Abstract: Populus euphraticais a dominant tree species of desert riparian forest in the arid region of northwest China, which plays an irreplaceable role in maintaining the stability of regional fragile ecosystem.P. euphratica forest has been damaged and severely degraded due to the harsh natural environment and human disturbance. Trunk hollow is extremely prominent, posing a great threat to its vitality, health, and survival. We set up a monitoring plot in P. euphratica forest in the Argan section along the lower Tarim River. By field sampling and laboratory measurement, we compared the growth, heartwood/sapwood water content, and wood density of hollow and non-hollow trees by testing the differences between two independent samples. The results showed that hollow trunk had significant negative impacts on tree height of P. euphratica, and increased crown loss (P<0.05), but did not affect crown width, crown/height ratio, crown area and crown deviation rate (P>0.05). Water content (243.9%) of heartwood of hollow trees with DBH of 25-35 cm and 35-45 cm was significantly higher than that of non-hollow trees (170.5%). The airdry water content (7.3%) of heartwood of hollow trees with DBH >25 cm was significantly lower than that of non-hollow trees (11.1%). Water content and air-dry water content of sapwood of hollow trees were lower than those of non-hollow trees (P<0.05), but the difference was not significant at DBH of 35-45 cm (P>0.05). Wood density, air-dry density, total dry density and basic density of heartwood of hollow trees were significantly lower than those of nonhollow trees (P<0.05). When DBH was at >25 cm, the four density indices of sapwood of hollow trees were lower than that of non-hollow trees (P<0.05). Therefore, trunk hollow may restrict the growth of tree height to a certain extent, resulting in decline of tree crown and heartwood/sapwood density. The results improve our understanding of the risk of trunk hollow on tree health and provide reference for the conservation and management of P. euphratica forest resources.

Key words: riparian forest, Populus euphratica, hollow tree, heartwood/sapwood water content, heart-sapwood density.