Funding from this grant has allowed us to document forest dynamics at different spatial scales over three millennia and provide a meaningful benchmark for land managers by indicating the scale of intervention needed to move California forests closer to their long-term historical conditions. This research weaves together paleo-ecological data, archival records, historical evidence, and modern inventories to understand the long-term forest conditions in Six Rivers National Forest, California. Results were used to evaluate the consequences of management activities, namely anthropogenic manipulation of fire and fire suppression, on forest biomass.

In our first publication under this grant, we documented forest structure and composition during the 1880s using public land survey data and compared it to modern forests conditions using FIA data. We found that modern forests have more Douglas-fir and are substantially denser than forests from the 1880s (Figures 1 and 2). The magnitude of change shown by this calculation was considerable: the contemporary forest in Six Rivers contains three times more trees than in the era of Euro-American colonization and a comparable increase in basal area, likely due to twentieth century fire suppression (Knight et al. 2020).

For our second publication, we developed an emerging fossil pollen analysis technique as the first step in quantitative reconstruction of past vegetation biomass (Knight et al. 2021). By modeling the relationship between modern pollen influx and modern biomass (Figure 3), we demonstrated that calibrated pollen influx-biomass relationships provide a robust means to infer changes in past plant biomass.

Lastly, we applied pollen-influx biomass models to 3000 years of pollen influx data, allowing the reconstruction of aboveground biomass in a mixed conifer forest over the late Holocene (publication forthcoming). To quantify the drivers of forest structure we used a mixed method approach, drawing from 1) Indigenous Knowledge concerning local fire histories, 2) paleo-ecological data from sedimentary cores, including dendrochronological analyses of fire scars, and 3) historic land survey and harvest data. Findings show tribal burning practices along with the lightning-based fire regime promoted the long-term stability of forest biomass. For the past three millennia, forest biomass was 100 Mg/ha, compared to over 250 Mg/ha today (Figure 4). Native depopulation after 1800 AD coupled with 20^th century fire suppression likely allowed biomass to increase, culminating in the current landscape: a closed Douglas-fir dominant forest unlike any period in 3000 years. Our findings suggest a large-scale intervention would be needed to return to historic forest biomass levels.

Land Acknowledgement:

This research took place on the ancestral territory of the Karuk and Yurok Tribes in what is now called Six Rivers National Forest, California. Members of these tribes have been living in the Klamath area and acting as stewards of the landscape for millennia, until Euro-American colonization in ~1850. For this work, we collaborated with tribal members, including co-author and paleo-ecologist Dr. Frank K. Lake, as well as the Karuk Tribal Historic Preservation Officer and archeologist Dr. Alex Watts-Tobin and Yurok Tribal Historic Preservation Officer Rosie Clayburn. We believe tribal consultation and engagement is needed to produce scientifically sound interpretations of historical data that concern the legacy of Indigenous people. We thank the Karuk and Yurok Tribes for their generous sharing of sovereign knowledge and permission to obtain ecological information from their traditional lands.

Knight CA, Cogbill CV, Potts MD, Wanket JA, Battles JJ (2020) Settlement-era forest structure and composition in the Klamath Mountains: Reconstructing a historical baseline. Ecosphere 11:e03250.

Knight CA, Baskaran M, Bunting MJ, Champagne C, Potts MD, Wahl DA, Wanket JA, Battles JJ (2021) Linking modern pollen accumulation rates to biomass: Quantitative vegetation reconstruction in the western Klamath Mountains. The Holocene. https://doi.org/10.1177/0959683620988038.

Conferences/Invited talks:

Knight CA, Cogbill CV, Potts MD, Wanket JA, and JJ Battles. 2020. Settlement-era forest structure and composition in the Klamath Mountains: Reconstructing a historical baseline” Presented in summer 2020 at the Ecological Society of America (virtual)

Knight CA, 2020. Historical forest ecology in the Klamath Mountains. Invited talk to California’s Air Resources Board.

Knight CA, Anderson L, Bunting MJ, Champagne M, Crawford JN, Klimaszewski-Patterson A, Knapp EE, Lake FK, Mensing SA, Potts MD, Wahl D, Wanket JA, Watts-Tobin A, Battles JJ. Anthropogenic management explains 3000 years of forest biomass levels in California’s Klamath Mountains. Presenting in April 2021 at the International Association for Landscape Ecology – North America (virtual)