Floral free fall in the Swiss lowlands: environmental determinants of local plant extinction in a peri‐urban landscape

Abstract

Summary1 Local floras are being depleted by a host of human activities, including habitat destruction and fragmentation, eutrophication, and the intensification of agriculture. Species with particular ecological demands or life-history attributes are more prone to extinction than species with a broader niche. 2 We used an old herbarium from the municipality of Küsnacht (Swiss lowlands) as a historical record for comparison with contemporary plant diversity. This comparison revealed that 17% to 28% of all vascular plants that occurred between 1839 and 1915 were extinct by 2003. 3 Species of different habitats and life-forms had significantly different rates of extinction: wetlands, disturbed sites and meadows lost most species, whereas forests and rocky habitats were least affected; aquatics and annuals were most prone to extinction, geophytes and hemicryptophytes were intermediate, and phanerophytes and chamaephytes were least affected. 4 Species adapted to nutrient-poor soils suffered highest extinction in all habitats, indicating that eutrophication poses an urgent threat to species diversity. Light and soil moisture requirements also had significant effects on extinction, but the direction of the effect varied by habitat. 5 When species were grouped into IUCN categories of the red list of Switzerland, the rank order of the observed extinction matched the red list assignment. 6 Because many of the remaining species had high estimated extinction probabilities and because extinction is often delayed (extinction debt), a substantial part of the remaining flora of Küsnacht is likely to go extinct in the near future. This will increase the dominance of the common species that already comprise 81% of the local flora. 7 The rates and patterns of extinction in Küsnacht are probably representative of surrounding Swiss lowlands and peri-urban landscapes in most developed countries. Studies such as ours can serve as a call for action and form a basis for future monitoring of biodiversity.

Changes in Plant Species Composition and Structure in Two Peri-urban Nature Preserves over 10 Years

“…Native species declined over 70% in Central Park in New York City, New York, U.S.A. over the last 100 years while nonnative species, mostly species widespread throughout the city, increased (DeCandido et al, 2007). Over 20% of native vascular plants species present in a periurban area in Switzerland in 1915 were extirpated by 2003 (Stehlik et al, 2007).…”

“…This change in land use is generally attributed to 'urban sprawl' caused by rapid population growth and/or the changing patterns of commercial life in urban centers (Mieszkowski and Mills, 1993;Brueckner, 2000). In comparison to long established urban areas, peri-urban habitats, defined as areas surrounding formal urban boundaries, are undergoing rapid land use changes often resulting in habitat loss (McKinney, 2008) and decreases in biodiversity (McKinney, 2008;Stehlik et al, 2007). This is unfortunate as these peripheral habitats can act as dispersal corridors between rural and urban environments (Snep et al, 2006).…”

Change and causes of change in the vascular plant flora of Ireland: 1970–1999

“…This approach, which generates an Index of Change across a whole flora, has since been used to show change in regional floras in the UK, Belgium, the Netherlands, Switzerland, France amongst others (Preston et al, 2002a, Walker, 2003, van der Veken, 2004, Tamis et al, 2005, Stehlik et al, 2007, van Calster et al, 2008, van Landuyt et al, 2008.…”

Do plant reproductive traits influence species susceptibility to decline?

“…Several studies have examined the distribution of rare vs. common species across a variety of ecological and lifehistory traits, such as competitive ability, habitat specialisation, growth form, plant height, dispersal mode, seed size, seed number, clonality, specific leaf area, flowering period (Lahti et al 1991, Cadotte & Lovett-Doust 2002, Lavergne et al 2004, Pilgrim et al 2004, Bekker & Kwak 2005, Kolb & Diekmann 2005, Farnsworth 2007, Stehlik et al 2007, Farnsworth & Ogurcak 2008, Gargano et al 2009, Cornwell & Ackerly 2010, Duncan et al 2011). Some traits have been shown to correlate with extinction risk in plants, such as plant height, longevity, growth form, seed mass, and the size and persistence of the seed bank (Pimm et al 1988, Leach & Givnish 1996, Stöcklin & Fischer 1999, Williams et al 2005.…”