sediment erosion and accumulation along the Chilean climate gradient
    (Copernicus Gesellschaft MBH, 2023) Grigusova, Paulina; Larsen, Annegret; Brandl, Roland; Río López, Camilo del; Farwig, Nina; Kraus, Diana; Paulino, Leandro; Pliscoff, Patricio; Bendix, Joerg
    Animal burrowing activity affects soil texture, bulk density, soil water content, and redistribution of nutrients. All of these parameters in turn influence sediment redistribution, which shapes the earth's surface. Hence it is important to include bioturbation into hillslope sediment transport models. However, the inclusion of burrowing animals into hillslope-wide models has thus far been limited and has largely omitted vertebrate bioturbators, which can be major agents of bioturbation, especially in drier areas.Here, we included vertebrate bioturbator burrows into a semi-empirical Morgan-Morgan-Finney soil erosion model to allow a general approach to the assessment of the impacts of bioturbation on sediment redistribution within four sites along the Chilean climate gradient. For this, we predicted the distribution of burrows by applying machine learning techniques in combination with remotely sensed data in the hillslope catchment. Then, we adjusted the spatial model parameters at predicted burrow locations based on field and laboratory measurements. We validated the model using field sediment fences. We estimated the impact of bioturbator burrows on surface processes. Lastly, we analyzed how the impact of bioturbation on sediment redistribution depends on the burrow structure, climate, topography, and adjacent vegetation.Including bioturbation greatly increased model performance and demonstrates the overall importance of vertebrate bioturbators in enhancing both sediment erosion and accumulation along hillslopes, though this impact is clearly staggered according to climatic conditions. Burrowing vertebrates increased sediment accumulation by 137.8 % +/- 16.4 % in the arid zone (3.53 kg ha(-1) yr(-1) vs. 48.79 kg ha(-1) yr(-1)), sediment erosion by 6.5 % +/- 0.7 % in the semi-arid zone (129.16 kg ha(-1) yr(-1) vs. 122.05 kg ha(-1) yr(-1)), and sediment erosion by 15.6 % +/- 0.3 % in the Mediterranean zone (4602.69 kg ha(-1) yr(-1) vs. 3980.96 kg ha(-1) yr(-1)). Bioturbating animals seem to play only a negligible role in the humid zone. Within all climate zones, bioturbation did not uniformly increase erosion or accumulation within the whole hillslope catchment. This depended on adjusting environmental parameters. Bioturbation increased erosion with increasing slope, sink connectivity, and topography ruggedness and decreasing vegetation cover and soil wetness. Bioturbation increased sediment accumulation with increasing surface roughness, soil wetness, and vegetation cover.