Abstract
Forest aboveground biomass (AGB) is an important variable in assessing carbon stock or ecosystem functioning, as well as for forest management. Among methods of forest AGB estimation laser scanning attracts attention because it allows for detailed measurements of forest structure. Here we evaluated variables that influence forest AGB estimation from airborne laser scanning (ALS), specifically characteristics of ALS inputs and of a derived canopy height model (CHM), and role of allometric equations (local vs. global models) relating tree height, stem diameter (DBH), and crown radius. We used individual tree detection approach and analyzed forest inventory together with ALS data acquired for 11 stream catchments with dominant Norway spruce forest cover in the Czech Republic. Results showed that the ALS input point densities (4–18 pt/m2) did not influence individual tree detection rates. Spatial resolution of the input CHM rasters had a greater impact, resulting in higher detection rates for CHMs with pixel size 0.5 m than 1.0 m for all tree height categories. In total 12 scenarios with different allometric equations for estimating stem DBH from ALS-derived tree height were used in empirical models for AGB estimation. Global DBH models tend to underestimate AGB in young stands and overestimate AGB in mature stands. Using different allometric equations can yield uncertainty in AGB estimates of between 16 and 84 tons per hectare, which in relative values corresponds to between 6% and 37% of the mean AGB per catchment. Therefore, allometric equations (mainly for DBH estimation) should be applied with care and we recommend, if possible, to establish one’s own site-specific models. If that is not feasible, the global allometric models developed here, from a broad variety of spruce forest sites, can be potentially applicable for the Central European region.
Highlights
Forests provide multiple ecosystem services at various spatial scales and constitute an important sink of sequestered atmospheric carbon [1,2]
Forest inventory and airborne laser scanning (ALS) data for this study were collected at 11 small forested stream catchments that are located across the Czech Republic (Figure 2)
This study explored variables influencing estimation of aboveground biomass (AGB) for Norway spruce dominated forests from ALS data
Summary
Forests provide multiple ecosystem services at various spatial scales and constitute an important sink of sequestered atmospheric carbon [1,2]. Carbon stocks are an important input in climate models, and responsible forest management is a way to mitigate the impact of global climate change [3]. Accurate and consistent estimation of AGB can help to reduce current uncertainties regarding carbon fluxes [4,5]. Several methods exist for calculating AGB, these range from destructive methods to satellite-based estimations. Estimation can be improved by combining multiple approaches [6,7]. Forest AGB and carbon stocks have been assessed by measuring tree dimensions in permanent field plots and using allometric equations (e.g., [8,9]).
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