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The edoc server is the Open Access publication server and institutional repository of the Humboldt-Universität zu Berlin. It is available to university members for the publication of academic work as a first or second publication. In addition to text publications, research data can also be published via the edoc server. These publications are available to the general public worldwide, free of charge and for the long term.
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Recent Submissions
2022-08-06Zeitschriftenartikel
Modelling cropland expansion and its drivers in Trans Nzoia County, Kenya
(Lebenswissenschaftliche Fakultät) Kipkulei, Harison Kiplagat; Bellingrath-Kimura, Sonoko Dorothea; Lana, Marcos; Ghazaryan, Gohar; Boitt, Mark; Sieber, Stefan
Population growth and increasing demand for agricultural production continue to drive global cropland expansions. These expansions lead to the overexploitation of fragile ecosystems, propagating land degradation, and the loss of natural diversity. This study aimed to identify the factors driving land use/land cover changes (LULCCs) and subsequent cropland expansion in Trans Nzoia County in Kenya. Landsat images were used to characterize the temporal LULCCs in 30 years and to derive cropland expansions using change detection. Logistic regression (LR), boosted regression trees (BRTs), and evidence belief functions (EBFs) were used to model the potential drivers of cropland expansion. The candidate variables included proximity and biophysical, climatic, and socioeconomic factors. The results showed that croplands replaced other natural land covers, expanding by 38% between 1990 and 2020. The expansion in croplands has been at the expense of forestland, wetland, and grassland losses, which declined in coverage by 33%, 71%, and 50%, respectively. All the models predicted elevation, proximity to rivers, and soil pH as the critical drivers of cropland expansion. Cropland expansions dominated areas bordering the Mt. Elgon forest and Cherangany hills ecosystems. The results further revealed that the logistic regression model achieved the highest accuracy, with an area under the curve (AUC) of 0.96. In contrast, EBF and the BRT models depicted AUC values of 0.86 and 0.77, respectively. The findings exemplify the relationships between different potential drivers of cropland expansion and contribute to developing appropriate strategies that balance food production and environmental conservation.
2022-10-21Zeitschriftenartikel
Assessment of Maize Yield Response to Agricultural Management Strategies Using the DSSAT–CERES-Maize Model in Trans Nzoia County in Kenya
(Lebenswissenschaftliche Fakultät) Kipkulei, Harison Kiplagat; Bellingrath-Kimura, Sonoko Dorothea; Lana, Marcos; Ghazaryan, Gohar; Baatz, Roland; Boitt, Mark; Chisanga, Charles B.; Rotich, Brian; Sieber, Stefan
Maize production in low-yielding regions is influenced by climate variability, poor soil fertility, suboptimal agronomic practices, and biotic influences, among other limitations. Therefore, the assessment of yields to various management practices is, among others, critical for advancing site-specific measures for production enhancement. In this study, we conducted a multiseason calibration and evaluation of the DSSAT–CERES-Maize model to assess the maize yield response of two common cultivars grown in Trans Nzoia County in Kenya under various agricultural strategies, such as sowing dates, nitrogen fertilization, and water management. We then applied the Mann–Kendall (MK), and Sen’s Slope Estimator (SSE) tests to establish the yield trends and magnitudes of the different strategies. The evaluated model simulated long-term yields (1984–2021) and characterized production under various weather regimes. The model performed well in simulating the growth and development of the two cultivars, as indicated by the model evaluation results. The RMSE for yield was 333 and 239 kg ha −1 for H614 and KH600-23A, respectively, representing a relative error (RRMSE) of 8.1 and 5.1%. The management strategies assessment demonstrated significant feedback on sowing dates, nitrogen fertilization, and cultivars on maize yield. The sowing date conducted in mid-February under fertilization of 100 kg of nitrogen per hectare proved to be the best strategy for enhancing grain yields in the region. Under the optimum sowing dates and fertilization rate, the average yield for cultivar KH600-23A was 7.1% higher than that for H614. The MK and SSE tests revealed a significant (p < 0.05) modest downwards trend in the yield of the H614 cultivar compared to the KH600-23A. The eastern part of Trans Nzoia County demonstrated a consistent downwards trend for the vital yield enhancement strategies. Medium to high nitrogen levels revealed positive yield trends for more extensive coverage of the study area. Based on the results, we recommend the adoption of the KH600-23A cultivar which showed stability in yields under optimum nitrogen levels. Furthermore, we recommend measures that improve soil quality and structure in the western and northern parts, given the negative model response on maize yield in these areas. Knowledge of yield enhancement strategies and their spatial responses is of utmost importance for precision agricultural initiatives and optimization of maize production in Trans Nzoia County.
