Regeneration of Quaking Aspen and Understory Vegetation Change After Fire Risk Reduction Treatment

Quaking aspen (Populus tremuloides Michx.) is a keystone species that, when coexisting with conifers (i.e., seral aspen), often undergoes stand-replacing disturbances to sustain long term vigor. Historically, mixed-to-high severity fire reduced fuels and regenerated aspen, but such disturbances have become less common in recent decades. This has often led to high fuel loading, and many seral aspen stands are at now risk of an unpredictable, high-severity fire, posing a threat to development in the wildland-urban-interface. The lack of a commercial market for aspen, and the risk of conducting prescribed fire, means there are few alternate management options. This has led to the development of a novel method called roller-felling, a mechanical treatment designed specifically to reduce fuel loading and restart succession of late seral-stage, now conifer-dominated, aspen communities. This study assessed the short-term impacts (one- and two-year) of roller-felling on aspen regeneration and understory vegetation. We compared metrics of stand composition, structure, and aspen regeneration densities to determine treatment response. Roller-felling eliminated the overstory and resulted in prolific aspen suckering; this corresponded to changes in forb and shrub composition and ground covering of biotic functional groups. Decreased slash retention and scarification of mineral soil promoted aspen regeneration and higher densities of early-successional forbs. Greater slash retention and less machinery traffic reduced aspen regeneration and influenced understory composition, resulting in greater shrub cover and forbs of mid- to late-successional status. Well-established dynamics (e.g., greater aspen prior to disturbance or lessened slash retention promoting sucker densities) of early-successional aspen regeneration were observed, suggesting roller-felling acted as a stand-replacing disturbance and restarted succession, effectively reducing the risk of high-severity fire. This study established a baseline for long-term monitoring of these areas, furthering the understanding early successional aspen ecology, which will have application to forest management regionally, where the goals are to reduce fire risk and promote aspen across western US

Tamm Review: Quaking Aspen\u27s Influence on Fire Occurrence, Behavior and Severity

Quaking aspen (Populus tremuloides Michx.) stands have historically been referred to as “firebreak” forest types that can reduce fire activity, but high-intensity and high-severity fires have been observed to burn through aspen stands. Clearly, fire activity in aspen is highly variable, which may be due to the wide variation in aspen stand composition and structure and because the species occurs across wide geographic, environmental, and climatic gradients. In the western U.S., there is growing interest in promoting aspen stands within wildland-urban interface communities to reduce fire risk, but studies that refer to the low flammability of aspen stands rely on limited citations. If promoting aspen to reduce fire risk is a desirable forest management practice, consolidating the available literature is necessary to understand when, where, and how management might achieve this goal. Here, we synthesized literature and conducted a survey of forest and fire managers to assess current understanding of how fire interacts with aspen stands, as well as to examine possible factors that influence fire occurrence, behavior, and severity in aspen communities. We found evidence that the presence of aspen reduces fire occurrence, fire behavior, and fire severity, but this effect is dependent on many factors, including the percentage of aspen vs conifers in the overstory, load and type of understory fuels, weather, and season. We did not find any quantitative management guidelines on how to create, maintain, or use aspen stands to reduce fire risk. The large gap between “common knowledge” and empirical evidence regarding aspen’s ability to inhibit fire requires further research