Discussion on position of China’s north-south transitional zone by comparative analysis of mountain altitudinal belts

The Qinling Mountains has always been regarded as an essential dividing line between the warm temperate zone and the subtropical zone in eastern China and plays a vital role in the geoecological pattern of China.However,there is controversy about the specific location of this geographical boundary in the academic community.As a product of the combined effects of zonal and non-zonal factors,the mountain altitudinal belts(MABs)can reflect both the horizontal zonality and the vertical zonality of vegetation distribution.Using the MAB information,we can not only profoundly understand the complex mountain system of QinlingDaba Mountains but can also judge its nature as a geographical boundary more scientifically.Therefore,based on the comparative analysis of basal belt,dominant belt characteristics and belt structure characteristics of the MABs in Qinling-Daba Mountains,subtropical and temperate mountains,this paper analyzed the MAB differences and similarities among Qinling-Daba Mountains,subtropical and temperate typical mountains,to reveal the vegetation distribution characteristics in the north-south transitional zone.The results show that:(1)The MABs of the southern part of QinlingDaba Mountains(southern slope of the Daba Mountains)are the same or similar to those of the Subtropical Mountains,and the MABs of the northern part of Qinling-Daba Mountains(northern slope of the Qinling Mountains)are similar to those of the temperate mountains.While it shows obvious transitional characteristics in the vast area between the northern slope of the Daba Mountains and the southern slope of the Qinling Mountains:the basal belts gradually transit from the evergreen broadleaved forest belt(basal belt in subtropical mountains)to the evergreen and deciduous broad-leaved mixed forest belt,and the dominant belts also transit from the evergreen broad-leaved forest belt to the evergreen and deciduous broad-leaved mixed forest belt or the deciduous broad-leaved forest belt.(2)The transitional zone between the subtropical zone and the warm temperate zone is located between the northern slope of the Daba Mountains and the southern slope of the Qinling Mountains.The southern boundary of the transitional zone is along the northern slope of Shennongjia Mountain-the northern slope of Micang Mountain-Baishuijiang Nature Reserve,and the northern boundary is along the southern slope of Funiu Mountain-the southern slope of Taibai Mountain-Lianhua Mountain.Additionally,in the transitional zone,the average temperature in January is between-5°C and 1°C,the annual average temperature is between 10°C and 13°C except Hanzhong Basin and Hanshui Valley,and the accumulated temperature above 10°C ranges from 2000°C to 4000°C,the annual rainfall is about 800-1000 mm.The results provide a scientific basis for revealing the characteristics of China’s north-south transitional zone and scientific division of the boundary between the subtropical zone and warm temperate zone in China.

The implication of mass elevation effect of the Tibetan Plateau for altitudinal belts

The heating effect （or mass elevation effect, MEE） of the Tibetan Plateau （TP） is intense due to its massive body. Some studies have been undertaken on its role as the heat source in summer and its implications for Asian climate, but little has been known of the im- plications of its MEE for the distribution of mountain altitudinal belts （MABs）. Using air tem- perature data observed and remotely sensed data, MAB/treeline data, and ASTER GDEM data, this paper compares the height of MABs and alpine treelines in the main TP and the surrounding mountains/lowland and explains the difference from the point of view of MEE. The results demonstrate： 1） at same elevation, air temperature and the length of growing season gradually increase from the eastern edge to the interior TP, e.g., at 4500 m （corre- sponding to the mean altitude of the TP）, the monthly mean temperature is 3.58℃ higher （April） to 6.63℃ higher （June） in the interior plateau than in the Sichuan Basin; the 10℃ iso- therm for the warmest month goes upward from the edge to the interior of the plateau, at 4000 m in the Qilian Mts. and the eastern edges of the plateau, and up to 4600-5000 m in Lhasa and Zuogong; the warmth index at an altitude of 4500 m can be up to 15℃-month in the in- terior TP, but much lower at the eastern edges. 2） MABs and treeline follow a similar trend of rising inwards： dark-coniferous forest is 1000-1500 m higher and alpine steppe is about 700-900 m higher in the interior TP than at the eastern edges.

EVOLUTION AND DIFFERENTIATION OF THE PHYSICO-EOGRAPHICALENVIRONMENT OF THE QINGHAI-XIZANG (TIBETAN) PLATEAU

The intense uplift of the Qinghai-Xizang Plateau givesrise to drastic changes of natural environment and distinctdifferentiation of the Plateau proper. This paper focuses on theevolution of subtropical environment at low altitude to frigidenvironment at high altitude of the region since Pliocene and thechanges effected by cold-warm amplitude bf global change. Bycomparative study on the structure-type of the altitudinal belt, adistributional model diagram with close relevance to highlanduplift effect has been generalized. Based on regjonaldifferentiation of the Qinghai-Xizang Plateau, a number ofstriking geo-ecological phenomena such as moisture corridor, dryvalleys and high cold-arid core area are investigated anddiscussed.

