IMPACTS OF XANTHIUM STRUMARIUM L. INVASION ON VASCULAR PLANT DIVERSITY IN POTHWAR REGION (PAKISTAN)

Studies on the impacts of alien plants help to understand extent of biological invasion. Multiple analyses of diversity parameters at different locations allow general explanations of impact on species diversity and richness in plant communities. The current study assessed impact of Xanthium strumarium invasion on native plant diversity in Pothwar region of Pakistan. The approach used for study was random samplings with two categorical factors: invaded and non-invaded plots under same habitat conditions. Differences in species frequency (N), species richness (R), evenness (J'), Shannon diversity index (H') and Simpson index of dominance (λ) were compared between invaded and control plots by t-test series. Control plots harbored by average 1.3 more species/10m2. The control category was more diverse (H'=2.00) than invaded category (H'=1.82). Non-invaded plots showed a higher floristic richness than invaded ones. At multivariate scale, ordination (nMDS) and ANOSIM showed significant magnitude of differences between invaded and control plots. The decrease in diversity indices in invaded over control sites indicated that plant communities become less biodiverse due to Xanthium strumarium invasion. This makes X. strumarium a candidate of consideration for appropriate control measures. keywOrds: Alien species, biOlOgicAl pOlluTiOn, diversiTy indices, cOnservATiOn sTrATegies, MulTivAriATe AnAlysis 74 Qureshi h. , AnwAr T. , ArshAd M. , OsunkOyA O.O. , Adkins s.w. / Ann. Bot. (Roma), 2019, 9: 73–82 in early 1980s. Massive migration of Afghan nomads and their livestock resulted in small to large patches of this aggressive weed. Spiny fruits of plant clinging to wool of sheep/goats have been major force of its spread. Now it is ubiquitous weed found in orchards, agricultural and wastelands (Hashim and Marwat, 2002). Reduced biodiversity, negative effects on agricultural yield of row crops (soybean, cotton, maize and groundnut), host of crop pathogens, cattle poisoning and contamination of sheep wool by lodging of burs are adverse effects related to this weed. Facilitated dispersal of prickly burs by adhering to human clothing and animals, by water, as contaminant of wool, viability of seeds up to five years, photo-insensitivity and allelopathy are traits related to invasiveness of the weed (Hussain et al., 2013; Qureshi et al., 2014). The major allelopathic compounds found in X. strumarium are: xanthinin, xanthumin, xanthatin, xanthostrumarin, atractyloside, carboxyatractyloside; phytosterols, xanthanol, isoxanthanol, xanthinosin, 4-oxo-bedfordia acid, hydroquinone, xanthanolides, caffeoylquinic acids, α and γ-tocopherol, thiazinedione, deacetyl xanthumin, carboxyatractyloside, linoleic acid and several sesquiterpene lactones (Kamboj & Saluja, 2010). X. strumarium weed is predominant in some countries in the world including Pakistan, Australia, India, America and Turkey (Shafique et al., 2007); its presence and invasiveness in Pakistan were also reported earlier in Islamabad (Khan et al., 2010); North-west Pakistan (Marwat et al., 2010); Khyber Pakhtunkhwa (Khan et al., 2011); upper Indus plains in Punjab (Malik et al., 2012). Nowadays this species is one of the worst weeds present in Pakistan. No previous study is reported from Pothwar region regarding X. strumarium diversity impacts. Current study was carried out to assess: (1) extent of invasion impact of this weed on diversity indices in different districts of Pothwar region; (2) if invasion impacts on vascular plant diversity differ between different sites (districts) in the area. MaterIals and Methods