Managing Piñon, Juniper Woodlands and Sagebrush Ecosystems Exhibiting Tree Expansion
Piņon and juniper trees are native species that occur naturally in woodland vegetation types, but that also are expanding into mid- to upper-elevation sagebrush vegetation types throughout much of their range. Expansion of the tree species into sagebrush types typically results in an increase in tree biomass and, thus, woody fuel loads, and a decrease in the understory species associated with the sagebrush type. Higher fuel loads increase the risk of larger and more severe fires, and higher severity fires further deplete the understory species. The net effect of tree expansion on sagebrush ecosystems often is a decrease in ecological resistance to invasive species and in ecological resilience or the capacity to recover after fire. Managers throughout the region are using fire and fire surrogate treatments in an attempt to decrease fuel loads and the risk of catastrophic fire and to increase the ecological resistance and resilience of sagebrush ecosystems. The Great Basin Ecology Lab is studying (1) the factors influencing the rate and magnitude of tree expansion, (2) the effects of tree expansion on sagebrush ecosystems, and (3) the response of sagebrush ecosystems to fire and fire surrogate treatments aimed at removing the tree species. Results are being used to develop decision support tools for managing piņon and juniper woodlands and sagebrush ecosystems exhibiting tree expansion.