| Natural regeneration is an important way for the continuous improvement and self-restoration of forest ecosystems.In forest ecosystems,sustainable natural regeneration is an important manifestation of the healthy development of forests,which plays an important role in the stability of forest ecosystems and the maintenance of biodiversity.In the field of forest ecology,understanding and understanding the mechanism of natural forest regeneration has always been the goal of forestry and forest ecologists,and has become a hot spot in the related research fields.As an important guarantee for the continuous improvement and perfection of plantation forest ecosystem,natural regeneration of plantation forest is an effective booster for the healthy,stable and sustainable development of forestry industry,which has been attached great importance by forestry workers.Therefore,the in-depth study of forest natural regeneration has a far-reaching impact on the substantial progress of forestry industry and the construction and development of ecological environment.In this study,Pingxiang City,Guangxi province,China Academy of Forestry Sciences Tropical Experimental Center,mixed forest of C.hystrix and P.massoniana was selected as the research object.Based on a large number of survey data,such as natural regeneration status of Pingxiang,forest environment and structure,physical and chemical factors of forest soil,natural regeneration characteristics and seasonal dynamics of C.hystrix,distribution pattern of natural regeneration of C.hystrix and natural regeneration of C.hystrix were comprehensively carried out.The results showed that:(1)In the artificial mixed forest of C.hystrix and P.massoniana in the south subtropical zone,the average total density of natural regeneration of(C.hystrix in dry and wet seasons reached 148250 trees/ha and 194300 trees/ha,respectively,and the corresponding density of natural regeneration seedlings of C.hystrix in dry and wet seasons showed a downward trend with the increase of height grade.In both dry and wet seasons,the S? grade of the regenerated seedlings accounted for 51.33%and 49.72%of the total density respectively,and the S? grade accounted for the least(4.18%and 4.30%respectively).In addition to SI and S?,there were significant differences in seedling densities of S?(F=5.39,P = 0.032),S?(F= 5.26,P = 0.017),S?(F=4.854,P = 0.008),and total seedling densities in dry and wet seasons reached extremely significant levels(F = 9.695,P= 0.001,P<0.01).(2)The aboveground and underground biomass of natural regeneration seedlings of P.massoniana in dry and wet seasons increased with the increase of height level in the mixed forest of C.hystrix and P.massoniana in the south subtropical zone,and the aboveground and underground biomass of regeneration seedlings at all levels in wet season was higher than that in dry season.The analysis of variance showed that there was a significant difference in the total biomass between above-ground and below-ground in dry and wet seasons(P<0.01).Except for S? and S? the above-ground and underground biomass of S?and S? reached a significant difference level(P<0.05),while that of S? reached a very significant difference(P<0.01).(3)The survival curves of regenerated seedlings of P.massoniana ×C.hystrix plantation in south subtropical zone are basically the same in dry season and wet season,and tend to type ? structure,i.e.diagonal survival curve,which indicates that the Regenerated Seedling population shows relatively stable growth and decline rate at present.Five validations,including variance mean ratio(C),negative binomial parameter(K),cluster index(Ii),Morisita distribution pattern index(?)and Casie index(CA),showed that the overall spatial distribution pattern of regenerated seedlings in dry and wet seasons and the spatial distribution pattern of regenerated seedlings at different height levels were clustered,but the overall spatial distribution pattern of regenerated seedlings in wet season was stronger.The degree of concentration is slightly stronger than that of dry season.In addition,the aggregation degree of S? highly regenerated seedlings was weaker than that of S?,S?,S? and,SV in both dry and wet seasons.(4)Among the 25 forest stands and soil environmental factors studied,some factors have significant or extremely significant correlation with seedling density at all levels of regeneration,which may have an impact on natural regeneration of C.hystrix.Among them,grade SI was significantly correlated with soil total potassium content and near-layer leaf area index,and significantly correlated with soil total phosphorus content,pH,elevation and near-layer transmittance coefficient;grade S?was significantly correlated with soil total phosphorus content,with elevation and upper-layer average leaf dip angle;grade S? was significantly correlated with soil total phosphorus and elevation,and with upper-layer average leaf dip angle.S? was significantly correlated with soil total nitrogen,near-stratum transmittance coefficient and nitrate nitrogen content,while SV was significantly correlated with near-stratum leaf area index and above-ground and below-ground biomass of regenerated seedlings;SV was significantly correlated with soil total phosphorus,with soil ammonium nitrogen,above-ground and below-ground biomass of regenerated seedlings,and with altitude.(5)Redundancy(RDA)analysis showed that the explanatory rate of spatial pattern variation of natural regeneration seedling density of C.hystrix was 66.01%with 25 combinations of stand and soil environmental factors,and the explanatory effect was significant(F= 2.0229;P = 0.027,P<0.05).From the information content of the sorting axis,the first four sorting axes account for nearly two-thirds of the total information.Therefore,the natural regeneration of the C.hystrix can be explained by the first four sorting axes.By explaining the comprehensive information of the correlation table between variables and ordination axis and the corresponding ordination chart,it was found that among the six factors of soil total phosphorus,altitude,average leaf inclination of upper layer,soil pH,near-layer leaf area index and near-layer transmittance coefficient,the effects of the first three factors on the spatial distribution pattern of regenerated seedlings of C.hystrix reached a very significant level(P<0.01),and the last three reached a very significant level(P<0.01).At the significant level(P<0.05),it can be determined that these six factors are the main influencing factors,while the soil total phosphorus,elevation and the average leaf inclination of the upper layer of the stand are the most important influencing factors. |
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