| Thuja is an evergreen tree belonging to Cupressaceae.It is a species endemic to China,a national Class I protected plant and one of the endangered plant species recognized by the International Union for Conservation of Nature.This thesis uses the main distribution areas of Thuja—Xuanhan County,Wanyuan City,and Kaijiang County in Sichuan Province,Chengkou County and Kaizhou District in Chongqing City,as research areas.The remote sensing image interpretation of land use/land cover data integrated by Landsat 7 ETM+and Landsat 8 OLI,ASTER terrain data,BioClim climatically data,HWSD soil data,NDVI data,Thuja field distribution,and related geographical elements data are used as the basic data sources.The Pearson correlation analysis of the 32 variables used is conducted,and 22 valid environmental variables are selected for model operation.By using the maximum entropy niche model,prediction and simulation of the potential distribution areas of Thuja in the research areas are carried out.According to the environment variables response curse and contribution report of the model,9 key contributing environmental variables the quantitative assessment of the mathematical parameter values and ranges of the key environment variables that meet the habitat conditions of Thuja are analysised.Using the InVEST Model,based on the interpretation of the land use/land cover data,statistical analysis is conducted on the habitat degradation level and habitat quality in the research areas in 2000,2010 and 2016,as well as the habitat scarcity in 2000 and 2010.The habitat quality in the research areas is assessed.By comprehensive analysis of the habitat appropriateness and habitat quality of Thuja in the research areas,and the analysis and discussion of the interrelationships between the habitat appropriateness and habitat quality,the temporal and spatial in the distribution of Thuja habitat are defined.Based on the research results,the habitat optimization strategy of the rare and endangered plant Thuja is proposed.Finally,the following conclusions are obtained.(1)In 2000-2010 years,the effect of returning farmland to forest is remarkable,the proportion of arable land decreased by 0.98%;the proportion of woodland area increased by 1.07%;the grassland was damaged a little,the proportion of grassland decreased by 0.40%;the proportion of wetland and water area increased by0.18%;with the population expansion and deepened urbanization,the proportion of construction area increased by 0.13%in the study area.In 2010-2016 years,the proportion of arable land decreased by 0.67%;the proportion of woodland area increased by 1.03%;the grassland was damaged,the proportion of grassland decreased by 0.52%;the proportion of wetland and water area dercreased by0.14%;the proportion of construction land area increased by 0.30%in the study area.(2)The potential distribution areas of Thuja are mainly most of the Chengkou County,the Daba Mountain area in the northeast of Kaizhou District,Kaijiang County,and the Mingyue Mountain area in the south of Kaizhou District in Chongqing City,and the southeast of Wanyuan City and the rest of the Daba Mountain in northeast of Xuanhan County in Sichuan Province.Area of inappropriate Thuja habitat is 12226.86km~2,accounting for 73.43%of the research areas;less inappropriate area is 1066.43km~2,accounting for 6.40%of the research areas;appropriate area is 1802.45km ~2,accounting for 10.82%of the research areas;the most appropriate area is 1555.64km ~2,accounting for 9.34%of the research areas.There are nine environmental variables that contribute greatly to the prediction of potential distribution area of Thuja and the study of habitat appropriateness,including the highest temperature in the warmest month bio-5(49.2%),the precipitation variation coefficient bio-15(7.5%),clay content t-clay(6.7%),monthly mean temperature difference between day and night bio-2(6.0%),annual average precipitation bio-12(5.9%),the minimum temperature in the coldest month bio-6(4.7%),carbonate and limestone content t-caco3(4%),rubble volume percentage t-gravel(3%),and isothermality bio-3(2.7%).The cumulative contribution rate of these nine environmental variables reaches 89.7%.The most appropriate habitat conditions for Thuja are the highest temperature in the warmest month 18.4~32.6°C,the precipitation variation coefficient 62~74,the clay content20~23%weight,the monthly average temperature difference between day and night6.6~9.0°C,and the average annual rainfall 1110~1428mm,the lowest temperature in the coldest month-8.7~2.8°C,carbonate or limestone content 0%,the rubble volume percentage 4~9%vol,and isothermality 24-29.(3)The proportion of area with high scores in habitat degradation in the research areas increased more than that areas with low scores.The degradation area further expanded,and the degradation of habitat worsened.The lands such as woodlands and grasslands that are close to arable lands faced with habitat threat factors and construction lands,with high sensitivity,become the most degraded areas.The habitat quality in the research areas has been severely declined.The areas with high scores in habitat quality have experienced a significant decline and the decline is tended to accelerate.This is especially the case with arable lands and construction land,where the quality of habitat is the worst.There are natural habitats such as woodlands to replace arable lands and other unnatural lands as the scarce habitat types.The areas with high scores in habitat rarity have increased.Ecological functions and structures of natural lands such as woodlands and grasslands are severely damaged.This shows that with the economic and social development in the study area,land use/land cover change has become more intense,and the contradiction between man and land has become more prominent.In general,non-natural land are gradually occupying natural land.The original habitat of Thuja has been seriously damaged and interfered.(4)It can be seen from the discussion of potential distribution areas of Thuja and the law of temporal and spatial changes of the habitat of Thuja that,the habitat appropriateness level of areas with good habitat quality is not necessarily high,and the habitat quality of areas with high appropriateness level may also be poor.However,from the highest appropriateness level to the lowest,the proportion of the area with the best habitat quality decreases from 96.12%to 29.20%,showing a significant downward trend,and the proportion of the area with extremely poor habitat quality increases obviously from 10.21%to 46.30%.This change shows that Thuja's habitat appropriateness has a certain correlation with habitat quality,but not all of them are in a simple and proportional relationship. |
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