One of the characteristics of highly invaded ecosystems is that invasive species are often poor invaders of edaphically severe sites, which become refuges for native flora. To investigate the invasive potential of Lolium multiflorum (Hick.) into alkali sites in California, an ex-situ reciprocal transfer experiment was carried out using seeds from populations of L. multiflorum taken from three sites differing in alkalinity (and inundation), including alkali sink soils (pH 8.5) and sink-edge soils (pH 7.4) located within meters of each other, and non-sink soils (pH 5.0) located several km away. Survivorship, plant height, leaf number and seed production were assessed. In addition, a native composite, Hemizonia pungens (Hick.), commonly found on alkali sinks was also sampled at the sink and sink-edge microsites. Lolium multiflorum plants grown from alkali sink and sink-edge seeds produced fewer leaves and seeds but taller plants than plants grown from non-alkali seeds, the latter perhaps an adaptation to inundation. Non-alkali genotypes fared poorly in sink soils for all traits, both in comparison to their growth on non-sink soils, and in comparison to the sink and sink edge genotypes. This suggests the existence of L. multiflorum ecotypes adapted to inundated alkali sinks, a genotypic difference that occurs on a broad spatial scale (kilometers) but not so obviously on the micro-site scale (meters) between sink and sink-edge populations. These data suggest that edaphic refuges from invasives may be temporary, as invaders with tolerance for these severe sites arrive or evolve.
Dawson, K., K.E. Veblen, and T.P. Young. 2007. Experimental evidence for an alkali ecotype of Lolium multiflorum, an exotic invasive annual grass in the Central Valley, CA, USA. Biological Invasions 9: 327-334.