Study On The Gap Characteristics And Regeneration In Castanopsis Fissa Natural Forest In Northern Fujian

Gap is the indispensable factor in the development of forest ecosystem,also is an important stage in forest ecosystem regeneration cycle.Not only can promote the forest ecological system update,still maintain the stability of ecosystem community.The paper studied the general gap characteristics and disturbance regimes of the forest gaps through the field investigation on 28 forest gaps in Castanopsis fissa natural forest in northern F ujian.Then the quantitative characteristics of tree species in gaps and non-gaps were analyzed,and also the regeneration responses of the major tree species to gaps size and the structure of tree species in gaps and non-gaps stands were investigated in Castanopsis fissa natural forest.The species diversity of forest gaps and non-gaps and its reflection to gap size,as well as the species diversity changes in gap gradients were analyzed in this paper.The results showed that the canopy gaps of 10～20 m2 occupied the highest percentage in number and size.For expanded gaps,the gaps of<50m2 had the biggest quantity proportion,while the area percentage of the gaps of 50～100m2 was the highest.The biggest proportion of gap age was 10～15 yr.The main manner of gap formation in the forest was the combined effect of both stem breakage and uprooting(57.14%of the total).Most gaps were formed by 1～4 gap makers,with an average of 4.04 trees per gap.The diameter at breast height of most gap makers was 10cm and 20cm accounted for 82.30%of the total.The linear gap density in the forest was 12.84 gaps/km,the formation rates of canopy gaps and expanded gaps were 2.08 m·km-1 and 7.02m·km-1·year-1 respectively,and the disturbance cycle of gaps was 476.19 years.The importance value of different species were different in gaps and non-gaps.According to the different importance value,tree species in gaps and non-gaps could be classified in to 6 groups:species only occurred in gaps,species only occurred in non-gaps,response not significant to gaps regeneration,moderate positive response,moderate negatively response,strong response.The regeneration responses of major tree species and gap size were different of major tree species and gap size.Regeneration densities peak of Castanopsis fissa and Castanopsisfargesii turned up at the gap size about 150～200m2,and Castanopsis carlesii,Schima superba,Cyclobalanopsis glauca and Machilus chrysotricha at the size about 100～50m2.The proportion of stumpage would be maximum when the d of each area’s gap was less than 2.5cm.And the proportion would decrease along with the increase of size class.The major height in different size class gaps was young seedlings which do not overtop 3m,the proportion of tupelo that overtop 12m was seldom.The species diversity of tree layer,shrub layer and shrub-herb layer in forest gaps was bigger than in non-gaps.In tree layer,the Margalef index(R),Shannon-Wiener index(H),Pielou evenness index(E)and evenness-dominance-abundance index(Z)reached to the maximum when the gap area was in the range of 100-150m2,and the ecological dominance index(λ)was the biggest in gaps of 150-200m2.In shrub layer,the results were opposite(i.e.the former four species diversity indices were the minimum in gaps of 100-150m2 and the ecological dominance index was the smallest in gaps of 150-200m2).In shrub-herb layer,the gaps of 50-100m2 had the maximum Margalef index(R),Shannon-Wiener index(H),Pielou evenness index(E)and evenness-dominance-abundance index(Z),the maximum ecolo gical dominance index(λ)was in gaps of 150-200m2.From forest gaps to non-gaps,it turned out to have a downward trend on species number(S),the Margalef index(R),Shannon-Wiener index(H),Pielou evenness index(E)and evenness-dominance-abundance index(Z)while the ecolo gical dominance index(λ)showed an upward trend.