Testing for synergistic effects of natural and anthropogenic disturbance on ecological communities at a landscape scale

Context

Anthropogenic and natural disturbances may interact synergistically, magnifying their individual effects on biodiversity. However, few studies have measured responses of ecological communities to multiple stressors at landscape scales.

Objectives

We use a long-term dataset to test for synergistic effects of anthropogenic and natural disturbance on plant community diversity and composition in a large protected area.

Methods

We quantified changes in plant communities over two decades in 98 plots in Waterton Lakes National Park, Canada. Fifty-three plots burned in a wildfire in the interim. We modeled the effects of wildfire, proximity to trails or roads, and their interaction on changes in species richness, community composition, relative abundance of disturbance-associated species, and colonization by exotic species.

Results

Interactions between wildfire and proximity to roads and trails affected all metrics except species richness. Only one interaction was synergistic: the relative abundance of disturbance-associated species following wildfire was magnified closer to recreational corridors. The other community metrics showed unexpected patterns. For example, plots with no exotic species in the baseline survey that burned in the wildfire were more likely to gain exotic species than unburned plots only when they were distant from recreational corridors.

Conclusions

Our study demonstrates interactive effects of natural and anthropogenic disturbance at landscape scales within a protected area. Plant community response to wildfire was influenced by proximity to recreational corridors, sometimes in surprising ways. As the frequency and severity of anthropogenic and natural disturbances both continue to rise, documenting the prevalence and magnitude of interactions between them is key to predicting long-term effects and designing mitigation strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10980-024-01844-w.

Vegetation type and trail use interact to affect the magnitude and extent of recreational trail impacts on plant communities

Protected areas may prohibit large-scale deforestation and development, but still allow recreation via networks of roads and trails. Managers need to understand how the type of trail usage and the habitat the trail traverses influence the nature and extent of the trail impact. We measured the effect of trails on plant communities in a large, protected area in the southern Rocky Mountains of Alberta, Canada. We surveyed 118 transects adjacent to trails and 24 control transects at least 100 m from trails, recording the presence and abundance of all vascular plant species. We modelled changes in species richness, community composition, and the presence of exotic species as a function of trail type, vegetation type, and the distance from the trail edge. Overall, species richness increased with proximity to trails and community composition shifted significantly, with a greater likelihood of exotic species presence closer to trails. Heightened species richness and greater probability of exotic species presence extended a greater distance from off-highway vehicle trails than from footpaths, but only in shrubland and mixed forest vegetation. In addition, exotic species at higher elevations were most often associated with off-highway vehicle trails. Our study shows that the magnitude and extent of trail impacts on plant communities varies depending on trail type, vegetation type, and sometimes interactions between the two. The high frequency and intensity of off-highway vehicle trail use likely increases both propagule pressure and the severity of disturbance, while vegetation type determines light availability and hence invasibility. Managers can use this information to prioritize trail areas for exotic species monitoring and restrict high-intensity off-highway vehicle trails to less sensitive vegetation types at lower elevations.