Effects Of Land Use Change On Net Primary Productivity Of Ecosystem In Hulunbuir Region

Net primary productivity(NPP),one of the global change research hot spot,can represent the production capacity of vegetation and is one of the most important indicators to assess the sustainability of ecosystem.Taking HulunBuir as the study area,the LUCC dataset collected from Chinese Academy of Sciences were used to analyze the LUCC dynamics.Besides,MODIS-EVI,LSWI combined with meteorological data were used to analyze temporal-spatial characteristics of vegetation NPP in HulunBuir from 2000 to 2015 by using Vegetation Photosynthesis Model.The results showed that:(1)The main land use type in Hulun Buir is woodland(47.3%),which was followed by dense grass(21%),sparse grass(17%)and dry land(7%).While the proportion of paddy land(0.07%)is the smallest.During 2000 and 2015,the area and spatial patterns of all land use types have changed a lot.The area of woodland has decreased by 396.72km~2;while the area of grass has decreased by778.44km~2.On the contrary,the areaof cropandand construction land has continuously increased.The changes of land use types and area will make influence of the NPP.(2)The spatial pattern of NPPinHulunBuirshowsagoodstrip regularitythatthereis an obvious increase trend from southwest to northeast.According to values of NPP,the distribution of NPP can be classified into four classes: the low values region in the west grass area,the medium and high region in the west area ofGreat Khingan,the medium region in the Great Khingan and the high values in the cropland in the east part ofHulunBuir.(3)From 2000 to 2015,the NPP of HulunBuir showed an decrease trend in the first few years while an increase trend in the rest years.The average annual NPP of HulunBuir has increased from 330.9gC/(m~2·a)in 2000 to 362.8 gC/(m~2·a)in 2015.During 2000 and 2005,74.5% of the whole study area show an decrease trend with an annual reducing rate at 5.38gC/(m~2·a).Between 2005 and 2010,most of the NPP pixels show an increasing trend with a rate of 5.28gC/(m~2·a).While during 2010 and 2015,the increasing rate is becoming bigger and bigger,which is 9.56gC/(m~2·a).Overall,during 2000 and 2015,76.5% of the NPP pixels show an increasing trend,and 47.6% of them have an increasing rate between 0 and 5gC/(m~2·a).When it comes to thecharacteristic value,the range of NPP in Hulun Buir was mainly between 200 and 400gC/(m~2·a)which accounts more than 40%.It is followed by the range 0-200 and 400-600gC/(m~2·a),which account about 30%and20%.The proportion of the 600-800gC/(m~2·a)is under 10%,and the percentage of>800gC/(m~2·a)is under 5%,which is the smallest.Although not too much high values of NPP were found in Hulun Buir,its proportion is increasing year by year.(4)The NPP values of different land use types show great differences.From highest to lowest,the NPP order of land use types are as follows : dry land(534.3gC/(m~2·a)>paddyland(461.8gC/(m~2·a))>woodland(384.2gC/(m~2·a))>othertrees(361.1gC/(m~2·a))>wetland(355.6gC/(m~2·a))>densegrass(202.0 gC/(m~2·a))> sparse grass(141.9 gC/(m~2·a))> built-up land(108.4 gC/(m~2·a))> used land(46.7 gC/(m~2·a))> water(45.9 gC/(m~2·a)).Except for sparse grass,there are more increased NPP pixels than decreased ones.As a whole,the NPP of these land use types showed an increasing trend despite with fluc tuations in some years.(5)Compared to the average annual air temperature,the effects of annual precipitation of the average annual NPP was more significant.In the perspective of correlation coefficient,the Pearson's correlation coefficient between precipitation and NPP was 0.47.If the hysteresis effect was taken into account,the coefficient can be as high as 0.77.When the annual precipitation is over 400 mm,the effects of it on average NPP would be more significant.