Vegetation management with glyphosate has little impact on understory species diversity or tree growth in a sub boreal spruce plantation – A case study

Abstract

In central British Columbia (BC), forest management practices have altered natural stand development pathways by controlling ''non commercial'' tree species and other competing species with the objective of maximizing crop tree growth. This potentially decreases overall diversity within the stand. We conducted a retrospective study on a 13-year-old stand to investigate the impacts of vegetation management with glyphosate on tree growth, species diversity and forest health in central BC. Results revealed that spruce was marginally taller than birch in the herbicide treated area and significantly shorter than birch in the untreated area. There was no difference in spruce diameter at breast height (DBH) and mean stem volume by treatment. White pine weevil attack was significantly reduced in the untreated area. In total, 133 plant species were recorded from 2002 to 2006, but 30% of the species present in 2002 were not present in 2006. Species' richness and alpha diversity were similar between treatments but beta diversity was relatively low indicating little treatment effect. There was a greater occurrence and abundance of ''weedy'' and pioneer species in the herbicide-treated area. Overall, this study suggests that glyphosate application does not remove all birch and showed minimal or no impact on under-story vegetation. Therefore, a move away from broadcast vegetation control to spot control where warranted could result in better tree growth, improved forest health and structural diversity.

Plant Community Diversity and Tree Growth Following Single and Repeated Glyphosate Herbicide Applications to a White Spruce Plantation

“…Species richness and the Shannon index did not differ between treated and untreated areas, indicating the small potential for impacts to plant community diversity resulting from operationally applied herbicide treatments, which is consistent with findings of several other studies [12,27,31]. Haeussler et al [13] report the potential for increases in species richness and other diversity indexes following herbicide treatment, which was also evident in our study when the single treatment applied in 2004 was compared to untreated areas.…”

How much birch (Betula papyrifera) is too much for maximizing spruce (Picea glauca) growth: a case study in boreal spruce plantation forests

“…Considering potential savings with a targeted brushing program, a higher broadleaf component could be financially advantageous in addition to the noted biological benefits. In another study Hawkins et al (2012) reported that broadcast brushing did not remove all birches and suggested a move away from broadcast vegetation control to spot control, where warranted, could result in better tree growth, improved forest health and structural diversity. Therefore the inclusion of other broadleaf species in these complex processes may have more beneficial effects on spruce growth.…”

Birch (Betula papyrifera) × white spruce (Picea glauca) interactions in mixedwood stands: implications for management

“…This may lead to unnecessary herbicide application costs for attaining a free growing standard and it may have a detrimental impact on ecosystems although a study by Hawkins et al (2012b) reported that herbicide application showed minimal or no impact on understorey vegetation diversity in central BC. From our investigation, birch densities up to 4,000 stems·ha -1 in 15-20 years old stands appear not to significantly influence spruce productivity in the northern BC interior.…”