Study On Natural Regeneration Of Castanopsis Fargesii Population In Secondary Forest

As one of the main dominant species and cultivated species of mountain evergreen broad-leaved forest in Fujian,the Castanopsis fargesii population is mainly distributed in less than 1000 meters of the mountainous,with a strong ability of soil fertilization and water maintaining.Due to the common influence of climate environment and human factors,the existing natural evergreen broad-leaved forests dominanted by the Castanopsis fargesii population are mainly secondary forests,with slowing down obviously in natural regeneration rate and declining in distribution area.Therefore,it is the general concern of the broad forestry workers to promote the natural regeneration of Castanopsis fargesii population,developing long-term and stably,thus play a greater economic,social and ecological benefit.Based on silviculture,population ecology and geo-statistics,the age structure,the spatial distribution pattern and interspecies relationships of Castanopsis fargesii population were studied,and,the spatial heterogeneity of tree seedling regeneration,soil nutrient under the forest,the relation of regeneration and spatial heterogeneity of soil nutrient were analyzed,then the static life table of Castanopsis fargesii population was established with a view to provide scientific basis on the restoration of the secondary forest and the ecosystem protection.The main findings were as the following:(1)The Castanopsis fargesii population accounted for an absolute advantage in this secondary forest,and its regeneration accounted for 32.29%.The population density of sunny slope was lower than that of shady slope,so as the seedling and saplings(DBH<7.5 cm),but the density of medium trees(7.5 cm≤DBH<22.5 cm)and large trees(DBH>22.5 cm)were higher than that of shady slope.The amount of seedlings and saplings were much more abundant than that of medium and large trees,whereas the amount of medium and large trees were scarce on both slopes,showing a growth form.There was no significant difference in the density distribution of the seedling and saplings in ground diameter and heights classes,and with the increasing,the overall trend was decreasing.The distribution of ground diameter follows the shape of an inverse "J" and the height shows a asymmetric mountain-like curve obviously,more close to the seedling and young trees average high,showing that the seedling and young trees structure in ground diameter and heights classes were good,and stable supply.(2)The Castanopsis fargesii population showed an aggregated spatial distribution on both slopes,and the maximum aggregation intensity appeared within 1 m distance around the target individual,and in general,changed to random distribution with the increase of the scale gradually.The distribution pattern of different developmental stages(class Ⅰ～Ⅳ)showed similar distribution patterns on both slopes.Class Iin all scales mainly showed aggregated spatial distributions;classⅡ and Ⅲ existed in significantly random distribution,but aggregated in individual scale;class IV mainly fit random distribution,but uniform in individual scale,which showing an aggregate to random or uniform distribution in generally.The limitation of seed and habitat heterogeneity explained the population pattern of aggregated distribution on a certain extent.Density control was the main form of regulating the pattern of different developmental stages.The spatial heterogeneity of the regeneration seedlings and saplings showed that the maximum radius of the aggregated patches was 12.63 m on the sunny slope and 8.7 m on the shady slope.There was a strong spatial autocorrelation of regeneration,with more than 90%of variation coming from structure factors.The spatial distribution presented a significant anisotropy(p<0.05),with a completely opposite spatial pattern on the two slopes.(3)The spatial correlation between different developmental stages was different and varies with the scale.There were mainly positive correlation between classIand class Ⅱ,Ⅲ,IV at less 21m scales on the sunny slope,and 7-20 m scales on the shady slope,but no significant correlations at the other scales.Class Ⅱ and Ⅲ,class Ⅱ and IV were presented an no significant correlations on the sunny slope,but a negative association at some scales on the shady slope.A negative association was exhibited between class Ⅲ and Ⅳ in less 6 m scales on two slopes.There had a relatively stable intrinsic relationships and intrinsic competition occur mainly between the class Ⅲ and IV.On the sunny slope,there were more positive interspecific correlations between the different regeneration seedlings and saplings,and weakened with the scale increasing,that mainly presented a positive and ecological relationship with the regeneration of Castanopsis fargesii.However,there were negative correlations between the regeneration of Castanopsis fargesii and the medium and large trees(DBH>7.5 cm)of Castanopsis carlesii(Hemsl.)Hay.,Machilus velutina Champ.ex Benth,Cinnamomum austrosinense H.T.Chang and Sassafras tsmu,which curbed the regeneration in small scales.On the shady slope,there were negative correlations between the regeneration seedlings and saplings of Castanopsis fargesii and Castanopsis carlesii(Hemsl.)Hay.,Machilus velutina Champ.ex Benth,Castanopsis tibetana Hance in 2 m scales,Eurya loquaiana Dunn.in 11 m scales.There were negative correlations between the regeneration of Castanopsis fargesii and the medium and large trees(DBH>7.5 cm)of Castanopsis carlesii(Hemsl.)Hay.,Ziziphus jujuba Mill.var.spinosa(Bunge)Hu ex H.F.Chow,Cyclobalanopsis glauca(Thunb.)Oerst,which curbed the regeneration in small scales,too.