Weed community structure in upland farming system of the middle mountain region in far-western Nepal

Weeds are recognized worldwide as an important environmental and economic burden in the human dominated landscape, particularly in the agro-ecosystems. Management of weeds is highly context specific and requires the knowledge of weed community structure at local levels. Additionally, periodic assessment of weed flora is essential because the weed community structure modifies over time due to changes in cropping patterns and arrival of invasive alien weeds. In this study we assessed the agricultural weed flora and weed community structure in legume fields (Macrotyloma uniflorum, Vigna angularis and Vigna mungo crops) dominated by invasive weed Ageratum houstonianum in a remote mountain village Gokuleshwor of Darchula district in north-west Nepal. Weed flora of the study area was inventoried by transect walk method and weed community structure in three crop fields were analyzed by quadrat sampling. We recorded 75 vascular plant species belonging to 67 genera and 29 families as agricultural weeds. Among them, 21 species (28%) were alien species naturalized in Nepal and 9 of these naturalized species were invasive. Asteraceae (18 species) was the most species-rich family, followed by Poaceae (10 species) and Malvaceae (5 species). Out of 75 weed species, 65 were also listed in the World Compendium of Weed. A. houstonianum had the highest biomass and the importance percentage in all three crop fields. Weed species richness and A. houstonianum biomass did not vary significantly among the three crop fields. The weed species richness significantly declined with increasing A. houstonianum biomass. The results suggest that the alien species contributed significantly to the weed flora of the upland farming system and an invasive weed became a dominant species of the weed community. Control of such weeds at their early stage of invasions can prevent them from becoming dominant weeds and protect the crop production systems from their negative impacts.