Abstract: Aiming to determine the characteristics of gap disturbance in secondary forest ecosystem in a montane area of eastern Liaoning Province, the spatial distribution of photosynthetic photon flux density (PPFD) and air temperature in gaps at two different slope aspects were explored in this study. The selected gaps were formed after trees had been damaged by snow or wind. The results showed that the spatial distribution patterns of PPFD and air temperature were similar on the northeast and southeast slopes, but differing in values. Frorn 8:00—10：00, the highest PPFD existed in the west of gap center (169 μmol·m^-2·s^-1 on northeast slope, 350 μmol·m^-2·s^-1 on southeast slope) and it occurred in the north direction of gap center  (234 μmol·m^-2·s^-1 on northeast slope, 400 μmol·m^-2·s^-1 on southeast slope) between 11:00 and 14:00. However, from 14:00 to 16:00, the highest PPFD occurred in the east direction (74 μmol·m^-2·s^-1 on northeast slope, 56 μmol·m^-2·s^-1 on southeast slope) of the two gaps. There was a significant difference in PPFD between the two gaps at the two slope aspects during various periods (P<0.05). The average air temperature in the two gaps was higher at western points and lower at eastern points between 8:00 and 10:00, but was opposite between 14:00 and 16:00. From 11:00 to 13:00, the average air temperature at northern points was higher than at southern points. The air temperature in the gap of northeast slope was significantly lower than that of southeast slope between 8:00 and 10:00 (P<0.01) and between 11:00 and 13:00 (P<0.01), but significantly higher than that of southeast slope between 14:00 and 16:00 (P<0.01). The results indicated that the heterogeneity of PPFD and air temperature in gaps resulted from differences in slope aspects and positions, playing a critical role in forest regeneration and succession via affecting seed germination, seedling growth as well as species distribution.

Key words: cold resistance, anatomical structure, semilethal low temperature (LT₅₀)