Abstract:

The Qinling-Daba Mountains, as the north-south transition zone of China and the watershed between the Yellow River and the Yangtze River, are characterized by multi-dimensional and high-degree heterogeneity and variations in climate and landscape. Especially, the spectra of altitudinal belts show outstanding areal differentiation in the study region and could be considered to serve as a criterion for determining the boundary between warm temperate and subtropical zones in the Qinling-Daba Mountains. This paper designs a digital integrated system for 33 spectra of altitudinal belts in the study region and analyzes their structures and the spatial patterns of the main altitudinal belts from north-south, from west-east and with exposures. The results show that: (1) From south to north, the basal belt gradually transfers from subtropical evergreen broadleaved forest to warm temperate deciduous broadleaved forest; the spectra of altitudinal belts change from complex to simple; the dominant belt changes from mixed broadleaf-conifer forest and evergreen-deciduous broadleaved mixed forest, and then to deciduous broadleaved forest belt; and the upper limit of the evergreen-deciduous broadleaved mixed forest decreases from 1600-2000 m in the Daba Mountains to 700-800 m in the Xunhe Basin of the Qinling Mountains. (2) From west to east, the structures of altitudinal belt spectra show a complex pattern in the eastern and western sections but a simple one in the middle section; the upper limits of both evergreen-deciduous broadleaved mixed forest belt and mountain deciduous broadleaved forest belt present a quadratic curve distribution pattern in longitude direction; however, the upper limit of mountain broadleaf-conifer mixed forest belt exhibits a nearly linear decrease in west-east direction from 2700 m to 2000 m in the Qinling Mountains and from 3300 m to 1600 m in the Daba Mountains. (3) In the Qinling Mts., the basal belt is just warm temperate deciduous broadleaved forest both in the northern and southern flanks, with only some evergreen trees mixed in the basal belt in the southern flank; while in the Daba Mts., the basal belt is evergreen-deciduous broadleaved mixed forest in the northern flank and evergreen broadleaved forest belt in the southern flank. The north flanks of the Qinling and Daba Mountains have similar dominant belts, namely, mountain broadleaf-conifer mixed forest belt or mountain deciduous broadleaved forest belt. However, the southern flank of the Daba Mountains has its own unique dominant belt, i.e., evergreen-deciduous broadleaved mixed forest belt. This implies that the Daba Mountains are more appropriate than the Qinling Mountains to act as the boundary between subtropical and warm-temperate zones in central China.

Key words: Qinling-Daba Mountains, mountain altitudinal belt, latitude, longitude, quadratic curve