Natural disturbances like storms and wildfires continue to affect plant communities, but in a context of increasingly human-altered landscapes. We know that the amount and configuration of natural habitat on a landscape can influence the trajectory of plant community recovery. What is less clear is whether more subtle ‘press’ disturbance – such as outdoor recreation in protected areas – can influence the resilience of plant communities to natural disturbance. These two types of stressors may interact, such that the effect of one depends on the level of the other. Alternatively, they may operate independently. We tested this by comparing historical and current plant community data from 98 permanent plots in Waterton Lakes National Park, Alberta. A wildfire burned half of the plots in 2017. If natural and recreational disturbance interact, we predicted that changes in species richness and community composition, and the probability of colonization by exotic species, would be greater in severely burned plots, and that this effect would be heightened in plots close to recreational trails. Alternatively, if there was no interaction, then the changes recorded after the wildfire would not be affected by trail proximity, and the effect of trail proximity would not vary with burn severity.
Results/Conclusions
We found significant interactions between burn status and proxies of recreational disturbance levels. The change in community composition from the past to the present was greatest in severely burned plots regardless of trail proximity, but in moderately burned plots there were greater shifts in composition closer to recreational trails. In contrast, unburned plots saw greater shifts in composition as distance from trails increased. Colonization by new exotic species occurred more often in unburned plots if they were closer to a trail; but contrary to our prediction, burned plots were more likely to be colonized by new exotic species if they were farther away from a trail, especially if they lacked exotic species in the past. Our results suggest that plant community response to wildfire can be mediated by recreational disturbance, sometimes in surprising ways. Whether this will alter the resilience of these communities over the long-term will require consistent monitoring of plant community change in protected areas with increasing recreational use.
