Abstract
Spatio-temporal patterns of rain-use efficiency (RUE) can explicitly present the steady-state of ecosystem water use and thus ecosystem functioning. The west of Songliao Plain, located along the east fringe of the agro-pasture transitional zone in northern China, is highly sensitive to global change. In this study, satellite-based RUE was calculated using time series SPOT VEGETATION (SPOT-VGT) Normalized Difference Vegetation Index (NDVI) images and precipitation data for the study area from 1999 to 2011. Based on regression model by fitting simple linear regression through the pixel-based time series of RUE in the growing season and calculating the slopes, the change trend of RUE was determined. The grey relational analysis (GRA) method was extended to the spatial scale, and used to select sensitive climate and socio-economic factors that affected RUE variations. The result demonstrated that vegetation RUE increased slightly with an undulating trend, implying the ecosystem function tended to improve between 1999 and 2011. In total, 4.23% of the total area had experienced a significant increase in RUE, whereas 1.29% of the total area presented a significant decrease. Areas showing increased RUE trends mostly coincided with areas of land cover conversions from grassland to forest, shrub to forest and cropland to forest, which suggested a positive linkage with ecological protection policy and projects at national and local levels. Based on the obtained spatial Grey Relation Grade (GRG) values, the pattern of the impact factors clearly showed a spatial heterogeneity. Spatially, sunshine duration, temperature and population density were most closely related to RUE in the west of Songliao Plain between 1999 and 2011.
Highlights
Vegetation affects several processes, including water balance, absorption and reemission of solar radiation, latent and sensible heat fluxes, the carbon cycle, etc
Rain-use efficiency (RUE) values were increased from center to the surrounding in the whole
SPOT-VGT datasets of Normalized Difference Vegetation Index (NDVI) and rainfall were used in this paper to analyze variations in vegetation rain-use efficiency and their relationship with climate and human activity in the west of Songliao Plain, China
Summary
Vegetation affects several processes, including water balance, absorption and reemission of solar radiation, latent and sensible heat fluxes, the carbon cycle, etc. Rain-use efficiency (RUE) is defined as the ratio of ANPP to precipitation, i.e., the number of kilograms of aerial dry matter phytomass produced over one ha in a year per one millimeter of rain fallen [3]. Le Houérou et al stated that a stable value (« four kilogram dry matter/ha/year/mm rainfall) could be found throughout the various arid and semi-arid zones of the world and is independent of the plant species [4]. A decrease in RUE reflects a declined capacity of the vegetation to transform water (and nutrients) into biomass [5,6]. The process of vegetation degradation may involve a range of processes including the loss of vegetation cover, the decreasing availability of plant nutrients or the increases in run off due to compaction of top soil [7]. RUE provides an index of degradation that is independent of the effects of rainfall [8,9,10]
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