Abstract
A reinventory of the rare forest grasses Festuca altissima , Hordelymus europaeus , Bromus benekenii and Bromus ramosus showed a nearly unchanged distribution pattern in the province of Skåne, S. Sweden, compared to 25–50·years ago. Only Bromus ramosus probably has decreased. As forest soil pH in general has decreased by 0.5 – 1.0 pH-units, there is evidence for a frequency curve displacement towards lower pH during the last 50 years. Field data suggest the following order of sensitivity to low soil pH: Bromus ramosus > Bromus benekenii > Hordelymus europaeus > Fesluca altissima . These observations were confirmed by a pot experiment on germination and growth in an acid forest soil treated with CaCO 3 /MgCO 3 to attain 10 different pH-levels. The lowest pH (H 2 O) for noticeable germination was 5.0 for B. ramosus, 4.6 for B. benekenii and H. europaeus and 4.3 for F. altissima . Growth increased linearly in the pH range 4.1 to 6.0 in all species except F. altissima that did not show improved growth above pH 4.5. In a second experiment, the same soil was treated with CaCO 3 /MgCO 3 , SrCO 3 and CaCl 2 /MgCl 2 , respectively. As in experiment 1, germination and growth were poor in the untreated soil. Addition of CaCl 2 /MgCl 2 did not improve germination or growth. However, establishment and growth of the grasses were promoted considerably by raising the pH to 4.7 ng SrCO 3 or CaCO 3 /MgCO 3 . Growth in the SrCO 3 -treatment was almost as good as in the CaCO 3 /MgCO 3 treatment. The experimental results and their significance for thc distribution of the rare grasses in S. Sweden are discussed. It is concluded that soil acidity at a level characteristic of an increasing number of south Swedish deciduous forests limits establishment of the studied species.
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