Project Summary
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The US Forest Inventory and Analysis program (FIA) uses nationwide maps of tree canopy cover for post-stratification of field plots to reduce the variance of estimates of forest structure variables such as forest area and timber volume at county and state level. Canopy height models (CHM) derived from airborne lidar correlate strongly with many forest structure variables and have been shown to improve stratification, but the low frequency of lidar collection prevents its use for stratification in areas of change. Digital aerial photogrammetry (DAP) is an alternative method of creating CHMs that could be accomplished every 2-3 years with aerial imagery from the US National Agriculture Imagery Program. CHMs derived from DAP could supplement FIA data in areas of non-response and trees-outside-forests and also improve population estimates of forest structure, particularly in areas of change that occur between FIA field collection cycles of 5-10 years. We will evaluate the accuracy of DAP CHMs against lidar CHMs and FIA field measurements of tree height and compare the differences in the precision of post-stratified estimates of forest area, volume, and biomass using strata derived from the nationwide tree canopy cover maps and DAP CHMs. These comparisons will be made for multiple forest types in Colorado in 2019 and 2021 including ponderosa pine, mixed conifer montane forests, subalpine forests, and pinyon-juniper woodlands. A second objective of this work is to compare the ability of using pre- and post-fire lidar and DAP CHMs for calculating the change in forest structure across burn severity levels for the Cameron Peak and East Troublesome fires of 2020. Determining sensitivity of lidar and DAP CHMs to disturbance will aid in developing approaches for FIA data augmentation to support higher accuracy of forest structure estimates between field visits.
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Research Questions
Question 1How does the accuracy of DAP canopy height measurements compare to lidar across forest types at different scales?
Question 2What are the relative efficiencies of post-stratified estimators of forest structure attributes when using DAP and lidar CHMs as stratifying layers?
Question 3What is the sensitivity of two-date DAP change maps to different burn severities?
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Figure 1. Preliminary comparisons of NAIP DAP and airborne lidar across a strip of Colorado forest (non-height normalized so showing elevation of points on the y axis).
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Figure 2. Date of Colorado lidar datasets available for DAP comparisons, and the location of the 2020 wildfires analyzed for two-date DAP sensitivities to change.
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Project Outputs
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Publications
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Spatial Data Products
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Project Team & Funding
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Collaborators
Dr. Karen Schleeweis - USDA Forest Service
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Funding Agency
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