辽东山区次生林林窗内秋季最低温度的时空分布特征

Spatiotemporal distribution of minimum temperature during autumn at different slope aspects of secondary forest gap in montane zone of eastern Liaoning Province

为探讨辽东山区次生林林窗内早霜冻的变化规律,对秋季不同坡向林窗内最低温度的时空变化特征进行了研究。结果表明,3个不同坡向林窗内的最低气温存在极显著差异(P<0.01),9月以东北坡最高(-4.61℃),10月以西北坡为最高(-7.24℃);土壤下层5 cm深处最低温度在各坡向林窗间差异不显著(P>0.05),9月和10月的最低值分别出现在西北坡(4.87℃)和东南坡(2.05℃)林窗内。各林窗内最低气温和5 cm深处土壤最低温度的空间分布总体表现为不对称性的随时间动态变化,且高值区均出现在林窗边缘。秋季前期(9月28日之前),东北坡和西北坡林窗内的最低气温要高于东南坡,后期则以西北坡最高,东北坡最低;各坡向均第一次降低到0℃以下,且坡向间两两温度差值大于前期。与最低气温相比,土壤下层5 cm深处最低温度明显偏高,变化幅度也小,但其逐日变化规律与最低气温相同。由此说明,不同坡向林窗内最低温度的位置、强度随时间不同而存在差异,从而构成了区域内因低温霜冻造成的受害程度的不同,最终影响到森林的更新。

Aiming to determine the change pattern of early frost in gaps of secondary forest ecosystem in montane zone of eastern Liaoning Province,the spatiotemporal distribution characteristics of the minimum temperature in forest gaps during autumn at different slope aspects were analyzed in this study. The results showed that there was a significant difference in the minimum temperature among gaps at three slopes（ P〈0.01）. The highest values of minimum temperature occurred at the northeast slope in September（- 4. 61 ℃） and the highest values occurred at the northwest slope in October（-7.24 ℃）. No significant difference was found in the minimum soil temperature at 5 cm depth among gaps at the three slopes（ P〉0.05）. The lowest values of minimum soil temperature in September and October occurred in the northwest（ 4.87 ℃） and southeast（ 2.05 ℃） slope gaps,respectively. The spatial distribution of minimum air temperature in gaps and minimum soil temperature at 5 cm depth varied asymmetrically with time,and the highvalue area existed at the gap edge. In early autumn（ before 28 September）,the minimum air temperature of the northwest slope and the northeast slope within gaps were higher than that of the southeast slope. In late autumn,however,the minimum air temperature of the northwest slopewas the highest,and that of the northeast slope was the lowest. In addition,the air temperatures within gaps fell below 0 ℃ just after the early autumn,and the differences of the air temperature between different slope aspects were greater than those in the early autumn. Compared with the minimum air temperature,the minimum soil temperature was much higher,with smaller fluctuation,but their daily variation was similar. All these results indicated that the minimum air and soil temperatures within gaps varied with slope aspects,positions within gaps and time. The minimum air and soil temperatures influenced the frost dynamics and its level of damage. Thus,better understanding the spatiotemporal distribution of the minimum air and soil temperatures within gaps played a critical role in forest regeneration and succession.