Trade-offs in forest disturbance management for plant communities and ungulates

Land and wildlife managers use disturbance to reset forests to earlier successional stages and improve the quality and quantity of forage available to ungulates. However, management of vegetation communities to increase forage nutrition has additional implications for other non-forage vegetation. To evaluate responses of vegetation to management of fire and timber harvest, we measured and modeled 3 metrics of vegetative response in 3 forested areas in Montana, USA during 2017-2019: forage nutrition for mule deer (Odocoileus hemionus), invasive species biomass, and floristic quality, a measure of plant communities' tolerance of disturbances and fidelity to particular environments using native species conservatism scores. We found differences in all 3 metrics of plant responses that were specific to disturbance type and study area, and associations between disturbance and vegetation outcomes that were both desirable and undesirable. Generally, deer forage nutrition and invasive species biomass both increased in disturbed areas, whereas floristic quality increased with disturbance in 2 study areas but decreased in the third. Biomass of particular invasive species varied according to both study area and disturbance type. Lastly, we used decision analysis to illustrate trade-offs and overall support for different management actions while also accounting for underlying differences among study areas. For example, management actions with the greatest increase in mule deer forage nutrition tended to also increase invasive species biomass. Compared to other management actions, low-severity harvest scored highly in 2 study areas due to its association with increased forage nutrition while also limiting invasive species biomass and maintaining floristic quality. However, different weighting schemes according to different management priorities among management outcomes alter the relative ranking of actions. Our data show area-specific trade-offs in vegetation outcomes that result from disturbance management, which can be combined with decision analysis to help managers balance objectives and compare potential management actions.