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In an old-growth forest in Central Germany, sap flux was studied in five broad-leaved tree species that were assumed to differ in drought sensitivity. Under moist soil conditions, average daily sap flux density (J s ) in the outermost xylem varied by a factor of 2.3 among the species (67-152 g cm −2 per day, n=5 trees per species), and declined in the sequence Fagus sylvatica > Acer pseudoplatanus > Tilia cordata > Carpinus betulus > Fraxinus excelsior. Decreasing soil moisture content ( ) resulted in linearly reduced J s in four of the species. During a dry period, J s was reduced by 44% in T. cordata, 39% in F. sylvatica, 37% in A. pseudoplatanus and 31% in C. betulus compared to sap flux at equal vapour pressure deficit (D) in the wet period. F. excelsior, the only ring-porous species studied, lacked a significant response in J s to D and . The relative reduction in water use during the dry period was not related to the assumed drought sensitivity of the species as inferred from their abundance in natural woodlands. J s was positively correlated with tree diameter at breast height (DBH) in three species but decreased with DBH in two species. Dyeing experiments revealed that DBH accounted for 94% of the variation in sapwood area found in a bulk sample of all diffuse-porous trees. This suggests that DBH is a reliable estimator of sapwood area of temperate diffuseporous species irrespective of species identity. In contrast, sap flux density was found to be greatly dependent on tree species. The estimated whole-plant water use for diffuseporous trees of a given diameter (49 cm) ranged between 74 and 168 kg per day per species under moist soil conditions. Thus, in temperate mixed forests, species-specific differences in water use can result in a considerable spatial heterogeneity of canopy transpiration.

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Leaf litter fall is an important nutrient flux in temperature deciduous forests which supplies a large part of the rapidly mineralisable nutrient fraction to the soil. This study investigates nutrient return with leaf litter fall in 36 old-growth forest stands of Fagus sylvatica across a broad gradient of soil fertility covering 9 mesozoic and kaenozoic parent material types ͑three limestones, two sandstones, two clay stones, one sand and one loess substrate͒. Study objectives were to analyse ͑i͒ the dependency of leaf litter nutrient concentrations on soil fertility, and ͑ii͒ the relationship between soil fertility and nutrient return with leaf litter at the stand level. Beech stands on the nine parent material types produced similar annual leaf litter masses irrespective of soil fertility or acidity. Leaf litter from the nine parent materials showed only minor variation with respect to N and K concentrations ͑factors of 1.5 and 1.4͒, moderate variation for Ca, Mg and P concentrations ͑factors of 2.2 to 2.9͒, and high variation for Al and Mn concentrations ͑factors of 6.7 and 10.5͒. Consequently, annual nutrient return with litter fall ͑leaf litter mass x litter nutrient concentration͒ was more similar among the parent materials for N ͑165-273 mmol m -2 yr -1 ͒ and K ͑16-30 mm m -2 yr -1 ͒ than for Ca, P, Mg, Mn and Al. A possible explanation is increased N deposition in recent time. According to a correlation analysis, return rates of N, P, K and Mg ͑but not Ca͒ were independent of the pool size of the respective nutrient in the soil. N return rate was neither influenced by the soil pools of N t , plant-available P ͑P a ͒ or exchangeable Ca, K and Mg, nor by soil acidity or the exchangeable Al pool. P return, in contrast, showed a negative relation to soil fertility. We hypothesize that nutrient fluxes with leaf litter fall do not necessarily reduce the fitness of tree populations as has been postulated from a tree-centred view. Rather, we suggest that nutrient fluxes with litter fall can increase, instead of decrease, plant fitness by improving nutrient availability in the densely rooted topsoil which reduces the roots' carbon and nutrient costs of nutrient acquisition.