Did recent climatic shifts affect productivity of grass-dominated vegetation in southern Switzerland? Evidence from time series of two semi-natural grasslands and a maize field

Time series of crop data from three grass-dominated ecosystems in southern Switzerland were selected for a comparison with climatic variables over the past decades. Standing crop from two permanent species-rich grasslands at Prugiasco and Salorino and the kernel yield of maize planted every year in monoculture at Cadenazzo were measured using standardised methods under controlled conditions in experimental areas over 13 (1988-2000) or 28 (1972-1999) years, respectively. The maize series was corrected for effects of sowing density and genetic variation due to the change of varieties over time. The sensitivity of crop variables to climatic variables, temperature, precipitation, relative humidity and duration of sunshine, recorded at Locarno-Monti, was calculated for 3-month and half-year intervals in 1-yr periods previous to harvest dates. Yields in semi-natural grasslands and in the maize field significantly responded to climatic variables, which were not subject to long-term trends, relative humidity or sunshine, respectively, during the growth period. A series of extremely dry summers negatively affected yields of the maize field and triggered a lagged shift towards a reduced grass-forb ratio in the harvest of the more intensively mown meadow. Dry summers were explained by a lee-effect of upper-level winds blowing from a more northward direction over the Alps in 1989-1991. It is concluded that grass-dominated vegetation in the Southern Alps was more sensitive to changing precipitation patterns than increased temperatures. The vegetation response to climate depended on the methods of human interference.