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Using satellite image data to estimate aboveground shelterbelt carbon stocks across an agricultural landscape

Czerepowicz, L., Case, B.S., Doscher, C.
Agriculture, ecosystems & environment 2012 v.156 pp. 142-150
aboveground biomass, agroforestry, carbon, carbon sequestration, carbon sinks, computer software, conifers, ecosystem services, equations, grasslands, image analysis, landscapes, models, regression analysis, satellites, shelterbelts, trees, variance, New Zealand
Shelterbelts are prominent features of agroforestry systems that provide a range of ecosystem services, including the sequestration of carbon (C). However, shelterbelts are not easily characterized in a spatially explicit manner, and carbon accounting methods for shelterbelts are lacking. A study was conducted for a 48km² agricultural area on the Canterbury Plains, New Zealand, to investigate an approach that uses remotely sensed data to provide a good first-approximation of aboveground biomass (AGB) and C quantities in coniferous shelterbelts on an area basis. First, shelterbelts were delineated for a pan-sharpened QuickBird II image (0.6m resolution) using Feature Analyst, a feature extraction software. This method correctly extracted 73% of conifer shelterbelt area across the image, and estimated that these shelterbelts comprised 2.5% of the study area. Second, AGB was estimated for trees in 96 field-sampled conifer shelterbelts using a published allometric equation and then scaled up to obtain total shelterbelt AGB estimates. Third, a regression model was developed for predicting shelterbelt AGB based on spatial and spectral attributes extracted for field-sampled shelterbelts. This model explained 71% of the variance in shelterbelt AGB based on two significant predictors: shelterbelt area and red band mean. Lastly, this model was then applied to shelterbelts identified with Feature Analyst to produce a map of estimated shelterbelt C density across the study area. Results suggest that conifer shelterbelts represent a small, yet significant carbon reservoir on the Canterbury Plains, sequestering on average 237±77tCha⁻¹ of shelterbelt. As such, conifer shelterbelts contribute up to an additional 6tCha⁻¹ to the ‘grassland with woody biomass’ carbon pool in New Zealand, which is currently estimated at 29tha⁻¹. With improvements, these methods have the potential to be used to quantify shelterbelt carbon across New Zealand and other countries with significant shelterbelt resources.