Window of opportunity of Liparis loeselii populations during vegetation succession on the Wadden Sea islands

Donovan Amatirsat,Annemieke Kooijman,Gerard Oostermeijer,Chantal Bland,Ab Grootjans,Jörg Petersen,Annelies Van De Craats,Pieter Stuyfzand,Rohani Shahrudin

doi:10.1007/s11852-016-0448-6

Abstract

The present study aims at assessing the life span of populations of the orchid L. loeselii during successional in dune slacks on the Wadden Sea islands. An inventory of Liparis loeselii populations was carried out on 6 islands, while the population structure was assessed in more detail on the island of Texel. The occurrence of the orchid was related to soil factors and hydrological conditions. Groundwater levels were measured in a dune area with natural dune slack formation. The groundwater composition was analyses and the freshwater lenses were modelled. Various scenarios were investigated, including sea level rise and sand nourishment. The window of opportunity for L. loeselii to colonize a new slack is relatively narrow. Under favorable management, the population can survive c. 20 years. Soil pH was positively correlated with the occurrence of L. loeselii populations, while a high organic matter content was negatively correlated. Sites with large populations of L. loeselii, were situated in young dune slacks, that functioned as flow-through lakes and has top soilsinfluenced by anoxic calcareous groundwater. Modelling showed that the freshwater lens would decrease due to sea level rise, while artificial sand nourishment could counteract this effect. The populations of the Hors area on Texel, the Netherlands, can survive for several decades due to continuous formation of new slacks. Discharge of calcareous groundwater is essential to keep the pH on a high level. The hydrological systems that supply dune slack with groundwater are relatively small and are vulnerable for changes in sea level rise.

Highlights

Liparis loeselii loeselii (L.) Rich. is a small orchid which in coastal wetlands thrives on mineral soils (Jones & Etherington 1992, Lammerts & Grootjans 1998, Petersen 2000, Oostermeijer & Hartman 2014)
We addressed two questions: (i) what is the window of opportunity for L. loeselii under regular mowing of the vegetation compared to a strategy of Dynamic Coastal Management in which natural processes create new dune slacks?, and (ii) which eco-hydrological conditions are favourable for the long-term survival of L. loeselii populations on the Wadden Sea islands?
In 2010 the highest number of individual of Liparis loeselii on the Wadden Sea islands were found on the island of Texel (± 18,000 at the south-eastern part of the island, most of them occurring in dune slacks of 5–15 years old (Table 1)

Summary

Introduction

Liparis loeselii loeselii (L.) Rich. is a small orchid which in coastal wetlands (interdunal slacks) thrives on mineral soils (Jones & Etherington 1992, Lammerts & Grootjans 1998, Petersen 2000, Oostermeijer & Hartman 2014). Is a small orchid which in coastal wetlands (interdunal slacks) thrives on mineral soils (Jones & Etherington 1992, Lammerts & Grootjans 1998, Petersen 2000, Oostermeijer & Hartman 2014). Liparis loeselii has a wide distribution, ranging from the northeast of the United States and Canada, to northern and Central European countries, Russia and even several localities in Siberia Despite this wide distribution area, populations of L. loeselii are in serious decline along most of its geographical range. In Central Europe it is considered as an endangered species (Schnittler & Günther 1999) and has been listed in Annex II and Annex IV of the Council Directive 92/ 43/EEC on the Conservation of natural habitats, making it a priority species for conservation in most European countries

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Conclusion