Invasion patern and distribution of Parthenium hysterophorus (Congress grass) across diferent agroclimatic zones of India

Abstract:

How far has Parthenium hysterophorus spread across the diverse agroclimatic regions of India, and what factors drive its invasion success? This research examined the invasion patern and spatial distribution of P. hysterophorus, commonly known as Congress grass, across eight agroclimatic zones of India through a systematic review and geospatial analysis of published field surveys, herbarium records, and satellite-derived vegetation indices. Data were compiled from 127 peer-reviewed sources spanning 2001 to 2022, covering arid, semi-arid, sub-humid, humid tropical, sub-tropical, transitional, coastal, and per-humid zones. Plant density, percentage ground cover, and frequency of occurrence served as the main distribution metrics. The sub-humid Indo-Gangetic Plains recorded the highest plant density at 43.6 plants per square metre with 38.1 per cent ground cover, followed by the transitional Central Highlands at 37.2 plants per square metre. Arid zones of western Rajasthan and per-humid areas of the north-east showed the lowest colonisation levels, at 12.3 and 8.4 plants per square metre, respectively. Dispersal pathway analysis pointed to anthropogenic corridors such as road networks, railway lines, and contaminated grain movement as the chief vectors driving range expansion beyond natural wind and water dispersal. Species diversity indices in heavily invaded sites were 34.7 per cent lower than in non-invaded reference plots, confirming a negative relationship between P. hysterophorus density and native plant richness. Temperature, rainfall seasonality, and soil disturbance history emerged as the strongest environmental predictors of invasion intensity. These results provide a zone-wise baseline that can guide targeted management and biocontrol strategies for this aggressive alien weed across the Indian subcontinent.