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Tropical forest light regimes in a human‐modified landscape

机译:人工改造景观中的热带森林光照制度

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摘要

Light is the key energy input for all vegetated systems. Forest light regimes are complex, with the vertical pattern of light within canopies influenced by forest structure. Human disturbances in tropical forests impact forest structure and hence may influence the light environment and thus competitiveness of different trees. In this study, we measured vertical diffuse light profiles along a gradient of anthropogenic disturbance, sampling intact, logged, secondary, and fragmented sites in the biodiversity hot spot of the Atlantic forest, southeast Brazil, using photosynthetically active radiation sensors and a novel approach with estimations of vertical light profiles from hemispherical photographs. Our results show clear differences in vertical light profiles with disturbance: Fragmented forests are characterized by rapid light extinction within their low canopies, while the profiles in logged forests show high heterogeneity and high light in the mid‐canopy despite decades of recovery. The secondary forest showed similar light profiles to intact forest, but with a lower canopy height. We also show that in some cases the upper canopy layer and heavy liana infestations can severely limit light penetration. Light extinction with height above the ground and depth below the canopy top was highest in fragmented forest and negatively correlated with canopy height. The novel, inexpensive, and rapid methods described here can be applied to other sites to quantify rarely measured vertical light profiles.
机译:光是所有植被系统的关键能量输入。森林的光照制度很复杂,冠层内部的垂直光分布受到森林结构的影响。热带森林中的人为干扰会影响森林结构,因此可能会影响光照环境,从而影响不同树木的竞争力。在这项研究中,我们使用光合有效辐射传感器和一种新颖的方法,沿着人为扰动的梯度测量了垂直漫射光分布,在巴西东南部大西洋森林的生物多样性热点中采样了完整的,记录的,次要的和零散的站点从半球照片估计垂直光分布。我们的结果表明,垂直光分布在受到干扰的情况下存在明显差异:零散的森林的特征是低矮冠层内的快速灭光,而采伐森林的轮廓在恢复数十年后仍表现出较高的异质性和中冠高光。次生林的光分布与完整林相似,但树冠高度较低。我们还表明,在某些情况下,上层冠层和严重的藤本植物侵扰会严重限制光的穿透。在零散的森林中,海拔高度高于地面且冠层顶部以下的深度的光消光最高,并且与冠层高度呈负相关。此处描述的新颖,廉价,快速的方法可以应用于其他位置,以量化很少测量的垂直光分布。

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