2023-02-27Zeitschriftenartikel
Seasonal and diurnal patterns of littoral microhabitat use by fish in gravel pit lakes, with special reference to supplemented deadwood brush piles
(Lebenswissenschaftliche Fakultät) Maday, Andreas; Matern, Sven; Monk, Christopher T.; Klefoth, Thomas; Wolter, Christian; Arlinghaus, Robert
The habitat quality of the littoral zone is of key importance for almost all lentic fish species. In anthropogenically created gravel pit lakes, the littoral zone is often structurally homogenized with limited fish habitats. We supplemented deadwood brush piles in the littoral zone of eight gravel pit lakes and investigated the diurnal and seasonal use of this and other typical microhabitats by six dominant fish species. Shoreline habitats were sampled using point abundance electrofishing during day and night in all four seasons, and patterns of fish abundance were compared amongst unstructured littoral habitats, emerged macrophytes and brush piles. We caught a total of 14,458 specimens from 15 species in the gravel pit lakes. Complex shoreline structures were used by all fish species that we examined, especially during daytime, whilst the use of unstructured habitats was highest during night. The newly added brush piles constituted suitable microhabitats for selected fish species, perch ( Perca fluviatilis ), roach ( Rutilus rutilus ) and pike ( Esox lucius ), particularly during winter. Supplemented deadwood provides suitable fish habitat in gravel pit lakes and may to some degree compensate for the loss of submerged macrophytes in winter by offering refuge and foraging habitat for selected fish species.
2022-03-23Zeitschriftenartikel
Who Opts Out? The Customisation of Marriage in the German Matrimonial Property Regime
(Kultur-, Sozial- und Bildungswissenschaftliche Fakultät) Nutz, Theresa; Nelles, Anika; Lersch, Philipp M.
This study examines the prevalence of marital contracts across marriage cohorts (1990–2019) in Germany. We further investigate the characteristics of spouses who signed a marital contract. Using cross-sectional data from the German Family Panel (pairfam, 2018/19), we employ complementary log–log and multinomial logistic regression models to predict the prevalence and the type of marital contracts. The results show that 5% of all married couples opt out of the default matrimonial property regime by signing a contract in Germany. Differentiating between contract types, most couples either specify a separation of property (40%) or modify the default community of accrued gains (31%). We find an increase in the prevalence of marital contracts across marriage cohorts. The decision to opt out of the default is strongly positively associated with self-employment that often requires the customisation of asset ownership structures within marriage. Married individuals with prior divorce experiences are more likely to opt for the separation of property, indicating that the awareness of the economic consequences of divorce promotes the individualisation of marriage. Our results are in line with the cross-national trend towards customised marriages, although the trend in Germany is less pronounced than in other countries.
2022-08-12Zeitschriftenartikel
The Nexus between Methods and Power in Sociological Research
(Kultur-, Sozial- und Bildungswissenschaftliche Fakultät) Schmitz, Andreas; Hamann, Julian
This article develops an integrative perspective on the nexus between power and sociological research methods. By reflecting upon two of the most widely used methodological approaches in sociology – standardized survey research and qualitative interview research – we develop a comprehensive heuristic framework for examining the ways in which the use of sociological methods affects and intersects any social scientific practice: (1) the power effects that societies and institutional settings exert on methods and the use of methods, (2) power in the use and implementation of methods, and (3) the power effects that methods and the use of methods exert on societies and institutional settings.