The orchid’s geographical distribution pattern in the Hengduan Mountains
Mapping the suitability of orchids with all conditions (see Appendix S2.4), we intend to provide a reference for the conservation of orchids in the Hengduan Mountains.
A wide range of suitable habitats for orchids existed in the Hengduan Mountains, both in the all-layer and in the total layer, with the area of suitable habitats ranging from 58510 km2 to 187226 km2 (the differences caused by different models), with the lowest suitable area accounting for 9.77% (R-total) and the highest reaching 31.25% (G-all) of the total area of the study area. Suitability maps displayed noticeable geographic distribution centers. The primary distribution center was located in the northeastern part of the study area in the mountainous region with a north-south vertical distribution, while another center was located in the eastern part of the study area which was a mountainous region. Such a distribution pattern likewise coincided with terrestrial orchids, which were widely distributed in the study area, varying in area from 55808 km2 (R-t) to 160956 km2 (G-t), accounting for 9.31% and 26.86% of the total area, respectively, with the presence of two geographic centers. The situation was completely changed for mycoheterotrophic and epiphytic orchids, firstly, they were less widely spread than terrestrial orchids. The suitable area range of mycoheterotrophic orchids was 2742 km2 (R-m) to 77071 km2 (G-m), accounting for 0.46% and 12.86% of the study area, respectively. The suitable area interval for epiphytic orchids was 3468 km2 (R-e) to 30637 km2 (G-e), which accounted for 0.58% and 5.11% of the study area, respectively. Although the distribution pattern of mycoheterotrophic to that of terrestrial orchids, they tended to be found in the northeastern mountains of the study area (especially in M-m and R-m), while the distribution pattern of epiphytic orchids was more prominent, with the southern to the southwestern part of the study area being the preferred region.
Using spatial analysis, we counted the suitable area of counties for all suitability maps and performed the same double-ranking (see Appendix S3.3), this enables us to avoid the bias of prediction results caused by the different modeling approaches used. The results indicated equally that the terrestrial orchids were almost consistent with the whole orchid ranking priority counties and area weighting counties, and the crucial areas were located in Muli, Yangyuan, Wenchuan, Jiuzhaigou, and Pingwu counties, and the sorting priority county for mycoheterotrophic orchids was the same as the first two, but the area weighting county was Jiuzhaigou County as far as the integrated model results were concerned. Epiphytic orchids also showed different results, and the suitable area ranking priority counties were located in the south to the southwest part of the study area, and the area weighting analysis result was Tengchong County (see Fig. 5).