(4)Based on the population life table,the habitat has a great influence on the structure and regeneration of Castanopsis fargesii population.Three peaks of mortality rate and vanishing rate existed in the Castanopsis fargesii lifespan:one in the 1th age class periods,one in the 6th age class periods and the other in the 10th age class periods.The survival curves of Castanopsis fargesii population was Deevey-Ⅱ.The change trend of population survival rate and cumulative mortality curve was opposite to each other,with a significant change in the 6th age class(slowing down);the death density and the risk curve were consistent.Spectral analysis showed that there was a obvious basic and small cycle fluctuations of the population dynamics,which could promote population update and population stability.(5)Under the secondary forest cultivated by Castanopsis fargesii population,there was no significant difference in pH(P>0.05),while significant differences in total potassium,total phosphorus,total nitrogen,nitrate nitrogen,ammonium nitrogen,available phosphorus and available potassium between the two slopes(P>0.05).The heterogeneity of soil nutrient was significant in the secondary forest of Castanopsis fargesii,and there were significant differences in the contents of soils in different spatial samples.The pH,total phosphorus,nitrate and available potassium on the sunny slope showed significant spatial autocorrelation on the larger scale(effective range of 203.16 m,99.87 m,77.059 m,53.642 m),while total potassium,ammonium nitrogen and available phosphorus showed strong spatial autocorrelation variation in relatively small scale range(13.47 m,16.98 m,15.72 m,8.94 m,respectively).And the variability caused by structural factors was More than 63.2%.The pH,total potassium and nitrate nitrogen on the shady slope showed significant spatial autocorrelation variation on the larger scale(followed by 53.75 m,79.71 m,55.18 m),while the total phosphorus and ammonium nitrogen showed strong spatial autocorrelation variation with the larger scale(243 m,52.52 m,respectively).Structural factors accounted for more than 60%.But,total nitrogen,available phosphorus and available potassium showed obvious spatial autocorrelation variation at a relatively small scale(followed by 25.84 m,25.79 m,43.15 m),and structural and random factors were equally important for spatial variability of the three indicators(spatial structure is slightly greater than 50%).(6)There was a certain degree of correlation between the regeneration seedlings and saplings and the soil nutrients of Castanopsis fargesii,and the difference was significant on the two slopes.On the sunny slope,the spatial positive correlation between the regeneration pattern and the soil available potassium,nitrate nitrogen and total nitrogen heterogeneity was significant,generating more seedlings and saplings in the patches with higher concentration;the spatial negative correlation between the regeneration pattern and the soil pH and total potassium,generating more seedlings and saplings in the patches with relatively low concentration;while the spatial correlation with available phosphorus and ammonium nitrogen heterogeneity was not obvious.There was no significant correlation between the regeneration pattern and the spatial heterogeneity of soil 8 indicators on the shady slope.(7)We can take different human disturbance on the two slopes to promote the regeneration of Castanopsis fargesii population in secondary forest in the future.Such as appropriate cut down of the medium and large trees of Castanopsis carlesii(Hemsl.)Hay.,Machilus velutina Champ.ex Benth,Cinnamomum austrosinense H.T.Chang and Sassafras tsumu which around saplings of Castanopsis fargesii to reduce its inhibition on the sunny slope,and the seedling and saplings of Castanopsis carlesii(Hemsl.)Hay.,Machilus velutina Champ.ex Benth,Castanopsis tibetana Hance in the range of 2 m and the medium and large trees of Ziziphus jujuba Mill.var.spinosa(Bunge)Hu ex H.F.Chow to reduce its competition for the nutrient,light and space on the shady slope.In addition,increasing the space and light of medium trees can leave its success into the large trees,occupying the top of the stand.