临安次生灌丛植物多样性对林火烈度空间异质性的响应

以同一过火3a后临安市太阳镇天然次生灌丛为对象,采用样地调查法按不同林火烈度设置火干扰样地进行植物群落调查,以检验林分内部的林火烈度异质性是否与局部的植物多样性变化相关。结果表明:研究区共有高等植物83种,分属于38科67属,群落区系组成以亚热带科属为主,表现出常绿阔叶林已退化过渡到位于演替早期阶段的落叶次生灌丛群落的性质;低林火烈度对灌木层的树种组成有影响,但不明显;中烈度林火对灌木层的物种组成影响较大;低、中林火烈度下草本层的物种组成变化都很明显;灌木层的物种数和多样性指数都表现出低烈度火未火烧中烈度火的趋势;草本层的物种数、多样性指数和均匀度指数表现出中烈度火低烈度火未火烧的趋势;草本层的物种组成和多样性受林火烈度的影响较灌木层更大。研究表明次生灌丛群落过火区内部林火烈度异质性在初期会引起植物多样性的响应差异;低烈度火干扰可以增加次生灌丛生物多样性、促进群落更新;中烈度火干扰下木本植物物种多样性丧失较大,而草本植物多样性显著增加,不利于群落的正向演替。

Effects of spatial heterogeneity of forest fire severity on plant diversity in a secondary shrub community in Linan

Natural secondary brush communities in degraded evergreen broadleaved forests may regenerate gradually after firewood harvesting stops. However, external interferences are likely to cause disturbance, especially as a result of brushfires caused by people in surrounding urban areas. A theoretical basis for the successional restoration of natural secondary scrub can be obtained by comparing the responses of community biodiversity to different forest fire intensities. To test whether heterogeneity of forest fire severity inside a stand is related to microenvironmental plant diversity, fire plots were established in a burned secondary shrub area according fire severity and were surveyed after 3 years in a suburb of Taiyang, Linan City. The plots contained 83 species of higher plants, which belonged to 67 genera in 38 families (mostly subtropical), including 21 tree species. The plant community height was less than 2 m and was characterized by deciduous secondary shrub degraded from evergreen broadleaved forest. Low fire severity had no obvious effect on species composition of the shrub layer, but medium fire severity had significant effects. The species composition of the herb layer changed significantly under low and medium fire severity. Fire severity influenced shrub richness and diversity in the following order:low fire severity > unburned > medium fire severity. Richness, diversity, and evenness of the herb was influenced as follows:medium fire severity > low fire severity > unburned. The species composition and diversity of the herb layer was more strongly affected by fire than was the shrub layer. Our results showed obvious spatial heterogeneity of fire severity in the stand, with a mosaic of unburned patches and low and medium fire severity even within a small area. This indicated that spatial heterogeneity of forest fire severity within a section of secondary shrub could cause difference initial diversity responses. Low fire severity would lead to increased plant diversity and community regeneration, but medium fire severity would decrease the diversity of woody plants and increase the diversity of the herb layer, which would inhibit succession from secondary shrub to evergreen broadleaved stand. It is important to cut grasses and remove competing stems around target trees. Although the spatial heterogeneity of forest fire severity in a small area caused spatial heterogeneity in vegetation composition and diversity, it is uncertain whether this heterogeneity will continue to lead to different forest types in the medium-to long-term periods.