Weed Species Shifts with Increasing Field Age in Alaska

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Abstract
Vegetative cover of weeds was determined in 84 agricultural fields representing a number of crops in Alaska. Multivariate statistical techniques were used with weed, soil, and management data to determine if weed vegetation was related to particular environmental and management variables. Field age was the variable that best explained the variation in vegetation composition. In fields recently cleared, native species were most important, being replaced by introduced weed species with increasing field age. Field horsetail (Equisetum arvense L.) was an exceptional native species that persisted under cultivation. Total weed cover was low in the first few years of cultivation, but increased as introduced species such as common lambsquarters (Chenopodium album L.), common chickweed [Stellaria media (L.) Cyrillo], quackgrass [Agropyron repens (L.) Beauv.], and foxtail barley (Hordeum jubatum L.) became more prevalent. A number of introduced species such as hempnettle (Galeopsis tetrahit L.) and Pennsylvania smartweed (Polygonum pensylvanicum L.) were restricted to just a few fields, emphasizing the importance of using weed-free seed and other management practices to minimize the spread of introduced weeds.