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Land Degradation Assessment and Monitoring of Drylands
Published in Prasad S. Thenkabail, Remote Sensing Handbook, 2015
Marion Stellmes, Ruth Sonnenschein, Achim Röder, Thomas Udelhoven, Stefan Sommer, Joachim Hill
Therefore, it is essential to first set up a hypothesis that identifies major underlying drivers of LUCC. For instance, in Spain and Greece, the Common Agricultural Policy subsidies of the European Union (EU) were identified as one of the important drivers. These largely influenced agricultural developments like intensification and land abandonment, where abandonment of marginal areas involved forest expansion and bush encroachment (Lorent et al., 2008; Serra et al., 2008; Améztegui et al., 2010). In the grasslands of Inner Mongolia/China, many factors explained observed grassland degradation between 1990 and 2000 and the reduced degradation rate between 2000 and 2005, which were altitude, slope, annual rainfall, distance to highway, soil organic matter, sheep unit density, and fencing policy. Fencing policy was negatively correlated suggesting that fencing of sensitive areas can reduce land degradation (Li et al., 2012). The analysis of cropland degradation in the Khorezm Region, Uzbekistan, based on MODIS time series (Dubovyk et al., 2013) revealed that one-third of the area was characterized by a decline of greenness between 2000 and 2010. Groundwater table, land use intensity, low soil quality, slope, and salinity of the groundwater were identified as the main drivers of degradation. These examples show that the combination of remote sensing supported LUCC, and underlying and proximate causes may reveal the most important drivers of land degradation. However, this analysis is often hampered by the fact that for each study area (1) all potential and relevant drivers have to be identified and (2) spatially explicit information of each driver or a proxy has to be available with a sufficient spatial resolution.
Environmental and Social Impact
Published in Ajai, Rimjhim Bhatnagar, Desertification and Land Degradation, 2022
In many parts of the south-western United States, grasslands have been invaded by shrubs, decreasing the vegetation cover in these areas. Grazing, climate change and fire suppression have been indicated as the potential factors responsible for grassland degradation (Okin 2002).
Ecosystems: Diversity
Published in Yeqiao Wang, Terrestrial Ecosystems and Biodiversity, 2020
Grasslands are ubiquitous ecosystems, occupied exclusively by low-growth vegetation that contributes to its open nature. Grasses and sedges are the dominant species, together with flowering herbs, including many kinds of composites and legumes. Grasslands are usually devoid of woody species. However, while temperate grasslands are usually treeless, tropical grasslands have scattered small trees. Temperate species are C3 plants while tropical species are C4 plants based on their photosynthetic pathways. Grasslands can be classified by the unidirectional approach of successional linear replacement into types such as pioneer and climax, or less commonly into increasers, decreasers, neutrals, invaders, and retreaters,[15] depending upon their responses to factors such as grazing, drought, and fire. Annuals or short-lived perennials are pioneer grassland species that readily invade and colonize exposed soils and thrive in full sunlight. Grasslands are found in areas where the moisture content of soil is too low for a closed forest canopy, and grass-dominated communities are maintained through vegetative growth cycles in a seasonal pattern. Grassland areas include prairie in North America, pampas in South America, steppe in central Asia, and savanna in tropical Africa, Australia, South America, and Asia. They are the grazing grounds for both wild and domestic herbivores. Their primary production supports diverse fauna. Plants respond morphologically, structurally, and chemically to herbivory, and herbivores evolve by developing different feeding strategies regarding food source, body size, and feeding behavior. Plant-herbivore interactions and the effects of grazing by large generalist herbivores are generally accounted for by predation, disturbances arising from the evolutionary history and the selective pressures of grazing,[16] and the feedback mechanism between plants and grazers that is manifested in the switching capabilities of plant species and competition modes, especially in grasslands with a long grazing history.[17] Grasses are highly adapted to repetitive grazing and fire, which stimulate shoot regeneration from leaf meristems near the soil surface or by tillering after defoliation. Grassland can be maintained by moderate grazing intensity or fire, which prevents fire-intolerant woody species from successional recovery, and by mowing and other management practices. The long-term sustainability of pastures is threatened by grassland degradation attributable to climate change, desiccation, and over-grazing.
Global degradation trends of grassland and their driving factors since 2000
Published in International Journal of Digital Earth, 2023
Ziyu Yan, Zhihai Gao, Bin Sun, Xiangyuan Ding, Ting Gao, Yifu Li
Grassland degradation is broadly defined as a decline in grassland condition, more specifically, a multifactorial-caused process that drives a persistent decline in grassland productivity (Bardgett et al. 2021). The identification process of grassland degradation and improvement consists of two steps. The first is the long-time series of grassland productivity trends quantitatively assessed based on NPP. Therefore, we used the Sen + MK statistical test method to analyze the variations in productivity. Compared with traditional parametric tests, the major advantage of the Sen + MK method is that this non-parametric statistical test method does not require samples to follow a specific distribution and is not disturbed by outliers (Gilbert 1987). It is more suitable to objectively characterize the overall trend for the long-time series in all distribution types. To assess for statistical significance of the trend and reduce the probability of grassland degradation and improvement being missed throughout the identification process, all tests were considered at a chosen level of significance α = 0.1. For the results involving significant downward changes, we define them as expanding and aggravating grassland degradation; conversely, the significant increase part demonstrates improvement and restoration of grassland. For the insignificant trends, degradation or improvement may still be found after excluding the influence of climatic factors. Subsequently, we accessed Pearson's correlation coefficient between the grassland productivity proxy and MI, and then investigated its putative response relationships with changes in climatic conditions to make a further judgment (Gao et al. 2016). If the significant changes in grassland productivity are a normal response to climate, it is considered that the grassland is in a relatively stable state over the period. Otherwise, there is observed degradation and improvement.