In this paper, the summer climate of 1991 in North China is simulated by using the high-resolution regional climate model (RegCM2) and the effects of the grassland desertification on summer drought in the central and ...In this paper, the summer climate of 1991 in North China is simulated by using the high-resolution regional climate model (RegCM2) and the effects of the grassland desertification on summer drought in the central and the northern parts of North China as well as Mongolia are studied. It shows that the regional climate model essentially catches the characteristics on distribution and seasonal variation of the precipitation that keep good agreement with the observation. The desertification makes precipitation in the central part of North China during its flood period decrease obviously in July. The border of the precipitation or the soil moisture reduction in the desertification region extends about one latitude southeastward and beyond the southeast edge of the desertification. Thus, vegetation in the border region approaches desertification further. However, there appears evident difference of variation of precipitation over the whole desertification region. The grassland desertification greatly changes the transfers of fluxes between land and atmosphere. The secondary circulation or secondary circulation cells in the desertification region are excited and as a result moisture transport is changed. The variation of flux transfers between land and atmosphere as well as the vertical motion of atmosphere is closely related to that of precipitation.展开更多
Using the Normalized Difference Vegetation Index （NDVI） as an indicator of vegetation growth, we explored the characteristics and differences in the response to drought of five vegetation biomes in Northeast China, ...Using the Normalized Difference Vegetation Index （NDVI） as an indicator of vegetation growth, we explored the characteristics and differences in the response to drought of five vegetation biomes in Northeast China, including typical steppe, desert steppe, meadow steppe, deciduous coniferous forest and deciduous broad-leaved forest during the period 1982 2009. The results indicate that growing season precipitation may be the primary vegetation growth-limiting factor in grasslands. More than 70% of the temporal variations in NDVI can be explained by the amount of precipitation during the growing season in typical and desert steppes. During the same period, the mean temperature in the growing season could explain nearly 43% of the variations in the mean growing season NDVI and is therefore a dominant growth-limiting factor for forest ecosystems. Therefore, the NDVI trends differ largely due to differences in the vegetation growth-limiting factors of the different vegetation biomes. The NDVI responses to droughts vary in magnitude and direction and depend on the drought-affected areas of the five vegetation types. Specifically, the changes in NDVI are consistent with the variations in precipitation for grassland ecosystems. A lack of precipitation resulted in decreases in NDVI, thereby reducing vegetation growth in these regions. Conversely, increasing precipitation decreased the NDVI of forest ecosystems. The results also suggest that grasslands under arid and semi-arid environments may be more sensitive to drought than forests under humid environments. Among grassland ecosystems, desert steppe was most sensitive to drought, followed by typical steppe; meadow steppe was the least sensitive.展开更多
Grassland ecosystems in North America have been significantly altered through various disturbances from past to present. This paper has identified and examined major disturbances in the grassland ecosystems, which inc...Grassland ecosystems in North America have been significantly altered through various disturbances from past to present. This paper has identified and examined major disturbances in the grassland ecosystems, which include grazing, fire and drought. A brief history of each disturbance is reviewed and its impact on the grassland ecosystem is discussed, by synthesizing previous research efforts available in the current literature. The paper intends to understand the grassland ecosystem from a comprehensive perspective and particularly tries to articulate the compound effect of the major disturbances in the same context instead of viewing them in isolations. It is concluded that a holistic understanding of the interaction between disturbances and plant communities is essential for sustainable grassland management, which demands comprehensive research effort in this area. The paper also points out the challenges we are facing in the current researches and suggests potential future improvement.展开更多
文摘In this paper, the summer climate of 1991 in North China is simulated by using the high-resolution regional climate model (RegCM2) and the effects of the grassland desertification on summer drought in the central and the northern parts of North China as well as Mongolia are studied. It shows that the regional climate model essentially catches the characteristics on distribution and seasonal variation of the precipitation that keep good agreement with the observation. The desertification makes precipitation in the central part of North China during its flood period decrease obviously in July. The border of the precipitation or the soil moisture reduction in the desertification region extends about one latitude southeastward and beyond the southeast edge of the desertification. Thus, vegetation in the border region approaches desertification further. However, there appears evident difference of variation of precipitation over the whole desertification region. The grassland desertification greatly changes the transfers of fluxes between land and atmosphere. The secondary circulation or secondary circulation cells in the desertification region are excited and as a result moisture transport is changed. The variation of flux transfers between land and atmosphere as well as the vertical motion of atmosphere is closely related to that of precipitation.
基金supported financially by the National Basic Research Program of China under Grant No. 2010CB950504the General Program from the National Natural Science Foundation of China(No. 41175125)
文摘Using the Normalized Difference Vegetation Index （NDVI） as an indicator of vegetation growth, we explored the characteristics and differences in the response to drought of five vegetation biomes in Northeast China, including typical steppe, desert steppe, meadow steppe, deciduous coniferous forest and deciduous broad-leaved forest during the period 1982 2009. The results indicate that growing season precipitation may be the primary vegetation growth-limiting factor in grasslands. More than 70% of the temporal variations in NDVI can be explained by the amount of precipitation during the growing season in typical and desert steppes. During the same period, the mean temperature in the growing season could explain nearly 43% of the variations in the mean growing season NDVI and is therefore a dominant growth-limiting factor for forest ecosystems. Therefore, the NDVI trends differ largely due to differences in the vegetation growth-limiting factors of the different vegetation biomes. The NDVI responses to droughts vary in magnitude and direction and depend on the drought-affected areas of the five vegetation types. Specifically, the changes in NDVI are consistent with the variations in precipitation for grassland ecosystems. A lack of precipitation resulted in decreases in NDVI, thereby reducing vegetation growth in these regions. Conversely, increasing precipitation decreased the NDVI of forest ecosystems. The results also suggest that grasslands under arid and semi-arid environments may be more sensitive to drought than forests under humid environments. Among grassland ecosystems, desert steppe was most sensitive to drought, followed by typical steppe; meadow steppe was the least sensitive.
文摘Grassland ecosystems in North America have been significantly altered through various disturbances from past to present. This paper has identified and examined major disturbances in the grassland ecosystems, which include grazing, fire and drought. A brief history of each disturbance is reviewed and its impact on the grassland ecosystem is discussed, by synthesizing previous research efforts available in the current literature. The paper intends to understand the grassland ecosystem from a comprehensive perspective and particularly tries to articulate the compound effect of the major disturbances in the same context instead of viewing them in isolations. It is concluded that a holistic understanding of the interaction between disturbances and plant communities is essential for sustainable grassland management, which demands comprehensive research effort in this area. The paper also points out the challenges we are facing in the current researches and suggests potential future improvement.
