Vegetation Health Assessment Of Typical Steppe In Xilingol Based On Terrestrial Laser Scanning And Ground Survey

The present study assessed the vegetation health of typical grassland in Inner Mongolia,using terrestrial laser scanning technology combined with ground-based measurement technology.The experiment was set up in Xilingol typical grassland experimental demonstration base of Institute of Grassland Research,Chinese Academy of Agricultural Sciences under four grazing intensities,including grazing exclusion(CK,0 SSU·d·hm^-2·y^-1),light grazing(GI170,170 SSU·d·hm^-2·y^-1),moderate grazing(GI340,340 SSU·d·hm^-2·y^-1)and heavy grazing(GI510,510 SSU·d·hm^-2·y^-1).The representative parameters of grassland ecosystem sensitive to grazing were measured,and their responses to different grazing intensities were detected.The vegetation health of typical grassland under different grazing intensities was evaluated by entropy weight method and grey relation analysis based on the VOR and（P+）VOR model.The reasonable grazing thresholds were determined and vegetation health evaluation results were verified based on soil-vegetation-livestock monitoring data.The results are as follows:（1）The responses of vegetation parameters to different grazing intensities were explored based on the terrestrial laser scanning data and ground survey data in 2017.Vegetation canopy coverage under different grazing intensities showed a tendency that GI170>CK>GI340>GI510,while plant community height,plant area proportion which height>0.20 m,aboveground biomass,community coverage,community vertical structure complexity index showed the tendency that CK>GI170>GI340>GI510.No significant difference was observed in all the vegetation parameters under CK,GI170 and GI340（p>0.05）,while GI510 was significantly lower than CK and GI170（p<0.05）.（2）The present study provided the（P+）VOR model based on the VOR model,and evaluated grassland vegetation health under different grazing intensities based on above two models.The assessment results from VOR and（P+）VOR models were almost consistent.The vegetation health under four grazing intensities showed a tendency that GI170>CK>GI340>GI510,indicating the improvement and maintenance of reasonable grazing on vegetation health.Moreover,the difference of vegetation health comprehensive scores between GI340 and CK were reduced by（P+）VOR model,which was more in line with the actuality.This result indicated that the evaluation of grassland vegetation health by taking the element（P+）into account had an ecological significance in practice.（3）The present study comprehensively evaluated and analyzed the grassland ecosystem under different grazing intensities in 2014,2017 and 2020（initial stage-remote sensing monitoring period-recent stage）by‘maximum index optimal+optimal index number’method based on 11 important vegetation parameters in the three aspects of vegetation-soil-livestock.The results showed that grassland ecosystem was best under CK in 2014,GI170 in 2017,and GI340 2020,indicating that the moderate grazing benefited grassland ecological production functions,and the impact of grazing on the grassland ecosystem would be regulated by the grazing period.Within the spatial and temporal scales of this study,the reasonable grazing intensity threshold was 170-340 SSU·d·hm^-2·y^-1,and the vegetation health evaluation results based on both VOR and（P+）VOR models were consistent with the results of the multi-indicator comprehensive evaluation.