PLS 147 Lecture Notes - Lecture 20: Pinus Albicaulis, Rockfall, Solar Irradiance
Timberline: the upper limit of continuous cover of upright trees
Timberline (subalpine) trees of California
● Whitebark pine (albicaulis)
● Western white (monticola)
● Sierra juniper (Juniperus grandis)
● Mountain hemlock (Tsuga mertensiana)
● Limber (Pinus Flexilis)
● Foxtail (Balfouriana)
● Bristlecone (Longaeva)
● Lodgepole (contorta)
Treeline: no upright trees OR no trees
Alpine: high mountain areas above the limit of tree growth
In California, timberline tends to "peter out" (fade out in a gradient): timberline, treeline, tree species
line, alpine zone
Things that affect treeline
● cold air drainage, snowbed/snowpack, avalanches, no substrate, rockfall, avalanches, fire,
logging, grazing, water-logging
inverted timberline: impeded drainage valley where cold air settles, too cold for trees
Upper (cold) limit for trees
● frost damage
○ freezes roots
○ damage cell walls
(ice crystals)
○ dehydration
● low mean temperature
● low max vs low min
○ soil vs air
● short growing season
○ insufficient C
assimilation
○ insufficient hardening
Upper (drought) limit for trees
● lower precipitation
● less snowpack above timberline
● wind loss so less moisture
● increased evaporation
● soils more rocky/sandy, therefore hold less water
● frozen water not available
● timberline lower at high latitudes ~ around 4000
meters (10k-12k ft)
○ timberline lower at islands or more isolated
mountains
○ higher latitudes are colder, so mountains are
colder. upper cold limit is therefore lower on
mountains at higher latitudes where it is as
cold as southern mountains at a lower
elevation
positive feedbacks : help create a distinct and abrupt micro-climate transition for tree
seedlings
