Browsing by Subject "Ecosystem function"

Now showing 1 - 2 of 2

Simulating the impact of land use change on ecosystem functions in data-limited watersheds of Mountainous Mainland Southeast Asia
(2015) Lippe, Melvin; Cadisch, Georg
The presented PhD thesis deals with the development of new modelling approaches and application procedures to simulate the impact of land use change (LUC) on soil fertility, carbon sequestration and mitigation of soil erosion and sediment deposition under data-limited conditions, using three mountainous watersheds in Northern Thailand, Northern and North-western Vietnam as case study areas. The first study investigated if qualitative datasets derived during participatory processes can be used to parameterize the spatially-explicit, soil fertility-driven FALLOW (Forest, Agroforest, Low-value Landscape Or Wasteland?) model. Participatory evaluations with different stakeholder groups were conducted in a case study village of Northwest Vietnam to generate model input datasets. A local colour-based soil quality classification system was successfully integrated into the FALLOW soil module to test scenarios how current or improved crop management would impact the evolution of upland soil fertility levels. The scenario analysis suggested a masking effect of ongoing soil fertility decline by using fertilizers and hybrid crop varieties, indicating a resource overuse that becomes increasingly irreversible without external interventions. Simulations further suggested that the success rate of improved cropping management methods becomes less effective with increasing soil degradation levels and cannot fully restore initial soil fertility. The second case study examined the effects of LUC on the provisioning of long-term carbon sinks illustrated for a case study watershed in Northern Thailand. Based on land use history data, participatory appraisals and expert interviews, a scenario analysis was conducted with the Dyna-CLUE (Dynamic and Conversion of Land use Effects) model to simulate different LUC trajectories in 2009 to 2029. The scenario analysis demonstrated a strong influence of external factors such as cash crop demands and nature conservation strategies on the spatial evolution of land use patterns at watershed-scale. Coupling scenario-specific LUC maps with a carbon accounting procedure further revealed that depending on employed time-averaged input datasets, up to 1.7 Gg above-ground carbon (AGC) could be built-up by increasing reforestation or orchard areas until 2029. In contrast, a loss of 0.4 Gg in AGC stocks would occur, if current LUC trends would be continued until 2029. Coupled model computations further revealed that the uncertainty of estimated AGC stocks is larger than the expected LUC scenario effects as a function of employed AGC input dataset. The third case study examined the impact of land use change on soil erosion and sediment deposition patterns in a small watershed of mountainous Northern Vietnam using a newly developed dynamic and spatially-explicit erosion and sediment deposition model (ERODEP), which was further coupled with the LUCIA (Land Use Change Impact Assessment) model building on its hydrological and vegetation growth routines. Employing available field datasets for a period of four years, ERODEP-LUCIA simulated reasonably well soil erosion and sediment deposition patterns following the annual variations in land use and rainfall regimes. Output validation (i.e. Modelling Efficiency=EF) revealed satisfying to good simulation results, i.e. plot-scale soil loss under upland swiddening (EF: 0.60-0.86) and sediment delivery rates in monitored streamflow (EF: 0.44-0.93). Cumulative sediment deposition patterns in lowland paddy fields were simulated fairly well (EF: 0.66), but showed limitations in adequately predicting silt fractions along a spatial gradient in a lowland monitoring site. In conclusion, data-limited conditions are a common feature of many tropical environments such as Northern Thailand and Northern/North-western Vietnam. Environmental modellers, decision makers and stakeholders have to be aware of the trade-offs between model complexity, input demands, and output reliability. It is not necessarily the challenge of data-limitations, but rather the decision from the very beginning if the aim is to develop a new model tool or to use existing model structures to support environmental decision making. Future modelling-based investigations in data-limited areas should combine scientifically-based approaches with participatory procedures, because scientific assessment can support environmental policy making, but stakeholders’ decision will finally determine the provisioning of ecosystem functions in the long run. A generic assessment framework is proposed as synthesis of this study to employ dynamic and spatially-explicit models to examine the impact of LUC on ecosystem functions. The application of such a generic framework is especially useful in data-limited environments such as Mountainous Mainland Southeast Asia, as it not only provides guidance during the modelling process, but also supports the prioritisation of input data demands and reduces fieldwork needs to a minimum.
