The effect of low-temperature event on the survival and growth of <Emphasis Type="Italic">Juglans mandshurica</Emphasis> seedlings within forest gaps

In forest ecosystems, gap formation changes the allocation of abiotic resources and thus affects the survival and growth of understory plants. However, how tree seedling survival and growth respond to low-temperature events and the influencing mechanisms remain unclear. To clarify how low-temperature event limits the survival and growth of tree seedlings in the montane regions of eastern Liaoning Province, northeast China, we investigated temperature and light intensity within secondary forest gaps, and the survival and growth of Juglans mandshurica seedlings after a low-temperature event in the spring of 2014. Damage to seedlings due to low temperature significantly varied in different aspects. Seedlings in gaps on southeast-facing slopes were the most seriously damaged, followed by those in gaps on northeast-facing slopes. In contrast, seedlings in west-facing gaps and in control plots without slope aspect were not damaged. The freezing injury index for seedlings was negatively correlated with minimum temperature (r = ? 0.608, P < 0.01), but it was positively correlated with light intensity (r = 0.818, P < 0.01). In addition, height and root collar diameter of damaged seedlings were significantly lower than those of the undamaged seedlings (P < 0.01) during the early growing season (April–July), but no significant difference were observed during the late growing season (July–October) (P > 0.05). The extent of seedling damage was directly related to slope aspect. Low temperature and high light intensity were found to be the dominant factors affecting extent of damage to seedlings on southeast- and northeast-facing slopes.