Effect of weed control methods on growth of five temperate agroforestry tree species in Saskatchewan

Most tree species in agroforestry plantings are intolerant to vegetative competition and sites must be intensively cultivated to eliminate weeds. Many studies have been conducted to investigate what factors limit seedling growth because of the presence of vegetative competition in forest environments; however on agricultural sites there are few studies on weed management options for tree planting. This research quantified and compared growth of Manitoba maple (Acer negundo), green ash (Fraxinus pennsylvanica), Colorado spruce (Picea pungens), Scots pine (Pinus sylvestris) and Walker poplar (Populus x Walker) in response to combinations of in-row and between-row weed control methods. The study was established on an agroforestry planting on agricultural soils in Saskatchewan. Treatments included in-row weed control using herbicides or plastic mulch and between-row weed control using tillage compared with a non-weeded control. Weed control positively affected annual height increment, basal diameter and height of the agroforestry species. The impacts of weed control versus no weed control were significant in almost all instances. However, tree species responded differently to the method of weed control. Weed control by herbicide and plastic mulch were not significantly different for four of the five species under investigation. This research will help with prescribing weed control methods for agroforestry and afforestation plantings on agricultural soils.