Characterizing Canopy Openness Across Large Forested Landscapes Using Spherical Densiometer and Smartphone Hemispherical Photography
Characterizing Canopy Openness Across Large Forested Landscapes Using Spherical Densiometer and Smartphone Hemispherical Photography
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DOI：
10.1093/jofore/fvab046
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发表时间：
2021-08
影响因子：
2.3
通讯作者：
Katie L Beeles;J. Tourville;M. Dovciak
中科院分区：
文献类型：
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作者：
Katie L Beeles;J. Tourville;M. Dovciak
林冠开放度是与林下光环境和生产力相关的重要森林特征。尽管存在许多方法来估计树冠开放度，但它们的性能比较往往集中在相对狭窄的树冠条件和森林类型范围内。为了解决这一差距，我们比较了两种流行的估算树冠开放度的方法，即传统的球形密度计和现代智能手机半球形摄影，涵盖了美国东北部四个州的各种树冠条件（从封闭的树冠到大间隙）和森林类型（从低海拔阔叶林到高海拔针叶林）。我们进行了 988 次田间冠层开放度测量（每个仪器 494 次），并使用线性回归和 t 检验在冠层条件下进行比较。广泛的重复使我们能够量化方法之间的差异，否则这些差异可能会被忽视。相对于密度计，无论森林类型如何，智能手机摄影都会高估低树冠开放度（10％）。我们比较了美国东北部大范围森林结构测量树冠开放度的两种流行方法（智能手机半球形摄影和球形密度计）。我们发现，如果仔细应用，传统的球形密度计可以像现代智能手机冠层摄影一样有效地表征不同冠层条件（包括封闭冠层）的冠层开放度。尽管智能手机摄影减少了现场测量时间和复杂性，但它比密度计更容易受到天气的影响。尽管正确方法的选择取决于研究目标，但我们为这两种跨不同冠层的流行方法提供了校准。
Canopy openness is an important forest characteristic related to understory light environment and productivity. Although many methods exist to estimate canopy openness, comparisons of their performance tend to focus on relatively narrow ranges of canopy conditions and forest types. To address this gap, we compared two popular approaches for estimating canopy openness, traditional spherical densiometer and modern smartphone hemispherical photography, across a large range of canopy conditions (from closed canopy to large gaps) and forest types (from low-elevation broadleaf to high-elevation conifer forests) across four states in the northeastern United States. We took 988 field canopy openness measurements (494 per instrument) and compared them across canopy conditions using linear regression and t-tests. The extensive replication allowed us to quantify differences between the methods that may otherwise go unnoticed. Relative to the densiometer, smartphone photography overestimated low canopy openness (10%), regardless of forest type. We compared two popular ways of measuring canopy openness (smartphone hemispherical photography and spherical densiometer) across a large range of forest structures encountered in the northeastern United States. We found that, when carefully applied, the traditional spherical densiometer can characterize canopy openness across diverse canopy conditions (including closed canopies) as effectively as modern smartphone canopy photography. Although smartphone photography reduced field measurement time and complexity, it was more susceptible to weather than the densiometer. Although selection of the right method depends on study objectives, we provide a calibration for these two popular methods across diverse canopies.