Vegetation and soil seedbank dynamics in Parthenium hysterophorus L. invaded subtropical grassland in Nepal
Parthenium hysterophorus is a noxious invasive weed and is ever expanding in its introduced range including Nepal. Understanding vegetation dynamics including soil seedbank in Parthenium invaded communities and the growth pattern of the weed itself is essential for effective management of Parthenium. We monitored growth of Parthenium (height, density, cover and soil seedbank) and plant species composition of associated species for 5-year period from 2009 in a grassland invaded by Parthenium in south-central Nepal. We found that Parthenium cover and height decreased from 2009 to 2010 and then slightly increased in 2013. Parthenium density decreased from 2009 to 2010 and then was variable until 2013. Year x grazing interactions had significant effect on Parthenium cover and density. Parthenium soil seedbank was eight times higher near the soil surface than in deep soil. It increased from 2009 to 2012 but decreased in 2013. Seedbank was also affected by interactions of year x depth, depth x grazing, and year x depth x grazing. Altogether, 87 plant species were recorded in Parthenium invaded sites and their species richness decreased until 2012 but slightly increased in 2013. The composition of associated plant species was affected by animal grazing intensity, Parthenium density, cover, and their interactions. Parthenium invasion has been ever increasing in our study site and many palatable plant species are under potential threat. Thus, there is an urgent need to carry out awareness campaign, formulate proper management plans, and implement such plans properly to manage Parthenium weed in Nepal.