| Grassland is one of the important components of terrestrial ecosystems and one of the important economic resources for the development of stock grazing.Grassland plays an important role in the ecological environment and economy in China and around the world.The Qinghai-Tibet Plateau has rich ecological chains,which was known as "the third pole in the world".The Qinghai-Tibet Plateau has natural resources and plays an important role in global ecological security and economic activities.In recent years,the grassland of the Qinghai-Tibet Plateau have shown varying degrees of degradation under the combined influence of global warming and human activities,which increased the carbon release from the huge carbon pool of the Qinghai-Tibet Plateau.Therefore,it is important to study the current situation of grassland degradation in the Tibetan Plateau and the impact of meteorological factors and human influence factors on grassland.We combined data collection methods and remote sensing monitoring methods to analyzed the changes of climatic factors,population,grazing intensity and grassland Grass Primary Productivity,and we also analyzed the correlation of these factors to grassland Grass Primary Productivity with different degradation degrees of grasslands.The main results were as follows:(1)The temporal and spatial variation characteristics of meteorological factors in the study area covered by grassland in Qinghai-Tibet Plateau from 1982 to 2015 showed: The annual and spatial temperature is increasing and the spatial distribution of the mean temperature is weakened from the northwest to the southeast.The annual average precipitation is increasing from 1982 to 2015 and the spatial distribution of the mean precipitation showed is weakened from the west to the east.The annual average humidity showed a decreasing change from the period of 1982-2015,and the spatial distribution of the mean humidity showed increased trends from northwest to southeast of study area.At the same time,the average annual solar hours showed a decreasing trend and the spatial distribution of the mean solar hours in most areas also showed a decreased trends.The annual average wind speed showed a decreasing trend during 1982-2015 and the spatial distribution of the mean wind speed showed decreased trends from the northwest to the southeast of the study area.(2)The temporal and spatial variation characteristics of human activity factors and grassland vegetation indicators of the Qinghai-Tibet Plateau from 1982 to 2015 showed: The population of the Qinghai-Tibet Plateau showed a continuous increasing trend from 1982 to2015 and the the spatial distribution of population was more densely populated in the easternregion,with a lower population density in the most area of the Tibet.The high value area of grazing intensity was distributed in the eastern area of the Qinghai-Tibet Plateau.The grazing intensity increased significantly from 1982 to 2015 and the rate of grazing intensity was increasing in the same time,so the pressure of grazing on grasslands was also increasing.The annual average Fractional Vegetation Cover of grassland showed an increased trend from1982 to 2013,and the spatial distribution of the mean grassland Fractional Vegetation Cover was showed increased trends from northwest to southeast.The most areas of our study area showed an increased trends.The average annual grassland GPP of the Qinghai-Tibet Plateau from 1982 to 2015 showed an increasing trend.The grassland GPP changes fluctuated greatly in the spatial distribution.The grassland GPP showed increased trends in most areas and the high values were mainly distributed in most counties of Qinghai Province and some eastern Tibet.The temporal and spatial Fractional Vegetation Cover and the GPP of grassland of the Qinghai-Tibet Plateau from 1982 to 2013 indicated that the overall grassland recovery and the local degradation.(3)The relationship between meteorological factors and grassland GPP: The average annual grassland GPP of the Qinghai-Tibet Plateau was significantly positively correlated with the annual average temperature in the area with 90%,which indicated that the increase in temperature may promote grassland productivity.There was no significant correlation between the grassland GPP and the interannual precipitation.There was a significant positive correlation between grassland GPP and precipitation in the northwestern area of the Qinghai-Tibet Plateau.The inter-annual variation of grassland GPP and humidity during1982-2015 was negatively correlated,and the correlation of spatial distribution between the two factors was decreasing from west to east.In addition,the wind speed was negatively correlated with the interannual variation of grassland GPP,and it showed a significant negative correlation between two factors in the study area with 83%,and this result may be related to the increase in wind speed and the increase in vegetation evapotranspiration which reduced the impact of humidity on the productivity of grassland.The correlation between annual average solar hours and grassland GPP from 1982 to 2015 was not significant,and the correlation of spatial distribution was significant from northwest to southeast.(4)In most areas of the study area,grassland GPP has a significant positive correlation with population and the population statistics of areas was relatively small.The interannual trend of the grassland GPP and population showed a significant positive correlation,it can be seen that the increase in population of the area may promote the growth of grassland vegetation.The correlation coefficient between grazing intensity and grassland GPP wassignificant,and the proportion of areas with positive and negative significant correlation was similar.The correlation between the interannual variability of grazing intensity and grassland GPP was significant positive,which indicated that the grazing intensity was less relevant to the most areas.(5)The relative contribution of meteorological and human activities to grassland vegetation of the Qinghai-Tibet Plateau study showed: The increased population and deeper grazing intensity may affect the growth of grassland vegetation and may not affect when the grassland degradation does not reach a certain level.When the degree of grassland degradation is heavier,the increased population and excessive grazing may have a negative impact on grassland if the pressure exceeds the load limit of the grassland.It is indicated that grassland may have different responses to anthropogenic and natural factors with different degraded grasslands.Therefor,a reasonable grazing policies should be combined with local environmental and human activities factors.Only in this way,the grassland of the Qinghai-Tibet Plateau would be protected to the greatest extent. |
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