Georgia Hart-Fredeluces discusses her recently published Journal of Ecology article: ‘Simulated Indigenous fire stewardship increases the population growth rate of an understory herb‘. Find out more about about the importance of understanding Indigenous management practices to protecting plant biodiversity.

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Plant biodiversity is foundational to ecosystem integrity and human well-being, yet it continues to decline with global change. While there is ongoing and important research concerning how global change drivers are influencing plant biodiversity, little attention has historically been given to the potential for Indigenous stewardship to help promote and protect plant biodiversity. Here we explored the potential for reintroduction of Indigenous stewardship to promote plant conservation under novel forest conditions through simulation models.

Our project was focused on an ecologically and culturally significant understory plant in the Pacific Northwest of the U.S. called beargrass (Xerophyllum tenax). Beargrass is used in the weaving technologies of Indigenous Peoples and has ceremonial significance. For example, it is used for various types of baskets and regalia. Beargrass leaves and flowers are also ecologically significant as a source of food and materials for insect pollinators, small mammals, deer, elk and bears. As a perennial plant, it is an important source of early forage for deer and elk as the snow melts in spring. Indigenous stewardship practices for beargrass vary over space and time, but often include frequent low- to moderate-severity fire, followed a few years later by leaf harvest. Leaves from recently burned plants have qualities that are preferred by many weavers, such as pliability.

Federal and State fire suppression and fire exclusion policies, as well as the broader policies and practices of European Colonization, almost entirely removed Indigenous fire from the landscape. As a fire-adapted plant, beargrass populations have suffered; they have been reported to have declined over time in terms of both abundance and leaf quality for weaving.

In order to explore the impacts of fire suppression on beargrass, as well as the promise of Indigenous stewardship to support the persistence of beargrass under novel forest conditions, we collected demographic data (growth, survival and reproduction) on individual beargrass plants across three sites over three years. We measured these demographic traits on plants that were in areas recently burned with low-severity fire, recently burned with high-severity fire, and in areas that did not burn. We also measured the early-season soil moisture and light availability (canopy openness) of each plant so that we could explore how these factors may interact (or not) with fire to influence growth, survival and reproduction. We conducted a leaf harvest experiment where we removed a small number of leaves from 20% of randomly-selected large plants. This leaf harvest experiment simulated one type of Indigenous harvest.

Commercial harvest of beargrass for the floral greens industry is also a major concern for the persistence of beargrass, but we did not simulate this more intense level of harvest in this study. Our data was used to build linear and generalized linear mixed models for each part of the beargrass life cycle (growth, survival and reproduction). These models were then combined into an integral projection model (IPM) which is used to predict if population size will increase or decrease under different conditions. We used these IPMs to simulate various fire and leaf harvest scenarios. In particular, we compared business as usual, Indigenous fire stewardship (more frequent and less severe fires) and no fire. We also simulated each scenario with and without leaf harvest for cultural use.

We found the Indigenous fire stewardship increased beargrass population growth rate, while business as usual and no fire did not. We also found that leaf harvest increased beargrass population growth rate only in combination with Indigenous fire stewardship, but not in the context of business as usual or no fire. Indigenous fire stewardship increased population growth rate due to increased survival of large individuals and increased growth and reproduction compared to high-severity fire. In combination with leaf harvest, Indigenous fire stewardship increased vegetative reproduction and this further increased overall population growth rate.

Our results suggest that reintroduction of Indigenous stewardship in forested ecosystems of the Pacific Northwest could support the persistence of beargrass populations. The increased population growth in the presence of both Indigenous fire and leaf harvest further suggests that Indigenous stewardship has holistic and synergistic properties such that benefits of reintroduction may depend on restoring multiple aspects of these stewardship relationships. Finally, beargrass coexists with other understory plants such as huckleberries and reintroduction of Indigenous stewardship in novel contexts may also support a broader range of plant and animal diversity that depends on or is supported by fire and fire-dependent habitats. While these are encouraging results that suggest the value of further collaborations between Tribal Nations, U.S. government, non-governmental organizations, and university managers and scientists, they remain to be tested on the ground in different contexts through the ongoing work of Tribal and non-tribal managers and scientists.

Georgia Hart-Fredeluces Idaho State University, USA

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You can read the full paper online: Simulated Indigenous fire stewardship increases the population growth rate of an understory herb