Mass elevation effect and its forcing on timberline altitude

The concept of mass elevation effect （massenerhebungseffect, MEE） was introduced by A. de Quervain about 100 years ago to account for the observed tendency for temperature-related parameters such as tree line and snowline to occur at higher elevations in the central Alps than on their outer margins. It also has been widely observed in other areas of the world, but there have not been significant, let alone quantitative, researches on this phenomenon. Especially, it has been usually completely neglected in developing fitting mod- els of timberline elevation, with only longitude or latitude considered as impacting factors. This paper tries to quantify the contribution of MEE to timberline elevation. Considering that the more extensive the land mass and especially the higher the mountain base in the interior of land mass, the greater the mass elevation effect, this paper takes mountain base elevation （MBE） as the magnitude of MEE. We collect 157 data points of timberline elevation, and use their latitude, longitude and MBE as independent variables to build a multiple linear regression equation for timberline elevation in the southeastern Eurasian continent. The results turn out that the contribution of latitude, longitude and MBE to timberline altitude reach 25.11%, 29.43%, and 45.46%, respectively. North of northern latitude 32°, the three factors＇ contribution amount to 48.50%, 24.04%, and 27.46%, respectively; to the south, their contribution is 13.01%, 48.33%, and 38.66%, respectively. This means that MBE, serving as a proxy indi- cator of MEE, is a significant factor determining the elevation of alpine timberline. Compared with other factors, it is more stable and independent in affecting timberline elevation. Of course, the magnitude of the actual MEE is certainly determined by other factors, including mountain area and height, the distance to the edge of a land mass, the structures of the mountains nearby. These factors need to be inctuded in the study of MEE quantification in the future. This paper could help build up a high-accuracy and multi-scale elevation model for alpine timberline and even other altitudinal belts.

基于垂直带谱的南北过渡带1:5万植被类型图遥感制图研究——以太白山为例

The compilation of 1:250,000 vegetation type map in the North-South transitional zone and 1:50,000 vegetation type maps in typical mountainous areas is one of the main tasks of Integrated Scientific Investigation of the North-South Transitional Zone of China.In the past,vegetation type maps were compiled by a large number of ground field surveys.Although the field survey method is accurate,it is not only time-consuming,but also only covers a small area due to the limitations of physical environment conditions.Remote sensing data can make up for the limitation of field survey because of its full coverage.However,there are still some difficulties and bottlenecks in the extraction of remote sensing information of vegetation types,especially in the automatic extraction.As an example of the compilation of 1:50,000 vegetation type map,this paper explores and studies the remote sensing extraction and mapping methods of vegetation type with medium and large scales based on mountain altitudinal belts of Taibai Mountain,using multi-temporal high resolution remote sensing data,ground survey data,previous vegetation type map and forest survey data.The results show that:1)mountain altitudinal belts can effectively support remote sensing classification and mapping of 1:50,000 vegetation type map in mountain areas.Terrain constraint factors with mountain altitudinal belt information can be generated by mountain altitudinal belts and 1:10,000 Digital Surface Model(DSM)data of Taibai Mountain.Combining the terrain constraint factors with multi-temporal and high-resolution remote sensing data,ground survey data and previous small-scale vegetation type map data,the vegetation types at all levels can be extracted effectively.2)The basic remote sensing interpretation and mapping process for typical mountains is interpretation of vegetation type-groups→interpretation of vegetation formation groups,formations and subformations→interpretation and classification of vegetation types&subtypes,which is a combination method of top-down method and bottom-up method,not the top-down or the bottom-up classification according to the level of mapping units.The results of this study provide a demonstration and scientific basis for the compilation of large and medium scale vegetation type maps.

Distribution patterns of SOC/TN content and their relationship with topography,vegetation and climatic factors in China’s north-south transitional zone

The spatial distributions and variation mechanism of key soil indices in the Qinling-Daba Mountains are important indicators for the identification of the transitional effect and regional characteristics of the north–south transitional zone in China.This manuscript analyzes the spatial variations in soil organic carbon(SOC)and total nitrogen(TN)and corresponding relationships with major geographical factors based on spatial analysis and geostatistics considering data obtained from the Second National Soil Survey.The results indicate that the spatial distributions of the SOC and TN contents are consistent,and three high-content areas,one secondary high-content area and one low-content area are observed.High content values are located in the high-altitude regions of the Qinling-Daba Mountains and mountainous areas to the west of the Jialing River,the low-content area occurs on the north slope of the Qinling Mountains,and the secondary high-content area mainly encompasses both sides of the Hanjiang River and regions in the Qinling-Daba Mountains at altitudes below 1000 m.The SOC and TN contents vary between the above two ranges,with the gradual increase in content revealing a horn-shaped pattern.Considering the spatial variations and functions of vegetation,topography and climate factors,it is found that the SOC/TN range in the secondary high-content area remains consistent along the 1000 m contour line,the upper limit of the transitional mountain altitudinal belt,the 0℃isotherm line in January and the 24℃isotherm line in July.This region constitutes the main body of the transitional zone between the subtropical and warm temperate zones,and the northern boundary is roughly distributed along the Dujiangyan-Maoxian-Pingwu-Wenxian line to the west of the Jialing River and the 1000 m contour line on the southern slope of the Qinling Mountains,while the southern boundary occurs along the Dujiangyan-Beichuan-Qingchuan line to the west of the Jialing River and the 1000 m contour line on the northern slope of the Daba Mountains.SOC/TN spatial variation provides a reference for the demarcation of the subtropical and warm temperate zones,and further identification of the soil processes and ecological effects in typical regions can help reveal multidimensional transitional characteristics and variation mechanisms.