Lidar-derived carbon estimates in encroaching juniper woodlands

Woody encroachment is thought to contribute significantly to the global carbon (C) sink. The global- and continental-scale estimates of this contribution, however, have large uncertainties. The woody encroachment contribution to the C sink needs to be estimated at regional and local scales to address uncertainties as well as to balance restoration activities with greenhouse gas mitigation goals. We present a new technique to estimate aboveground C storage in distinct encroachment phases of juniper woodlands in the South Mountain watershed, southwestern Idaho, USA using 3-dimensional lidar measurements of individual juniper trees. We mapped and measured 2,613 juniper stems in 85 field plots. Lidar-derived juniper tree heights, canopy cover, and density were strongly correlated with field-measurements (R² > 0.84, p < 0.001). The canopies of 60,628 individual juniper trees were identified via a segmentation approach. Aboveground biomass of the trees were then estimated using lidar-derived height and crown area (Adj. R² = 0.76). The mean aboveground woody biomass was 13.53 Mg/ha with a mean aboveground woody C storage of 677 g/m². At a broader scale, this would translate to a total C sink of 32,232 MgC across the juniper woodland distribution of 30 million acres in the USA when assuming a complete shift from sagebrush steppe vegetation to juniper woodlands. This technique could be applied to quantify changes in aboveground C, which in conjunction with estmates of belowground C pools are necessary to understand how woody encroachment alters the C pools and determine whether juniper encroachment leads to a net C sink or source.