IntroductionThere exists a need in politics, administration, and in practice of forest management for knowledge anddecision support information on conservation and sustainable use of biological diversity in German forests.Therefore the present study investigated the following hypotheses:1)As a consequence of forest management, there exists a higher number of vascular plant species per unitarea in the herb layer of managed forests in relation to ecologically comparable non managed forests.2)With growing management intensity, species composition in vascular plants shifts towards higherfractions of indicator species for disturbance.MethodsVegetation analysis was conducted in 1997 and 1998 in broadleaved lowland forests of Northern Germany onrich soils (county of Herzogtum Lauenburg, east of Hamburg: “SH”) as well as on moderately rich soils(beech,Fagus silvatica, forests of the Mueritz National Park “MV”). Virgin forests do not exist in Germany. So,non-managed (at least for 30 years, up to more than 150 years) forests were contrasted against managed forestsof different management intensity. The latter was measured among others as cubic metres of timber taken perhectare and per year. Soil quality and water supply as well as tree species composition and stand age were ascomparable as possible. Contrary to no longer managed forests, thinning and final timber harvest wereconducted in managed forests.ResultsIn almost every comparison, higher mean species numbers per unit area were found in managed forests asopposed to no longer managed forests (Fig. 1 and 2).In every investigated forest stand, managed or not, the widespread and frequent indicator species for the foresttypes ofQuerco-FageteaandFagetalia(“typical” forest species in a narrow sense)existed in similar densities. Onthe other hand, a significantly higher distribution and density was observed in managed forests for nitrophytesand for indicator species for light (open canopy) and for soil compaction (Tab. 1 and 2). The steadyness valuesof these latter species grows further with raising intensity of forest management (Tab. 1, Fig. 1).ConclusionsHigher numbers of vascular plant species per unit area are possible in managed forests due to a better lightclimate in the herb layer as a consequence of forest operations for timber harvest that open up the canopy.Additionally, heterogeneous soil conditions (bare, accumulated, compacted, etc.) are caused by timber movingoperations and a higher forest road density, both leading to better conditions for establishment and growth ofvascular plants at least temporarily.