辽东山区次生林不同大小林窗光照特征比较

以辽东山区天然次生林中3种不同大小林窗(G₁，670 m²;G₂，290 m²和G₃，90 m²)为对象，通过对林窗内光强进行连续观测，比较光量子通量密度(PPFD)的时空分布.结果表明：3种林窗的PPFD日变化均呈现北高南低，且面积越大，PPFD高值区范围越广，异质性越明显;3种林窗的PPFD月变化规律为：林窗内各方位PPFD最大值集中在生长季初期(4—5月)，最小值出现的月份则有所差异;3种林窗东部和西部的PPFD出现极值的时间基本一致，且春季光强均明显高于夏、秋季(P<0.05);G₁、G₂、G₃中心点的月平均PPFD分别占全光照的66.59%、49.05%和30.37%，在生长旺盛期，中心点光强分别是林内的37.8倍、27.9倍和10.3倍.受林窗面积不同，以及地形、边缘木高度(林窗形状)等因素的影响，不同大小林窗接收的光强及其分布格局不同，这是导致林窗内更新格局、物种组成发生变化的关键因素.

Comparison of light characteristics in different size gaps in eastern Liaoning montane secondary forests.

With three different size gaps (G₁, 670 m²; G₂, 290 m²; and G₃, 90 m²) in eastern Liaoning montane secondary forests of China as test objects, and through a continuous measurement of light intensity, the spatiotemporal distribution of photosynthetic photon flux density (PPFD) in the gaps was compared. The results showed that the diurnal variation of PPFD in the gaps was greater at northern than at southern position. The larger the forest gap, the broader the higher PPFD value area, and the more obvious the heterogeneity. As for the monthly variation of PPFD, the maximum PPFD at each position of the gaps appeared at the beginning of growth season (i.e., in April and May), while the minimum PPFD occurred in different months. The maximum PPFD at the eastern and western positions of each gap was basically appeared in the same months, and the PPFD was significantly higher in spring than in summer and autumn (P<0.05). The mean monthly PPFD at the centers of G₁, G₂, and G₃ was 66.59%, 49.05%, and 30.37% of full sunlight, respectively, and in growth season, the PPFD at gap center was 37.8, 27.9 and 10.3 times higher than that at understory. It was suggested that owing to the different size and shape of forest gap and the effects of landform, the light intensity and its distribution in forest gap were different, being the key factors leading to the heterogeneity of regeneration pattern and the variation of species composition in forest gap.