The relationship between dry grassland vegetation and microclimate

Abstract

Bruelheide, H.; Jandt, U.: The relationship between dry grassland vegetation and microclimate along a west-east gradient in Central Germany. – Hercynia N.F. 40 (2007): 153 -176.In the southern Harz and Kyffhäuser Mountains dry grasslands are found on calcareous soils on gypsum bedrock along a steep climatic gradient. With only little differences in soils and land use, climate can be assumed to be the main factor controlling the occurrence of different vegetation types of dry grasslands. For gradient studies at broader scales, climate data are normally available only from official weather stations and, thus, refer to macroclimate. As the microclimate encountered by plants on a specific site usually differs considerably from standard weather station recordings, this paper addresses the questions (1) whether a gradient in the study area is also apparent in microclimate, (2) whether macroclimate is reflected in microclimate, and (3) to which degree microclimate explains the floristic gradient in the study area. Climate data were compiled at three different temporal scales for twelve sites along a gradient running from north-west to south-east at equal altitudes: (1) long-term averages from official meteorological stations, (2) hourly temperature records over one year from automatic microclimate datalogger and monthly precipitation recordings from 12 dry grassland sites, and (3) half-hourly temperature, air humidity and evaporation data over one day from a measurement campaign carried out simultaneously at all sites. The results showed that a microclimate gradient was clearly apparent in precipitation but not in temperature. Dry grasslands in the southern Harz and Kyffhäuser Mountains encounter more or less the same microclimatic conditions with respect to temperature but differ considerably in amount of precipitation. In consequence, there was no correlation between microclimate and macroclimate for temperature but a significant relationship for precipitation. The floristic inventory of the study sites showed a clear gradient from west to east, which is well reflected in microclimate conditions. Among all climate variables measured, stronger correlations with floristic composition were encountered for precipitation than for temperature. We conclude from this that the most relevant climate factor for the differentiation of dry grassland vegetation along the studied gradient is precipitation rather than temperature.