﻿ESTIMATING 
  COMPARATIVE 
  YIELDS 
  AND 
  VALUES 
  

  

  Yields 
  

  

  To 
  evaluate 
  species 
  alternatives 
  in 
  terms 
  of 
  

   wood 
  production 
  for 
  a 
  given 
  period 
  of 
  time, 
  

   some 
  means 
  are 
  needed 
  for 
  estimating 
  com- 
  

   parative 
  volume 
  yields 
  of 
  different 
  species 
  for 
  

   a 
  particular 
  site. 
  This 
  involves 
  an 
  estimate 
  

   of 
  growth 
  potential 
  of 
  individual 
  species 
  in 
  

   different 
  site 
  and 
  habitat 
  situations. 
  At 
  the 
  

   present 
  time, 
  not 
  enough 
  reliable 
  data 
  are 
  

   available 
  to 
  permit 
  making 
  an 
  ideally 
  accur- 
  

   ate 
  estimate. 
  However, 
  some 
  approaches 
  to 
  

   yield 
  estimates 
  do 
  exist 
  and 
  can 
  provide 
  a 
  

   working 
  approximation. 
  

  

  Site 
  index 
  is 
  commonly 
  used 
  to 
  indicate 
  

   relative 
  land 
  quality 
  for 
  any 
  given 
  species. 
  

   Generally, 
  site 
  80 
  land 
  will 
  grow 
  more 
  of 
  a 
  

   given 
  species 
  than 
  will 
  site 
  60 
  land. 
  But 
  site 
  

   index 
  primarily 
  reflects 
  the 
  capacity 
  of 
  the 
  

   trees 
  to 
  attain 
  a 
  specified 
  height 
  at 
  a 
  given 
  

   age, 
  usually 
  50 
  years. 
  It 
  does 
  not 
  tell 
  how 
  

   much 
  timber 
  the 
  site 
  will 
  produce 
  in 
  a 
  speci- 
  

   fied 
  time. 
  In 
  spite 
  of 
  its 
  limitations, 
  however, 
  

   site 
  index 
  does 
  afford 
  a 
  means 
  of 
  separating 
  

   broad 
  classes 
  of 
  land 
  quality 
  with 
  which 
  the 
  

   land 
  manager 
  must 
  work. 
  

  

  In 
  existing 
  yield 
  tables 
  for 
  major 
  species 
  

   growing 
  on 
  white 
  pine 
  land, 
  gross 
  cubic-foot 
  

   volumes 
  are 
  based 
  on 
  the 
  assumption 
  that 
  

   every 
  tree 
  is 
  100 
  percent 
  sound. 
  Projecting 
  

   stand 
  growth 
  over 
  long 
  periods 
  of 
  time 
  re- 
  

   quires 
  downward 
  adjustments 
  for 
  cull, 
  mor- 
  

   tality, 
  and 
  growth 
  loss 
  from 
  natural 
  causes. 
  

  

  Despite 
  the 
  uncertainty 
  of 
  growth 
  and 
  

   losses, 
  a 
  realistic 
  look 
  at 
  the 
  potential 
  yield 
  

   of 
  any 
  given 
  stand 
  will 
  reveal 
  that 
  the 
  yield 
  

   can 
  be 
  expected 
  to 
  fall 
  within 
  some 
  defined 
  

   range. 
  Using 
  species 
  yield 
  tables, 
  the 
  manager 
  

   can 
  determine 
  some 
  probable 
  minimum 
  and 
  

  

  maximum 
  volumes, 
  barring 
  a 
  catastrophic 
  

   wipeout. 
  Then, 
  by 
  ranking 
  the 
  stand 
  for 
  risk, 
  

   the 
  land 
  manager 
  may 
  make 
  an 
  estimate 
  of 
  

   future 
  yields 
  within 
  the 
  probable 
  range 
  and 
  

   define 
  the 
  confidence 
  he 
  has 
  in 
  the 
  estimate. 
  

  

  Values 
  

  

  Estimates 
  of 
  future 
  value 
  yield 
  must 
  be 
  

   based 
  on 
  some 
  assumption 
  about 
  future 
  

   stumpage 
  prices. 
  Presently 
  there 
  are 
  differ- 
  

   ences 
  in 
  average 
  net 
  stumpage 
  prices 
  among 
  

   major 
  species. 
  However, 
  a 
  recent 
  study 
  by 
  

   Benson 
  and 
  Kirkwold 
  5 
  indicates 
  that 
  price 
  

   differences 
  among 
  species 
  have 
  been 
  shrink- 
  

   ing 
  over 
  the 
  past 
  several 
  years; 
  the 
  prices 
  of 
  

   formerly 
  low-value 
  species 
  have 
  been 
  rising, 
  

   while 
  the 
  prices 
  of 
  formerly 
  high-value 
  species 
  

   have 
  been 
  dropping. 
  

  

  If 
  this 
  trend 
  continues, 
  species 
  price 
  differ- 
  

   ences 
  for 
  stands 
  now 
  being 
  regenerated 
  could 
  

   become 
  insignificant. 
  On 
  the 
  other 
  hand, 
  

   these 
  price 
  differentials 
  may 
  not 
  narrow 
  below 
  

   their 
  present 
  spread, 
  or 
  they 
  could 
  widen 
  

   again 
  in 
  the 
  future. 
  

  

  Although 
  estimation 
  of 
  future 
  stumpage 
  

   prices 
  is 
  highly 
  speculative, 
  the 
  land 
  manager 
  

   will 
  have 
  to 
  make 
  some 
  price 
  assumptions 
  in 
  

   the 
  course 
  of 
  species 
  evaluations. 
  In 
  doing 
  

   so, 
  he 
  should 
  recognize 
  that 
  uniformity 
  of 
  tree 
  

   size 
  and 
  amount 
  of 
  merchantable 
  wood 
  per 
  

   acre 
  do 
  influence 
  the 
  net 
  stumpage 
  values. 
  It 
  

   is 
  generally 
  recognized 
  that 
  logging 
  and 
  tree 
  

   conversion 
  costs 
  vary 
  inversely 
  with 
  tree 
  size 
  

   and 
  volume 
  per 
  acre. 
  

  

  •'■Benson, 
  Robert 
  E., 
  and 
  Larry 
  L. 
  Kirkwold. 
  Mar- 
  

   ket 
  trends 
  for 
  western 
  white 
  pine. 
  U.S. 
  Forest 
  Serv. 
  

   Res. 
  Note 
  INT-65, 
  8 
  pp., 
  illus., 
  1967. 
  

  

  9 
  

  

  