Flora 206 (2011) 622–630 Contents lists available at ScienceDirect Flora journal homepage: www.elsevier.de/flora Long-term population dynamics of Dactylorhiza incarnata (L.) Soó after abandonment and re-introduction of mowing Joachim Schrautzer a,∗ , Andreas Fichtner a , Aiko Huckauf a , Leonid Rasran b , Kai Jensen c a Ecology Centre, University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany b Michael-Otto-Institut im NABU, Goosstroot 1, 24861 Bergenhusen, Germany c Biocenter Klein Flottbek, University of Hamburg, Ohnhorststr. 18, 22609 Hamburg, Germany article info Article history: Received 8 July 2010 Accepted 5 November 2010 Keywords: Secondary succession Relative light availability Shade avoidance Litter production Wet grassland restoration abstract The orchid Dactylorhiza incarnata (L.) Soó is a highly polymorphic species listed as endangered in many regional red lists of Central Europe and Scandinavia. The dramatic decline of its populations during recent decades has been caused by the loss and degradation of their natural and semi-natural habitats (fens and wet meadows, respectively) as a result of secondary succession following intensification or abandonment of traditional land use. In this study, we analysed the effects of abandonment and re-introduction of mowing on the long-term (28 years) population dynamics of Dactylorhiza incarnata at Lake Barsbek in northern Germany. In this area, to preserve a remaining population of D. incarnata, an annual mowing regime was re-established in 1981 on site M-1 of the investigated plots after a period of abandonment. Annual mowing was introduced on a second site, M-2, in 1987. Two- to three-year mowing was introduced on a third site, M-3. Site A, abandoned since 1970, was used as a reference. On each of these sites, flowering individuals were counted once a year. Population structure and accompanying vegetation were recorded simultaneously. In 2006, light measurements were carried out in the mowed areas. The D. incarnata population at M-1 increased exponentially during the first 10 years after re- introduction of mowing. Pronounced decreases in the number of flowering individuals were recorded in 1997 and 2003. Population dynamics at M-2 generally resembled the temporal development at M-1. D. incarnata disappeared on site A during the investigation period, while vegetation height and litter layer increased by 60 and 100%, respectively. D. incarnata was able to withstand reduced light availability to a certain extent by increasing its vertical growth (shade avoidance). It is concluded that the maintenance of D. incarnata populations in Central Europe requires continuation or re-establishment of wet meadow management. On previously abandoned sites, an initially higher mowing frequency is recommended. Management intensity can be reduced after phytomass production of the vegetation has declined. © 2011 Elsevier GmbH. All rights reserved. Introduction The early-marsh orchid (Dactylorhiza incarnata (L.) Soó) is a highly polymorphic species (Hedrén and Nordström, 2009; Vallius et al., 2008), listed as “endangered” in many regional red lists of Central Europe and Scandinavia (GBIF, 2009). Its severe population decrease in recent decades has been caused primarily by loss and degradation of natural habitats (nutrient-poor, base-rich or calcare- ous fens) and semi-natural habitats (wet meadows) due to land use intensification, or, in the case of wet meadows, abandonment of ∗ Corresponding author. E-mail addresses: jschrautzer@ecology.uni-kiel.de (J. Schrautzer), afichtner@ecology.uni-kiel.de (A. Fichtner), ahuckauf@ecology.uni-kiel.de (A. Huckauf), Leonid.Rasran@NABU.de (L. Rasran), kai.jensen@botanik.uni-hamburg.de (K. Jensen). traditional moderate land use. Consequently, D. incarnata is a typ- ical target species for the restoration of fens and species-rich wet grasslands (Rosenthal, 2003; Schrautzer et al., 2007). The structural development of wet grasslands after abandon- ment has been described in several studies (Diemer et al., 2001; Moog et al., 2002; Rosenthal, 2010; Schrautzer and Jensen, 1998). In the first phase of secondary succession, competitive, tall, clonal, herbaceous species, regularly present, but suppressed in grazed or mown stands, become dominant. The following phase is character- ized by immigration and establishment of herbaceous, nitrophilous species such as Urtica dioica, Galium aparine and Galeopsis tetrahit. Succession proceeds by way of immigration and establishment of woody species, typically willows and alders. Other, less competi- tive species are sensitive to abandonment. According to an indirect successional analysis of Schrautzer and Jensen (1998), D. incar- nata belongs to those species that disappear relatively early after abandonment of wet grasslands. It exhibits highest abundance in 0367-2530/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2010.11.008