Dissipation of four forest-use herbicides at high latitudes
Dates
Year
2008
Citation
Newton, M., Cole, E., and Tinsley, I., 2008, Dissipation of four forest-use herbicides at high latitudes: Environmental science and pollution research international, v. 15, no. 7, p. 573-583.
Summary
Background, Aim and Scope:: Large-scale deforestation is occurring in subarctic North America following clearing by salvage logging or insect attack, numerous shrubs, herbs and deciduous tree species tend to dominate areas on which stands of white spruce have grown. In the absence of economically advantageous mechanical methods, several herbicides have value in efforts to reforest by planting white spruce. Glyphosate, imazapyr, triclopyr and hexazinone are all capable of selectively removing many competing species, but there is concern about whether they would degrade naturally or persist owing to the frigid climate. Materials and Methods: We established test plots with all four herbicides in upland and riverbottom sites at 65oN and [...]
Summary
Background, Aim and Scope:: Large-scale deforestation is occurring in subarctic North America following clearing by salvage logging or insect attack, numerous shrubs, herbs and deciduous tree species tend to dominate areas on which stands of white spruce have grown. In the absence of economically advantageous mechanical methods, several herbicides have value in efforts to reforest by planting white spruce. Glyphosate, imazapyr, triclopyr and hexazinone are all capable of selectively removing many competing species, but there is concern about whether they would degrade naturally or persist owing to the frigid climate. Materials and Methods: We established test plots with all four herbicides in upland and riverbottom sites at 65oN and 58o N latitudes. The northern site has extremely cold winters, with soils that freeze to a depth of 1-2 m, and precipitation of 275 mm/yr. the southern site has heavy rain and snowfall, amounting to 2250 mm/yr evenly distributed. Soil seldom freezes deeply. On each test plot, one of the four herbicides was applied at twice the normal operational use rate to facilitate detection. They were applied at the normal timing, with hexazinone, imazapyr and triclopyr applied in June, and glyphosate applied in fall. Soils were sampled immediately after treatment, and those samples used as references for dissipation data gathered over the next 11-14 months from soil 0-15 and 15-45 cm depths. Results: Dissipation rates did not follow first order rates, because freezing conditions interrupted most microbial activity. All products did dissipate to close to or below detection limite within the time of the study. Dissipation from vegetation was substantially more rapid, and depended on the nature of the plants treated as well as the product used. While residues dissipated more slowly than in temperate regions, they did display consistent dissipation patterns during above-freezing conditions, and also the influence of microbial activity. Mobility was very limited with all products but hexazinone. Residues in plant material dissipate far more rapidly than those in soil. Discussion: These products dissipate during summer in high latitudes much as they would in temperate climates. Winter changes are small, but are not unlike some changes reported elsewhere under freezing conditions. Unlike many other studies, soil water did not influence dissipation heavily, but the high latitude, semi-arid climate also did not create severely droughty soils. Residues in plants were much higher than those in soils, but denatured the vegetation quickly, leading to unsuitability for forage in any case. Conclusions: Low toxicity of these products and their metabolites combined with consistent dissipation and low mobility suggest that toxic hazard of their use at high latitudes need not be a matter of serious concern to humans, terrestrial wildlife or aquatic systems. Recommendations and Perspectives: This paper will provide insight into safety and mobility of four herbicides of value for maintaining the boreal forests of Alaska, Canada, and perhaps elsewhere. It provides evidence of immobility and patterns of dissipation that can be adapted from patterns developed in warmer latitudes. Herbicides of these types are not persistent where summer soil temperatures permit microbial action.