Author(s): Karen Rasmussen (1,2,*), Jakob Thyrring (3,*), Robert Muscarella (1), Finn Borchsenius (4)
Climate is one of the most important determinants of species distributions at regional and global scales (Parmesan & Yohe, 2003; Burrows et al., 2011). Human-induced climate change is affecting global vegetation patterns, ecosystem functions and the distribution range of multiple terrestrial and aquatic species (Cramer et al., 2001; Gonzalez et al., 2010). One dramatic effect of climate change is the shift in species distribution range and phenological interactions (Parmesan & Yohe, 2003; Visser & Both, 2005), which can change the pollen season and lead to increases in local pollen production (Rogers et al., 2006). Allergic responses such as rhinitis (hayfever) and asthma, caused by plant pollen are therefore globally an increasing public health concern (Albertine et al., 2014; Essl et al., 2015; Hamaoui-Laguel et al., 2015; Schindler et al., 2015).
Among allergenic plants, ragweeds (Ambrosia L., Asteraceae) are considered to be among the most potent aeroallergens. Ambrosia is distributed from Mexico to Canada and contains at least 40 species (Essl et al., 2015). Ragweed species flower from July to October and each plant is able to produce millions of wind-dispersed pollen grains that may be transported over long distances, with reports ranging to over 1,000 km (Belmonte et al., 2000; Bullock et al., 2013; Hamaoui-Laguel et al., 2015). Ragweed pollen is a significant cause of allergic reactions (Frenz, 2001; Ziska et al., 2011). The threshold for provoking allergic rhinitis in ragweed pollen sensitized patients is below 20 grains m-3 , and in sensitive patients be as low as 1-5 grains m-3 (Déchamp et al., 1997; Sikoparija et al., 2009) compared to 50 grass pollen grains (Davies & Smith, 1973). Ragweed pollen furthermore induces asthma about twice as often as other types of pollen (Skjøth et al., 2010). In this regard, common ragweed (A.artemisiifolia ), perennial ragweed (A. psilostachya ) and giant ragweed (A.trifida ) are of special concern as they rank among the most widespread allergenic plants (Bassett & Crompton, 1982; Ghosh et al., 1994; Rich, 1994; Frenz, 2001). The medical cost of allergies in the United States is estimated to an annual cost in excess of $18 billion a year (Centers for Disease Control and Prevention, 2011). Ragweed is the major cause of late summer allergic rhinitis (hay fever) in the United States and Canada (Arbes Jr et al., 2005), and is also a significant problem in Southern and Southeastern Europe where allergy is the most common chronic disease (Papadopoulos et al., 2012). Estimated medical costs of ragweed-related allergies are substantial in the affected countries. In Hungary, where 25% of the population is allergic to ragweed, Kazinczi et al. (2008) estimated the annual cost to exceed [euro]110 million per year; in Austria Gerber et al. (2011) put the cost around [euro]88 million per year (for a comprehensive review, see Task 5 in Bullock et al. (2013)).
Ragweed populations remain relatively rare in Northern Europe, where low autumn temperatures prevent ragweed species from flowering...
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