Relationship between settlements and topographical factors:An example from Sichuan Province,China

Terrain can influence the spatial distribution of settlements. Studies on the terrain characteristics of settlements can help to understand the effects of the environment on human activities. This paper provides a quantitative analysis of the relationship between settlements and topographical factors. A statistically significant sample of residential locations and ASTER GDEM V2 were used to investigate terrain traits and settlements distributions. We selected eight topographical factors and introduced a practical concept, distributive entropy, into assessing the aggregation extent of the settlements' spatial distribution. The study showed that topography varies within the study area, and distributive entropy indicates that settlements have distinctive distribution tendency in statistic approach. According to the results of this study, mountain inhabitants prefer to settle in valleys. Additionally, with distributive entropy, residential suitability was divided to three levels: suitable, normal, and unsuited. The results showed that suitable area is small in Sichuan Province, accounting for 8.2%～29.9%; however, unsuited area is large, accounting for 33%～63.3%.

Rubber plantation and its relationship with topographical factors in the border region of China, Laos and Myanmar

Rubber plantation is the major land use type in Southeast Asia. Monitoring the spa- tial-temporal pattern of rubber plantation is significant for regional land resource development, eco-environmental protection, and maintaining border security. With remote sensing tech- nologies, we analyzed the rubber distribution pattern and spatial-temporal dynamic; with GIS and a newly proposed index of Planted Intensity （PI）, we further quantified the impacts and limits of topographical factors on rubber plantation in the border region of China, Laos and Myanmar （BRCLM） between 1980 and 2010. The results showed that： （1） As the dominant land use type in this border region, the acreage of rubber plantation was 6014 km2 in 2010, accounting for 8.17% of the total area. Viewing from the rubber plantation structure, the ratio of mature- （〉10 year） and young rubber plantation （〈 10 year） was 5：7. （2） From 1980 to 2010, rubber plantation expanded significantly in BRCLM, from 705 km2 to 6014 km2, nearly nine times. The distribution characteristics of rubber plantation varied from concentrated toward dispersed, from border inside to outside, and expanded further in all directions with Jinghong City as the center. （3） Restricted by the topographical factors, more than 4/5 proportion of rubber plantation concentrated in the appropriate elevation gradients between 600 and 1000 m, rarely occurred in elevations beyond 1200 m in BRCLM. Nearly 2/3 of rubber plantation concentrated on slopes of 8^-25~, rarely distributed on slopes above 35~. Rubber plantation was primarily distributed in south and east aspects, relatively few in north and west aspects. Rubber planted intensity displayed the similar distribution trend. （4） Comparative studies of rubber plantation in different countries showed that there was a remarkable increase in area at higher elevations and steeper slopes in China, while there were large appropriate topog- raphical gradients for rubber plantation in Laos and Myanmar which benefited China for rubber trans-boundary expansion. （5） Rubber plantation in BRCLM will definitely expend cross borders of China to the territories of Laos and Myanmar, and the continuous expansion in the border region of China will be inevitable.

Spatial distributions of intra-community tree species under topographically variable conditions

Growing public awareness of the importance of protecting biodiversity requires the development of forest practices that increase the complexity of stand structure.Understanding the ecological processes of different forest vegetation provide insights into community coexistence mechanisms.In this paper,the spatial patterns of three different communities,evergreen broadleaf forest,deciduous broadleaf forest,and mixed needleleaf and broadleaf forest at Mt.Huangshan,China,were quantified with four structural parameters,the mingling index,the uniform angle index,the diameter dominance index and the crowdedness index.All trees with a diameter at breast height of more than 5 cm were measured.Our analyses highlighted that most trees in the three communities were extremely dense and slightly clumped,with a moderate size differentiation and high mixed structure.In mixed needleleaf and broadleaf forest,the distribution pattern of tree species was better than the other two forests.Overall,spatial patterns in mixed needleleaf and broadleaf forest exhibited a strong stability-effect,that is,the stand had a suitable environment for the stable survival of the forest.With the increasing of elevation,the degree of the mingling index and the crowdedness index increased,however,there was no influence on the uniform angle index and the diameter dominance index.Further,at the same elevation,four structural parameters of shady slope were larger than that of sunny slope.Then we found the relationship between stand spatial structure and environment factors had important influence on forest structure.Our work contributes to the knowledge of population structure,and further provide theoretical basis for the sustainable development of forest resources and protecting biodiversity of Huangshan Mountain.In future studies,it is necessary to explore the limiting factors of community spatial distribution by combining species diversity and functional traits.

