| Net Primary Production?NPP?is an important indicator to measure vegetation growth and reflect ecosystem function.Studying its spatial and temporal differentiation characteristics and main impact factors can provide a scientific basis for tackling climate change and carrying out effective ecological protection measures.In this paper,the Qinling-Daba Mountains was selected as the stduy area.Based on MOD17A3 data from 2000 to 2015,meteorological data,vegetation type data,DEM data and other basic data,the methods of Sen trend analysis,coefficient of variation,Hurst index and correlation analysis were used to research the NPP in study area.Firstly,we analyzed the temporal and spatial variation characteristics of vegetation NPP in Qinling-Daba Mountains,and discussed the characteristics of regional differentiation in term of administrative area,elevation,latitude and longitude,watershed and ecological function division.Secondly,we analyzed the difference of NPP between time and space in different vegetation types,such as forest,grassland,and farmland.Finally,we explored the impact of topography and climate change on vegetation NPP.The main conclusions were listed as following.?1?The average NPP of vegetation in Qinling-Daba Mountains was 495.82gC·m-2·yr-11 from 2000 to 2015,which showed a slight upward trend during 16 years,and the coefficient of variation was small scale,which meant a relatively stable state.The NPP values were low in the northeast and high in the southwest on the spatial distribution.The growth NPP areas accounted for about 78.73%of the total area,and they mainly distributed in the northwest and central region of the study area.The reduced value areas?19.35%?mainly distributed in the eastern part of the study area.About 83.87%of the prefecture-level cities were mainly increased vegetation NPP areas.Aabout 61.32%of regional vegetation NPP values were anti-continuity in the future.From the perspective of regional differentiation,the ecological sub-region of the deciduous broad-leaved-coniferous and broad-leaved mixed forest in Qinling Mountains?I1501?had the most significant growth.In the vertical direction,the increased NPP areas presented an"increasing-stable-lowering"trend with increasing altitude.In the level direction,the increased NPP areas had“increasing-lowering-stable”trend from west to east,and they had a continually increasing trend from south to north.In term of watershed,the growth areas of NPP in Jialing River Basin and Hanjiang River Basin was better than those in Tao River Basin and Luo River Basin.?2?The proportion of vegetation types in Qinling-Daba Mountains was statisticsed as follows,meaning forest vegetation 66.84%,farmland vegetation 19.44%,and grassland vegetation 8.19%.The annual average NPP value of evergreen coniferous forest in forest vegetation was the largest with 557.97 gC·m-2·yr-1.Except evergreen coniferous forest and evergreen coniferous shrub forest,the other forest vegetation type showed an upward trend.Among grassland vegetation,the annual average NPP value of meadow vegetation was the largest with 489.03 gC.m-2.yr-1,and the growth trend of grassland was the largest one.Among farmland vegetation,the annual average NPP value of paddy fields(539.45 gC·m-2·yr-1)was greater than dry land(445.67 gC·m-2·yr-1),but the growth trend of dryland NPP was larger than that in paddy fields.In terms of spatial distribution,the NPP of the three vegetation types increased areas was more than decreased areas,and the NPP of the same vegetation type had different performances in different ecological functional zone.The NPP of forest vegetation grew significantly in deciduous broad-leaved forest,deciduous broad-leaved shrub forest and evergreen coniferous forest,mainly distributed in Qinling Mountain and the northern region of Daba Mountains.The NPP of grassland vegetation mainly growed in grass which were mainly distributed in the northwest of the study area.The NPP of farmland vegetation mainly grows in dry land,and mainly distributed in the northwestern part of the study area and the Hanjiang River basin.?3?Among the topographic factors,the vegetation NPP in Qinling-Daba Mountains mainly affected by the elevation.The trend increased first and then decreased with the elevation rising.The productivity was the largest where the aspect was south,and the smallest in north.The change of slope has little relationship with the vegetation NPP.Among the related climate factors,the correlation coefficient between vegetation NPP and climatic factors were effective precipitation with 0.511,annual precipitation with 0.311,effective temperature with 0.230,hydrothermal product index?K?with 0.169,and annual average temperature with 0.135,perspectively.The partial correlation coefficient were effective precipitation with 0.540,effective temperature with 0.515,annual average temperature with 0.472,and annual precipitation with-0.190.The largest area ratio of significant level?P<0.1?was the partial correlation coefficient of effective precipitation.The results showed that vegetation NPP of study area was mainly affected by the effective precipitation.The water and thermal product index?K?had little effect on the vegetation of the study area.The relationship between climate and vegetation NPP can more truly responese to effective precipitation and effective temperature than annual average temperature and annual precipitation.The degree of different vegetation types responsed to climate factors was different.Forest vegetation NPP in Qinba Mountains mainly affected by effective precipitation.While grassland vegetation NPP was more strongly responsive to effective temperature.The paddy field NPP mainly affected by effective temperature,while NPP in dry land mainly affected by effective precipitation. |
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