期 刊 ：生态学报 2008年 28卷 6期 页码：2554~2554～2562
Keywords:evergreen broad-leaved forest, fragmentation, seed bank, natural regeneration,
摘 要 ：生境片断化扰乱了种子的生产和扩散机制，越来越严重地威胁着生物多样性。华东地区的常绿阔叶林片断化程度较为严重，以古田山自然保护区为中心，在周边另选取5个常绿阔叶林的典型片断，采用样线法采集土壤样品，通过网筛分选和温室萌发相结合的方法对其种子库特征进行了研究，同时，在样地各土样采集点附近设立天然萌发小样方，对种子库的天然更新机制进行了研究。结果显示：（1） 5个片断化样点的种子库密度为(207±38)~(1332±337)ind./m2，共有29~57种植物种子。而古田山连续常绿阔叶林样点的种子库密度为(1776±344) ind./m2，分布有46种植物种子。各样点的种子库物种组成主要以乔木和灌木树种为主，草本种类非常稀少，并且不能反映地上植物的组成。（2）片断化样地土壤上层（0~5cm）与下层（5~10 cm）的种子密度比平均为3.6∶1，而连续森林样地为2.5∶1，说明连续森林土壤种子垂直下移相对较深，有利于更多物种种子的储存。（3）幼苗的天然更新强度受种子物种丰富度的影响较大（P=0.005），而受种子密度的影响不明显（P=0.159）。（4）同一生境条件很难同时满足较高的种子库密度和较快的幼苗天然更新速率。生境片断化降低了种子库密度和物种丰富度，但由于林隙的大量存在和较低的乔冠层盖度，却促进了幼苗的快速更新。
Abstract:Habitat fragmentation poses a wide spread threat to biodiversity by disrupting seed production and dispersal. To understand the seed bank and natural regeneration patterns of the evergreen broad-leaved forest (EBLF), we selected five isolated fragments and one continuous forest of the typical EBLFs in the mountain ranges at the boundary of Zhejiang, Fujian, Jiangxi and Anhui Provinces in Eastern China. The six fragments are of similar age and have similar constructive species (Castanopsis eyrei and Schima superba).The seed bank were investigated during the early winter 2005 (December), later spring 2006(May), early winter 2006 (December) and later spring 2007(May), the sampling times (early winter and later spring) considered to be critical periods. At each sampling time, five 10 m intervals parallel lines were laid out through each of the patches at all six sites and each line had five 5 m intervals soil sampling frames. The sampling frame measured 10 cm×10 cm by 10 cm deep. Soil was carefully excavated in two 5-cm layers and bagged separately. The twenty-five samples, each comprising two depth subsamples, were taken for each site. Thus, 600 soil samples were obtained during the study：25 samples × 6 sites × 2 replicates × 2 seasons. At the same time, we had set twenty-five 1 m×1 m plots at each site to assess the natural regeneration pattern, each plot was 2 m away from the placement of the soil sampling frame. We censused and marked the seedlings of each plot in 2006, and all of the plots were recensused after one year. Soil samples were dried and passed through sieves to remove large stones, litter and sieved out larger seeds. The remaining soils were placed in plastic trays. They were held in a greenhouse with 12∶12 photoperiod, and mean temperatures of 25℃.Samples were watered daily and checked for emerging seedlings every two days for 6 months. All the seeds and seedlings were identified to species level. The result shows： (1) Significant differences were found among fragments in seed densities with values ranging from (207±38) to (1332±337) ind./m2, corresponding to 29-57 species. However, the seed density was (1776±344) ind./m2 in the continuous forest which located in Gutian Mountain National Nature Reserve, and corresponding to 46 species. The seed banks were mainly composed of tree species and shrub species, and there were rare herb species. In general, the plant species composition of the soil seed banks did not closely reflect the composition of the above-ground communities. (2) The mean proportion of the upper layer (0-5cm) seeds density was 3.6 times higher than that of the lower layer (5-10cm) in the five fragments, which was higher than the continuous forest’s 2.5 times. It suggested that the continuous forest was more suitable for seeds to sink down and could storage more kinds of seeds. (3) Seedling regeneration appeared to be quite sensitive to seed bank species richness rather than seed density (P=0.005, 0.159, respectively). (4) Seed-seedling conflicts had occurred during some of these habitats if conditions or traits that were favorable for seeds were unfavorable for seedlings. Habitat fragmentation had reduced the density and species richness of seeds, however, because of more and more gaps caused by fragmentation and the following lower canopy coverage, it had positive effects on seedling establishment.
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