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Forests 2017, 8(6), 212; doi:10.3390/f8060212

Tree Density and Forest Productivity in a Heterogeneous Alpine Environment: Insights from Airborne Laser Scanning and Imaging Spectroscopy

1
Remote Sensing Laboratories (RSL), University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
2
Center for Research and Development of Northern Zagros Forests, Faculty of Natural Resources, University of Kurdistan, 66177-15175 Sanandaj, Iran
*
Author to whom correspondence should be addressed.
Academic Editors: Christian Ginzler and Lars T. Waser
Received: 8 March 2017 / Revised: 9 June 2017 / Accepted: 9 June 2017 / Published: 16 June 2017
(This article belongs to the Special Issue Optimizing Forest Inventories with Remote Sensing Techniques)
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Abstract

We outline an approach combining airborne laser scanning (ALS) and imaging spectroscopy (IS) to quantify and assess patterns of tree density (TD) and forest productivity (FP) in a protected heterogeneous alpine forest in the Swiss National Park (SNP). We use ALS data and a local maxima (LM) approach to predict TD, as well as IS data (Airborne Prism Experiment—APEX) and an empirical model to estimate FP. We investigate the dependency of TD and FP on site related factors, in particular on surface exposition and elevation. Based on reference data (i.e., 1598 trees measured in 35 field plots), we observed an underestimation of ALS-based TD estimates of 40%. Our results suggest a limited sensitivity of the ALS approach to small trees as well as a dependency of TD estimates on canopy heterogeneity, structure, and species composition. We found a weak to moderate relationship between surface elevation and TD (R2 = 0.18–0.69) and a less pronounced trend with FP (R2 = 0.0–0.56), suggesting that both variables depend on gradients of resource availability. Further to the limitations faced in the sensitivity of the applied approaches, we conclude that the combined application of ALS and IS data was convenient for estimating tree density and mapping FP in north-facing forested areas, however, the accuracy was lower in south-facing forested areas covered with multi-stemmed trees. View Full-Text
Keywords: tree density; forest productivity; airborne laser scanning; Airborne Prism Experiment (APEX); local maxima approach; Swiss National Park tree density; forest productivity; airborne laser scanning; Airborne Prism Experiment (APEX); local maxima approach; Swiss National Park
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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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MDPI and ACS Style

Fatehi, P.; Damm, A.; Leiterer, R.; Pir Bavaghar, M.; Schaepman, M.E.; Kneubühler, M. Tree Density and Forest Productivity in a Heterogeneous Alpine Environment: Insights from Airborne Laser Scanning and Imaging Spectroscopy. Forests 2017, 8, 212.

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