IS THE CA-AL RATIO SUPERIOR TO PH, CA OR AL CONCENTRATIONS OF SOILS IN ACCOUNTING FOR THE DISTRIBUTION OF PLANTS IN DECIDUOUS FOREST

The distributions of vascular plants in south Swedish deciduous forest s were related to exchangeable (exc) and soil solution concentrations of H+ (pH), Ca, Al and the Ca:Al ratios within these fractions. Topsoi ls (0-5 cm) of 172 sites with a pH(KCl) of 3.2-3.9 (corresponding to 3 .7-4.4 in soil solution) were used. In the soil solution both total Al , and quickly reacting Al, were determined. Exchangeable concentration s were generally well related to plant distributions, the highest corr elation coefficients usually being given by pH(KCl)>Ca-exc>Al-exc.>(Ca :Al)(exc). The (Ca:AI),,, ratio was clearly inferior. Out of the soil solution variables studied, Ca concentration, followed by pH, was best correlated with plant distributions, Al-t, Al-r, and the Ca:Al ratios having similar and lower coefficients. It is concluded that the use o f Ca:Al ratios as a general measure of Al toxicity in controlling plan t distributions is rather problematic. It seems difficult to apply evi dence for Ca-Al interactions from solution culture experiments to fiel d conditions when measured as exchangeable or soil solution concentrat ions of the soil.