Abstract
AbstractImproving the accuracy of carbon accounting in terrestrial ecosystems is critical for understanding carbon fluxes associated with land cover change, with significant implications for global carbon cycling and climate change. Semi‐arid ecosystems account for an estimated 45% of global terrestrial ecosystem area and are in many locations experiencing high degrees of degradation. However, aboveground carbon accounting has largely focused on tropical and forested ecosystems, while drylands have been relatively neglected. Here, we used a combination of field estimates, remotely sensed data, and existing land cover maps to create a spatially explicit estimate of aboveground carbon storage within the Great Basin, a semi‐arid region of the western United States encompassing 643,500 km2 of shrubland and woodland vegetation. We classified the region into seven distinct land cover categories: pinyon‐juniper woodland, sagebrush steppe, salt desert shrub, low sagebrush, forest, non‐forest, and other/excluded, each with an associated carbon estimate. Aboveground carbon estimates for pinyon‐juniper woodland were continuous values based on tree canopy cover. Carbon estimates for other land cover categories were based on a mean value for the land cover type. The Great Basin ecosystems contain an estimated 295.4 Tg in aboveground carbon, which is almost double the previous estimates that only accounted for forested ecosystems in the same area. Aboveground carbon was disproportionately stored in pinyon‐juniper woodland (43.7% carbon, 16.9% land area), while the shrubland systems accounted for roughly half of the total land area (49.1%) and one‐third of the total carbon. Our results emphasize the importance of distinguishing and accounting for the distinctive contributions of shrubland and woodland ecosystems when creating carbon storage estimates for dryland regions.
Highlights
Quantifying aboveground carbon stored in ecosystems is a critical component of understanding overall carbon storage and measuring carbon fluxes associated with land cover change (Houghton 2007)
Pinyon-juniper woodlands have the potential to contribute a significant amount of aboveground carbon storage (Huang et al 2009); carbon storage in woodlands is directly related to tree cover and can be highly variable in these ecosystems, even over short distances (Rau et al 2012)
One-third (~32%) of the Great Basin was excluded from carbon accounting because it was classified as agricultural, introduced grass, barren, developed, or water, which should account for very little aboveground carbon (Fig. 2)
Summary
Quantifying aboveground carbon stored in ecosystems is a critical component of understanding overall carbon storage and measuring carbon fluxes associated with land cover change (Houghton 2007). In North America, semi-arid systems account for roughly 17% of the total land area (Lal 2004), but the amount of carbon stored in these woodland and shrubland ecosystems has not previously been quantified. The Great Basin is a semi-arid region of western North America with ecosystems ranging from sparsely vegetated salt desert shrubland (Atriplex spp.) to sagebrush steppe (Artemisia spp.) and pinyon-juniper woodlands (Pinus spp., Juniperus spp.). While mapping carbon storage in pinyon-juniper woodlands using remote sensing rather than field population estimates can provide the combined benefits of high spatial detail and regionalscale estimates (Chojnacky et al 2012), most remote sensing-based studies of carbon in the Great Basin have focused on estimating expansion rates of pinyon-juniper woodlands over relatively small areas (Sankey and Germino 2008, Strand et al 2008, Huang et al 2009). Creating a spatially explicit baseline estimate of aboveground carbon storage in this region is critical for future carbon management
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