Fire, leaf harvest, and abiotic factors drive demography of an ecologically and culturally important understory plant

Abstract

Abstract Understanding how multiple simultaneous drivers interact to influence plant demography is critical for protecting plant diversity in the context of global change. Fire is a key disturbance in forested ecosystems, but the interactive effects of fire and other abiotic and management factors on understory plants are poorly understood. Beargrass (Xerophyllum tenax) is perennial herb that provides food, habitat, and nesting material for a wide range of animals. Beargrass populations are prescribe‐burned by Native American experts, and leaves are subsequently harvested at low‐intensity for use in weaving. Leaves for weaving are reportedly becoming harder to find due to lack of fire and competition with commercial harvesters. To elucidate the effects of fire and its interactions with leaf harvest and abiotic factors on beargrass populations, we collected demographic data on more than 1000 individuals over three years across fire severities in combination with individual‐level soil moisture and light measurements. We also conducted an experiment simulating low‐intensity leaf harvest. We built mixed‐effects models to test our predictions that fire would increase growth and reproduction, and that it would mediate the effects of soil moisture and leaf harvest on beargrass growth. Fire increased growth as well as sexual and vegetative reproduction, providing evidence that beargrass is fire‐adapted. Leaf harvest both reduced survival probability and increased the probability of vegetative reproduction. Individual growth increased with early growing season soil moisture in unburned and low‐severity fire areas but did not vary with soil moisture in high‐severity areas. In sum, fire is a key driver of beargrass demography and fire interacted with other factors to influence beargrass vital rates. Understanding the impacts of changes to management and abiotic factors on understory species such as beargrass, and the ecosystem services they provide, requires attention to interactions among multiple environmental factors.

Keywords

• beargrass
• fire severity
• interacting drivers
• non‐timber forest products
• soil moisture
• Xerophyllum tenax