Spatial and temporal variations of microorganisms in grassland soils : influences of land-use intensity, plants and soil properties
(2019) Boeddinghaus, Runa S.; Kandeler, Ellen
Grassland ecosystems provide a wide range of services to human societies (Allan et al., 2015) and plants and soil microorganisms have been identified as key drivers of ecosystem functioning (Soliveres et al., 2016). Therefore, understanding soil microbial distributions and processes in agricultural grassland soils is crucial for characterizing these ecosystems and for predicting how they may shift in a changing environment. Yet we are only beginning to understand these complex ecosystems, which account for about 26% of the world’s terrestrial surface (FAOSTATS, 2018), making it especially urgent to gain better insights into the effects of land-use intensity on soil microbial properties and plant-microbe interactions. This thesis was conducted to evaluate the impact land-use intensity has on soil microbial biogeography of grasslands with respect to both spatial patterns and temporal changes in soil microbial abundance, function (in terms of enzyme activities), and community composition. It also investigated the relationships between plants and the spatial and temporal distributions of soil microorganisms. Thereby both, land-use intensity effects and plant-microbe interactions, were assessed in light of ecological niche and neutral theory. This thesis is based on three observational studies conducted on from one to 150 continuously farmed, un-manipulated grassland sites in three regions of Germany within the Biodiversity Exploratories project (DFG priority program 1374). The first study assessed the effects of land-use intensity and physico-chemical soil properties on the spatial biogeography of soil microbial abundance and function in 18 grasslands sites from two of the three regions, sampled at one time point. The second study analyzed spatial and temporal distributions of alpha- and beta-diversity of arbuscular mycorrhizal fungi in a low land-use intensity grassland with six sampling time points across one season. The third study investigated both legacy and short-term change effects of land-use intensity, soil physico-chemical properties, plant functional traits, and plant biomass properties on temporal changes in soil microbial abundance, function, and community composition in 150 grassland sites across three regions, with particular regard to direct and indirect land-use intensity effects. Although the three studies used different approaches and assessed different soil microbial properties, general patterns were detectable. Abiotic soil properties, namely pH, nitrogen content, texture, and bulk density played fundamental roles for spatial and temporal microbial biogeography. Since these factors were specific and unique for each investigated site, they formed the background based on which other processes occurred. In addition to abiotic soil properties, impacts of land-use intensity and plants were detected, though to various degrees in the three studies. Land-use intensity played a much smaller role than anticipated in the first and third study. No influence on the spatial distribution of soil microbial abundance and function could be detected in the first study. In the third study, short-term changes in and legacy effects of land-use intensity played a minor role with respect to short-term changes in soil microbial abundance, function, and community composition. Where detected, changes in land-use intensity had a direct and negative effect on soil microbial properties in structural equation modelling; i.e., increases in land-use intensity reduced, e.g., soil microbial enzyme activities, while legacy effects of land-use intensity were shown to act both directly and indirectly on soil microbial properties. Thereby indirect legacy effects were mediated via plant functional traits. Only one of the three studies detected minor plant diversity effects on soil microbial properties. Instead, functional properties of the plant communities, i.e., plant functional traits, biomass, and nutritional quality, were significantly related to spatial and temporal distributions of soil microorganisms. Finally, the findings of the three studies suggest that processes related to niche and neutral theory both drive spatial and temporal patterns of soil microbial properties at the investigated plot scale (up to 50 m × 50 m). This thesis concluded that in order to gain deeper insights into the complex functions and processes occurring in grassland ecosystems, a multidisciplinary approach investigating fundamental physico-chemical site characteristics, microbial soil properties, and plants is necessary. The results of the thesis suggest that focus be turned to functional properties of plant and microbial communities, as they are closely intermingled, provide more detailed insights into plant-microbe interactions, and are able to reflect effects of human impacts on grassland soils better than diversity measures.