Grassland fire is a major disturbance to ecosystems and economies throughout the world. Research on the spatial pattern of grassland fire is therefore important in understanding the dynamics of fire disturbance and providing evidence for fire management and prevention. In this study we used a spatial point process modeling approach to study the factors contributing to fire occurrence in the Hulunbeir grassland of the Inner Mongolia Autonomous Region. In previous studies, Ripley忆 K function, Kernel density and Poisson model have been used in the studies of spatial鄄temporal pattern of forest fires. But the distribution pattern of grassland fires was usually described by overlaying fire points on top of the administrative districts or study regions. The properties of spatial distribution, such as clustering, dispersion, randomness, were often omitted. In this study, Repley忆s K function was used to investigate the spatial distribution pattern of human鄄 caused fires in the Hulunbeir grassland. The distribution of fire locations was found to be spatially clustered in the months of fire season and between years. The distances of spatial cluster distribution were less than 250km, 265km, 245km, 200km and 245km in April, May, June, September and October respectively. The statistical test showed that the cluster distributions were significant except for October. The distances of spatial cluster distribution were less than 210km, 280km,
In China, the alpine tundra of Changbai Mountain is one of only three areas in China with this type of rare alpine tundra. The vegetation has undergone significant change in recent decades. Herbaceous species from the ' Betula ermanii zone爷 , represented by Deyeuxia angustifolia, have invaded the alpine tundra zone on Changbai Mountain. This incursion represents a unique phenomenon in the mountainous areas of China. We examined the incursion process of D. angustifolia using GPS ( Global positional system) techniques based on spectral and image analysis. In the study area, GPS equipment was used to identify individual D. angustifolia patches. Spectral analysis, particularly the red edge bands, was conducted by comparing the hyperspectral data between the invasive D. andustifolia and the native species, Rhododendron chrysanthum.The spectral diversity of the invasive and native species忆 enabled us to compare their NDVI ( Normalized Difference Vegetation Index) , which was used to analyze within patch changes in vegetation. Landsat TM images from 1983, 1999 http: / / www.ecologica.cn 2002, 2006 and 2008 were used to calculate the NDVI index. The results showed that the incursion of D. angustifolia began in the 1980s. Currently, D. angustifoliahas successfully invaded this alpine landscape with the gradual trend following an altitudinal gradient. The incursion range has extended from relatively low elevations to higher elevations. Moreover, the inference is that D. angustifolia patches at lower elevations are interconnected forming relatively large patches. At higher elevations in the tundra landscape, these D. angustifolia patches were smaller and more scattered.We also investigated the ecological consequences of the D. angustifolia invasion using plant community surveys and soil tests. The D. angustifolia patches were defined as patches at different times of invasion, which consisted of three different invasive levels ( low, medium and high levels of invasion) . In the newly formed plant community D. angustifolia was the dominant species. While this invasion altered the native plant community structure and enhanced biodiversity, it altered some soil properties including both physical and chemical properties. Compared with the native plant community, dominated by R. chrysanthum, the invasive patches showed higher Shannon鄄Wiener diversity and species richness. Changes in abundance and evenness of the community suggested that D. angustifolia would occupy the most dominate position in that community. The change of community structure resulted in the reduction of shrubs and increased the number of herbaceous species. The change of vegetation directly or indirectly led to changes in soil properties. The progression of invasion resulted in a decrease in the carbon / nitrogen ratio, soil humus and total nitrogen. However, the available nitrogen and soil water content increased. The changes in soil nutrients were closely related to changes in physical soil properties, especially for soil water content. The increases in soil...
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