Antelope bitterbrush flowering, survival, and regeneration following ponderosa pine forest restoration treatments

To further understanding of the dynamics of antelope bitterbrush (Purshia tridentata) recruitment in a ponderosa pine (Pinus ponderosa) forest in western Montana, we measured bitterbrush seed viability and germination, flower numbers in 1997 and 1998, seed depredation, seedling survival between 1994 and 2002, and population changes between 1992 and 2002 on four forest restoration treatments. Treatments included a control, a shelterwood cut, a shelterwood cut followed by a low consumption burn, and a shelterwood cut followed by a high consumption burn. Bitterbrush flower numbers did not differ between treatments, but caged bitterbrush had greater flower numbers (P < 0.001) than their uncaged pairs, indicating that browsing reduced flower numbers. Seed depredation by rodents and birds caused a small reduction (P < 0.050) in seed crop in 1997. Bitterbrush seed viability and seedling survival (percent) were both high; although, the number of surviving bitterbrush seedlings averaged only 15 plants per treatment between 1994 and 2002. In the control treatment there has been a continual decline in bitterbrush numbers totaling 26 percent between 1992 and 2002; whereas, in the shelterwood cut and burn treatments bitterbrush numbers have stabilized since 1994. If bitterbrush stands are desired as a future part of this landscape, it seems clear that disturbance will be necessary. Failure to allow for disturbances that reduce forest overstory and increase mineral soil coverage may ultimately result in loss of bitterbrush from these stands.