先住民の焼畑がクラマスの森を千年にわたり形成してきた理由(How Indigenous burning shaped the Klamath’s forests for a millennia)

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2022-03-14 カリフォルニア大学バークレー校(UCB)By Kara Manke

科学的データと先住民族の口承歴および生態学的知識を組み合わせて、クラマス山脈の先住民族であるカルク族とユロック族が、ヨーロッパの植民地化以前、少なくとも千年にわたってこの地域の森林の形成に貢献した文化的焼畑を明らかにしています。

先住民の焼畑がクラマスの森を千年にわたり形成してきた理由(How Indigenous burning shaped the Klamath’s forests for a millennia)

Dense stands of Douglas fir trees surround South Twin Lake in California. Decades of logging and fire suppression have shifted the composition of forests in the region, favoring fire-sensitive softwoods, like fir, over fire-resistant hardwoods, like oak. (Photo by Clarke Knight, summer 2018)


<関連情報>

カリフォルニア州クラマス山脈における過去1000年間の森林構造と組成の主要なトレンドは土地管理によって説明できる Land management explains major trends in forest structure and composition over the last millennium in California’s Klamath Mountains

Clarke A. Knight 、Lysanna AndersonM. Jane Bunting , and John J. Battles 、Authors Info & Affiliations

March 14, 2022 | 119 (12) e2116264119 | https://doi.org/10.1073/pnas.2116264119

Significance

We provide the first assessment of aboveground live tree biomass in a mixed conifer forest over the late Holocene. The biomass record, coupled with local Native oral history and fire scar records, shows that Native burning practices, along with a natural lightning-based fire regime, promoted long-term stability of the forest structure and composition for at least 1 millennium in a California forest. This record demonstrates that climate alone cannot account for observed forest conditions. Instead, forests were also shaped by a regime of frequent fire, including intentional ignitions by Native people. This work suggests a large-scale intervention could be required to achieve the historical conditions that supported forest resiliency and reflected Indigenous influence.

Abstract

For millennia, forest ecosystems in California have been shaped by fire from both natural processes and Indigenous land management, but the notion of climatic variation as a primary controller of the pre-colonial landscape remains pervasive. Understanding the relative influence of climate and Indigenous burning on the fire regime is key because contemporary forest policy and management are informed by historical baselines. This need is particularly acute in California, where 20th-century fire suppression, coupled with a warming climate, has caused forest densification and increasingly large wildfires that threaten forest ecosystem integrity and management of the forests as part of climate mitigation efforts. We examine climatic versus anthropogenic influence on forest conditions over 3 millennia in the western Klamath Mountains—the ancestral territories of the Karuk and Yurok Tribes—by combining paleoenvironmental data with Western and Indigenous knowledge. A fire regime consisting of tribal burning practices and lightning were associated with long-term stability of forest biomass. Before Euro-American colonization, the long-term median forest biomass was between 104 and 128 Mg/ha, compared to values over 250 Mg/ha today. Indigenous depopulation after AD 1800, coupled with 20th-century fire suppression, likely allowed biomass to increase, culminating in the current landscape: a closed Douglas fir–dominant forest unlike any seen in the preceding 3,000 y. These findings are consistent with precontact forest conditions being influenced by Indigenous land management and suggest large-scale interventions could be needed to return to historic forest biomass levels.
1304森林環境
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