Estimation of biomass change in montane forests in Norway along a 1200 km latitudinal gradient using airborne laser scanning: a comparison of direct and indirect prediction of change under a model-based inferential approach

Abstract

ABSTRACTThe current study compared two approaches for estimating change of aboveground biomass (AGB) in montane forests in Norway using field- and remotely sensed data from airborne laser scanning (ALS) from two points in time (four-year interval). The first was an indirect method that involved modeling and prediction of AGB at two points in time using ALS metrics as predictors, estimating the change from differences between AGB predictions. The second was a direct method, where change was modeled and predicted directly using differences between corresponding ALS metrics derived at the two measurement occasions as predictors, and the estimate was based on the predicted differences. Both methods were applied over a 1500 km long and 250 m wide transect from south to north in Norway comprising 250 m2 grid cells. The results showed that the indirect method was more precise than the direct method. The indirect method estimated 0.65 Mg ha−1 change in AGB over the observation period, with a corresponding 95% confidence interval of ±0.27 Mg ha−1. The corresponding figures for the direct method was 0.54 and ±0.51 Mg ha−1. The direct method has been recommended previously. We conclude that the indirect method is both more precise and versatile.