Context

Though people have used fire to alter landscapes across North America for millennia, there remains a debate whether Native Americans altered California’s mountainous forests to create an anthropogenic landscape.

Objective

We use paleoecological reconstructions and paleolandscape modeling to test whether climate or Native Americans were the driving force of pre-historic forest composition change. Understanding pre-historic forests and land-use legacies becomes more critical in a warming climate as wildfires become deadlier and more extensive.

Methods

We performed a sub-centennial pollen and charcoal reconstruction for the last 1200 years using standard techniques. We then used a forest succession model to quantitatively test drivers of change: climatic fires only, or the addition of Native American-set surface fires. Hypothesized periods of anthropogenic burning were inferred from the pollen record (more open canopy taxa than climatically expected). Modeled outputs were compared against the paleorecord to determine which drivers best explained changes in the empirical record. Periods of occupation from the archaeological record were compared to hypothesized periods of burning.

Results

Pollen and charcoal reconstructions showed intermittent periods inconsistent with climatic expectations. Modeled scenarios including surface fires set by Native Californians during these periods had the greatest correlation with the observed paleoecological record. Inferred periods of burning corresponded temporally with site used based on the archaeological record.

Conclusions

California’s pre-historic forests were altered by the traditional use of fire as a tool by Native Americans. Modeled outputs hint that incorporating indigenous resources management practices could improve forest health and decrease the likelihood of catastrophic wildfires.