Vegetation structural characteristics and topographic factors in the remnant moist Afromontane forest of Wondo Genet, south central Ethiopia

For forest ecosystem management to be effective, knowledge of the horizontal and vertical structural diversity of a forest is essential. The moist Afromontane highlands of Wondo Genet in south-central Ethiopia present an opportunity to restore and rehabilitate and enhance the ecosystem services to be obtained from this forest sustainably. We focused on the forest structural characteristics to better understand the current forest conditions to assist in the sustainable management of this resource. A total of 75 （20 m × 20 m） quadrats were sampled and diame- ter at breast height （DBH） 〉2 cm and stem height 〉2 m were measured. Species identity and abundance, elevation, slope, and aspect were recorded for each plot. Structural characteristics were computed for each plot. Relationship of topographic factors with vegetation characteristics was conducted using R-Software. A total of 72 woody species was re- corded. Whereas, the overall diameter distribution shows an inverted J-shaped curve, the basal area followed a bell-shaped pattern. Five types of population structures are revealed. The mean tree density and basal area was 397.3 stems.ha-1 and 31.4 m2.ha-1, respectively. Only 2.8% of the tree species have densities of 〉25 stems.ha^-1 and the percentage dis- tribution of trees show 56.2% in the DBH class 2-10 cm, indicating that the forest is dominated by medium-sized trees. Celtis africana （8.81 m2.ha^-1） and Pouteria adolfi-friederieii （5.13 m2.ha^-1） make the highest contribution to the basal area and species importance value index. The families/species with the highest importance value index are Ulmaceae, Fabacea and Sapotaceae. Species abundance （r2 = 0.32, p 〈0.001） and species richness （P =0.50, p 〈0.001） are positively related with tree density. Tree density is negatively related with elevation （~ = -0.36, p 〈0.001）, slope （r2 =-0.15, p 〈0.001） and aspect （r2 = -0.07, p 〈0.05）. While basal area is negatively related with elevation （r2 =-0.14, p 〈0.001）, it has a positive relationship with tree density （r2 =0.28, p 〈0.001 and species richness （r2 =0.098）. Species with poor population structure should be assisted by restoration tasks and further anthropogenic distur- bance such as illegal logging and fuel wood extraction should be re- stricted.

Spatio-temporal variation of ecosystem service values adjusted by vegetation cover:a case study of Wuyishan National Park Pilot,China

Ecosystem service values(ESV)are strongly influenced by the vegetation cover,which is heterogeneous across different vegetation types.We develop a dynamic evaluation model of ESV for Wuyishan National Park Pilot adjusted by the rate of inflation and the fractional vegetation cover,which is calculated by an enhanced vegetation index from 2000 to 2018.The spatio-temporal variation of vegetation was also examined.The results demonstrated that:(1)the unit area of ecosystem service values adjusted by vegetation cover(ESVVC)shows a gradient of forest>tea plantation>grassland>cropland,and the major ecosystem services provided by forests include soil formation and conservation,climate regulation,and biodiversity maintenance;(2)the ESV_(VC) increased to 2.1 billion yuan(The reference rate announced by the People’s Bank of China is the US dollar to 6.42 Yuan per dollar.)from 2000 to 2018.Higher and lower ESV_(VC) are predominant in the northwest and southeast region,respectively.In addition,changes of ecological protection structures and human disturbances negatively affected vegetation cover,leading to a decreased ESVVC from 2000 to 2005 in the Jiuqu Stream Ecological Protection Area and the Wuyishan National Scenic Spot.The implementation of ecological protection policies from 2010 to 2018 enhanced the ESV_(VC) in the study area;and,(3)the ESVVC is highest in the southeast and 25°–35°area with altitudes of 800–1000 m.Our model can provide timely and helpful information of changes in ESV for use in ecological corridor design and ecological security monitoring.

