Influencing factors of the mortality of Populus euphratica trees in different diameter at breast height classes in the lower reaches of the Tarim River
Tree death severely threatens the regular regeneration and succession processes of forests.However,it remains unclear whether the factors influencing the mortality of trees with different diameters at breast height(DBH)are consistent.This study explored the factors influencing the mortality of the Populus euphratica desert riparian forest in the lower reaches of the Tarim River.The biotic factors(e.g.,DBH and conspecific neighbor density)and abiotic factors(e.g.,soil salinity,pH,and moisture content)were incorporated into logistic generalized linear mixed models and random forest models to predict the driving factors and their relative importance in the mortality of Populus euphratica plants in different DBH classes.The results indicated that for the individuals with DBH≤10 cm,soil salinity had the greatest impact on mortality,and the mortality increased significantly with the increase in soil salinity.Soil moisture content and ammonium nitrogen content were also influential,whereas conspecific neighbor density within a 20 m radius and DBH had minimal effects.For the individuals with 10 cm<DBH≤30 cm,DBH was the most significant factor,and larger DBH reduced the mortality(P<0.001).Soil salinity and conspecific neighbor density within a 30 m radius also played important roles,while total phosphorus content and soil pH had minimal effects.For the individuals with DBH>30 cm,conspecific neighbor density within a 15 m radius exerted the greatest influence,followed by DBH and soil salinity,while ammonium nitrogen and soil organic carbon had the least impact.The random forest model demonstrated high predictive accuracy,effectively classifying most Populus euphratica individuals and predicting the mortality.The findings provide theoretical guidance for the sustainable management of Populus euphratica riparian forests in the lower reaches of the Tarim River and contribute to understanding the mechanisms driving the mortality of Populus euphratica.
Tarim RiverPopulus euphraticatree deathgeneralized linear modelrandom forest
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