Research On Natural Regeneration Of Rare And Endangered Species Cupressus Gigantea

Cupressus gigantea is a species endemic to Tibet.At present,the natural regeneration of Cupressus gigantea is difficult,and the population is in a declining state.Natural regeneration is a means of self repair for forest ecosystems and a foundation for maintaining positive community succession.To explore the natural regeneration process of Cupressus gigantea,this paper selects sparse pure forests of different land types(habitats)in the main natural distribution areas of Cupressus gigantea as the research objects.Through sample plot investigation,fixed-point observation,and indoor experimental analysis,the seed rain dynamics and seed bank characteristics,seed quality,seedling settlement,sapling establishment,and factors affecting natural regeneration habitats of Cupressus gigantea were studied.The main research results showed that:(1)The seed rain of Cupressus gigantea showed great spatial heterogeneity in the propagation direction and distance,and its seasonal dynamic change was obvious;The seed density and quality of soil seed banks also showed significant spatiotemporal differences.The average spatial density of seed rain is 1140.9 seeds/m~2,and its diffusion direction and distance are influenced by land type and wind direction,mainly distributed within 1-5m from the mother tree(trunk),and decrease with increasing distance from the mother tree.The seed rain has a long diffusion time,and although the diffusion is relatively concentrated from September to November,it exhibits a bimodal diffusion characteristic in April and November.The average seed density of the Cupressus gigantea soil seed bank during the stable period from December to May of the following year was 299 seeds/m~2.After the germination period,the seed bank became smaller and the average density decreased by 43.4%.The seeds in the soil seed bank were mainly distributed within a horizontal distance of 1-5m from the mother tree trunk and a soil depth of 0-5cm,accounting for 89%of the seed bank storage.In terms of seed quality,the proportion of seeds with vitality in the population of Langxian County is the highest,with an average of 65.7%;The second is the Milin population,with an average of 34.3%;The lowest is the Nyingchi population,with an average of only 24.3%.(2)The spatial distribution pattern of Cupressus gigantea seedlings was similar to that of seed rain and soil seed banks,with significant differences in survival numbers among different land types and decreasing year by year.Seedlings are mostly concentrated within a range of 3-7m from the mother tree trunk,with the highest number of seedlings in the waterline type,followed by terraces,and the lowest number on slopes.The control experiment showed that the optimal water condition for the growth of Cupressus gigantea seedlings was 30%-50%soil moisture,the optimal light condition was 30%-50%shade,the optimal temperature condition was 20-30℃,and the optimal matrix formula was farmland soil+river sand+humus soil=3:2:1 soil matrix.The correlation between habitat influencing factors and the results of principal component analysis indicated that the process of seedling settlement is significantly positively correlated with waterline land types and gravel cover,while significantly negatively correlated with slope orientation,extreme temperature,soil dry crust,grazing,and intensity interference.(3)The overall distribution of Cupressus gigantea saplings is random,and the number of saplings in the natural distribution area is relatively small,and there were significant differences in the survival rate and growth situation of saplings in different land types.Starting in May2020,the survey would be conducted every 2 months,and a cycle will be repeated in 2021.In the 5th survey,the number of young trees on the waterline was the highest and the survival rate was 100%;The number of young trees on the slope comes second,with a survival rate of 97.5%;The number of young trees on the terrace is the lowest,with a survival rate of 92.5%.The average height growth of Cupressus gigantea young trees in waterline terrain was the highest at 17.6cm,followed by 12.4cm on slopes,and the average height growth of terraces(9.5cm)was the lowest.The growth trend of ground diameter and root length is consistent with the average tree height growth.The simulation experiment results of transplanting Cupressus gigantea saplings showed that all growth indicators of the transplanted saplings were better than those of the same age saplings under natural conditions,and the growth performance trend of each indicator was consistent with the results of field investigations of saplings.5a is the key period for the transition from seedlings to saplings.The correlation between habitat influencing factors and the results of principal component analysis indicated that the establishment of young trees was significantly positively correlated with waterline land types,and extremely significantly negatively correlated with tree canopy shading below 50%.(4)During the natural regeneration process of Cupressus gigantea,the conversion rate from seed rain to the establishment of young trees is only 0.8%.The intensity of habitat screening varies at each stage of its life cycle,and corresponding regeneration management measures were needed to protect the near natural regeneration and recovery of Cupressus gigantea.The resilience of seedlings was weak,and the settlement process of seedlings can’t smoothly overcome habitat limitations,resulting in a shortage of reserve resources.In addition,the number of young trees in the natural distribution area of 10-20a was very small,and the population structure was unreasonable,resulting in a lack of regeneration foundation for Cupressus gigantea.This paper systematically studied the key influencing factors of Cupressus gigantea seed rain and soil seed bank,seedling settlement,young tree establishment,and natural regeneration.Based on the aforementioned research results,the following innovative viewpoints were proposed:(1)The seed rain and soil seed bank had abundant seed reserves and a large seed base,and although the quality of seed sources to some extent affected the natural regeneration of Cupressus gigantea,it had not become a limiting factor for natural regeneration of Cupressus gigantea;(2)The process from seedling settlement to saplings establishment was greatly hindered by conditions such as water,light,temperature,surface cover,species competition,and intensity interference,resulting in difficulties in natural regeneration of Cupressus gigantea.This study explored the characteristics,influencing factors,and resource interaction patterns of natural regeneration stages of Cupressus gigantea,further understanding the endangered mechanism of Cupressus gigantea.In the future,the conservation of Cupressus gigantea populations should mainly consider how to effectively coordinate the regulatory mechanism from seedling settlement to young tree establishment in the natural regeneration process,in order to maximize the improvement of the natural regeneration status of Cupressus gigantea and promote the sustainable development of the Cupressus gigantea population.