Canadian Forest Service Publications

Using TLS-measured tree attributes to estimate aboveground biomass in small black spruce trees. 2021. Wagers, S.; Castilla, G.; Filiatrault, M.; Sanchev-Azofeifa, G. A. Forests 12(11):1521.

Year: 2021

Issued by: Northern Forestry Centre

Catalog ID: 40859

Language: English

Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.3390/f12111521

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Research Highlights: This study advances the effort to accurately estimate the biomass of trees in peatlands, which cover 13% of Canada’s land surface. Background and Objectives: Trees remove carbon from the atmosphere and store it as biomass. Terrestrial laser scanning (TLS) has become a useful tool for modelling forest structure and estimating the above ground biomass (AGB) of trees. Allometric equations are often used to estimate individual tree AGB as a function of height and diameter at breast height (DBH), but these variables can often be laborious to measure using traditional methods. The main objective of this study was to develop allometric equations using TLS-measured variables and compare their accuracy with that of other widely used equations that rely on DBH. Materials and Methods: The study focusses on small black spruce trees ( < 5 m) located in peatland ecosystems of the Taiga Plains Ecozone in the Northwest Territories, Canada. Black spruce growing in peatlands are often stunted when compared to upland black spruce and having models specific to them would allow for more precise biomass estimates. One hundred small trees were destructively sampled from 10 plots and the dry weight of each tree was measured in the lab. With this reference data, we fitted biomass models specific to peatland black spruce using DBH, crown diameter, crown area, height, tree volume, and bounding box volume as predictors. Results: Our best models had crown size and height as predictors and outperformed established AGB equations that rely on DBH. Conclusions: Our equations are based on predictors that can be measured from above, and therefore they may enable the plotless creation of accurate biomass reference data for a prominent tree species in a common ecosystem (treed peatlands) in North America’s boreal.

Plain Language Summary

Black spruce peatlands are a common feature of Canada’s boreal forest. The trees are often smaller than in upland forest, because soils are waterlogged and the trees hang on little mounds or hummocks, stunting their growth. The biomass (dry weight) of these trees is important because it relates closely to the carbon stored in them. Biomass is often estimated using published equations based on the tree’s height and trunk diameter. These equations are usually fitted using commercially sized trees, and may not work as well for small trees. In this study, we developed biomass equations specific to peatland black spruce. We used a terrestrial laser scanner (TLS) to create digital replicas of small circular plots where we measured different tree attributes for our equations and compared their estimates with the lab-measured biomass of nearly 100 trees harvested from those plots. Our best equation performed better than those currently used by the National Forest Inventory. Instead of trunk diameter, it uses crown area, which has the potential to be measured using laser scanners mounted on drones or airplanes. Hence, this study lays out the groundwork for accurately estimating biomass in black spruce peatlands without setting foot in the peatlands themselves.