Effects Of Neighborhood Competition On Growth Of Typical Trees In Coniferous And Broad-leaved Mixed Forest In Jiaohe,Jilin

The coniferous and broad-leaved mixed forest in Northeast China is a typical forest vegetation area in the Changbai Mountains in northeastern China.Compared with other forest areas of the same latitude,the coniferous and broad-leaved mixed forest area has more typical species and rich species diversity.It is an important research area of forest community construction mechanism.At present,global climate change has caused changes in the biodiversity of forest communities,which has led to changes in species interactions within communities,especially among individuals in the neighborhood.Ecologists have long recognized that differences in phenotypic traits between species play an important role in maintaining species diversity within communities.The same functional trait may vary widely among different species,and these interspecies differences may potentially affect the performance of a species in terms of competition processes and survival strategies.Previous experimental studies on the role of functional traits in competitive interactions have focused on annual plants or perennial herbs.There is a limited understanding of the competitive performance of functional traits within the neighborhood of individual trees within the forest community,especially the association mechanism between functional traits and competition in temperate forests in northeastern China is worthy of further exploration.Based on the 2015-2017 neighborhood competition experiments established in coniferous and broadleaved mixed forests in Jiaohe City,Jilin Province,Northeast China(including three different stages of development: middle-aged forest,near-mature forest,old-growth forest;two types of target species:conservative species and colonized species;two types of competition indices: single tree competition index and neighborhood model framework),by analyzing the degree of influence on the relative growth rate of the target tree,exploring the individual tree competition in the coniferous and broad-leaved mixed forest and the underlying mechanism.The following main results have been achieved:1)Using different single tree competition indices to assess the competitive pressure on the growth of two target species(conservative species: Pinus koraiensis and colonized species: Ulmus laciniata)in coniferous and broad-leaved mixed forests,it was found that the competition index related to tree height was important Species grew better,while the classic trial breast diameter relative size and distance and distance competition index did not show advantages.This indicates that in the broadleaved P.koraiensis forest in the research institute,the competition pressure on individual species growth is more from the competition for vertical space and light resources.2)Conservative species(P.koraiensis)and colonized species(U.laciniata)in coniferous and broadleaved mixed forest stands were selected as research species,and a neighborhood model framework was used to quantify the specific performance of functional traits in neighborhood competition.It was found that the individual growth of the two species,P.koraiensis and U.laciniata faced competition pressure from different types of neighboring competitive trees.The relative growth rate of P.koraiensis was inhibited by the chest height cross-sections of intraspecfic and ieterspecfic competing wood individuals in its neighborhood.The relative growth rate of U.laciniata was mainly affected by the competitive inhibition of heterogeneous competing trees and the mutual benefit of the same competing trees.Different functional traits have different effects on the growth of the target tree.The differences between the nitrogen and carbon content in the leaves between P.koraiensis and its competing trees can inhibit the growth of P.koraiensis.The growth pressure of U.laciniata individuals mainly comes from the tree height of surrounding competing trees,leaf carbon content and leaf carbon-nitrogen ratio.3)Tree individuals with different DBHs face varying degrees of competitive pressure from surrounding tree individuals.Compared with individuals with larger DBHs,the growth of a single target tree with a smaller DBH was more inhibited by surrounding competitors.Neighborhood competition also differs depending on the target tree species.The growth of P.koraiensis with a smaller DBH is negatively affected by heterogeneous competitors,while individual P.koraiensis with a larger DBH is more affected by competing trees from the same species.Competitive pressure.The growth of individuals with smaller DBH was larger than that of individuals with larger DBH.The growth of individuals with larger DBH was more inhibited by competition from neighboring competitive trees.At the same time,the competition effects of target trees with different DBH sizes are reflected in the performance of different functional traits.The growth of small P.koraiensis trees is inhibited by ieterspecifc individuals in terms of tree height and specific leaf area.Competitive inhibition of functional traits acquired by individuals in all relevant resources.The growth of small-leaf tree was inhibited by the related traits of light acquisition by competing trees,and the big tree was mainly affected by competition from the same species.4)As the distance between the target tree and its competing tree increases,the influence of the competing tree on the relative growth rate of the target tree decreases.Competitive effects of functional traits of the same species on the growth of the target P.koraiensis were found.In addition to tree height,other traits also showed similar trends with changes in the neighborhood.The relative growth rate of P.koraiensis was most affected by competing trees in the neighborhood of a radius of about 4 to 8 m.It was determined that the leaf area and specific leaf area of heterogeneous competing trees had a strong competitive inhibition effect on the growth of P.koraiensis.However,the effects of other traits on the growth of the target tree were not observed to show a strong change as the area of the neighborhood increased.Within a distance of 8m,the relative growth rate of U.laciniata was affected by the surrounding competing trees.The effect of functional traits of the same species on the growth of the target tree weakened as the distance from the target tree increased,and it showed a positive effect before the distance reached 6 m.The competition between the competitors and the target tree regarding the acquisition of light and nutrition resources mainly occurs within a range of4 to 8 m from the target tree.5)According to the competition index of P.koraiensis in three different stands of old-growth forest,near-maturity forest and middle-aged forest,it was found that there are differences in the competition index of P.koraiensis in different forest stands.Among them,the competition index related to DBH was the highest in middle-aged forests,and the smallest in near-mature forests.This indicates that there are more competitive individuals with larger distances and larger DBH in the middle-aged P.koraiensis neighborhood.The competition index related to tree height indicates that the competition pressure is lowest in the old-growth forest and highest in the middle-aged forest.As for the competition index of competitive wood traits,the average trait index value of P.koraiensis in oldgrowth forest is significantly higher than that of near-mature and middle-aged forests,while the direct difference between the average trait index of the P.koraiensis trees in the near-mature forest and the middle-age forest is small.6)In different development stages of coniferous and broad-leaved mixed forests,the growth of P.koraiensis is subject to competition inhibition from competitive wood traits.It was found that the early growth of P.koraiensis in broad-leaved P.koraiensis forest was mainly affected by the leaf area and specific leaf area of competing trees in the neighborhood.Competition inhibition.The growth of P.koraiensis in the middle development period is mainly inhibited by the competitive tree in tree height and leaf area,while the growth of P.koraiensis individual in the late development period of coniferous and broad-leaved mixed forest is mainly affected by the competition of the same species and the competition of the different species.Competition inhibition on tree height,specific leaf area and leaf carbon content.In summary,individual competition in coniferous and broad-leaved mixed forest is related to the size of the neighborhood,tree species,relative DBH size,and specific development stages of the stand.In predicting and quantifying species competition in the forest,multiple types of competition indexes need to be considered.Different competition indexes have differences in explaining the competitive pressures on the growth of different species.Compared to the single competition index,the neighborhood competition model framework comprehensively considers the influence of the basal area and functional traits of target trees and competing trees in the neighborhood,which has advantages in explaining neighborhood competition.It shows that in studying the biological interactions in forest communities and their effects on tree growth,more consideration of the differences in traits and relative distances between individual organisms can help accurately evaluate biological interactions in the neighborhood.The competition pressure on the growth of different tree species in coniferous and broad-leaved mixed forests,which are the specific characteristics of competing trees,needs more time to study.