LB 10-134 - The characterization of riparian vegetation in agriculture drains impacted by Phragmites australis: a Southwestern Ontario case study

Background/Question/Methods:

In agriculturally dominated regions of the Laurentian Great Lakes basin, drainage systems are impacted by Phragmites australis which is managed by a suite of practices – chemical application, cutting and dredging – reset vegetational communities towards more homogenous species. The extent to which vegetational communities can enhance and offer new ecosystem services provided by drains remains underexplored and requires further research into vegetational communities and functions offered by species assemblages. To address this knowledge gap, we conducted vegetational surveys across 10 agricultural drains in Windsor-Essex region in southwestern Ontario. Sites were sampled at a range of scales using three randomized transects upon which six random 1m² quadrats were placed (3 on each bank). Within each quadrat, we estimated alpha diversity (number of species), estimated cover and calculated overall biomass within and across sites. We calculated and compared diversity indices across sites (beta diversity). We conducted stream habitat assessments including time since last management action (i.e., dredging or bank clearance) and applied a suite of multivariate statistics. We hypothesized that in drains with high impacted from Phragmites management, we would find lower biodiversity and drains with lower impact from Phragmites management we would find higher levels of biodiversity.

Results/Conclusions:

Across sites, we identified 120 different species of plants on riparian banks with the most common plant groups spread across grasses, thistles, goldenrods, dogwoods, avens, and asters. The number of species ranged between 9-59 species at a given site, Shannon’s diversity indices ranged 3.04-0.78 and Simpson’s index ranged 0.93 to 0.47. The composition of plant groups differed across sites, heavily managed drains contained primarily (+90%) graminoid species (grasses, sedges, and rushes) while less managed drains had a larger mix of plant groups. Roadside drains (n=6) contained more graminoid species then completely field side drains (n=4) and further, the riparian banks adjacent to roadsides also contained more graminoids compared to their opposing drain bank. While differences across sites were primarily insignificant, this research shows that these drain environments can provide important areas for native vegetational biodiversity, even when impacted by invasive Phragmites. Further insight into functional traits offered by this range of vegetational species will help advance efforts to rethink riparian vegetation buffers as offering multiple services and co-benefits for nature and society.