How the Northern Limit of Chinese Orchid Distribution Is Affected by Climate

From the Spring and Autumn period to the present is only a little over two thousand years, which for the formation and changes of the Earth is but a single instant, and the climate would not have changed very greatly. (1) Temperature The curve of temperature change in China over the past nearly 5000 years, developed by Zhu Kezhen, is the main basis for judging temperature change over the past two thousand years and more (as shown in the figure). As shown in the figure above: temperature changes in a wave-like pattern, being highest in the early years of the Common Era after Confucius (551-479 BC), lowest after 1000 AD and around 1700 AD, and rising somewhat again in the past hundred years. The difference between the highest and lowest is 2-3 degrees, and the Confucius era was nearly 10 degrees higher than the present. How to use current temperatures to infer the temperature of the Confucius era is an important question; currently Jinan has an annual average of 14.2 degrees, and Zhengzhou also 14.2 degrees. Trying to use the Supan line method, the values recorded in the "Encyclopedia of Chinese Agriculture," the values from the Meteorological Research Office of the Crop Research Institute of the Shandong Academy of Agricultural Sciences (hereafter referred to as the Meteorological Office) and from Chen Xinqi and Ji Zhanhe's "ChineseOrchidsComplete Book," and comparative calculations using two points selected from 159 measurement sites nationwide with similar elevation and longitude, are all difficult to reconcile. It is more reasonable to raise the temperature by 1 degree, or even 2 degrees, on the basis of already recorded temperature. The temperature that limits the survival of Chinese orchids is mainly the extreme low temperature. According to Wei Yasheng's research, Lu Sicong's survey on Mount Emei, and Zhang Rijin's report, around -5 degrees is suitable, and any lower makes survival difficult for Chinese orchids. Meteorological Office records for 1949-1977: at the Shandong Academy of Agricultural Sciences in the eastern suburbs of Jinan, extreme low temperatures varied between -10.8 degrees and -22.5 degrees; when the louvered screen box read -22.5 degrees, the ground was -30.0 degrees, and -16.1°C to -19°C accounted for 64.% of all years. In summary, even if the temperature in the Confucius era was 2 degrees higher than now, Chinese orchids in central and western Shandong would have difficulty overwintering in the open, and it would have been fundamentally impossible for them to move north to 44 degrees N. (2) Precipitation Analyzing from the perspective that climate change is mainly affected by solar radiation and atmospheric circulation, and from the analysis of temperature change, precipitation over the past two thousand years would also not have changed very greatly. According to Chen Xinqi's regionalization, of 159 measurement sites nationwide, 86 fall within the region; of these, 5 sites have especially little precipitation, all of them plateau sites, with elevations of 3242-3704 m. Of the remaining 81 sites, 67 have annual precipitation above 1000 mm, accounting for 82.72% of the total; 8 sites have annual precipitation of 900-1000 mm, accounting for 9.88% of the total; 6 sites have annual precipitation of 800-900 mm, accounting for 7.41%; among these 6 sites, 1 is in a remote southern area (south of Kunming); 1 is a plateau site with an elevation of 2617 m; and the remaining 4 sites are all around 33 degrees N. In addition, along the Yangtze line including Shanghai, Nanjing, Wuhan and Chongqing Shapingba, annual precipitation ranges from 1069-1204.5 mm; southward from this line rainfall gradually increases, for example Hangzhou (30 degrees 14' N) has annual precipitation of 1398.9 mm, and Guangzhou (23 degrees N) 1694.1 mm. In summary, the annual precipitation for the survival of Chinese orchids should be above 1000 mm, similar to Lu Sicong's value of 1500-2500 mm for orchid-producing areas. Northward from the Yangtze line annual precipitation gradually decreases, for example Jinan (36 degrees 41' N) has only 685.0 mm (Zhengzhou 640.9 mm), and the dry season and rainy season are clearly distinct. According to Meteorological Office records, precipitation in July and August accounts for 55.3% of the annual total, while precipitation from late April to mid-June, when plants begin to revive, accounts for 13.0% of the annual total; though both are two months of the year, precipitation differs by 42.3%, hence the climatic characteristic of "spring drought in nine years out of ten." Insufficient water and a clear distinction between dry and rainy seasons are both extremely unfavorable to the growth of Chinese orchids. (3) Relative Humidity and Dry Hot Winds Chinese orchids prefer moisture and require an air relative humidity of 70%-90%. The air humidity of the North China Plain is dry; for example, although Jinan lies in the warm temperate zone, its continentality is 64.9%, strong winds are frequent in spring, and the air is very dry. From early April to mid-June, when plants revive, air relative humidity is consistently below 60%; only in July and August and in early to mid-September can air relative humidity reach above 70%, with the highest, in mid-August, only 81%, far from theorchid'srequirements. The average monthly temperature rise in the North China Plain is 5-6°C, that is, a rise of 1 degree every 5-6 days; high temperature and drought are the precondition for dry hot winds, and together with the foehn warming effect caused by the topography of the Taihang Mountains, this makes central Hebei, southern Hebei, eastern Henan, northern Henan, western Shandong and northwestern Shandong a severe drought and hot wind region, mostly occurring from late May to mid-June. Both dry air and the occurrence of dry hot winds are unfavorable to the growth of Chinese orchids. (Wang Tao)