陕北安塞不同林龄刺槐林下幼苗更新的动态变化特征

为了探讨黄土丘陵沟壑区刺槐林下幼苗更新的动态变化特征,进而为黄土高原地区人工刺槐林生态恢复与功能提升提供参考依据,在陕北安塞纸坊沟流域不同林龄(10 a,20 a,30 a,40 a)的刺槐林下共设置8个典型样地作为研究对象,调查分析林下幼苗的物种组成、密度及月动态变化特征。结果表明:(1)幼苗和地上植物间相似性系数表现为10 a>20 a>40 a>30 a,都以菊科、禾本科、豆科为主,生活型以多年生草本和一年生草本植物为主。(2)4—10月间,不同林龄林下均有大量刺槐幼苗萌发; 随林龄增加,林下幼苗更新过程各异,10 a林以狗尾草、猪毛菜幼苗为主,20 a林以猪毛菜、臭草、狗尾草、裂叶堇菜幼苗为主,30 a林以长芒草、裂叶堇菜幼苗为主,40 a林以翠雀、榆树幼苗为主。(3)随林龄增加,幼苗物种数与密度均呈降低趋势; 幼苗种类在4月、6月、9月较多; 幼苗密度在4月和6月相对较高。(4)林下草本植物幼苗大多数存活时间短; 在刺槐林恢复初期(10年),田旋花幼苗容易建植成功; 在刺槐林恢复的中、后期(20 a,30 a,40 a),裂叶堇菜、臭草、长芒草幼苗容易建植成功。因此,在陕北黄土高原丘陵沟壑区,根据刺槐林的恢复时期及林下不同物种幼苗存活特性对幼苗进行合理地抚育管理,促进林下植被的恢复与更新。

Dynamic Characteristics of Seeding Regeneration in Robinia pseudoacacia Plantations with Different Ages in Ansai County of Northern Shaanxi Province

To explore dynamic characteristics of seeding regeneration in Robinia pseudoacacia plantations in the hilly-gully region of the Loess Plateau,and to provide reference for the ecological restoration and functions promotion of Robinia pseudoacacia plantation in the Loess Plateau region,8 typical plots were selected to analyze the species composition,specie density in plantation and their monthly variation in different-aged Robinia pseudoacacia plantations(10 years,20 years,30 years,40 years)in Zhifanggou watersed in Ansai County of Northern Shaanxi Province.The results showed that:(1)the order of similarity coefficient between seeding bank and ground vegetation decreased in the order:10 years>20 years>40 years>30 years;Compositae,Gramineae and Leguminosae dominated the seedling bank and stand vegetation,while perennial herbaceous and annual herbaceous dominated the growth types;(2)from April to October,large amounts of Robinia pseudoacacia seedlings germinated in undergrowth plantation of different ages;the regeneration process of undergrowth seedlings varied with the increase of forest age;Setaria viridis and Salsola collina were main seedling types in 10-year plantation,Salsola collina,Melica scabrosa and Viola dissecta were main seedling types in 20-year plantation,Stipa bungeana and Viola dissecta were main seedling types in 30-year plantation,and Delphinium grandiflorum and Ulmus pumila were main seedling types in 40-year plantation;(3)the number of seedling species and density of seedlings decreased with the increase of forest age;seedling species in April,June and September were more than those in other months;the higher seedling density was found in April and June.Thus,a proper management measures of seedings according to the restoration period of Robinia pseudoacacia plantations and survival characteristics of different species are conductive to vegetation restoration and succession in the hill-gully region of the Loess Plateau.