Landsat-based detection of mast events in white spruce (Picea glauca) forests
Landsat-based detection of mast events in white spruce (Picea glauca) forests
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DOI：
10.1016/j.rse.2020.112278
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发表时间：
2021-03
影响因子：
13.5
通讯作者：
Matthew Garcia;B. Zuckerberg;J. M. LaMontagne;P. Townsend
中科院分区：
文献类型：
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作者：
Matthew Garcia;B. Zuckerberg;J. M. LaMontagne;P. Townsend
针叶树杆播具有空间同步和时间变化的特点。大型桅杆播种事件（称为“桅杆年”）可以是一种视觉上令人惊叹的生态重要现象，支持营养相互作用和种子捕食者的生存以及森林再生。记录桅杆播种的模式通常是劳动密集型的，需要在长时间内在一致和广泛的地点重复视觉锥计数，以量化锥生产的时空变异性。本研究的目的是评估Landsat多光谱植被指数（VIs）与加拿大育空Kluane地区白云杉（Picea glauca）森林桅杆播种地面观测数据的对应关系。考虑到白云杉杆状种子的视觉特征，我们测试了：1)光合取向和颜色取向的VIs能否识别杆状年夏末和秋季云杉球果的衰老；2)水分取向的VIs能否区分球果在衰老期间和种子释放后与周围云杉冠层植被的明显干燥。我们假设云杉林后期VI下降的斜率与树冠有关（即树冠年VI下降幅度较大）。利用广义线性混合效应模型（GLMM），我们比较了超过100个站点年的桅杆/非桅杆观测组合，建立了基于vi的回归模型。我们发现，利用水分导向VIs识别丰年取得了一些成功，而利用光合作用和颜色导向VIs的模型不受数据支持。然而，我们发现包含两个类别的多个vi的模型比任何单一vi模型更成功，准确地预测了现场观测的16个桅杆事件中的4个。我们提供了令人信服的证据，桅杆播种模式可以检测使用湿度导向的陆地卫星观测在大针叶林地区。需要进一步的工作来区分桅杆事件的信号与混杂干扰相关的影响，并区分可归因于桅杆生产力的VI信号变化与气候变率对反射率的影响。
Mast seeding in conifers is characterized by the spatially synchronous and temporally variable production of seed cone crops. Large mast seeding events (known as “mast years”) can be a visually stunning and ecologically important phenomenon, supporting trophic interactions and survival of seed predators as well as forest regeneration. Documenting patterns in mast seeding is generally labor-intensive, requiring repeated visual cone counts at consistent and widespread locations over long periods to quantify the spatiotemporal variability of cone production. Our goal in this work was to evaluate the correspondence of multispectral vegetation indexes (VIs) from Landsat with ground-based observations of mast seeding in white spruce (Picea glauca) forests of the Kluane region, Yukon, Canada. Given the visual characteristics of mast seeding in white spruce, we tested: 1) whether photosynthesis- and color-oriented VIs can identify senescence of spruce cones in late summer and autumn during mast years, and 2) if moisture-oriented VIs can distinguish the significant drying of seed cones from the surrounding spruce canopy vegetation during that senescence and after seeds are released. We hypothesized that the slope of late season decline in VIs in spruce forests would be related to masting (i.e., greater decline in VI during mast years). Using generalized linear mixed-effects modeling (GLMM), we compared more than 100 site-year combinations of mast/non-mast observations to develop VI-based regressions. We found some success identifying mast years with moisture-oriented VIs, while models using the photosynthesis- and color-oriented VIs were not supported, given the data. However, we found that models containing multiple VIs from both categories were more successful than any single-VI model, accurately predicting four of sixteen mast events in site observations. We provide compelling evidence that mast-seeding patterns may be detectable using moisture-oriented Landsat observations over large coniferous forest areas. Additional work is warranted to distinguish the signal for mast events from confounding disturbance-related effects and to differentiate variation in VI signals attributable to masting productivity in contrast to effects of climatological variability on reflectance.