| Casuarina equisetifolia is a main constructive species of coastal windbreak forest in Hainan Island and even in the south of China,which has good wind resistance,resistance to poor soil and the character of fast growth,but several studies have found that the Casuarina equisetifolia forest often has many problems,such as:difficult decomposition for thicker litters,simple stands layer structure,etc.The researches about natural regeneration characteristics weren't systematic,regeneration quality and regeneration influence factors,etc.of Casuarina equisetifolia coastal windbreak in Hainan Island.Therefore,the typical sampling method was adopted in this paper to investigate about natural regeneration,stands factors and main ecological factors in Casuarina equisetifolia coastal windbreak of 12 coastal cities and counties in Hainan Island.Total 73 temporary sample plots were established to collect data in order to analyze the characteristics of natural regeneration,and through the potential factors analysis of affecting Casuarina equisetifolia regeneration,such as climate,soil,forest stand structure and others to obtain the main factors of affecting Casuarina equisetifolia natural regeneration;the regeneration quality of Hainan Casuarina equisetifolia forest was evaluated according to the national regeneration quality standard.Based on single target and comprehensive analysis method,a good selection and evaluation method of regeneration tree species were established and species suitable for regeneration under Casuarina equisetifolia stands were selected.Through the study on the natural regeneration factors of affecting Casuarina equisetifolia forest,the main factors were found to provide theoretical guidance for the artificial promotion of natural regeneration.At the same time,the species with good performance of regeneration were selected according to the natural regeneration characteristics under Casuarina equisetifolia forest,and make them become afforestation tree species of coastal windbreaks and mixed afforestation with Casuarina equisetifolia.They not only can improve the species diversity of Casuarina equisetifolia windbreak and enhances the natural regeneration potential of Casuarina equisetifolia forest,and finally realizes from casuarina equisetifolia plantation to the transformation of the near natural forest.The results are as follows:(1)The average density of the Casuarina equisetifolia forest in the whole Island is 1396.00trees/hm~2,the average DBH is 11.63 cm,and the average tree height is 14.02 m.Most of the stand factors of Casuarina equisetifolia in the dry and wet climate regions are not much different,and only the difference in herb coverage is 20.03%(wet area)and 1.43%(semi-arid area).No signs of natural regeneration of Casuarina equisetifolia itself were found in the survey,but other tree species showed natural regeneration.(2)The density of natural regeneration is 1293.63 trees/hm~2,and the regeneration index is8756.97.The number of natural regeneration is less than that of other plantations or coastal natural windbreaks in Hainan.A total of 59 species belonging to 50 genera and 29 families could be regenerated in Casuarina equisetifolia coastal windbreaks.The regeneration diversity index was 2.5453(Shannon-wiener)and 0.8637(Simpson),respectively.The probability of interspecific encounter was 0.8639 and Shannon evenness index was 0.6242.The richness of natural regeneration of Casuarina equisetifolia forest is not ideal,but the tree regeneration is relatively good in limited regeneration,but the diversity is lower than that of shrubs.A relatively large number of species are clustered distribution,that is,limited regeneration tends to gather in a limited geographical area.(3)Climate region is an important factor affecting natural regeneration,Casuarina equisetifolia density is a direct affecting factor,and litter thickness and herb coverage are indirect affecting factors.Among them,the number,richness and diversity of regeneration in wet areas are significantly better than those in semi-arid areas.Climate factors,especially water conditions,will significantly affect the natural regeneration process.The regeneration of Casuarina equisetifolia forest is negatively correlated with the density of Casuarina equisetifolia itself,and stand factors such as litter thickness and herbaceous coverage also indirectly affect regeneration through affecting forest microenvironment.In addition,soil factors such as pH,organic matter and available phosphorus had no significant correlation with regeneration,but nitrogen(ammonium nitrogen)was significantly positively correlated with two classes of seedling density,while potassium(available potassium)was beneficial to the growth of young trees.(4)The regeneration quality of Casuarina equisetifolia forest in Hainan Island is not high.76.72%of the sample plots are non-regeneration or poor regeneration,of which 29.48%of the sample plots are non-natural regeneration,while 23.29%of the sample plots are above medium regeneration,of which only 15.07%are well regenerated.Compared with dry and wet areas,64.29%of the sample plots in semi-arid area have no natural regeneration,while only 28.81%in wet area.From the point of view of regeneration quantity,it can be judged that the regeneration situation in wet area is obviously better than that in semi-arid area.The single objective and comprehensive evaluation showed that Acacia auriculiformis and Litsea glutinosa among trees had the best regeneration potential,Brucea javanica and Pandanus tectorius and Polyalthia suberosa among small trees had better regeneration performance than other small trees,but Murraya koenigii,Atalantia buxifolia and Lantana camara among shrubs had relatively good regeneration performance.In summary,Casuarina equisetifolia can't be naturally regenerated in Hainan Island,but some other species are better in local areas.At the same time,wet climatic conditions,abundant soil nutrients and Casuarina equisetifolia forest with smaller density and DBH are beneficial to the occurrence of regeneration.Therefore,it is possible to increase the regeneration potential of forest land by attempting to fertilize in wet areas and appropriately cutting the Casuarina equisetifolia forest.According to the screening results of good regeneration tree species,it is possible to try mixing Acacia auriculiformis,Litsea glutinosa and Acacia confusa in the above forestland,and supplement Brucea javanica and Pandanus tectorius to increase the possibility of regeneration.The objective of transforming Casuarina equisetifolia plantation into near-natural forest was achieved by gradual popularization. |
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