Regeneration Characteristics And Influencing Factors Of Abies Fargesii Forests In Shennongjia National Nature Reserve

Abies fargesii is endemic to China and its distribution center is located in Qinling-Bashan Mountains. Abies fargesii is distributed mainly on certain attitude that ranges from 2000m to 3104.5m in shennongjia nature reserve. Community regeneration and the environmental causes of Abies fargesii forests in Shennongjia National Nature Reserve were studied by sampling plot method. Results showed that Forest gap disturbance, an important small scale disturbance, often occurs in forest community. It is one of the most important drives for maintaining of forest ecosystem, and has an important influence on forest structure, cycle and regeneration. Studies on forest gap have been one of the most active fields of forest ecology in foreign countries and our countries nowadays, after Watt defied the concept of forest gap. There has been no report about forest gap studies of Abies fargesii forest in Qilian Mountain. The paper, in order to show characters of distribution and formation of Abies fargesii forest gap, rules of temporal-spatial distribution of the gap microclimate, the characters of gap and regeneration of Abies fargesii forest gap are analyzed. All these will provide the scientific basis for studying the succession of Abies fargesii forest.The main results are as follows:(1) Forest gap regeneration was an important pathway for regeneration of Abies fargesii communities, and broad-leaved species such as Betula albo-sinensis Burk. and shade-tolerant species such as Abies fargesii in gaps differed from those under canopies in their regeneration characteristics; Abies fargesii was most predominant in the early gap regeneration but gradually displaced by other species with time, and accounted for 45.7% of the seedlings below age 3 and 6.3% of the saplings older than 7 years;(2) Correlation analysis of the gap micro-environment suggested varying controlling factors of Abies fargesii regeneration with developmental stages, and that irradiance and soil water were the most influential factors on growth of seedlings and saplings; correlation analysis of slope aspect and population density showed that Abies fargesii seedings were more abundant on the northern slope, and the shrub-herb layer was a potential barrier in the process of Abies fargesii regeneration.(3) In this paper, gap characteristics of Abies fargesii forest are analyzed. The results shows that the size of most expanded gaps is in the range of 32.6-274.2 m2, the gaps of 50-75 m2 occupies the highest percentage in number, while those of 75-100 m2 occupies the highest percentage in size. The size of most canopy gaps is in the range of 10.8-234.9m2,the gaps of 50-75 m2 occupies the highest percentage in number and size. The most important manner of gap formation is artificial cutting, and the secondly important manner is the breakage on stem. Gaps formed by 1-2 gap makers is of 80%, and by 4 gap makers is seldom. The gap maker of 8-12 m high occupies the highest percentage in number(60.6% of the total)(4) Microclimate factors of Abies fargesii forest gap are analyzed, it indicates:because of sun radiation, geography character and the tree, spatial distribution of air temperature and relative humidity show the phenomena about dynamic displacement; There is significant difference between microclimate factors of different area in the gap. The maximum air temperature and minimum relative humidity are at 16:00 in the gap and stand. Air temperature in the gap is higher than that of stand and relative humidity in the gap is lower in a day. The diversity of microclimate is different in different time, for the influence of radiation, at noon, it is distinct, and moreover, in night, the AM and PM, it is inconspicuous. The results supply a basis in further studying canopy gap microclimate and the relevant ecological phenomena.