川西米亚罗亚高山云杉林种子雨和土壤种子库研究

 对川西米亚罗亚高山20、30、60年人工云杉(Picea asperata)林及天然林的种子雨和土壤种子库进行了研究。结果表明：该区云杉种子雨一般从每年的10月初开始下落，一直到翌年的1月底结束，但不同林龄的云杉种子雨强度不同，60年人工林种子雨量最大，然后依次为30年人工林、天然林、20年人工林，其大小分别为(1 088.16±52.34)粒?m－2、(973.45±63.12)粒?m－2、(579.99±28.93)粒?m－2、(66.73±5.71)粒?m－2。云杉降雨历程与其林龄大小也有一定的关系，表现在种子雨发生时间和降雨高峰期的不同。30、60年人工云杉林及天然林下土壤种子库存在显著差异，两次取样（2003年3月26日和2003年8月21日）土壤种子库大小分别为(507.2±40.32)粒?m－2和(267.6±25.14)粒?m－2、(1 065.6±88.06)粒?m－2和(872.8±77.12)粒?m－2、(472.8±20.82)粒?m－2和(185.5±22.48)粒?m－2。土壤种子库中云杉种子主要都集中在枯枝落叶层，占66%左右，0～2 cm层占24%左右，2～5 cm层占10%左右。到8月21日，土壤中所有云杉种子都失去活力，腐烂死亡和动物取食是种子库损耗的主要因素。云杉种子库属于Thompson和Grime定义的第Ⅱ类。该区云杉幼苗一般在6月初开始出现，6月中旬左右达到出苗高峰，3种云杉林下幼苗密度差异很大，60年人工林下幼苗最多，其次为30年人工林和天然林。由于生境适合度低，死亡的幼苗数量较多，特别是自然死亡数。综合种子雨、种子库和转换的幼苗数量几个方面来看，在一定龄级范围内，人工林结实能力和更新潜力随林龄增加而增加，且人工林在更新潜力方面比天然林（约150年）要好。虽然该区云杉林下有大量种子下落，但由于种子大量损耗和幼苗死亡，种子萌发为幼苗再通过环境筛作用而最终补充到云杉种群的个体数量非常有限。

SEED RAIN AND SOIL SEED BANKS OF PICEA ASPERATA IN SUBALPINE SPRUCE FORESTS,WESTERN SICHUAN,CHINA

Subalpine coniferous forests dominate most parts of the forested areas in western Sichuan, including the upper reaches of the Yangtze River. Since the 1940s, natural coniferous forests have been cleared, and Picea asperata is an important species used for reforestation. Up to now, a total of ca. 13 000 hm2 of plantations have been planted with this species in this region. Hence, studies on seed source, dynamics of the soil seed bank and seedling survival of Picea asperata populations are of significance for the management and conservation of coniferous forest ecosystem. The seed rain and soil seed bank of spruce plantations that were 20, 30, and 60 years old and a 150 years old natural spruce forest in the Miyaluo subalpine coniferous forest in western Sichuan, China were studied using seed traps, sieving and counting seeds in the soil, conducting seed germination experiments, and measuring seedling density in the three plantations and the forest. The area is located on a high mountain valley in the transitional zone between the Qinghai-Tibet plateau and the Sichuan basin. The results showed that seed rain lasted from early October to the end of January. The intensity of seed rain of the different aged plantations increased in the following order; 20 years old plantation ((66.73±5.71) seeds?m-2) < natural spruce forest ((579.99±28.93) seeds?m-2) < 30 years old plantation ((973.45±63.12) seeds?m-2) < 60 years old plantation ((1 088.16±52.34) seeds?m-2). The timing of the seed rain and the peak fall differed among sites and was correlated with the age of the plantation age. The soil seed bank of the 30 years old, and 60 years old plantations and natural spruce forest at two sampling periods was (507.2±40.32) and (267.6±25.14), (1 065.6±88.06) and (872.8±77.12), (472.8±20.82) and (185.5±22.48) seeds?m-2, respectively. The vertical distribution of seeds in the soil bank showed that about 66% of the total seeds were distributed in the litter layer, 24% in the 0-2 cm layer and 10% at 2-5 cm depth. By August 21, 2003, all of the spruce seeds had lost viability in the soil, and the number and proportion of decayed seeds and vacant seeds greatly increased. Seed decay from soil pathogens and seed-predation by animals were the most important factors affecting soil seed bank dynamics. The proportion of seeds removed from the soil seed bank via germination was quite low. The spruce soil seed bank belongs to the type Ⅱ as defined by Thompson and Grime, namely, the soil seed bank only existed in winter and germinated in spring. There were significant differences in the seedling density in the 30 years old plantation ((28.57±6.39) seedlings?m-2) 60 years old plantation ((39.42±16.21) seedlings?m-2) and natural spruce forest ((10.75±2.37) seedlings?m-2). Seedling mortality was high due to poor habitat quality. The recruitment potential increased with plantation stand age, but the recruitment potential of spruce plantations were higher than that of natural spruce forests when seed rain, soil seed bank and seedling number were considered together. In Miyaluo spruce woodlands in western Sichuan, China, despite high seed production, the number of spruce seedlings recruited from the seed to seedling stage was relatively few.