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Remote Sens. 2018, 10(2), 338; https://doi.org/10.3390/rs10020338

Assessing Biodiversity in Boreal Forests with UAV-Based Photogrammetric Point Clouds and Hyperspectral Imaging

1
Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland
2
School of Forest Sciences, University of Eastern Finland, P.O. Box-111, 80101 Joensuu, Finland
3
Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, National Land Survey, Geodeetinrinne 2, 02431 Masala, Finland
4
Canadian Forest Service (Pacific Forestry Centre), Natural Resources Canada, 506 West Burnside Road, Victoria, BC V8Z 1M5, Canada
5
Department of Cartography, São Paulo State University, Roberto Simonsen 305, 19060-900 Presidente Prudente, Brazil
6
Catarinense Federal Institute, Rodovia Duque de Caxias, km 6, s/n, 89240-000 São Francisco do Sul, Brazil
*
Author to whom correspondence should be addressed.
Received: 8 January 2018 / Revised: 13 February 2018 / Accepted: 20 February 2018 / Published: 23 February 2018
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Abstract

Forests are the most diverse terrestrial ecosystems and their biological diversity includes trees, but also other plants, animals, and micro-organisms. One-third of the forested land is in boreal zone; therefore, changes in biological diversity in boreal forests can shape biodiversity, even at global scale. Several forest attributes, including size variability, amount of dead wood, and tree species richness, can be applied in assessing biodiversity of a forest ecosystem. Remote sensing offers complimentary tool for traditional field measurements in mapping and monitoring forest biodiversity. Recent development of small unmanned aerial vehicles (UAVs) enable the detailed characterization of forest ecosystems through providing data with high spatial but also temporal resolution at reasonable costs. The objective here is to deepen the knowledge about assessment of plot-level biodiversity indicators in boreal forests with hyperspectral imagery and photogrammetric point clouds from a UAV. We applied individual tree crown approach (ITC) and semi-individual tree crown approach (semi-ITC) in estimating plot-level biodiversity indicators. Structural metrics from the photogrammetric point clouds were used together with either spectral features or vegetation indices derived from hyperspectral imagery. Biodiversity indicators like the amount of dead wood and species richness were mainly underestimated with UAV-based hyperspectral imagery and photogrammetric point clouds. Indicators of structural variability (i.e., standard deviation in diameter-at-breast height and tree height) were the most accurately estimated biodiversity indicators with relative RMSE between 24.4% and 29.3% with semi-ITC. The largest relative errors occurred for predicting deciduous trees (especially aspen and alder), partly due to their small amount within the study area. Thus, especially the structural diversity was reliably predicted by integrating the three-dimensional and spectral datasets of UAV-based point clouds and hyperspectral imaging, and can therefore be further utilized in ecological studies, such as biodiversity monitoring. View Full-Text
Keywords: UAS; photogrammetry; remote sensing; structural diversity; size variability; dead wood; old growth; tree species; 3D; spectral UAS; photogrammetry; remote sensing; structural diversity; size variability; dead wood; old growth; tree species; 3D; spectral
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Saarinen, N.; Vastaranta, M.; Näsi, R.; Rosnell, T.; Hakala, T.; Honkavaara, E.; Wulder, M.A.; Luoma, V.; Tommaselli, A.M.G.; Imai, N.N.; Ribeiro, E.A.W.; Guimarães, R.B.; Holopainen, M.; Hyyppä, J. Assessing Biodiversity in Boreal Forests with UAV-Based Photogrammetric Point Clouds and Hyperspectral Imaging. Remote Sens. 2018, 10, 338.

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