Exploring on the climate regionalization of Qinling-Daba mountains based on Geodetector-SVM model

noted in Group III. This finding indicates that only some vegetation was significantly affected by these factors, whereas others were not. Based on the sensitivity of different vegetation types to the climatic environment and to remove redundant information, and to assure the equality of data for each training session, the first four variables with q-statistic values greater than 0.3 were selected as the independent variables of the index systems. Thus, three different index systems were generated as shown in Fig 4. Extracting boundaries and delimiting the transitional zone Three boundaries were output from the model. The three boundaries were not completely consistent, but the trends were similar. Specifically, from west to east, the three boundaries first increase sharply to a high latitude and then tended to be horizontal towards the east. The location of the boundary between the subtropical coniferous forest and the temperate conifer- ous forest (Fig 5b) was more south than the boundary between the tropical broad-leaved forest and the temperate broad-leaved forest (Fig 5a). The QDM were divided into two major areas, including the northwest, and the southeast, which also refer to the temperate and the subtropi- cal zones, by the boundaries. The similarities and differences among the three boundaries revealed that an exact boundary did not separate the temperate zone and subtropical zone of the QDM; a winding transitional zone was generated. In this paper, the transition zone was delimited by the composition of three boundaries. As shown in Fig 5c, from west to east, the

transition zone mainly passes through the cities of Heishui County, Kang County, Liuba County, Shanyang County, and Yichuan County and is, approximately 30 kilometers wide. The characteristics of vegetation gradually changed from south to north. Use of the concept of “the transitional zone” to address the issue of delimiting the temperate zone from the subtropi- cal zone, is more helpful in understanding the synergistic variation of various vegetation, cli- mate, and biological distributions. Fig 4. Index system of different vegetation. (a) Index system of Quercus wutaishanica forest and Quercus fabri forest; (b) Index system of Pinus tabuliformis forest and Pinus massoniana forest; (c) Index system of Populus davidiana forest and Clobalanopsis glauca forest. https://doi.org/10.1371/journal.pone.0241047.g004 PLOS ONE Climate regionalization based on Geodetector-SVM model PLOS ONE | https://doi.org/10.1371/journal.pone.0241047 November 2, 2020 10 / 16