Ecogeographical Potential of the Ambrosia artemisiifolia L. Northward Expansion in European Russia Estimated on the Basis of a Comparison of the Northern Limits of Its Primary and Secondary Ranges

摘要

Field studies made it possible to specify the actual modern Ambrosia artemisiifolia naturalization boundary in European Russia. This boundary passes through the southern parts of Bryansk, Kursk, and Saratov oblasts and through the northern part of Voronezh oblast. The total mileage of field survey routes was some 8900 km; 777 sampling points were surveyed. A comparative ecogeographical analysis and modeling of the species distribution in northern parts of its secondary range in European Russia and primary range in Canada were performed to determine the Ambrosia artemisiifolia potential for further northward expansion. It is established that the main factor limiting its northward expansion is insufficient heat supply during the seed ripening period. To determine the ecogeographical niche of A. artemisiifolia, a global map reflecting the distribution of accumulated degree days >10 degrees C was produced for the period starting from the date of the day length transition through 14 h after the summer solstice and ending with the sustainable transition of autumn temperatures through 0 degrees C (accumulated degree days taking into account the photoperiodic threshold (ADD(ppt))). ADD(ppt) values were determined for the northernmost annual ragweed naturalization points in European Russia and in Canada. A comparison of ecogeographical limits performed on the basis of the heat supply factor showed that the ecogeographical niche currently realized by the species in North America is generally wider in comparison with that in European Russia. Possible reasons behind the insufficient occupation of the A. artemisiifolia environmental niche in European Russia were examined; an assumption that the species can continue its northward expansion has been made. On the basis of the heat supply factor, annual ragweed can spread further to the north in European Russia: to Bryansk, Oryol, Lipetsk, Tambov, Saratov, and Orenburg oblasts; to the southern half of Penza oblast; and to southern parts of Ulyanovsk and Samara oblasts and the Republic of Bashkortostan. The northeastward expansion of the species can be hindered by adverse effects of another factor: insufficient moisture supply. At the northern distribution limit of A. artemisiifolia in Saratov oblast and east of it, the species is in the ecological pessimum zone in terms of both heat and moisture supply.