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N0. 150: Management of rich fens. Starting in habitats of fen orchid

Andersen, D.K., Ejrnæs, R., Vinther, E., Svendsen, A., Bruun, H.H., Buchwald, E. & Vikstrøm, T. 2015. Forvaltning af rigkær. Udgangspunkt i voksesteder af mygblomst. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 52 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 150. http://dce2.au.dk/pub/SR150.pdf

Summary

A rich fen is a groundwater dependent wetland type, which constitutes some of the most species rich plant communities of the temperate zone. Many of the typical rich fen species are either rare or threatened or they are restricted to this specific habitat type. Danish rich fen area has declined remarkably during the past 200 years as a consequence of drainage and cultivation of former wetlands. Further, the increased availability of nutrients in the Danish landscape has caused the stress-tolerant species to be outcompeted by more competitive species. In Denmark, the Fen orchid, Liparis loeselii, is restricted to groundwater impacted, nutrient poor wetlands such as rich fens. In sites with occurrence of Liparis loeselii, the number of other typical rich fen species is normally high. Further, the species is listed on the Annex II and IV and 12 Natura 2000 areas in Denmark are designated in order to protect this particular species. During the past 200 years Liparis loeselii has been recorded in 105 different locations, but today it is known from only 21 sites out of which some are situated geographically very close.

Despite an intensified awareness on Liparis loeselii and efforts to maintain the current populations, not all populations are stable and in some areas the species has disappeared during the past decades.

Therefore, the Nature Agency, Funen, has initiated a cooperation with Aarhus University and University of Copenhagen as part of the two LIFE-projects, LIFE-Helnæs and LIFE-kær with the purpose to focus the management of Liparis loeselii habitats. A special focus has been given to the two populations on Funen. Here, Liparis loeselii was used as representative of all the vulnerable plant species restricted to rich fens. Consequently, management in favour of Liparis loeselii should benefit the entire group of typical rich fen species.

The present report is the result of this cooperation. In the report the most important factors for the occurrence of Liparis loeselii are pointed out and some specific management tools related to different problems, such as eutrophication and altered hydrology, are suggested. These tools are based on the newest research on Liparis loeselii and the species’ habitat requirements.

The research was based on analyses of data from the National Monitoring Programme, NOVANA, of terrestrial habitats and supplementary field sampling from eight Liparis loeselii sites. Further, the effect of initiated management on nutrient status, light availability and plant species diversity was studied in two fens after several years of grazing and haymaking.

Two models were developed to identify which environmental parameters are having the largest influence on the quality of Liparis loeselii habitats. Further, the value of single species and species combinations as indicators of Liparis habitats were investigated Also, the degree of congruence between the important environmental parameters for typical rich fen species in general and those of Liparis loeselii was investigated.

The interpretation of the models shows that low nutrient status is of high importance. Suitable moisture, a relatively high pH and high light intensity are also important parameters. Further, low nitrogen (N) content in bryophyte tissue and a very low phosphorous (P) content in bryophyte tissue (resulting in a high N/P-ratio in bryophyte tissue) increases the probability of Liparis loeselii occurrence. A limited amount of plant available P in Liparis loeselii habitats is caused by a high content of calcium in the groundwater. There is a high correlation between important environmental parameters of Liparis loeselii occurrence and those of typical rich fen species in general, where nutrient status, light conditions, vegetation height and pH-conditions are the most important environmental parameters.

The models are also used to assess how many monitoring plots in the monitoring programme are suitable for Liparis loeselii. And based on this assessment a list of the sites with the highest number of suitable plots is given. This list is a good basis for a focused searching and management of the species aiming at improving the areas as habitat for Liparis loeselii and other typical rich fen species.