North America Holocene land cover: REVEALS-GMRF

As a contribution to the Past Global Changes (PAGES) LandCover6k Working
Group, we present a new suite of land cover reconstructions with
uncertainty for North America, based on a network of 1445 sedimentary
pollen records and the REVEALS pollen-vegetation model coupled with a
Bayesian spatial model. These spatially comprehensive land cover maps are
then used to determine the pattern and magnitude of North American land
cover changes at continental to regional scales. These Holocene
reconstructions for North America, along with similar LandCover6k products
now available for other continents, serve the Earth system modeling
community by providing better-constrained land cover scenarios and
benchmarks for model evaluation, ultimately making it possible to better
understand the regional- to global-scale processes driving Holocene
land-cover, carbon-cycle, and climate dynamics. Pollen-based land cover
reconstructions were performed using the REVEALS pollen-vegetation model,
and based on the standard protocol for PAGES LandCover6k.   We
reconstructed land cover for 25 time intervals that cover the Holocene.
These time intervals were defined according to the LandCover6k working
group protocol. Time intervals are specified in kiloyears before present
(ka), where present is defined as 1950 CE, but for time intervals
<1ka we also note the Common Era (CE) timescale. Intervals in the
period from 11.7 to 0.7 ka have a 500-year temporal grain (11.7 to 11.2
ka; 11.2 to 10.7 ka; etc.), while the three most recent intervals have a
finer temporal grain (0.7-0.35 ka [1250-1600 CE]: 350 years; 0.35-0.1 ka
[1600-1850 CE]: 250 years; 0.1-(-0.074) ka: 174 years [1850-2024 CE]) in
order to better capture the changes associated with intensifying
anthropogenic land use over the last five centuries. We used a grid
resolution of 1°x1°, also as specified by the LandCover6k protocol. Within
a grid cell, REVEALS reconstructions for multiple sites were averaged, as
is standard practice. Taxon-level reconstructions were aggregated to three
land cover categories: summergreen trees and shrubs (STS), evergreen trees
and shrubs (ETS), and open vegetation/land (OVL), which includes grasses,
herbs, and low-stature shrubs. We use the REVEALS-GMRF Bayesian
hierarchical model to spatially interpolate the REVEALS-based
land cover reconstructions.