﻿Gleason; 
  Some 
  appltcations 
  of 
  the 
  quadrat 
  method 
  81 
  

  

  Jaccard's 
  community 
  coefficient 
  

  

  betw 
  

  

  tation. 
  His 
  method 
  is 
  to 
  divide 
  the 
  total 
  number 
  of 
  species 
  in 
  

   both 
  areas 
  into 
  the 
  number 
  common 
  to 
  both. 
  Thus, 
  two 
  areas, 
  

   each 
  containing 
  30 
  species, 
  of 
  which 
  20 
  were 
  common 
  to 
  the 
  two, 
  

   contain 
  a 
  total 
  of 
  40 
  species, 
  and 
  the 
  community 
  coefficient 
  is 
  

   accordingly 
  50, 
  Jaccard's 
  method 
  fails 
  to 
  take 
  account 
  of 
  the 
  

   much 
  greater 
  importance 
  of 
  some 
  abundant 
  species, 
  and 
  the 
  

   resulting 
  error 
  of 
  computation 
  may 
  be 
  obviated, 
  in 
  part 
  at 
  least, 
  

   by 
  weighting 
  each 
  species 
  with 
  its 
  frequency 
  index. 
  Referring 
  

   to 
  columns 
  5 
  and 
  6 
  of 
  Table 
  I, 
  and 
  weighting 
  each 
  species 
  with 
  

   its 
  average 
  index 
  in 
  both 
  columns, 
  the 
  results, 
  shown 
  in 
  Table 
  II 
  

  

  TABLE 
  II 
  

  

  Pleris 
  aquilina 
  

  

  Vaccinhtm 
  pennsylvanicum 
  

  

  Gaylussacia 
  baccata 
  , 
  

  

  Aster 
  laevis 
  

  

  Carex 
  umbellata 
  

  

  Rhus 
  glabra 
  

  

  Rumex 
  Acetosella 
  

  

  Rubus 
  allegheniensis 
  

  

  Panicum 
  boreale 
  

  

  Danthonia 
  spicata, 
  . 
  . 
  . 
  

   Gaultheria 
  procumbens 
  

   Gnaphalium 
  deciirrens, 
  

   Populus 
  grandidentaia, 
  

   Hieracium 
  venosum. 
  . 
  . 
  

  

  Erigeron 
  canadensis. 
  . 
  . 
  . 
  

   Panictitn 
  xanthophysum 
  

   Diervilla 
  Lonicera 
  

  

  Solidago 
  canadensis, 
  , 
  , 
  

  

  Agrostis 
  hyemalis 
  

  

  Lactuca 
  canadensis. 
  . 
  . 
  . 
  

  

  Poa 
  compressa 
  . 
  , 
  

  

  Quercus 
  rubra 
  

  

  Coviandra 
  umbellata, 
  . 
  . 
  

   Amelanchier 
  canadensis 
  

  

  In 
  first 
  

  

  area 
  only 
  

  

  Common 
  to 
  

   both 
  areas 
  

  

  2.5 
  

  

  7-5 
  

  

  X 
  

  

  IS 
  

  

  13.5 
  

  

  

  - 
  

  

  99 
  

   80 
  

  

  42.5 
  

   33-S 
  

   38-5 
  

  

  20 
  

  

  26 
  

  

  8.5 
  

  

  13.5 
  

   II 
  

  

  S 
  

  

  4-5 
  

  

  2-5 
  

  

  433.5 
  

  

  

  In 
  second 
  

   area 
  only 
  

  

  5 
  

  

  1-5 
  

  

  I 
  

  

  8-5 
  

  

  are 
  obtained, 
  from 
  which 
  the 
  community 
  coefficient 
  of 
  the 
  two 
  

   areas 
  concerned 
  is 
  determined 
  as 
  95, 
  by 
  dividing 
  the 
  sum 
  of 
  the 
  

   three 
  columns, 
  455.5, 
  into 
  the 
  sum 
  of 
  the 
  center 
  column. 
  

  

  By 
  Jaccard's 
  method, 
  giving 
  equal 
  weight 
  to 
  each 
  species, 
  24 
  

   total 
  species 
  divided 
  into 
  15 
  common 
  species 
  = 
  CC 
  62. 
  

  

  