crops  by  studying  the  height  and  diameter  and  volume  of  growth 
of  the  various  size  classes,  together  with  the  gradual  diminution  in 
numbers  which  takes  place  in  a fully  stocked  crop. 
“ d'hcse  measurements  show  that  the  same  acre  always  produces 
annually  the  same  weight  of  dry  wood,  with  practically  whatever 
species  it  may  be  grown,  namely,  from  4,000  to  8,000  pounds  per 
acre,  according  to  the  quality  of  the  ground.  The  volume  may 
vary  according  to  the  specihc  gravity  of  the  wood  of  different 
species,  and  according  to  ihe  water  contents.  The  annual  pro- 
duction of  available  dry  wood  substance  abo\e  ground  varies, 
according  to  the  quality  of  the  climate  and  soil  from  3,500  pounds 
on  good  sites  to  1,200  pounds  on  the  poorest.  The  number  of  trees 
to  the  acre  is  of  no  consequence,  provided  that  a full  crown  cover 
is  always  kept. ’’ 
I have  on  previous  occasions  given  expression  to  the  fact  that 
overcrowding  should  be  avoided  and  most  practical  men  are  agreed 
on  this  point,  but  the  question  that  arises  is — what  constitutes  over- 
crowding? Let  us  take  a hint  from  nature. 
Dr.  F'ernow  tells  us  that  in  a pure  forest  of  one  species  (and  a 
rubber  plantation  may  be  regarded  as  such)  the  individual  trees  ot 
different  sizes  develop  side  bv  side  according  to  available  light, 
each  crowding  the  other,  unlil  the  laggards  are  kided  by  the  with- 
drawal of  light. 
As  an  example  of  this  he  instances  a stocked  acre  of  American 
white  pine,  containing  50,000  or  more  seedlings  in  a dense  thicket, 
excluding  all  light  from  the.  soil.  “ After  a few  years  the  lower 
branches  owing  to  tli^  absence  of  light  die  and  fall  off — in  the  case 
of  tropical  products  where  the  rate  of  growth  is  much  more  rapid 
this  would  occur  after  a few  months.  At  30  years  old  the  trees 
are  slender  poles  of  about  4 inches  diameter  and  20  to  25  feet  in 
height ; but  different  degrees  of  vigour  of  development,  according 
to  individual  constitution  and  accidental  opportunity,  can  now  be 
recognized,  and  three  classes  maybe  differentiated:  the  predom- 
inant, with  their  crowns  5 to  10  feet  above  the  general  level,  which 
are  the  trees  of  the  future;  the  sub-dominant,  ready  to  occupy  the 
air-space  of  any  of  the  superior  class  should  accident  remove  any 
of  them;  and  Iastl)q  the  suppressed  ones,  doomed  to  die.” 
“Out  of  the  tens  of  thousands  which  started,  only  2,000  or  3, 030 
survive,  and  as  each  tree  is  striving  with  its  neighbours  tor  as  much 
air-space  and  root-space  as  possible,  the  result  is  a continued  di- 
minution of  the  number  of  trees  occupying  the  acre.” 
“This  decimation  is  in  exact  mathematical  relation,  barring  ac- 
cidents, with  the  development  of  the  dominant  class  in  height- 
growth.  ” 
“ At  the  age  of  80,  not  more  than  400  to  500  trees  are  left. 
After  this  age  the  diminution  proceeds  more  slowly  until  at  last 
only  200  or  300  stems  occupy  the  ground,  the  number  varying  with 
s[)ecies,  soil  and  climate.” 
We  See  then  that  out  of  50,00a  seedlings  no  less  than  4^)'^^^ 
