Abstract:

Objective: This study aims to elucidate the origin, succession, and dispersal processes of the genus Cunninghamia, analyze the genetic diversity and genetic structure characteristics of modern Chinese fir (Cunninghamia lanceolata), and reveal the formation mechanisms of its contemporary distribution pattern. Method: Literature on Cunninghamia macrofossils, pollen fossils, and subfossil wood was reviewed to summarize the relationship between the genus’s origin, succession, dispersal during geological history and its modern distribution. Materials included: a national Chinese fir provenance trial forest established in 1981 in Dagangshan, Jiangxi Province (183 provenances, 1440 individual trees); a provenance trial forest in Shaowu, Fujian Province (14 individuals of Taiwan Chinese fir); and 20 individuals of Dechang Chinese fir from Dechang, Sichuan Province. Provenances were grouped into 10 provenance-region populations, 13 provincial populations, and 23 geographical provenance populations for genetic diversity and structure analysis. SSR sequencing was performed on 1352 individuals from 174 provenances. Chloroplast DNA (cpDNA) sequencing was performed on 531 individuals from 177 provenances, 4 individuals of Taiwan Chinese fir, and 6 individuals of Dechang Chinese fir. Result: Genetic variation within different geographical provenance populations of Chinese fir accounted for 98.20%–99.16% of the total variations, and only 0.84%–1.80% of the variations originated from among different geographical provenance populations. This indicates that the genetic composition and structure among different geographical provenance populations of Chinese fir have tended to be consistent, and there are no significant differences in the genetic structure among different geographical provenance populations. Chinese fir belongs to one genus and one species. Taiwanese Chinese fir may have been introduced from Zhejiang or Fujian. Due to long-term adaptation to local environmental conditions, the Dechang population has developed a relatively independent genetic structure, likely a result of localized cultivation and isolation from external gene flow. The low level of genetic differentiation among geographical provenances could be attributed to the relatively high level of gene flow (N_m = 2.689–6.328) among populations. However, this gene flow was not the result of natural processes, but rather the outcome of extensive and long-distance introductions and plantations over the past 2 000 years. Between 1000 and 1600 AD, reforestation was carried out by planting Chinese fir and other economic trees in the southern regions of China, which was called the great afforestation in southern China and marked the “first forest revolution” in Chinese history. The rapid development of Chinese fir plantations was the result of tax reforms in response to the “timber crisis in the Song dynasty”, successfully meeting the large demand for timber during the Song, Yuan and Ming dynasties and exerting an influence to this day. Chinese fir remains the largest afforestation tree species in terms of area and volume in China, with its largest area reaching 13.8 million hectares (1999—2003). Conclusion: During the last glacial maximum of the Quaternary period, Chinese fir was retreated to southern refugia, nearing extinction. Modern Chinese fir may be originated from the last relict population or individual plants formed by chloroplast haplotype H14. The lack of significant genetic structure differences among geographical provenance populations suggests that the 177 provenances originating before 1955 are essentially all derived from plantations. Two millennia of cultivation, particularly the extensive planting of Chinese fir in south China since the Song dynasty (which created the “first forest revolution” in China’s history), combined with long-distance introductions, cultivation, and a well-developed timber trade, has led to the near-complete disappearance of natural Chinese fir forests that have entirely converted into plantations, becoming a miracle in the history of world forestry. As a landmark tree species of this forest revolution, it implies that the establishment of the forestry system and the budding of afforestation theory and technology can be traced back to before the Song dynasty in China.

Key words: Cunninghamia lanceolata, origin, provenance, genetic diversity, genetic structure, the first forest revolution