Study On The Seed Fates Of Declining Castanopsis Fargesii On Jinyun Mountain

Forest decline has become an important factor in triggering various environmental crises and has received widespread attention.Evergreen broad-leaved forest,as a characteristic zonal vegetation and an important forest ecosystem in China,has faced with problems such as fragmentation in its habitat.In recent years,Castanopsis fargesii,a dominant species of evergreen broad-leaved forest,has also experienced recession.The dynamics and natural renewal of vegetation after declining of C.fargesii populations will directly affect the stability and function of the evergreen broad-leaved forest ecosystem.The seeds stage is a key life-history stage during a plant's natural regeneration process.Studying the impact of C.fargesii decline on seed fate plays an important role in predicting population dynamics.It can provide theoretical basis and guidance for the protection,restoration and management of the evergreen broad-leaved forest.Therefore,this study investigated the declining C.fargesii trees in the evergreen broad-leaved forest on Jinyun Mountain and monitored the its seed rain of three years.We discussed the decline characteristics of C.fargesii and the effects of C.fargesii decline on seed rain,seed production,seed traits and the seed fate.The main results are as follows:(1)In the evergreen broad-leaved forest in Jinyun Mountain,as many as 16.38%of the C.fargesii individuals are declining.The intermediate-decline and high-decline individuals are mainly adult trees with DBH between 20 and 50 cm.The spatial distribution of the declining individuals showed random distribution pattern at the spatial scale of 0~25 meters,indicated the decline of C.fargesii may has spatial independence.(2)From 2015 to 2017,the temporal pattern of the intermediate-decline and non-decline C.fargesii seed rain are similar,and the health of C.fargesii trees may not change its long-term solid dynamics and patterns.In the three years,the difference in mature and immature seed density between intermediate-decline and non-decline adults trees increased year by year.In 2017,the mature seed density of non-decline adults is significantly higher than that of intermediate-decline adults(P<0.05).The immature seed density of non-decline adults is significantly higher than that of intermediate-decline adults(P<0.01).And the insect-attacked seed density of non-decline adults is significantly higher than that of intermediate-decline adults(P<0.05).(3)Medium-weight(0.5-0.6 g)seeds of intermediate-decline and non-decline C.fargesii were the most abundant.The differences in the length,width,height,and weight of the intermediate-decline and non-decline C.fargesii seeds were not significant,and the seed traits were relatively stable.The decline of C.fargesii had little effect on the seed morphological characteristics.There were no significant differences between starch and soluble sugars and chemical elements such as C,N,P,K,Mn of the intermediate-decline and non-decline C.fargesii seeds;however,the tannin content of the non-decline seeds were significantly higher than intermediate-decline C.fargesii seeds(P<0.01),and the cellulose content of the non-decline seeds were also significantly higher than intermediate-decline C.fargesii seeds(P<0.05).The decline of C.fargesii will not affect the accumulation of nutrients inside the seeds,but it will affect the production of chemical defense substances.(4)The conversion rates of seeds to seedlings in non-decline(NDE)and intermediate-decline(DE)habits were 10.19%and 11.63%,respectively;the densities were 3.56 plants/m~2 and 2.72 plants/m~2,respectively.There are no significant difference of seedlings density and height in the two habitats(P>0.05).