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The influence of broad-scale environmental factors on the species composition of segetal weed communities in Tajikistan was investigated. The research was conducted throughout the country, analysing plots of root crops as well as cereals from all phytogeographical regions of Tajikistan, with the exception of the eastern Pamir. The study was based on 440 phytosociological relevées sampled between 2009 and 2013 and analysed using direct and indirect ordinations. A set of environmental variables was obtained for each plot: altitude, mean annual precipitation, mean annual temperature, pH, crop type, longitude, latitude and date of sampling (seasonality). Crop type was the major factor determining species composition, which was related to the different farming practices in roots and cereals. Major changes in weed species composition were also driven by altitude and correlated temperatures. The seasonality of weed communities also had a considerable effect on weed community structure. Samples from spring differed significantly from samples from summer and late summer. Only longitude and soil pH were found to be insignificant. The complete set of environmental variables used in a canonical correspondence analysis explained 8.3% of the species variation in sampled plots. The study showed that despite the very diverse climatic conditions and low intensity of agriculture in Tajikistan, agrocoenoses respond mainly to the type of cultivation practised in arable land. [ABSTRACT FROM AUTHOR]

Intensification of agriculture has significantly diminished the populations of segetal weeds worldwide in recent decades. Remarkable changes to the entire flora and vegetation of man-made habitats are being observed in agroecosystems. The present study analyses, for the first time, the threat status of segetal weeds in Tajikistan. A group of 871 weed species were evaluated against IUCN criteria. The assessment of threat status revealed that 214 weed taxa have to be regarded as threatened in Tajikistan, including 18 endemic and four subendemic plants. Five species have been classified as extinct, 27 as critically endangered, 27 as endangered, 39 as vulnerable, 34 as near threatened and 44 as in the 'least concern' category. For 38 species, the threat level was not possible, due to lack of data. The most threatened group of taxa is related to rice paddy fields. Numerous losses and disappearances were also observed in cereal communities. Percentages of threatened species in different chorological groups amounted to 58% in the Irano-Turanian, 17% in the Pluriregional, 11% in the Mediterranean, 9.5% in the Cosmopolitan and 4% in the Euro-Siberian species group. Assessment of the threatened status of the rich segetal flora of Tajikistan affords the opportunity to raise awareness of the value of this group of species in the country and may be useful in the conservation management of arable habitats. The results show that even though agriculture in Tajikistan is still based on traditional management and manual work, weed control causes a serious threat to its segetal flora. [ABSTRACT FROM AUTHOR]

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