Be it Horseweed or Common Reed: Invasion Sucks Indeed

Document Type


Publication Date

Summer 7-16-2019


Invasive alien species (IAS), which often differ in abundance and impacts in native and non-native ranges, need to be studied biogeographically for understanding such impacts. Here we demonstrate how common reed, Phragmites australis, and Canadian horseweed, Conyza canadensis, vary in abundance, impacts and genetic diversity within and across ranges. Our global scale field studies and controlled experiments revealed that both these species tend to drive out natives in the introduced ranges, but not at home. These species are biased in their competitive effects on species that co-occur with them in native and non-native ranges, suppressing the latter more than former. For instance, P. australis significantly reduces biomass, plant height and number of leaves of co-occurring species in non-native ranges than the native ranges. Invasive populations of P. australis showed highest levels of genetic diversity while the native populations showed the lowest. For C. canadensis, genetic diversity was relatively low and comparable between native and non-native ranges. Eco-physiological basis of variations in the behavior of invasive species and their impacts on key ecosystem functions are discussed. Insights from genetic variations and ecological impacts of two flagship global invaders at a transcontinental scale reiterate the need for integrated efforts worldwide to understand and manage the spread of IAS.

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Manzoor A. Shah is Associate Professor of Botany at University of Kashmir, Srinagar, J&K, India. His research interest in Himalayan invasive plant species span from molecular –to -macroecology, with primary focus on global patterns of abundance and impacts. He has 70 publications and has recorded numerous honors and awards. He has coordinated several research projects on invasive species, including Indo-German, Indo-Canadian, and Indo-US. He has been a faculty affiliate at UM.