The Study On Population Characteristics And Effects Of Different Light Intensity On Seedling Growth Of Hopea Hainanensis In Hainan Island

Hopea hainanensis is one of the National Key Protected Plants in China and was classified as an Extremely Small Population.It was also classified as a Critically Endangered Population by the International Union for Conservation of Nature(IUCN).The protection and restoration patterns of Hopea hainanensis populations has been the focus of local forestry work in Hainan Province since the 1960s.Traditional methods are mainly in-situ and ex-situ conservation,which have been used over 50 years but still have little effect on improving the original habitat of the population.Therefore,in this paper,we assessed species composition,structure characteristics and inter-specific association of dominant species at different levels in the communities of this species,population structure and dynamic comparison of the species under two different conservation modes,and the effects on the growth of seedlings in different light intensity.In order to provide scientific basis for the protection and restoration of Hopea hainanensis,the present situation and dynamic trend,and relationship between different protection modes.The findings are as follows:(1)366 species of 228 genera in 92 families were found in the community.Lauraceae,Rubiaceae,Euphorbiaceae,Fagaceae and Moraceae were the main families in the community.The species diversity of the community was tree layer>Shrub layer>Herb Layer.Correlation between Hopea hainanensis and other dominant species was not significant.Hopea hainanensis is positively correlate to 6 trees,13 shrubs and 2 herbaceous species but negatively to 6 trees species and 7 herbaceous species.The association between the Hopea hainanensis population and the herbaceous plant is more complex than that of the trees and shrubs,and the correlation with the dominant species of trees is more close.The community was unstable(36.84/63.16)due to the fragile ecology,indicated that the community was still in the early or middle stage of succession and led to the unstable structure and function of community.However,Hopea hainanensis and other species were in competition for the utilization of resources.Important values for the species are 23.5833 in herb layer,3.3023 in tree layer and 1.0776 shrub layer.Adult individuals with larger DBH and higher height,are in the small number;seedlings with higher coverage is more;while saplings was few,indicated the decline trend of Hopea hainanensis population.(2)The populations under both ex-situ and in-situ protections the growth type:young individuals made up the overwhelming majority,while middle-aged and elderly individuals were relatively few.Further,ex-situ protection population survival curves tended to be Deevey-I type,while the in-situ population survival curves tended to be Deevey-III.Time-series prediction analysis showed that the ex-situ population of Maple had a certain recovery potential,while in-situ population regeneration of the Bawangling population was difficult to maintain and is,thus,facing decline.According to analysis results,habitat has a strong environmental screening effect on the I age individuals and thus resulted in seedling mortality rates up to 99.5%—meaning only 0.53%can transition to young tree stage.Despite high seedling mortality rates(90.3%)in ex-situ populations,8.85%seedlings can transition to the young tree stage,demonstrating a more stable population.Therefore,Fengmu Woodland is a more suitable option for the survival of Hopea hainanensis populations.(3)Light is an important environmental factor that affects the seedlings of Hopea hainanensis.In the early(stage7-8 months before the seedling age),seedlings grow well under certain shading conditions and were suitable to grow under 21.61%NS(natural sunshine)light intensity while was the worst at 100%due to the inhibition by full light.As reached a certain stage(7-8 months after the seedling age),the growth of seedlings appeared light-loving characteristics and grow best under 100%NS light intensity.With the growth of the individual seedlings,the response to light changes for adapting to growth under adequate light.Hopea hainanensis is the later stage species of the succession in tropical rain forest.Its seeds can germinate and survive under the forest,but require a certain weak light environment in stage of 7-8 month-old.21.61%NS light intensity is benefit to the growth of young seedlings,while the full light is more suitable after 7-8 months.In conclusion,we can protect and restore Hopea hainanensis in the natural tropical rain forest by simulating the environment of Fengmu and creating the light environment suitable for the seedlings in different growth periods as far as possible.The seedlings need shading before 7-8 months and larger light transmittance after 7-8 months,so as to improve the natural regeneration ability of the population and relieve the endangered situation of this species.