title: Very small relict populations suggest high extinction debt of gingers in primary forest fragments of a tropical city.
abstract: OBJECTIVE
  Tropical plant communities in fragmented forests are likely to experience an extinction debt, i.e., the habitat cannot support as many species as are present due to reduced habitat size and connectivity. There are few estimates of the number of species that represent extinction debt, and the number of extinctions over time has rarely been recorded. We recorded population sizes to assess threats and extinctions in gingers (sensu Zingiberales) in fragmented rainforest in Singapore, ca. 200 yr after fragmentation began.
  
  
  METHODS
  We surveyed extant diversity and population sizes of gingers and used the results to estimate species survival. We critically assessed historic specimens to estimate initial extinctions and extinctions realized in present habitats.
  
  
  RESULTS
  We recorded 23 species, including five species previously presumed nationally extinct and four species omitted from the national checklist. The revised extinction rate is much lower than previously reported (12 vs. 37%). Most gingers have very small populations or miniscule ranges, implying that extinction debt has not been paid off.
  
  
  CONCLUSIONS
  Ginger diversity remains high, but the number of species at immediate risk of extinction outnumber recorded extinctions. Although tropical forest fragments remain arks of plant diversity for a long time, extinction debt may be prevalent in all plant groups in Singapore. Slow relaxation of extinction debt should be explicitly identified as a conservation challenge and opportunity. For conserving plant diversity in tropical fragments, relaxation must be reversed through restoration of degraded landscapes and, where feasible, targeted ex situ conservation and planting.
authors.affiliation: Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore matti.niissalo@gmail.com ted.webb@nus.edu.sg.
authors.forename: Matti A
authors.initials: MA
authors.lastname: Niissalo
authors.affiliation: Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Singapore 259569, Republic of Singapore.
authors.forename: Jana
authors.initials: J
authors.lastname: Leong-Škorničková
authors.affiliation: Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Singapore 259569, Republic of Singapore.
authors.forename: Gillian S
authors.initials: GS
authors.lastname: Khew
authors.affiliation: Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore matti.niissalo@gmail.com ted.webb@nus.edu.sg.
authors.forename: Edward L
authors.initials: EL
authors.lastname: Webb
mesh_terms: D003247:Conservation of Natural Resources / Q000379:methods; D017753:Ecosystem; D053476:Extinction, Biological; D005843:Geography; D020939:Zingiber officinale / Q000145:classification / Q000254:growth & development*; D011156:Population Density; D011157:Population Dynamics; D065947:Rainforest; D012846:Singapore; D013045:Species Specificity; D014329:Tropical Climate
keywords: Red List; Singapore; Zingiberales; deforestation; rarity