﻿ACADEMY 
  OF 
  SCIENCES. 
  287 
  

  

  The 
  trees 
  are 
  probably 
  affected 
  more 
  by 
  the 
  wind 
  than 
  any 
  other 
  vegetation, 
  

   on 
  account 
  of 
  their 
  height 
  not 
  permitting 
  them 
  to 
  be 
  shelterefl 
  behind 
  hills 
  

   which 
  would 
  protect 
  shrubs 
  or 
  herbs. 
  Thus 
  we 
  find 
  some 
  species 
  becoming 
  trees 
  

   elsewhere, 
  which, 
  on 
  the 
  exposed 
  portions 
  of 
  this 
  peninsula, 
  are 
  only 
  shrubs, 
  as 
  

   well 
  as 
  on 
  some 
  mountain 
  ridges, 
  assuming 
  the 
  aspect 
  of 
  trees 
  stunted 
  by 
  the 
  

   cold 
  on 
  Alpine 
  summits. 
  Dryness, 
  however, 
  is 
  still 
  more 
  influential 
  than 
  cold, 
  

   as 
  seen 
  in 
  many 
  inland 
  localities, 
  especially 
  in 
  the 
  Chestnut, 
  and 
  some 
  other 
  

   species, 
  which 
  are 
  lofty 
  trees 
  or 
  stunted 
  shrubs, 
  according 
  to 
  their 
  water 
  supply. 
  

   One 
  shrub 
  — 
  not 
  rare 
  here 
  — 
  the 
  Juneberry, 
  [Amelanchicr 
  alnifoiia) 
  becomes 
  a 
  

   tree 
  in 
  the 
  moister 
  but 
  cold 
  climate 
  of 
  Montana. 
  It 
  is 
  therefore 
  inadvisable 
  

   to 
  include 
  the 
  shrubs 
  and 
  trees 
  together 
  ; 
  the 
  former 
  being 
  influenced 
  by 
  

   quite 
  different 
  laws 
  of 
  distribution. 
  

  

  From 
  the 
  general 
  course 
  of 
  the 
  mountain 
  ranges, 
  being 
  nearly 
  northwest 
  in 
  

   this 
  region, 
  while 
  the 
  wind 
  strikes 
  their 
  southwest 
  slopes 
  obliquely, 
  and 
  the 
  sun 
  

   in 
  its 
  daily 
  course 
  shines 
  most 
  intensely 
  and 
  longest 
  upon 
  the 
  same 
  exposure, 
  it 
  

   follows 
  that 
  this 
  slope 
  is 
  almost 
  everywhere 
  destitute 
  of 
  trees, 
  though 
  a'ong 
  the 
  

   coast 
  exposed 
  to 
  the 
  greatest 
  rainfall 
  and 
  the 
  most 
  fog. 
  The 
  opposite, 
  or 
  north- 
  

   east 
  slopes, 
  therefore, 
  usually 
  have 
  the 
  greatest 
  tree-growth 
  ; 
  though, 
  in 
  some 
  

   cases, 
  especially 
  south 
  of 
  this 
  latitude, 
  they 
  have 
  less 
  than 
  the 
  southeast, 
  on 
  ac- 
  

   count 
  of 
  the 
  " 
  drawing 
  " 
  of 
  the 
  wind 
  up 
  valleys, 
  and 
  upon 
  them. 
  Were 
  it 
  not 
  

   for 
  the 
  " 
  Tomales 
  Wind 
  Gap," 
  we 
  should 
  doubtless 
  find 
  more 
  species 
  of 
  trees 
  

   growing 
  in 
  the 
  shelter 
  of 
  Mount 
  Tamalpais, 
  thus 
  approaching 
  us 
  nearer 
  from 
  

   the 
  north 
  than 
  from 
  the 
  south, 
  on 
  account 
  of 
  this 
  protection, 
  and 
  the 
  greater 
  

   rainfall 
  northward. 
  These 
  winds 
  seem 
  to 
  act 
  in 
  two 
  ways 
  : 
  First 
  ; 
  by 
  their 
  

   drying 
  power 
  ; 
  as 
  seen 
  in 
  the 
  absence 
  of 
  trees 
  on 
  slopes 
  of 
  hills 
  exposed 
  to 
  them, 
  

   while 
  trees 
  may 
  abound 
  on 
  the 
  opposite 
  slope, 
  though 
  facing 
  the 
  south, 
  and 
  

   more 
  exposed 
  to 
  the 
  sun. 
  Second 
  ; 
  by 
  their 
  coolness 
  not 
  permitting 
  the 
  sun's 
  

   beat 
  to 
  produce 
  a 
  tree-growth, 
  even 
  where 
  moisture 
  is 
  abundant. 
  This 
  acts 
  

   chiefly 
  on 
  the 
  seedling 
  tree, 
  as 
  many 
  species 
  are 
  found 
  to 
  do 
  well 
  when 
  planted 
  

   out 
  where 
  they 
  do 
  not 
  exist 
  naturally, 
  if 
  protected 
  when 
  very 
  young.* 
  

  

  The 
  nature 
  of 
  the 
  soil, 
  or 
  geological 
  formation, 
  influences 
  them 
  secondarily, 
  

   and 
  chiefly 
  in 
  proportion 
  to 
  the 
  amount 
  of 
  moisture 
  retained 
  ; 
  flat, 
  swampy 
  

   lands, 
  and 
  impervious 
  rocks 
  covered 
  by 
  a 
  deep 
  soil, 
  being 
  most 
  favorable. 
  

   Many 
  low 
  lands, 
  however, 
  though 
  very 
  wet 
  in 
  winter, 
  become 
  too 
  dry 
  in 
  sum- 
  

   mer. 
  The 
  summer 
  fogs, 
  also, 
  have 
  some 
  influence. 
  

  

  From 
  these 
  facts, 
  it 
  results 
  that 
  the 
  forests 
  are 
  chiefly 
  most 
  extensive 
  on 
  the 
  

   northeastern 
  mountain 
  slopes, 
  or 
  those 
  nearest 
  the 
  ocean, 
  in 
  exact 
  proportion 
  to 
  

   their 
  extent, 
  altitude, 
  and 
  latitude.f 
  The 
  only 
  tracts 
  within 
  our 
  limits, 
  which 
  

   can 
  properly 
  be 
  called 
  forests, 
  are 
  : 
  First 
  ; 
  the 
  tract 
  covered 
  by 
  the 
  Santa 
  Cruz 
  

   Mountains, 
  of 
  which 
  about 
  half 
  is 
  covered 
  by 
  coniferous 
  trees, 
  an 
  area 
  of 
  about 
  

   1,080 
  square 
  miles. 
  Second 
  ; 
  a 
  tract 
  of 
  less 
  than 
  half 
  this 
  extent, 
  northward 
  

  

  * 
  The 
  effect 
  of 
  wind 
  in 
  sijreading 
  fires 
  in 
  former 
  dry 
  seasons 
  may 
  also 
  have 
  had 
  an 
  influ- 
  

   ence 
  in 
  destroying 
  ancient 
  forests. 
  

  

  t 
  The 
  Sierra 
  Nevada, 
  from 
  their 
  greater 
  altitude, 
  catch 
  the 
  moisture 
  passing 
  east 
  of 
  the 
  

   Coast 
  Range 
  on 
  southwest 
  slopes, 
  wliile 
  the 
  sea-hreeze 
  does 
  not 
  affect 
  them. 
  

  

  