Abstract: Tree mortality is an important part of forest community dynamics. It is one of the important mechanisms regulating population structure and dynamics. In this study, a census was conducted on Juglans regia dead trees in the four slope directions of Xinjiang Wild Walnut Nature Reserve. We analyzed the characteristics of the quantitative distribution of four mortality types in J. regia trees, and the effects of diameter at breast height (DBH) and slope direction on the J. regia dead trees. The results showed that the main mortality types of J. regia trees in the reserve were freezing injury mortality (64.87%), disease mortality (31.94%), insect pest mortality (30.54%), and rot mortality (27.35%). Freezing injury mortality, disease mortality, and insect pest mortality occurred simultaneously. The largest proportion of dead J. regia trees in the four slope directions was on semi-shady slope (41.12%), followed by semi-sunny slope (29.34%), then shady slope (18.96%), and the smallest proportion was on sunny slope (10.58%). The proportion of  J. regia dead trees by age group was as follows: middle-aged trees (47.90%), mature trees (34.13%), young trees (9.78%), and old trees (8.18%). The proportion of  J. regia dead trees with the same mortality type differed significantly among the four slope directions and different age classes (P<0.05). Freezing injury mortality and disease mortality mainly occurred in middle-aged trees, while insect pest mortality and rot mortality primarily occurred in mature trees. The numbers of freezing injury mortality and insect pest mortality were significantly correlated with DBH, crown width, and slope direction (P<0.05). The numbers of disease mortality were extremely significantly correlated with DBH (P<0.01). This study can provide scientific reference for the protection of J. regia in Xinjiang Wild Walnut Nature Reserve.

Key words: Juglans regia, mortality type, diameter at breast height, slope direction