9. Hemiparasite abundance

Populations of the annual hemiparasites Melampyrum pratense and Melampyrum sylvaticum were studied at treeline of the Swiss Alps after three years of CO₂ enrichment. Total abundance of Melampyrum doubled and plant height of the more abundant and more evenly distributed M. pratense increased by 20%, number of seeds per fruit by 21% and total dry mass per fruit by 27%, but individual seed size did not change. These results suggest that rising atmospheric CO₂ will stimulate reproductive output and increase abundance of Melampyrum, most likely as a consequence of improved host carbon uptake, which given the influence of hemiparasites on the N cycle may have important effects on community dynamics and ecosystem processes in the alpine treeline ecotone.