Canadian Forest Service Publications
Spacial processes structuring riparian plant communities in agroecosystems: implications for restoration. 2016. Bourgeois, B.; Gonzalez, E.; Vanesse, A.; Aubin, I.; Poulin, M. Ecological Applications 26(7):21033-2115.
Year: 2016
Issued by: Great Lakes Forestry Centre
Catalog ID: 36360
Language: English
Availability: PDF (request by e-mail)
Abstract
The disruption of hydrological connectivity by human activities such as flood regulation or land-use changes strongly impacts riparian plant communities. However, landscape-scale processes have generally been neglected in riparian restoration projects as opposed to local conditions, even though such processes might largely influence community recovery. We surveyed plant composition of field edges and riverbanks in 51 riparian zones restored by tree planting (565 1-m2 plots) within two agricultural watersheds in southeastern Québec, Canada. Once the effects of environmental variables (hydrology, soil, agriculture, landscape, restoration) were partialled out, three models of spatial autocorrelation based on Moran's eigenvector maps and asymmetric eigenvector maps were compared to quantify the pathways and direction of the spatial processes structuring riparian communities. The ecological mechanisms underlying predominant spatial processes were then assessed by regression trees linking species response to spatial gradients to seed and morphological traits. The structure of riparian communities was predominantly related to unidirectional spatial gradients from upstream to downstream along watercourses, which contributed more to species composition than bidirectional gradients along watercourses or overland. Plant traits selected by regression trees explained 22% of species response to unidirectional upstream–downstream gradients in field edges and 24% in riverbanks, and predominantly corresponded to seed traits rather than morphological traits of the adult plants. Our study showed that even in agriculturally open landscapes, water flow remains a major force structuring spatially riparian plant communities by filtering species according to their seed traits, thereby suggesting long-distance dispersal as a predominant process. Preserving hydrological connectivity at the watershed-scale and restoring riparian plant communities from upstream to downstream should be encouraged to improve the ecological integrity of rivers running through agricultural landscapes.
Plain Language Summary
This paper investigates how plant communities situated along or near rivers are impacted by human disturbance and subsequent restoration in agricultural areas. We collected plant data from 51 sites in the Boyer watershed east of Quebec City that were i) situated along river ways bordered by farms and ii) had recently undergone site restoration. We developed three different statistical models associating plant community to variables describing how the river is connected, direction of flow and seed movement. Our results show that seed dispersal in the direction of flow of the river is more important at explaining how plant communities are organized than seed movement over land. Also, these spatial processes were mainly related to seed characteristics rather than their shape. Given these results, we conclude that shifting focus from short sections of river to entire watersheds would inform decision-making processes when planning restoration and conservation activities. This would likely improve results of restoration activities in areas affected by farming.
