Der Einfluß des kontrollierten Brennens auf Esparsetten-Halbtrockenrasen und Folgegesellschaften im Kaiserstuhl
[Controlled burning in the semi-dry grassland of the Kaiserstuhl]
This work ist concerned with the question whether the Onobrychido-Brometum (Esparsetten-Halbtrockenrasen), which was previously used as a meadow, can be preserved by prescribed burning. In some stands of this association which were abandoned for several years the accumulation of litter caused an obvious decrease in the population size of endangered species; sometimes it led to the initiation of potential natural vegetation. Two stands (of different subassociations) of the Onobrychido-brometum underwent prescribed burning during the winter. A maximum temperature of 130 °C was reached 1 cm above ground while at 5 cm above ground the maximum temperature was about 800 °C. One cm in the soil itself the temperature increased only a few degrees. In the spring the biomass net production on the burned plot clearly exceeded that of the unburned plot; in summer and autumn the opposite circumstances occurred. Litter production was higher on the burned plot. The loss which was caused by the burning will be compensated for in 3 to 4 years at the latest. The reaction of the different plant species depended on their life-forms. Species with subterranean stolons, with well developed rhizomes, or with the ability to form root sprouts were favoured even when the fire was weak. On the contrary, those tuft grasses, which are dominating in grassland communities, were sensitive to fire. Weak fires were followed by a slight increase in the number of species per frequency plot (25 cm x 25 cm). On the contrary, with strong fires, those plants tended to predominate which were deeply rooted pioneer species. It is not to be expected in the long run that prescribed burning alone can preserve this phytocoenose. A special problem is the penetration of fire resistent and undesirable species as Brachypodium pinnatum. Burning is not the way to prevent the intrusion of species with which the succession to high forb communities (Geranion sanguinei) begins. At best the author sees possibilities for using prescribed burning in practical nature conservation when combined with mechanical management procedures such as mowing.