Growth and leaf traits of four broad-leaved tree species along a hillside gradient

Abstract

In order to support an appropriate species selection for the establishment of mixed forest stands, we studied the changes in growth and leaf traits of four tree species (Fagus sylvatica L., Acer pseudoplatanus L., Tilia platyphyllos Scop., Fraxinus excelsior L.)along a hillside gradient. The nutrient-rich soils at the study site in North-Hesse (Central Germany) are derived mainly from basalt. The volumetric stone content was 10% on the lower slope and 25% on the upper slope (0–10 cm soil depth). Sycamore, beech and broad-leaved lime trees were planted after the breakdown of a Norway spruce stand. Ash migrated into the stand by natural regeneration. The studied trees were about 6 years old. In both study years, the height increment decreased along the gradient for all species. The increment was lowest for sycamore on the upper slope where only 16% of the increment on the lower slope was observed (beech 36%, broad-leaved lime 48%, ash 47%). Leaf sizes and leaf areas per tree decreased and stomatal densities increased along the gradient indicating a response to decreasing water supply. Within a species no significant differences of leaf δ13C values were observed on the different slope positions, which suggests that there was no change in the water use efficiency of photosynthesis at the leaf level. Foliar N and K contents were highest on the lower slope plot and lower on the mid- and upper slope, which does not reflect differences in soil chemical conditions. We assume that plant nutrition was impaired mainly by soil water shortage. Following these results, ash and broad-leaved lime appear to be more suitable tree species for the establishment of mixed forests at nutrient-rich sites with restricted water supply than sycamore. Beech occupied an intermediate position.