A Study on Relationship Between the Seed Crop in the Chinese Fir Orchards and Meteorological Factors

Abstract

Chinese fir (Cunninghamia lanceolata) is recognized as a highly produc tive, valuable tree species in the sub_tropical region of China. Chinese fir is monoecious, and self_fertilization is possible because time of pollen dispersal and seed cone receptivity overlap on the same tree. Since 1980s, 3 500 hm 2 s eed orchards of Chinese fir have been established, in order to provide lots of super ior seeds for the plantations. However, it takes about two_years from flower di fferentiation (from axillary buds of current_year lateral shoots) to seed matur ity. Many factors affect the seed crops during the flower differentiating, polli nation and seed development phases. As a result, master years vary from region t o region, and a good seed crop generally occurs every 2_3 years. In this case, t he managers of the seed orchard meet a lot of challenges to manage the seed orch ard of Chinese fir well. Based on the data of annual seeds crop of Chinese fir o rchards and corresponding meteorological factors collected from four forestry fa rms of Xitian, Anhui province; Yangkou and Guanzhuang, Fujian province; Xiaokeng, G u angdong province respectively, the Step Regression Analysis between seeds crops and 20 meteorological factors during anthesis, pollination and pubera was conduc ted so that the key factors to affect the seed crop would be detected. Furthermo re, the phenomena and meteorological reasons for the cycle of good and poor seed s year in Chinese fir orchards were also discussed. The results showed that ther e existed the phenomena of the fruiting cycle in the orchards of Chinese fir for different ages and various growth zones, and the cycle is 2_3 years rather than 4_5 years. Rainfall and sunlight during pollination and pubera affected the fru iting cycles significantly. When these two factors are abnormal, the pollination in the Chinese fir orchard was hindered. Although it changes with environment o f orchards, clones and density of orchards, the cycle is closely related with me teorological factors especially in March (pollination period). The changes of th e cycle will be more dramatic when rainfall and sunlight in June and July are un favourable for young cone development. It would be a good seed year if the weath er conditions are favourable both for pollination and pubera phrase, otherwise i t would be a poor seed year. At the same time, the suggestions to solve the pro blem of the fruiting cycle in Chinese fir orchards were discussed in the paper.