Studies On Short-Term Tree Mortality Dynamics Of Secondary Forest In Montane Region Of Eastern Liaoning Province,China

In order to explore the short-term dynamics and influencing factors of tree death in secondary forests in eastern Liaoning province mountainous areas,in this study,based on 4hm2 fixed monitoring sample plot,we selected the survey data in 2013 and 2018 to study individual woody plants with DBH≥1cm in the sample plot.The characteristics of dead trees in the sample plot in the five years were analyzed from the composition,quantitative change,diameter class distribution and spatial distribution of dead individuals of woody plants in the community.The effects of woody plant death on the spatial pattern and interspecific spatial association of dominant tree species were analyzed and tested by using spatial point pattern based on different null models and generalized linear mixed model.At the same time,the differences of influencing factors of woody plant death and survival in the sample plot were clarified.Our results will provide a theoretical basis for explaining the coexistence of community species,and have guiding significance for reasonably predicting the community dynamics of forest ecosystem.The research results are as follows:(1)In the five years,the number of tree species in the sample plot decreased from 52 to49.The number of independent individuals decreased from 9298 to 6830,and the number of dead individuals decreased from 2493.The basal area decreased from 101.04 m~2 to 95.58 m~2.The average DBH of 47 tree species increased.The diameter distribution of death individuals of different tree species in 2018 and 2013 was similar.There were more small-diameter dead individuals and less large-diameter dead individuals.At the same time,the spatial distribution patterns of death individuals of different tree species were also similar.At the small scale,it was mainly aggregated distribution,while at the large scale,it was random distribution.(2)Under the completely random null model,all tree species in the two surveys showed obvious spatial aggregation pattern at most scales.Compared with 2013,the proportion of tree species randomly distributed on a larger scale in 2018 increased with the increase of scale.After eliminating the effect of heterogeneity,there were only uniform and random distributions in the 2013 and 2018 under the heterogeneous Poisson process null model.However,the proportion of uniform distribution decreased and the proportion of random distribution increased in 2018.Under the completely random null model,the proportion of positive and negative tree species pairs at 0-50 m scale decreased compared with the results in 2013,while the proportion of unrelated tree species pairs increased.Under the heterogeneous Poisson process null model,the proportion of unrelated tree species pairs increased and the proportion of negatively correlated tree species pairs decreased in 2018.(3)At the community level,the survival of woody plants was mainly affected by DBH size,which was significantly positively correlated with DBH size.The survival of gravity-dispersal tree species was positively correlated with DBH and aspect.For wind-dispersal tree species,the individual survival was significantly positively correlated with DBH,and significantly negatively correlated with altitude and slope.At the tree species level,the survival of most tree species was significantly positively correlated with DBH,while some tree species were also significantly affected by the conspecific neighborhood basal area,heterospecific neighborhood basal area,altitude,soil p H,available potassium content and slope direction.