Grassland invasions: effects of manipulations of climate and management.
Climate change, in combination with the impacts of land use, will give rise to new opportunities for grassland invasion. This paper reports on the repercussions of a field experiment conducted near Buxton in Derbyshire, UK. Plant species, sown into experimental plots as part of a 6-year study investigating factors limiting the success of seedling invasions, were resurveyed in 1999, 3 years after terminating experimental manipulations of climate, soil fertility and disturbance. The most dramatic observation was the protracted expansion in populations of Brachypodium pinnatum, despite being at the northern limit of its distribution in UK. In contrast, all other sown species, including those of both southern and widespread distribution in UK, had become extinct, declined or remained unchanged in abundance. Patterns of establishment were strongly deterministic. Populations of the southern grass, B. pinnatum, were highest in areas of the experimental plots unamended by fertilizer and physical disturbance, but expansion was apparently promoted by cessation of management. Among invaders of widespread distribution, two were dependent upon fertilizer addition (Arrhenatherum elatius and Dactylis glomerata), one significantly increased its cover with a combination of fertilizer and disturbance (Holcus lanatus), and one benefited from disturbance (Plantago lanceolata). Two southern perennials, Origanum vulgare and Senecio erucifolius, remained present in 1999 in plots that were formerly heated and subject to drought (1991-96), whereas they had become extinct in control plots. Although the most successful invader was a rhizomatous perennial grass, an alternative strategy for survival and expansion was revealed after the severe drought in 1995: gap recolonization by annuals with a persistent seed bank. Most notably, this study revealed the hidden potential of a native species to establish beyond its current range of distribution and, contrary to many recognized weeds, the capacity to achieve dominance in the absence of eutrophication or disturbance. This highlights the potent effects of climate change when plant traits effective for establishment coincide with the removal of current barriers to dispersal.