Assessing vegetation community distribution characteristics and succession stages in mountainous areas hosting coming Winter Olympics Games

Alpine mountain ecosystem shows strong interactions between abiotic and biotic parameters.They also receive high attention from human activities(natural tourism,trekking,skiing,etc.).However,as the potential disturbance risk areas in alpine mountains are increasing,it is necessary to understand the relationship between environmental factors and plant communities.This is also the key consideration for the coming international events such as the Winter Olympic Games,which could generate uncontrolled ecosystem issues not previously studied.The Yin Mountains in Chongli district,Zhangjiakou City,Hebei Province,China will be the core area of the 2022 Winter Olympic Games.We hypothesize that disturbances will be caused,therefore,the previous relationships between the habitat factors and plant community and the main environmental limiting factors before hosting them must be assessed to design future restoration plans.Therefore,we used the two-way indicator species analysis(TWINSPAN)and market basket analysis(MBA)for vegetation classification in 91 sampling plots.Plant community and relationships among environmental variables(altitude,slope position,aspect,direction,inclination,soil porosity,soil bulk density,organic matter content and soil pH)were investigated through the trend correspondence(DCA)and canonical correspondence analyses(CCA).Also,the TWINSPAN was used to classify the vegetation into 6 different groups.CCA analysis showed that i)the spatial variation of soil moisture and the content of soil organic matter are the main factors limiting the development of shrub and herb communities;ii)the distribution of different forest communities was mainly affected by terrain factors(altitude,aspect and slope position);iii)the dynamic changes of vegetation communities in different altitudes were affected by the fluctuation of environmental factors and human disturbance,and the shrubs and herbaceous plants in mid-to-high altitude areas(above 1400 m)generally show the process of transformation from the pioneer community to transitional community in the competition.We concluded that under the strong interference of human activities in the core construction area of the Olympic venues,higher damage intensity and lower resilience in the low altitude area is observed compared with the pioneer community.Whereas in the low altitude area(below 1400m)with a fragile ecological environment,although the plant diversity and coverage are poor,the potential impact and damage degree of the Olympic Games are greatly reduced due to the distance from the construction area of the core venues and good resilience.This information can help land managers and policymakers to anticipate human disturbances on plant communities and support guiding the most efficient ecological restoration after the Winter Olympic Games in 2022.

InSAR Kalman Filter Phase Unwrapping Algorithm Based on SRTM DEM

PU （phase unwrapping） is the key step and important problem in DEM （digital elevation model） extraction and the measurement of surface deformation of InSAR （Interferometric synthetic aperture radar）. The CKFPUA （conventional Kalman filter phase unwrapping algorithm） can obtain reliable results in the flat terrain areas, but it caused error transmission not making the accurate inversion of surface deformation information in the steep terrain. Considering this situation, so it needs to introduce topographic information for guiding phase unwrapping. Here the 90 m resolution DEM data have been used and it is obtained by SRTM （shuttle radar topography mission） measured jointly by NASA （National Aeronautics and Space Administration） and NIMA （National Imaging Mapping Agency） of U.S. Department of Defense. This paper presents a SD-KFPUA （Kalman filter phase unwrapping algorithm） based on SRTM DEM. With SRTM DEM directing InSAR image to implement phase unwrapping, the speed and accuracy are improved. By analyzing with the conventional Kalman filter phase unwrapping algorithms, it is shown that the proposed method can achieve good results in particular to improve unwrapping accuracy in the low coherence region.

Land Use Changes of Valleys Based on Topographic Factors in Beijing Mountainous Regions of China

Land use changes in mountainous regions were greatly enhanced as the rapid development of economy due to the expanded population in developing countries. Acting geographically as the basic unit of mountainous regions, valleys are the primary sites of economic activities. Therefore optimization of land use policy in valleys is of critical important to the sustainable development in mountainous regions. On the basis of land use data in 1995 and 2012, this study explored the changes of land use according to the assessment of varied topographic factors （i.e., altitude and slope） in typical valleys of the Beijing mountainous regions, China. Our results showed that the valley is an efficiently geographical unit to evaluate land use changes in mountainous regions. We also found that major land use changes in mountainous regions of Beijing from 1995 to 2012 were the dramatic losses of grassland to the cultivated and construction lands, while most of these changes took place at the altitude of 0-400m and the slope of 6-15~. Considering the ever increasing economic development in Beijing mountainous regions, the increases of the construction and cultivated lands are inevitable, however, the great changes at a steeper slope imply the need to tailor land use structure coming into line with topographic factors, and suggesting ecological barriers and water conservation must be exercised in the developments of these areas.

