5·12地震后北川次生灾害迹地植被的自然恢复与更新

北川羌族自治县是5·12大地震的重灾区，次生灾害种类多样，植被受损严重。为了解5·12大地震后不同次生灾害迹地植物群落自然恢复情况，在北川羌族自治县选取落石、崩塌、滑坡、泥石流、堰塞湖等5种次生灾害迹地和1种未受损林地，通过设180个大小样方来进行野外调查和数量分析，研究植物群落的物种组成、结构特征、物种多样性及物种相似性。结果表明:①次生灾害迹地植物群落结构简单，多以菊科Compositae，禾本科Gramineae草本植物为主，群落物种数量由多到少依次为落石自然恢复地（B4）>桤木Alnus cremastogyne-樟树Cinnamomum camphora混交林（ck）>堰塞湖自然恢复地（B5）>泥石流自然恢复地（B2）=滑坡自然恢复地（B3）>崩塌自然恢复地（B1）。②次生灾害迹地乔木层优势种是桤木，灌木层优势种是水麻Debregeasia orientalis；草本层优势种是五节芒Miscanthus floridulus，千里光Senecio scandens等禾本科和菊科植物。③物种相似性在次生灾害迹地与未受损林地差异较大，其中物种相似性系数大小依次为:B4（0.19）> B5（0.13）> B2（0.10）> B3（0.06）> B1（0.02）；不同次生灾害迹地之间更为相似，且B2，B3，B4，B5样地之间物种相似性系数在0.28左右。

Vegetation restoration and regeneration of the secondary disaster area in Beichuan after the May 12, 2008 earthquake

In Beichuan, a severely afflicted area from the May 12, 2008 earthquake, vegetation was severely damaged with numerous secondary disasters. This study aimed to understand recovery of the natural vegetation for different types of disasters of the May 12, 2008 earthquake. Five different types of disasters in Beichuan County were selected, including avalanches (B1), rock fall (B2), debris flow (B3), landslides (B4), and barrier lakes (B5) with one intact forest (ck). A total of 180 quadrats of five different types of disasters in Beichuan, were selected to conduct vegetation investigation, adopting important value, Shannon-Wiener diversity index, Margalef richness index, Hurlbert evenness index and other indexes to be used to evaluate the plant community species composition, structure, species diversity, and similarity of species. Results indicated that (1) secondary disasters had a simple plant community structure, where Compositae and Gramineae herbs were dominant vegetation types, with the number of species being B4 > ck > B5 > B2=B3 > B1. (2) In the secondary disaster area, the dominant species of the tree layer was Alnus cremastogyne, the dominant species of the shrub layer was Debregeasia orientalis, and the dominant species of the herb layer were Miscanthus floridulus, Senecio scandens, and other Compositae plants. (3) For species similarity, the secondary disaster area and intact forest land had strong differences with species similarity coefficients being B4 (0.19) > B5 (0.13) > B2 (0.10) > B3 (0.06) > B1 (0.02). However, many similarities between different secondary disaster areas were found with similarity coefficients between B2, B3, B4, and B5 of about 0.28. In conclusion, the natural recovery and renewal were slower in the five different types of disasters in Beichuan.