Analyzing and modeling the spatiotemporal dynamics of urban expansion: a case study of Hangzhou City, China

Understanding the spatiotemporal characteristics of urban expansion is increasingly important for assisting the decision making related to sustainable urban development. By integrating remote sensing (RS), spatial metrics, and the cellular automata (CA) model, this study explored the spatiotemporal dynamics of urban expansion and simulated future scenarios for Hangzhou City, China. The land cover maps (2002, 2008, and 2013) were derived from Landsat images. Moreover, the spatial metrics were applied to characterize the spatial pattern of urban land. The CA model was developed to simulate three scenarios (Business-As-Usual (BAU), Environmental Protection (EP), and Coordination Development (CD)) based on the various strategies. In addition, the scenarios were further evaluated and compared. The results indicated that Hangzhou City has experienced significant urban expansion, and the urban area has increased by 698.59 km2. Meanwhile, the spatial pattern of urban land has become more fragmented and complex. Hangzhou City will face unprecedented pressure on land use efficiency and coordination development if this historical trend continues. The CD scenario was regarded as the optimized scenario for achieving sustainable development. The findings revealed the spatiotemporal characteristics of urban expansion and provide a support for future urban development

The strength of density‐dependent mortality is contingent on climate and seedling size

QuestionsDensity‐dependent processes may promote species diversity in plant communities. Here, we tested whether seedling survival was density‐dependent and varied by seedling size, species and climatic factors.LocationTropical rain forest, Xishuangbanna, southwest China.MethodsGeneralized linear mixed‐effects models were used to examine seedling survival (232 tree species) across 9 years of seedling census data from a 20‐ha tropical forest dynamics plot. Our predictor variables were conspecific and heterospecific neighbour density, size of the seedling and annual variation in climatic factors.ResultsWe found significant negative effects of conspecific tree density, but positive effects of heterospecific seedling density on the survival of tree seedlings in this plot. In general, conspecific negative density dependence (CNDD) was observed most frequently for large size classes of seedlings (≥20‐cm high), while heterospecific positive density dependence (HPDD) was similar at all size classes. CNDD for large seedlings was stronger during warm years, and HPDD for large seedlings was stronger during dry years.ConclusionsOur study suggests that the strength of density dependence varied through time, and this strength was influenced by water availability and temperature. Our results highlight the potential for changes in species composition and species co‐existence that could result from increasing temperature‐strengthening CNDD effects and decreasing precipitation strengthening HPDD effects.In this study, we tested the correlation between the strength of density dependence and climatic conditions across 9 years of censuses. We found the strength of density dependence fluctuates and is significantly correlated with temperature and precipitation. Our study highlights the alteration of the strength of density dependence with climate change which will alter community composition in tropical forest.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145578/1/jvs12645.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145578/2/jvs12645_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145578/3/jvs12645-sup-0001-AppendixS1.pd

Analysis of the spatiotemporally varying effects of urban spatial patterns on land surface temperatures

Urban heat islands (UHIs) are a worldwide phenomenon that have many ecological and social consequences. It has become increasingly important to examine the relationships between land surface temperatures (LSTs) and all related factors. This study analyses Landsat data, spatial metrics, and a geographically weighted regression (GWR) model for a case study of Hangzhou, China, to explore the correlation between LST and urban spatial patterns. The LST data were retrieved from Landsat images. Spatial metrics were used to quantify the urban spatial patterns. The effects of the urban spatial patterns on LSTs were further investigated using Pearson correlation analysis and a GWR model, both at three spatial scales. The results show that the LST patterns have changed significantly, which can be explained by the concurrent changes in urban spatial patterns. The correlation coefficients between the spatial metrics and LSTs decrease as the spatial scale increases. The GWR model performs better than an ordinary least squares analysis in exploring the relationship of LSTs and urban spatial patterns, which is indicated by the higher adjusted R2 values, lower corrected Akaike information criterion and reduced spatial autocorrelations. The GWR model results indicate that the effects of urban spatial patterns on LSTs are spatiotemporally variable. Moreover, their effects vary spatially with the use of different spatial scales. The findings of this study can aid in sustainable urban planning and the mitigation the UHI effect

Long-term influence of maize stover and its derived biochar on soil structure and organo-mineral complexes in Northeast China

The influence of biochar on the soil structure and aggregate stability has been debated in previous studies. To probe the action of biochar on soil aggregates, a 5-year field experiment was implemented in the brown earth soil of northeastern China. We determined the aggregate distribution (> 2000 μm, 250–2000 μm, 53–250 μm, and < 53 μm) and organic carbon (OC) and organo-mineral complex contents both in the topsoil (0–20 cm) and within the soil aggregates. Three treatments were studied as follows: control (basal application of mineral NPK fertilizer), biochar (biochar applied at a rate of 2.625 t ha−1), and stover (maize stover applied at a rate of 7.5 t ha−1), and all treatments received the same fertilization. The biochar and stover applications decreased the soil bulk and particle densities significantly (p < 0.05) and enhanced the soil total porosity. Both amendments significantly (p < 0.05) enhanced the total OC, heavy OC fractions, and organo-mineral complex quantities in the bulk soil as well as in all the studied aggregate fractions. Biochar and stover applications promoted the formation of small macroaggregates. A greater amount of organic matter was contained in the macroaggregates, which led to the formation of more organo-mineral complexes, thereby improving soil aggregate stability. However, the different mechanisms underlying the effect of biochar and stover on organo-mineral complexes need further research. Biochar and stover applications are both effective methods of improving the soil structure in Northeast China