The mid-domain effect of mountainous plants is determined by community life form and family flora on the Loess Plateau of China

Abstract

The mid-domain effect (MDE) explains altitudinal patterns of species diversity of mountainous plants at different elevations. However, its application is limited by the species life form and family flora in different layers of plant communities. To verify the MDE hypothesis at the plant community level, we chose a mountain with representative characteristics of the study area in the east of the Loess Plateau, China, such as obvious elevation (from 1324 to 2745 m) and latitude (from 36° 23' to 39° 03') gradients and considerable vegetation types (mainly coniferous and broad-leaved forests). We measured the life forms, families, and species diversity indices of tree, shrub, and herb communities along different elevations. We determined that the family numbers of the herb and shrub communities presented unimodal patterns across an altitudinal gradient, and the highest values occurred at intermediate elevations. The importance values of dominant families in the shrub and tree communities presented unimodal patterns, but the lowest values occurred at intermediate elevations. The species diversity indices of the herb, shrub, and tree communities conformed to unimodal change patterns following an altitudinal gradient, but the greatest diversity occurred at high, low, and intermediate elevations, respectively. At higher elevations, forbs and grasses grew well, whereas sedges grew well at lower elevations. Responses of different tree life forms to the altitudinal gradient were greater for evergreen coniferous tree species than for deciduous coniferous and deciduous broad-leaved tree species. We concluded that the MDE hypothesis of species diversity for mountainous plants is influenced greatly by the community life form and family at the plant community level in a temperate semi-arid region of the Loess Plateau, China. This conclusion tested and modified the MDE hypothesis and may be valuable for fueling prediction of biodiversity models and for the comparison with similar studies in arid and semi-arid mountainous regions.

Figure 1

Maps of the study area indicating vegetation types on the Loess Plateau (a), the topography in Shanxi Province (b), and aluminum alloy frame (c). Along an altitudinal gradient, communities across 9, 8, and 4 elevations were observed at Guancen Mountain (①), Guandi Mountain (②), and Wulu Mountain (③), respectively. In the interior of the frame, 100 grids were separated to accurately measure plant frequency and coverage. (a) and (b) were created by using ArcMap 10.2 (https://desktop.arcgis.com/zh-cn/arcmap/) in the ArcGIS software with the data on spatial distribution of vegetation types and geomorphic types being all derived from the Resource and Environmental Science and Data Center (http://www.resdc.cn/). The boundary map of the Loess Plateau in (a) and cities of the Shanxi Province in (b) were generated by the data from the National Earth System Science Data Center (http://gre.geodata.cn) and the Resource and Environmental Science and Data Center (http://www.resdc.cn/), respectively.

Figure 2

Variation in herb family number with an altitudinal gradient. The family number of the herb community was counted at each elevation, and curve fittings were conducted on the variation in family number with an altitudinal gradient. Data for the family number were obtained from 80 sub-quadrats at each elevation.

Figure 3

Distribution and variation of the importance values of grasses, sedges, and forbs at different elevations. The grass, sedge, and forb species belonged to Gramineae, Cyperaceae, and other families, respectively. At each elevation, species of the herb community were divided into these three life forms. Their importance values were used in regression analyses with the altitudinal gradient. Data for the importance values of grasses, sedges, and forbs were averaged from 80 sub-quadrats at each elevation.

Figure 4

Distribution and variation of importance values and numbers of shrub families at different elevations. There were 6 elevations for the shrub community. At each elevation, the importance values of the shrub families were arranged in ascending order to obtain the dominant family. Data for each shrub family were averaged from 64 sub-quadrats at each elevation. Finally, regression analyses were carried out on relationships between the family number of the shrub community and the importance value of the dominant family (Rosaceae) along the altitudinal gradient.

Figure 5

Distribution and variation of the importance values and numbers of tree families at different elevations. Thirteen elevations were observed for the tree community. At each elevation, the importance values of the tree families were arranged in ascending order to obtain the dominant family. Data for each tree family were averaged from 20 sub-quadrats at each elevation. Regression analyses were performed on the relationships between the family number of the tree community and the importance value of the dominant family (Pinaceae) along the altitudinal gradient.