Variation in leaf area index and stand leaf mass of European beech across gradients of soil acidity and precipitation

Leaf area index (LAI, the one-sided foliage area per unit ground surface area) is a key determinant of plant productivity which has a large influence on water and energy exchange between vegetation and the atmosphere. The variation in forest LAI across landscapes and environmental gradients and its causes are not sufficiently understood. We measured the LAI of European beech (Fagus sylvatica) by litter trapping in 23 closed, mature stands across gradients of rainfall and soil acidity or fertility. With a mean LAI of 7.4 m2 m−2 (minimum: 5.6, maximum: 9.5 m2  m−2), beech stands maintained a comparably high leaf area index with relatively small variation along steep environmental gradients. Contrary to expectation, decreasing water availability (rainfall gradient from 1030 to 520 mm yr−1) or increasing soil acidity (pH 3–7) had no significant effect on LAI. Stand leaf mass (Ml) increased slightly with soil fertility (C/N ratio, base saturation). We regressed parameters of site water availability (rainfall), soil fertility or acidity (pH, base saturation, C/N ratio, exchangeable Mg and Al content), and stand structure (stand age and stem density) against LAI and Ml in order to detect environmental controls of stand leaf area. Stand age was the most influential factor for both LAI and Ml (negative relationship). Stem density and the base saturation of the soil affected Ml significantly, but had a weak influence on LAI. We conclude that the leaf area index of beech is mainly under control of age-related physiological factors, whereas the influence of soil chemistry and rainfall is comparably low.