Plant community response to operational glyphosate application

Glyphosate (N-(phosphonomethyl) glycine) is the predominant active ingredient in many commonly used herbicides worldwide. Glyphosate-based herbicides (GBH) have been used throughout the agriculture and forest industry for decades since the introduction of Roundup® in the 1970s. Commonly used for silvicultural operations in forestry, GBH's offer cost-effective, broad-spectrum competition control in reforested cut blocks and are favored for their non-selective nature. Many studies exist that examine glyphosate residuals in an agricultural setting, and there is a growing body of literature that focuses on the long-term effects of glyphosate when used in an operational forestry setting. Some new findings suggest that glyphosate residues linger in the forest ecosystem longer than previously estimated. This has raised concerns among Indigenous communities and other stakeholders of Alberta's public forests about the effects of GBH on forest biodiversity, plant community composition, and availability of culturally significant plant species. This study analyzes plant community data collected from harvested cut blocks across Alberta that were operationally treated with GBH, to quantify the residual glyphosate concentration across multiple subregions, and to determine the change in plant community composition of culturally significant and frequently used plant species. Plant species identification was conducted across 38 individual sites spanning the western side of Alberta. Twenty sample plots were established in each of the cut blocks to identify plants of interest, as well as collect plant samples for glyphosate residue analysis. A Principal Coordinate Analysis (PCoA) was conducted to determine the correlation between species of interest, recovery time, and environmental factors. The results of this study indicate that glyphosate residual concentrations declined significantly in the years following herbicide application, to levels below the 0.1 ppm maximum residue limit set by the Government of Canada, and the plant community diversity did not change significantly. These findings show that, while GBH inhibits the development of competing species, the forest understory recovers to its previous state, indicating that GBH has no adverse effect on plant community composition or plant diversity.