Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations

<p>Recently, remotely sensed measurements of the near-infrared reflectance (NIRv) of vegetation, the fluorescence correction vegetation index (FCVI), and radiance (NIRvrad) of vegetation have emerged as indicators of vegetation structure and function with potential to enhance or improve upon c...

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Autores principales:	T. Merrick, S. Pau, M. Detto, E. N. Broadbent, S. A. Bohlman, C. J. Still, A. M. Almeyda Zambrano
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/5bf07e4cca8c496d9e0a7c652712c525
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spelling	oai:doaj.org-article:5bf07e4cca8c496d9e0a7c652712c5252021-11-25T12:41:12ZUnveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations10.5194/bg-18-6077-20211726-41701726-4189https://doaj.org/article/5bf07e4cca8c496d9e0a7c652712c5252021-11-01T00:00:00Zhttps://bg.copernicus.org/articles/18/6077/2021/bg-18-6077-2021.pdfhttps://doaj.org/toc/1726-4170https://doaj.org/toc/1726-4189<p>Recently, remotely sensed measurements of the near-infrared reflectance (NIRv) of vegetation, the fluorescence correction vegetation index (FCVI), and radiance (NIRvrad) of vegetation have emerged as indicators of vegetation structure and function with potential to enhance or improve upon commonly used indicators, such as the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI). The applicability of these remotely sensed indices to tropical forests, key ecosystems for global carbon cycling and biodiversity, has been limited. In particular, fine-scale spatial and temporal heterogeneity of structure and physiology may contribute to variation in these indices and the properties that are presumed to be tracked by them, such as gross primary productivity (GPP) and absorbed photosynthetically active radiation (APAR). In this study, fine-scale (approx. 15 cm) tropical forest heterogeneity represented by NIRv, FCVI, and NIRvrad and by lidar-derived height is investigated and compared to NIRv and EVI using unoccupied aerial system (UAS)-based hyperspectral and lidar sensors. By exploiting near-infrared signals, NIRv, FCVI, and NIRvrad captured the greatest spatiotemporal variability, followed by the enhanced vegetation index (EVI) and then the normalized difference vegetation index (NDVI). Wavelet analyses showed the dominant spatial scale of variability of all indicators was driven by tree clusters and larger-than-tree-crown size gaps rather than individual tree crowns. NIRv, FCVI, NIRvrad, and EVI captured variability at smaller spatial scales (<span class="inline-formula">∼</span> 50 m) than NDVI (<span class="inline-formula">∼</span> 90 m) and the lidar-based surface model (<span class="inline-formula">∼</span> 70 m). We show that spatial and temporal patterns of NIRv and FCVI were virtually identical for a dense green canopy, confirming predictions in earlier studies. Furthermore, we show that NIRvrad, which does not require separate irradiance measurements, correlated more strongly with GPP and PAR than did other indicators. NIRv, FCVI, and NIRvrad, which are related to canopy structure and the radiation regime of vegetation canopies, are promising tools to improve understanding of tropical forest canopy structure and function.</p>T. MerrickS. PauM. DettoM. DettoE. N. BroadbentS. A. BohlmanS. A. BohlmanC. J. StillA. M. Almeyda ZambranoCopernicus PublicationsarticleEcologyQH540-549.5LifeQH501-531GeologyQE1-996.5ENBiogeosciences, Vol 18, Pp 6077-6091 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
spellingShingle	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 T. Merrick S. Pau M. Detto M. Detto E. N. Broadbent S. A. Bohlman S. A. Bohlman C. J. Still A. M. Almeyda Zambrano Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
description	<p>Recently, remotely sensed measurements of the near-infrared reflectance (NIRv) of vegetation, the fluorescence correction vegetation index (FCVI), and radiance (NIRvrad) of vegetation have emerged as indicators of vegetation structure and function with potential to enhance or improve upon commonly used indicators, such as the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI). The applicability of these remotely sensed indices to tropical forests, key ecosystems for global carbon cycling and biodiversity, has been limited. In particular, fine-scale spatial and temporal heterogeneity of structure and physiology may contribute to variation in these indices and the properties that are presumed to be tracked by them, such as gross primary productivity (GPP) and absorbed photosynthetically active radiation (APAR). In this study, fine-scale (approx. 15 cm) tropical forest heterogeneity represented by NIRv, FCVI, and NIRvrad and by lidar-derived height is investigated and compared to NIRv and EVI using unoccupied aerial system (UAS)-based hyperspectral and lidar sensors. By exploiting near-infrared signals, NIRv, FCVI, and NIRvrad captured the greatest spatiotemporal variability, followed by the enhanced vegetation index (EVI) and then the normalized difference vegetation index (NDVI). Wavelet analyses showed the dominant spatial scale of variability of all indicators was driven by tree clusters and larger-than-tree-crown size gaps rather than individual tree crowns. NIRv, FCVI, NIRvrad, and EVI captured variability at smaller spatial scales (<span class="inline-formula">∼</span> 50 m) than NDVI (<span class="inline-formula">∼</span> 90 m) and the lidar-based surface model (<span class="inline-formula">∼</span> 70 m). We show that spatial and temporal patterns of NIRv and FCVI were virtually identical for a dense green canopy, confirming predictions in earlier studies. Furthermore, we show that NIRvrad, which does not require separate irradiance measurements, correlated more strongly with GPP and PAR than did other indicators. NIRv, FCVI, and NIRvrad, which are related to canopy structure and the radiation regime of vegetation canopies, are promising tools to improve understanding of tropical forest canopy structure and function.</p>
format	article
author	T. Merrick S. Pau M. Detto M. Detto E. N. Broadbent S. A. Bohlman S. A. Bohlman C. J. Still A. M. Almeyda Zambrano
author_facet	T. Merrick S. Pau M. Detto M. Detto E. N. Broadbent S. A. Bohlman S. A. Bohlman C. J. Still A. M. Almeyda Zambrano
author_sort	T. Merrick
title	Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
title_short	Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
title_full	Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
title_fullStr	Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
title_full_unstemmed	Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations
title_sort	unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution nirv, fcvi, and nirvrad from uas observations
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/5bf07e4cca8c496d9e0a7c652712c525
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Unveiling spatial and temporal heterogeneity of a tropical forest canopy using high-resolution NIRv, FCVI, and NIRvrad from UAS observations

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