Monitoring The Regeneration Of Abies Faxoniana In Tangjiahe National Nature Reserve

Tangjiahe National Nature Reserve is the biodiversity hotpot of southern western China,which is located in the southern of Motianling and north western of Longmen mountain,the northwest edge of Qingchuan County and the northern margin of Sichuan Basin.It is also an important part of the"Sichuan-Yunnan Ecological shield"in the"Two shields and Three Belts".It has great effect on the ecological security to Yangtze River Basin and even to the whole country.As it occupied by large amount of dark coniferous forest in Tangjiahe National natural reserve,which was dominated by mixed forests of Abies faxoniana and Picea brachytyla,and pure forest of Abies faxoniana at low and high altitudes respectively.As the dominant species of the coniferous forests,the regeneration and population dynamics of Abies faxoniana has great effect on the ecological function of the coniferous forests.However,previous studies of Abies faxoniana at Tang Jiahe National Nature Reserve found the difficulties of its natural population regeneration,with seriously death of adults,no saplings at high altitudes and few seedlings.In order to explore the reasons for the lack of saplings and seedlings during the process of its natural regeneration and provide scientific evidence for the tending of coniferous forests in the upper stream of the Yangtze river,systematically monitoring the species provenance dynamics of Abies faxoniana in the Tangjiahe National Nature Reserve:(1)The quadrat method was used to monitor the growth conditions of adult Abies faxoniana.In total,setting 15 quadrats.The mortality rate of the adult species of Abies faxoniana increased every year,with 41.86%,55.62%and 57.02%in 2016,2017 and2018,respectively.The percentage of scratched trees hurt by animals were different every year.Founding 7.16%trees had scratched markers in 2016,then 6.65%for 2017 and it maximized to 10.33%in 2018.(2)The seed yield and living conditions of adult trees were monitored using the transect line method.Three transect lines were set for observation since 2016.The results showed that the production of Abies faxoniana were unstable and obvious discriminate between years:in 2016,the proportion of firs at line 1 was 22.62%,that of line 2 was 0,and that of line 3 was 23.46%.In 2017,the proportion of trees with fruits at three lines was 8.20%,7.89%and 0.57%,respectively,while there was nothing found in 2018.Higher average production per individual of Abies faxoniana was found in 2017(188.56)compared to2016(47.92).GLM were used to interpret the relationship between climatic factors and production.It showed that the precipitation,wind speed and temperature during the pollination period had some influence on the seed production,and those might be the important factors affect the seed production.(3)Seed collectors were used to monitor seed rain.From the observation,it can be seen that the seed rain of Abies faxoniana started in September,and reached to the peak with29~35 seeds/m~2 from mid-late September to early October.After November,the seed rain of Abies faxoniana decreased significantly,and the seed rain stopped at mid-late December.There was significant difference of seed rain density across elevation in Abies faxoniana(P<0.001).Single peak curve of seed rain was found as the increasing of elevation.Highest density was found at the elevation between 2463-2480m.Significant positive relationship was found between the germination rate and the seed activity(P=0.006).The seed activity of Abies faxoniana was low with an average of 30%,and it also has low germination rate,less than 10%.The low seed activity and germination rate may be the major factor that affect the natural regeneration of Abies faxoniana population.(4)The soil seed back plot was observed,and the results showed that most seed were in upper(1~2cm)and medium soil(3~7cm),while less in the bottom one(8~12cm).In 2016,41.95%and 47.47%of seeds were found in upper and medium soil,while 67.13%and27.78%in 2018.The soil seed bank also showed a unimodal curve along the altitude.In2016 and 2018,the largest number of soil seeds were collected at the elevation from2463m to 2480m.In 2016,the upper,medium and bottom of soil seed bank density of were 38.21±18.77 seeds/m~2,48.40±33.92 seeds/m~2,and 24.62±18.39 seeds/m~2,respectively,while in 2018 it was 72.18±47.53 seeds/m~2,26.32±23.82 seeds/m~2,and0.85±0.85 seeds/m~2 for upper,medium and bottom ones,respectively.(5)The number of Abies faxoniana's seedlings in the quadrat was surveyed.The results showed that the seedling density of Abies faxoniana's was significantly different across different elevations(P<0.001).Single peak curve was found in the number of Abies faxoniana's seedlings between different sites.Highest number of seedlings were found at the elevation from 2463m to 2480m,where the high abundant of seed rain and soil seed bank was.From 2463m to 2480m,the seedling density was 408.3±96.1 plants/ha,25±14.4,and 1025±441.8 plants/ha for 2016,2017 and 2018 respectively.Fewer were found at both lower and higher altitudes.The annual variation was also found in the seedling number.Significant increase of seedlings in 2018 at each altitude was found.There was a significant positive correlation between the number of seedlings and the seed rain density,as well as soil seed bank density in the previous year(P=0.032,P=0.034).(6)Simulating the response of fir seedlings to different light intensity showed that 75%of the light intensity will facilitate the seedling growth and increase the leaf number.The seedling of Abies faxoniana had better adaptability compare to Abies chensiensis under the same condition.The survival rate of Abies faxoniana's seedling had no difference under different light intensity(P=0.596),which may due to short experimental time.All the result indicated that discriminate fruit production across different years,low production,low seed activity,small number of seedlings in the field and the requirement of light during earlier stage of seedling of Abies faxoniana.Considering that,we can collect seeds from other places as a supplementary for seeds bank,cultivate the seedling in the laboratory,cut the dead wood or shrubs to increase light in order to facilitate the natural regeneration of Abies faxoniana.