MONITORING OF A FOUNDER POPULATION OF THE HART’S TONGUE FERN (ASPLENIUM SCOLOPENDRIUM) ON A FORMER SEA-FLOOR (JAGERSVELD) OVER 34 YEARS (1985 - 2018).

摘要

Over a 34 year period a founding population of the Hart’s Tongue Fern was monitored in the Jagersveld near Lelystad (reclaimed polder O.-Flevoland; 1957), a young woodland plantation on a former sea-floor with a sandy clayish soil. In 1985 there wereonly two individuals, but numbers increased sharply in the late 1990s and since 2005 has matched the national trend. The first cohort consisted of plants that established independently and subsequent recruitment was strongly related to these founding plants. The longevity of sporelings, juvenile and subadult plants proved to be 1.1,1.6 and 1.7 years. Adults lived on average 4.4 years based on plants that completed their whole life cycle during the 34 years of monitoring. The half-life of the whole population was 4.5 years. Annual rainfall had a positive impact on the survival of adults, spring rainfall on the transition from juvenile to subadult. Severe winters had no impact, probably because winters became milder. Small-scale land-slips along the (dry) ditches and self-thinning were shown to be the most important factors in mortality. A further increase in population size is expected because of the increase in mild winters associated with climate change.