Plant Invasions in North America

Abstract

North America has accumulated more naturalized species, or “alien species that form self-sustaining populations in new regions,” than any other continent (5958; 3513 of which come from outside the continent). Over the last 35 years, North America has seen a rapid increase in the number of plant invasions; species have arrived through the horticulture and aquarium trades, as agricultural contaminants, and via other accidental and intentional pathways. Introduced populations have persisted and expanded on the continent with the help of extensive land use change and growing transportation networks. The main driving forces of naturalization in North America have been found to be habitat legacy (i.e., the habit affinities of a plant species in their native range), propagule pressure, and residence time, which are modulated by specific biological traits (e.g., flowering periods, vigorous clonal growth, and tall stature) interacting differently with these drivers. Within North America, more invasive plant species are found in cold temperate and Mediterranean climate zones than in arid, temperate arid, subtropical, and tropical climates. Economic activity (measured as per capita gross domestic product; GDP) also heavily influences the distribution of non-native species; areas with higher per capita GDP (~17,000 USD) have over twice the number of non-native plant species compared to regions with lower GDP. Currently, in the United States alone, over $100 billion per year is spent on losses, damages, and the control of invasive species, with the bulk of those funds going toward weed control for crops, pastures, and forests. In addition to being a drain on the economy, invasive non-native plants disrupt ecosystems and can often have negative effects on ecosystem services, including altered hydrological and fire regimes, impacts on native species, and changes in soil properties and nutrient cycling. National legislation and international agreements have been implemented in attempts to reduce threats from non-native species to biodiversity, the economy, and human well-being.