Land cover dynamics of different topographic conditions in Beijing,China

Topographic conditions play an important role in controlling land cover dynamic processes.In this study,remotely sensed data and the geographic information system were applied to analyze the changes in land cover along topographic gradients from 1978 to 2001 in Beijing,a rapidly urbanized mega city in China.The study was based on five periods of land cover maps derived from remotely sensed data:Landsat MSS for 1978,Landsat TM for 1984,1992,1996 and 2001,and the digital elevation model(DEM)derived from 1:250,000 topographic map.The whole area was divided into ten land cover types:conifer forest,broadleaf forest,mixed forest,shrub,brushwood,meadow,farmland,built-up,water body and bare land.The results are summarized as follows.(1)Shrub,forest,farmland and built-up consist of the main land cover types of the Beijing area.The most significant land cover change from 1978 to 2001 was the decrease of the farmland and expansion of the built-up area.Farmland decreased from 6354 to 3813 km^(2)in the 23 years,while the built-up area increased from 421 to 2642 km^(2).Meanwhile,the coverage of forest increased from 17.2%to 24.7%of the total area.The conversion matrix analysis indicated that the transformation of farmland to the built-up area was the most significant process and afforesta-tion was the primary cause of the replacement of shrub to forest.(2)Topographic conditions are of great importance to the distribution of land cover types and the process of land cover changes.Elevation has an intensive impact on the dis-tribution of land cover types.The area below 100 m mostly consists of farmland and built-up areas,while the area above 100 m is mainly covered by shrub and forest.Shrub has the maximum frequency in areas between 100 and 1000 m,while forest has dominance in areas above 800 m.According to the analysis of land cover changes in different ranges of elevation,the greatest change below 100 m was the process of urbanization.The process of the main land cover change occurred above 100 m was the transformation from shrub to forest.This result was consistent with the vertical change of natural vegetation distribution in Beijing.(3)Slope has a great influence on the distribution of land cover.Farmland and built-up areas are mostly distributed in flat areas,while shrub and forest occupy steeper areas compared with other land cover types.Forest frequency increased with the increas-ing slope.Land cover changes differed from the slope gradients.In the plain area,the land cover change occurred as the result of urbanization.With the increasing of the slope gradient,afforestation,which converts shrub to forest,was the process of the primary land cover change.

Variation of Soil Nutrition in a Fagus engleriana Seem.-Cyclobalanopsis oxyodon Oerst, Community Over a Small Scale in the Shennongjia Area, China

Soil nutrition is a key factor influencing species composition in a community, but it has clearly scaledependent heterogeneity. In the present study, geostatistics methods and canonical correspondence analysis （CCA） were used to detect： （i） the variation range of soil spatial heterogeneity; （ii） the influence of topographic factors on the distribution of soil nutrition; and （iii） the relationships between soil chemical properties and species in the community. In all, 23 soil variables were measured, including total N and organic C, AI, Ba, Ca, Cr, Cu, Fe, Ga, Li, Mg, Mn, Na, NH4-N, Ni, NO3-N, Pb, pH, P, Sr, Ti, V, and Zn. Semi-variograms of these variables were calculated and mapped. All indices showed autocorrelatlons, with ranges between 29 and 200 m. When the sample method was larger than these distances, spatial autocorrelations were avoided. The distribution patterns of Ca, Cr, Ga, K, Mg, organic C, P, Pb, and pH, and total N were related to the microtopography and the distribution of these compounds was clumped in water catchments area. The CCA method was used to investigate the relationship between plant species and soil properties in this community. Fagus engleriana Seem., Lindera obtusiloba BI. Mus., and Acer griseum （Franch.） Pax were correlated with organic C, available N, and P.

Species composition, stand structure, and regeneration status of tree species in dry Afromontane forests of Awi Zone, northwestern Ethiopia

Species composition,structure,and regeneration status of trees were assessed in five dry Afromontane forests.In each of the forests,trees having≥5 cm diameter at breast height were identified and measured in 80 quadrats(20×20m^(2)).We compared tree species composition and similarities,stem densities,frequencies,basal area and importance value index of trees.Harvesting index was calculated to 13.3%in the least disturbed and 22.5%in highly disturbed forests.A total of 1,655 individuals representing 38 species and 28 families were recorded.The tree densities varied from 364.1 to 664.1stem ha^(−1) with an average basal area of 20.7m^(2) ha^(−1).The analysis showed significant differences in basal areas of tree species between the least and highly disturbed forests.Seedling densities ranged from 2000 to 8162.5 stem ha^(−1) and sapling densities ranged from 512.5 to 2562.5 stem ha^(−1).The anthropogenic disturbances revealed high degradation of population structure and regeneration statutes of the trees in the studied forest ecosystem.In conclusion,the study provided empirical results on the dominance,population structure,importance value and regeneration status of tree species,which would be instrumental for the development of successful rehabilitation strategies for the studied forests.