Tree Biomass Equations from Terrestrial LiDAR: A Case Study in Guyana

• Main Authors: Alvaro Lau, Kim Calders, Harm Bartholomeus, Christopher Martius, Pasi Raumonen, Martin Herold, Matheus Vicari, Hansrajie Sukhdeo, Jeremy Singh, Rosa C. Goodman
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Forests
• Subjects: 3D tree modelling; aboveground biomass estimation; destructive sampling; Guyana; LiDAR; local tree allometry; model evaluation; quantitative structural model
• Online Access: https://www.mdpi.com/1999-4907/10/6/527

Large uncertainties in tree and forest carbon estimates weaken national efforts to accurately estimate aboveground biomass (AGB) for their national monitoring, measurement, reporting and verification system. Allometric equations to estimate biomass have improved, but remain limited. They rely on destructive sampling; large trees are under-represented in the data used to create them; and they cannot always be applied to different regions. These factors lead to uncertainties and systematic errors in biomass estimations. We developed allometric models to estimate tree AGB in Guyana. These models were based on tree attributes (diameter, height, crown diameter) obtained from terrestrial laser scanning (TLS) point clouds from 72 tropical trees and wood density. We validated our methods and models with data from 26 additional destructively harvested trees. We found that our best TLS-derived allometric models included crown diameter, provided more accurate AGB estimates (<inline-formula> <math display="inline"> <semantics> <msup> <mi>R</mi> <mn>2</mn> </msup> </semantics> </math> </inline-formula> = 0.92–0.93) than traditional pantropical models (<inline-formula> <math display="inline"> <semantics> <msup> <mi>R</mi> <mn>2</mn> </msup> </semantics> </math> </inline-formula> = 0.85–0.89), and were especially accurate for large trees (diameter &gt; 70 cm). The assessed pantropical models underestimated AGB by 4 to 13%. Nevertheless, one pantropical model (Chave et al. 2005 without height) consistently performed best among the pantropical models tested (<inline-formula> <math display="inline"> <semantics> <msup> <mi>R</mi> <mn>2</mn> </msup> </semantics> </math> </inline-formula> = 0.89) and predicted AGB accurately across all size classes—which but for this could not be known without destructive or TLS-derived validation data. Our methods also demonstrate that tree height is difficult to measure in situ, and the inclusion of height in allometric models consistently worsened AGB estimates. We determined that TLS-derived AGB estimates were unbiased. Our approach advances methods to be able to develop, test, and choose allometric models without the need to harvest trees.