Invasive alien weeds species in farmland and forest in Sichuan province.
Invasive alien weeds are plants which threaten the ecosystem, habitats, species and human health. Invasive alien weeds harm not only biological diversity, but also the society, economy, culture and so on. Sichuan province (China) is one of the most serious districts influenced by invasive alien weeds. Studies conducted from 1985 to 1987 and 2002 to 2006 showed that 63 alien invasive weeds of 21 families were discovered and among these species there were 2 aquicolous weeds (Alternanthera philoxeroides and Eichhornia crassipes), 62 terraneous weeds of 20 families (including an amphibious weed A. philoxeroides). Most of the weeds are Asteraceae (Compositae) weeds, then Leguminosae, Amaranthaceae, Gramineae and Solanaceae, corresponding to 23, 7, 6, 4 and 3 species, respectively. There are 9 destructive weeds (including regional destructive weeds), amounting for 14.29% of the total alien invasive weeds, that is to say, A. philoxeroides, Eupatorium coelestinum, Galinsoga parviflora, Echinochloa crus-galli, Eichhornia crassipes, Amaranthus retroflexus, Conyza canadensis and Avena fatua. Five poisonous species, 9.68% of the total, are Eupatorium coelestinum, Datura stramonium, Solanum khasianum, Lantana camara and Ricinus communis. There are 49 normal invasive alien weeds, accounting for 79.37%. In the process of controlling the invasive alien weeds, plant quarantine and other legal measures should be applied to prevent their propagation and infestation. Meanwhile, according to the local ecosystem, the integrated management of agricultural, biological, physical and chemical methods should be adopted to prevent the damage and infestation of alien invasive weeds in order to restore native ecology and control the weeds permanently.