Population quantitative characteristics and dynamics of rare and endangered plantDavidia involucratain Hunan Province

Davidia involucrata Baill is the only species in Davidiaceae.It originated from tertiary period and now is a relic plant known to the world.But now,it becomes one of the world famous ornamental tree for gardens and parks in many countries because its flowers look like flying doves(dove tree).In recent years,the increase of regional developing projects has led to decrease of this ancient and rare plant in nature,especially its habitats and populations.The plant has been listed in the rare and endangered plants in China.D.involucrata mainly distributed in very special niche habitats in the mountainous region of Youngzi River in China.To better understand its natural community and propose management strategy,we investigated the population structure and natural succession of D.involucrata in Hunan province.Seven plots were established in Badagongshan and Hupingshan Nature Reserves.We developed a static life table of D.involucrata based on the population life table and theory of survival analysis.Survivorship curves,mortality rate,killing power,survival rate,mortality density and hazard rate were determined.The results showed that the population structure of D.involucrata was an inverse-pyramid type.The death rate of young trees was higher.The D.involucrata population in Hunan province was declining.There were fewer young and old D.involucrata trees in Badagongshan and Hupingshan Nature Reserves.The young trees mainly belonged to sprouted seedlings.Population structure was fluctuated and the survival curve had trend to be the type between Deevey Ⅱ and Ⅲ.One peak of mortality rate and killing power existed in the lifespan in the 5th age class period.The population survival rate of D.involucrata increased monotonically,whereas the cumulative mortality rate decreased monotonically.Four survival functional curves showed that the D.involucrata population grew stably at young age,decreased very quickly in middle age and declined in old age.Limited natural regeneration from seeds was the mainly reason caused D.involucrata population decline.After exploring and sampling some natural populations,we summarized that the species became endangered plants mainly because of 1) narrow distribution(niche habitat).Dove tree usually grows in the deep areas of the moun-tain ranges,with warm summer and abundant moisture.2) Seed abortion.It is very serious and majority of embryos could not develop normally.3) Difficulty of natural regeneration.The seed of dove tree has a long period of after-ripening and a hard exterior covering.Germination usually occurred after three years,which leads to the significant loss of seed viability.4) Human disturbance.Habitat loss(logging) and collection of wild seedlings were one of the important reasons to reduce its populations.Dove tree was very sensitive to the change of habitat.The environment change would cause its reproduction difficulty.The number of individuals of dove tree was declined dramatically.Further studies on its protection and habitat restoration should be our priority.