Palaeoecological reconstructions of vegetation successions in two contrasting former turbaries in the Netherlands and implications for conservation

Abstract Terrestrialization stages of mire vegetation are important to Dutch nature conservancy because of high biodiversity, particularly of base-rich fens. In recent turbaries, terrestrialization has however not shown development of such a stage, while existing rich fens show accelerated development towards species-poor Sphagnum -dominated vegetation, due to acidification and lack of base-rich water input. We apply the analysis of microfossils and macroremains in two peat cores in order to get a better understanding of terrestrialization in the past, and thus provide information on actual vegetation successions, which is directly relevant to nature conservation. The sampling site Stobbenribben showed a vegetation succession under relatively nutrient-poor conditions. The site at Westbroek underwent two peat digging events with one vegetation sequence starting in the 16th/17th century under nutrient-poor conditions, and another during the last century under relatively nutrient-rich conditions. Results from Westbroek showed that if the pond is shallow, rich-fen bryophytes develop relatively close to the bottom of newly formed peat, due to structural support by species such as Equisetum fluviatile and Schoenoplectus lacustris . For Stobbenribben, where the pond is much deeper, rich-fen bryophytes only established after development of a floating root mat with Stratiotes aloides . For both Stobbenribben and 20th century Westbroek, the base-rich fen stage took 60 years to establish and remained for only 30 years without additional input of base-rich water. Our palaeoecological records can be used to provide a longer temporal perspective to address conservation issues of base-rich fens. We conclude that digging up new turf ponds may not be enough to meet the obligations of the Natura 2000 Habitat Directive, if extra measures to prolong the lifespan of rich fens through e.g. temporary inundations with base-rich and nutrient-poor water are not taken into account.