Prescribed Burning Has Limited Long-Term Effectiveness in Controlling Trembling Aspen (<em>Populus tremuloides</em>) Encroachment into Fescue Grassland in Prince Albert National Park

Abstract

Guedo, Digit D., and Eric G. Lamb. 2013. Prescribed burning has limited long-term effectiveness in controlling Trembling Aspen (Populus tremuloides) encroachment into fescue grassland in Prince Albert National Park. Canadian FieldNaturalist 127(1): 50-56.Encroachment into grassland by woody species is a global ecological phenomenon, and it is of particular concern in remnant fescue (Festuca) prairie at the aspen parkland-boreal forest ecotone. Fire suppression is thought to encourage encroachment; however, prescribed burning as a means of controlling encroachment and restoring system structure, function, and composition has had variable success. The objective of this study was to determine the effects of different season of burn, number of annual burns, and number of years after burning treatments on Trembling Aspen (Populus tremuloides) encroachment into the fescue grasslands within Prince Albert National Park, Saskatchewan. Temporal changes in density and cover of Trembling Aspen in grassland and grassland-forest transition plant communities were evaluated using data from a prescribed burn study conducted in Prince Albert National Park from 1975 to 2010. The effect of year (indicating varying amounts of time relative to prescribed burning) and the interaction between spring burning and year reflect a stimulatory effect of burning on Trembling Aspen suckering. increased Trembling Aspen cover in the forest transition community with more annual burns, burning in the fall, and the interaction between year and number of annual burns and increased Trembling Aspen cover in the grassland community with year indicate that none of the treatments had lasting control of Trembling Aspen encroachment. ongoing Trembling Aspen encroachment despite prescribed burning may be due to important missing interactions between fire and grazing. A change in the use and expectation of prescribed burning is needed when attempting to suppress Trembling Aspen encroachment into the fescue grasslands.

Grassland Resilience to Woody Encroachment in North America and the Effectiveness of Using Fire in National Parks

“…Species contributing to woody encroachment vary across the ecoregions within the Great Plains [12]. For example, in the Canadian prairies, shrubs, aspen, and lodgepole pine (Pinus contorta) have encroached into the native grasslands of foothills and parklands and the tallgrass prairie ecoregion due to the elimination of both fire and bison [18][19][20]. In the Northern Great Plains, Virginian juniper and Rocky Mountain juniper (Juniperus scopulorum) have been the most widespread encroachers with moderate and substantial encroachment rates [1].…”

“…The recovery trajectories are nonlinear, and the thresholds of intervention reversing the transition are different from the ones that maintained the previous grassland state. For example, in a hysteretic shrub-encroached grassland, low-intensity prescribed fires may have no long-term effectiveness and fail to shift the ecosystem to the previous intact grassland [19,51]. However, extreme prescribed fire under drought conditions may reverse woody encroachment by reducing the survival and density of woody resprouts [52], indicating that a "path back" exists and suggesting the possible consequences of a strong management intervention.…”

“…However, as a resprouting and clonal species, aspen regenerates prolifically via vegetative sprouting after fires, and the mineral soil exposed to high-severity fires may also favour aspen reproduction as it has long, silky seeds that disperse long distances [68]. Annual burning in different seasons from 1975 to 2010 did not reduce aspen cover in Saskatchewan, Canada [19]. Aspen canopy, aspen regeneration, and shrub expansion did not decline significantly after prescribed burning of native fescue grasslands [55].…”

“…Prescribed fires and wildfires have played some roles in protecting native grasslands, but in some cases have not been powerful enough to fully reverse shrublands and woodlands in parks [55,73]. Mechanical, chemical, and biological treatments have also been used in national parks to protect grassland ecosystems from woody encroachment and invasive species [19,55,73,74].…”

Seasonal Spectral Separation of Western Snowberry and Wolfwillow in Grasslands with Field Spectroradiometer and Simulated Multispectral Bands

“…WPE also takes place in the Canadian prairies, where tree encroachment (e.g., aspen, willow) has received more attention in the literature [18][19][20][21][22][23]. For instance, trembling aspen (Populus tremuloides) is the dominant tree species encroaching on grasslands and pastures within the aspen parkland ecoregion in western Canada [24].…”