Key climatic factors affecting the distribution of litchi in China

【Objective】Litchi(Litchi chinensis Sonn.) is a typical subtropical fruit tree and requires plenty heat and precipitation for survival and growth. With the impact of climate change, the area suitable for cultivation of litchi will expand, and the risk of cold and heat injuries may increase. Recently, some litchi cultivation areas in China have proved to be unsuitable for litchi cultivation. However, the reason is not clear.So, it is important to reveal the relationships between the distribution of litchi and climatic factors and to determine the key climatic factors affecting the distribution of litchi in order to correctly understand the impacts of climate change on the distribution of the species in the future and to regionalize litchi cultivation based on climate conditions. The aim of the paper is to analyze the relationships between the distribution of litchi and climatic factors and to identify key climatic factors affecting litchi distribution in China.【Methods】Climatic data from 1971 to 2000 were provided by the National Meteorological Information Center, China Meteorological Administration, and 38 climatic indexes calculated using Fortran software were used to reveal the relationship between the distributions of litchi and climatic factors. The distributions of litchi were mainly determined based on distribution records or data from litchi literatures, such as Chinese Fruit-Litchi, the Academic Fruit Cultivation Theory, Litchi in Guangdong, Litchi in Guangxi, the Tropical and South Subtropical Fruit Trees in China, Crops and Their Wild Relatives Plants In ChinaFruit Tree, and the Litchi. In addition, some records or data of distribution of litchi were collected from full-text database of the CNKI China periodical and SDOS full-text electronic journals(Elsevier full-text electronic journals). The geo-referencing methods based on an index of the Atlas of the People's Repub-lic of China, and Arc GIS 9.3 software was used to draw the distributions of litchi. The relationships between the distribution of litchi in China and climatic factors were analyzed by using the Arc GIS 9.3 software, and the principal component analysis in SPSS software was used to identify the key climatic factors affecting the distribution of litchi in China.【Results】The results showed that wild litchi scatters in a narrow area, while the cultivated litchi is distributed in a broader area in south China. The wild litchi is adapted to a climate with a mean annual temperature of 22.32 ℃, a lowest temperature of 1.33 ℃, the mean temperature in January of 15.16 ℃, the mean temperature in winter of 17.10 ℃, ≥10 ℃ accumulated temperature of 8 120.57 ℃, an annual precipitation of 1 665.17 mm, the precipitation in summer of 701.53 mm,the precipitation in autumn of 629.53 mm, the Thornthwaite humidity index of 9.41, and the Holdridge annual bio-temperature of 21.98 ℃. As for cultivated litchi, the suitable mean annual temperature is20.61 ℃, and the lowest temperature-0.94 ℃, the temperature in January 12.14 ℃, the temperature in winter 17.10 ℃, and ≥10 ℃ accumulated temperature 7 429.71 ℃, annual precipitation 1 573.51 mm,the precipitation in summer 690.36 mm, the precipitation in autumn 455.45 mm, the Thornthwaite humidity index 9.85, and the Holdridge annual bio-temperature 20.39 ℃. The ranges of all climatic factors that both wild litchi and cultivated litchi are adaptive to are very narrow. The ranges of climatic factors wild litchi is adaptive to are 3 291.14 for ≥10 ℃ accumulated temperature, 31 d for the duration of ≥10 ℃ accumulated temperature, 1 578.2 mm the range of annual precipitation, 240.34 for precipitation in spring,519.86 mm for the precipitation in autumn, 431.7 mm for the Thornthwaite potential evapotranspiration and 87.78 ℃ for the Kira warmth index. The ranges of climatic factors that cultivated litchi is adaptive to,are 6 502.98 ℃ for ≥10 ℃ accumulated temperature, 212 for the number of days ≥10 ℃ accumulated temperature, 1 863.2 mm for annual precipitation, 729.13 mm for the precipitation in spring, 560.90 mm for the precipitation in autumn, 792.47 mm for the Thornthwaite potential evapotranspiration, and150.57 ℃ for the Kira warmth index. The key climatic factors affecting the distribution of wild litchi include extreme low annual temperature, mean temperature in January, the lowest temperature in growing season, the Holdridge annual bio-temperature, the Thornthwaite potential evapotranspiration and the Kira warmth index, followed by the highest temperature in July, and the highest temperature in summer and autumn, and the precipitation in spring; and by annual precipitation, and the precipitation in autumn and summer, while the key climatic factors affecting the distribution of cultivated litchi include mean annual temperature, mean temperature in the coldest month, ≥10 ℃ accumulated temperature, the lowest temperature in autumn; followed by the highest annual temperature, the highest temperature in July, the highest temperatures in summer, autumn and winter, the precipitation in spring, and then by annual precipitation,the precipitation in summer and autumn, and the Thornthwaite humidity index.【Conclusion】The distribution of litchi is affected by various factors. Key climatic factors which influence the distribution of litchi are the low-temperature index, followed by high-temperature index, and then by precipitation index. Current litchi regionalization is only based on air temperature and rainfall factors. The results in our study showed that various climatic factors should be considered in litchi regionalization. Based on the existing data and technical conditions, by selecting different climatic indexes as far as possible, the relationship between the distribution of wild and cultivated litchi and climatic factors in China in large regional level are revealed. In addition, key climate factors influencing the distribution of litchi are also identified.These results provide not only new indexes for litchi regionalization but also important basis for analyzing the effect of climate change in future on the distribution of litchi.