The effect of tree density and height on tree-flagging of Lodgepole Pines in Niwot’s sub-alpine
forest
Michael D. SchusterWinter Ecology – Spring 2010
Mountain Research Station – University of Colorado, Boulder
Mechanisms of tree flagging• Predominately carried out by
wind• Krummholz: “Crooked Wood” in
German; These are the type of trees/shrubs near or at treeline
• Reasons for bareness of trunk: lack of SR
In the Big Picture
• Why is this important?• Useful for forestry practices • Can put in context of CC scenario• Affects passage of mammals
Observations and Hypothesis• I noticed that the trees had varying heights of bare trunk and
branches, and this general height changed when the trees were either taller or closer together
• Hypothesis: affected by amount of sun reaching lower branches, not by krummholz or wind as much– As the avg height increases, the height of the bare tree will also
increase– As the L.P. Pine density increases, the height of bare tree should also
increase (more trees-more coverage-less sun to ground)
Methods
• 10x10 m transect• Clinometer, field tape, flags, snow probe• Total density, density of conifers• Avg height (clinometer), snow depth
1 2 3 4 5 60
2
4
6
8
10
12
14
16
18
20
Average tree heights of Lodgepole Pines in the Niwot sub-alpine forest
Avg tree height
Height of bare tree
Site # (increasing elevation)
heig
ht (m
)
1 2 3 4 5 60
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Average Lodgepole Pine density per 10m2 transect, Niwot sub-alpine
forest
Site # (increasing with elevation)
Dens
ity o
f tre
es (#
tree
s per
m2)
8 10 12 14 16 18 20 22 240
10
20
30
40
50
60
70
80
f(x) = 2.9495186495504 x + 11.3637671757702R² = 0.188493100347563
f(x) = 0.149151441250783 x + 61.0416121762708R² = 0.00268070122608988
f(x) = NaN x + NaNR² = 0f(x) = NaN x + NaNR² = 0f(x) = NaN x + NaNR² = 0f(x) = NaN x + NaNR² = 0
% of bare tree per change in height Site 1
Linear (Site 1)
Site 2
Linear (Site 2)
Site 3
Linear (Site 3)
Site 4
Linear (Site 4)
Site 5
Linear (Site 5)
Site 6
Linear (Site 6)
total height of tree (m)
% o
f tre
e fla
gged
(with
nee
dles
)
P-value = 0.0128
10 20 30 40 50 60 700
10
20
30
40
50
60
70
f(x) = 0.373175015209742 x + 38.4578122098006R² = 0.826035429660517
% of bare trunk per density of transect
number of conifers
% o
f tre
e ba
re
Site # P value1 0.3669412 0.0375383 0.0674364 0.006195 0.0103936 0.762244
Conclusions
• Total L.P. Pine height increases with elevation• Bare trunk height is variable—other factors• Density increases with elevation• % of bare trunk increases with increase in
total height• No significant results—other variables are
affecting the outcome
Other variables to consider
– Slope of transect– Aspect of transect (tried to keep this constant)– Elevation– Type of forest (are there deciduous trees)– Amount of exposure (wind– Snow depth (how does this affect height of bare
tree)– Inaccuracies with measurements (10 m distance of
transect, from tree, density average)
Suggestions for next time
• Bring an altimeter, measure elevation• More accurate measurments of snow depth• Find a better way to measure density• Choose transects carefully, controlling for:– Slope, aspect, exposure, types of trees (no
deciduous)
Finally, for next time: BRING A CAMERA
Works Cited
• Reference articlesArno, Steven F. Timberline: Mountain and Arctic Forest Frontiers. Chp.1 excerpt, prepared by CU.
New York, 2007.
• Pictures:– http://www.daviddarling.info/images/vegetation_flagging.gif– http://www2.swgc.mun.ca/botany/burntisland/images/Flagging%201.
jpg
