Human paths have positive impacts on plant richness and diversity: a meta-analysis

We assess the impacts of human paths, trails and roads on plant species richness and Shannon diversity. Most reviews of this topic have not considered community-level measures, and have focused on excessive tourism impacts. We found significant positive effects of paths on plant richness and diversity. The effect size for richness was highest when studies included roads (paved) or trails (unpaved). The effect size found for diversity was highest when studies were in grasslands. We also found experimental designs comparing high levels of path use to low levels of path use, near-to-path vs. far-from-path and path-presence vs. path-absence comparisons obtained the largest effect sizes. There was no evidence that non-native species explained most increases in species richness or diversity. The effect sizes of human paths on plant communities are comparable in magnitude to those reported for other mammals’ disturbance and ecosystem engineering activities.