LIGHT REGIMES BENEATH CLOSED CANOPIES AND TREE-FALL GAPS IN TEMPERATE AND TROPICAL FORESTS
LIGHT REGIMES BENEATH CLOSED CANOPIES AND TREE-FALL GAPS IN TEMPERATE AND TROPICAL FORESTS
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DOI：
10.1139/x90-084
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发表时间：
1990-05-01
影响因子：
2.2
通讯作者：
WHITE, PS
中科院分区：
文献类型：
--
作者：
CANHAM, CD;DENSLOW, JS;WHITE, PS
利用完整森林冠层的鱼眼摄影和通过理想间隙计算光线穿透的模型，比较了五种温带和热带森林的封闭冠层和树木落差下的光线状况。在完整的冠层下，对冠层照片的分析表明，太阳斑可能贡献了37-68%的季节性总光合有效辐射。在所有森林中，潜在日斑持续时间是短暂的（4 ~ 6 min），但由于冠层几何形状和近期扰动历史的不同，潜在日斑持续时间的频率分布有所不同。对照片的分析表明，对于任何森林来说，封闭树冠下光合有效辐射的入射角通常都不是垂直的，但是在站点之间和站点内部，头顶照明和低角度照明的贡献都有相当大的变化。对原始道格拉斯冷杉铁杉林理想单树林隙的透光率计算表明，由于林隙的冠层高度与林隙直径之比较大，林隙对林下光照状况有一定的影响。然而，其他四种森林类型的单树林隙总体上显著增加了林下光照水平。单树林隙内和林隙周围的季节总辐射也存在显著的空间差异。我们的研究结果表明，在林隙附近的林下，特别是在高纬度地区，可能会有大量的光线穿透。随着林隙大小的增大，林隙内的平均光照水平和光照范围都增加，但即使在较大的林隙（约1000 m2）中，直射阳光的潜在持续时间通常也很短（< 4小时）。林隙光照状况的差异主要受冠层高度和纬度的影响。纬度的影响还应导致不同地理范围内不同森林类型的光照制度的差异。
Light regimes beneath closed canopies and tree-fall gaps are compared for five temperate and tropical forests using fish-eye photography of intact forest canopies and a model for calculating light penetration through idealized gaps. Beneath intact canopies, analyses of canopy photographs indicate that sunflecks potentially contribute 37-68% of seasonal total photosynthetically active radiation. In all of the forest, potential sunfleck duration is bried (4-6 min), but the frequency distributions of potential sunfleck duration vary because of differences in canopy geometry and recent disturbance history. Analysis of the photographs reveals that incidence angles for photosynthetically active radiation beneath closed canopies are not generally vertical for any of the forest, but there was considerable variation both among and within sites in the contribution of overhead versus low-angle lighting. Calculations of light penetration through idealized single-tree gaps in old growth Douglas-fir - hemlock forests indicate that such gaps have light effect on understory light regimes because of the high ratio of canopy height to gap diameter. However, single-tree gaps in the other four forest types produce significant overall increases in understory light levels. There is also significant spatial variation in seasonal total radiation in and around single-tree gaps. Our results demonstrate that there can be significant penetration of light into the understory adjacent to a gap, particularly at high latitudes. As gap size increases, both the mean and the range of light levels within the gap increases, but even in large gaps (ca. 1000 m2) the potential duration of direct sunlight is generally brief (< 4 h). The major differences in gap light regimes of the five forests are largely function of canopy height and latitude. The effects of latitude should also result in differences gap light regimes across the geographic range of individual forest types.