| Mountain Tai forest vegetation is a typical representative of plant community in warm temperate deciduous broad-leaved forest zone in North China,and its protection and management has great significance.Most of the forests in Mountain Tai were planted in the 1950 s and 1960 s.Although the short-term and large-scale afforestation at that time played a positive role in the rapid greening,limited to the economic and technical conditions and the constraints of germplasm resources at that time,the afforestation was mainly pure forest,and the main tree species were pines(Pinus)(mainly Oil Pine(Pinustabulaeformis)),Oak(Quercus),Black Locust(Robiniapseudoacacia)and Chinese Arborvitae(Platycladus orientalis),and the afforestation density was too large,resulting in a certain irrationality of the forest structure.In addition,the plantation of Mount Tai has basically reached the stage of mature forest or even over mature forest,and its ability to resist external interference has declined.When encountering external influences such as insect damage and extreme adversity,there would be serious damages and even a large number of dead trees.It is urgent to evaluate the health of Mount Tai forest and make scientific forest management on this basis.The purpose of this study is to analyze the distribution dynamics of dominant species of afforestation in Mount Tai State-owned Forest Farm,to explore the dynamic change law of forest distribution and its relationship with the health of forest ecosystem,and then to evaluate the health of Mountain Tai forest and find out the main restricting factors,on this basis,to put forward the corresponding forest management measures and suggestions.Taking Mountain Tai State-owned Forest Farm as the research area,based on remote sensing images,the dynamic change of the distribution of plantation stands was studied.On this basis,combined with the field investigation data of forest resources in the research area,the forest health evaluation was carried out.(1)Based on the implementation of Google Earth engine(GEE),multispectral Landsat Image data in 2000 and 2016 were obtained.In order to reduce the influence of mountainous terrain shadow,the terrain illumination correction model was applied to Landsat remote sensing images.(2)The current situation map of forest resources in each sub-ordinate management district of Mountain Tai Forest Farm(paper)in 2000 was collected,and the boundary lines of each district were loaded on the image.The mountain ridge,valley trend and obvious ground feature signs were combined with the paper forest resource status map,and the main stand samples in 2000 were animated on the GIS(Geographic Information System)platform.Stand samples in 2016 were from the forest resource inventory data based on ArcGIS,and the main stand distribution samples in 2016 were obtained by selecting the two attributes of tree species structure and dominant tree species at the same time.(3)The Landsat 7 ETM +(enhanced thermal mapper)image in 2000 and the Landsat 8 OLI(operational land imager)image in 2016 were applied respectively.On the basis of terrain illumination correction,combined with the sample data collected and processed under the GIS,the RF(random forest)classifier was applied to study the composition and distribution of stands in the two years in the study area,and the main tree species distribution maps in 2000 and 2016 were obtained.(4)In ArcGIS10.1,the stand classification results in 2000 and 2016 were transformed from grid format to vector format,and spatial superposition was carried out.By establishing new attribute fields,the tree species codes in 2000 and 2016 were compared,the unchanged area were deleted,and the changed areas were retained,and the stand distribution change results of the study area with a span of 16 years were obtained.(5)By setting up sample plots in the area with obvious stand changes and conducting detailed field investigation,the law and driving mechanism of stand distribution change in Mountain Tai plantation were analyzed.(6)Sentinel-2A remote sensing image data of the study area was downloaded on the ESA(European Space Agency)official website.By retrieving the vegetation health degree o f Mountain Tai forest through establishing two models,the inicator of forest vegetation health degree was obtained.(7)Combined the inicator extracted from Sentinel-2A data with the inicators extracted from the forest resources inventory data,and determined the weight of each indicator through the Analytic hierarchy process(AHP),the health condition of Mountain Tai forest was assessed.The distribution and driving mechanism of the main plantation types(Pines plantation,Oak plantation,Black Locust plantation and Chinese Arborvitae plantation)in Mountain Tai were discussed,and the forest health was evaluated.Based on the spatial superpositon of the classification results of 2000 and 2016 under ArcGIS,the result map of stand distribution change in the study area with a span of 16 years was obtained.According to the statistical function of GIS,Pines and Black Locust were two kinds of stands with large area change after 16 years of evolution.The percentage of Pines in Mountain Tai forest decreased from 55.69% to 50.22%,the decrease percentage was 5.47%.The area of Chinese Arborvitae stand decreased by 0.60%.The percentage of Black Locust increased from 10.15% in 2000 to 13.75% in 2016,with an increase of 3.60%.The area of Oak also increased to a certain extent,with an increase of 1.77%.The general trend is that the broad-leaved species continue to expand,and the coniferous forest area shrinks.Based on the results of the dynamic changes of the main stands,the reasons and the driving mechanism of the distribution and changes of the main tree species were analyzed through the investigation of the sample plots.The internal driving mechanism of the distribution dynamics of the four stands was that the broad-leaved species gradually turn the coniferous species into the undergrowth trees through competition and made them weak even die.In the sunny slope of the mountain,the broad-leaved trees invaded the coniferous trees more seriously than the shady slope.However,the process could be slowed down by the intervention of human activities on the growth of the broad-leaved species purposefully.As coniferous species,the rate of Pines decrease was faster than that of Chinese arborvitae.As broad-leaved tree species,when the Oak was in the upper position of Black Locust,it would invade the Black Locust forest.On this basis,based on the forest resources inventory data in 2016 and the Sentinel-2A remote sensing data in the same period,the evaluation indexes reflecting the forest health status of Mountain Tai were extracted.On the basis of the weight of each indicator obtained by AHP,the forest health status of Mountain Tai was evaluated in GIS system.The results showed that the area of high-quality forest(81.69 ha)and healthy forest(2670.48 ha)only accounted for 23.46% of the total area of Mountain Tai forest,and 60.65% of Mountain Tai forest was in sub-health state.The area of unhealthy forest is 1864.74 ha,accounting for 15.90% of the total area of Mountain Tai forest,including 96.92 ha extremely unhealthy forest,which means more than 3 / 4 of Mountain Tai forest was in sub-health or unhealthy state.This study found that the main factor affecting the forest health of Mountain Tai was that the tree species selection was single and the afforestation was not carried out in accordance with the principle of "suitable for the land and trees".In the process of forestry management,the lower forest was thinned too much,resulting in most of the forest being single-layer forest.In addition,the increase of temperature and the decrease of precipitation caused by the change of climate conditions were also a restricting factor to the forest health of Mountain Tai.Based on this,this study put forward the following suggestions for carrying out forest management activities in Mountain Tai forest farm in the next step: firstly,adjust the forest structure step by step.In area with steep slopes,poor soil layers and low water content,weak Oil Pine forest could be gradually thinned and shrub forest could be built;secondly,timely thinning,reduce the forest density,promote the regeneration of natural update,and build uneven forest and multi-layer forest;thirdly,according to the principle of "suitable for the land and trees",introduce local trees,b uild mixed forest and avoid large area of pure forest;fourthly,introduce trees with powerful drought resistance according to the climate change. |
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