Dylan Brown Winter Ecology Spring 2014 Mountain Research Station University of Colorado Boulder Introduction Mountain pine beetles are increasing the number of dead trees in our forests Dead trees with no remaining needles intercept less snow and solar radiation than live trees Pugh and Smal ID: 488740
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Slide1
The effect of trees on snowpack: live versus dead lodgepole pines in subalpine forest
Dylan Brown
Winter Ecology Spring 2014
Mountain Research Station, University of Colorado BoulderSlide2
Introduction
Mountain pine beetles are increasing the number of dead trees in our forests
Dead trees with no remaining needles intercept less snow and solar radiation than live trees (Pugh and Small, 2011)
Live trees emit long-wave (IR) radiation and therefore increase the temperature directly underneath the tree (Viglietti
et al
., 2009) Slide3
Question
Q: How do live and dead trees differ in their influences on the snowpack stability?
To answer this question I compared:
snow depth
isolated column tests
slab size
weak layer size and typeSlide4
Methods
Changing Variables: snow depth, stability, and type of layers, grain size
Constant variables: Aspect: NE, elevation: 3000m (9800 ft.) , slope: 27°, species:
Pinus contorta
(lodgepole pine), moderate canopy cover
Variables that are more difficult to control: air temperature, new snow, incoming solar radiationSlide5
Methods
Measurements taken directly next to trees; temperature measured at surface, middle, and bottom; snowpack layers described, isolated column test, and slab size
Analysis: t-test between live and dead tree: snow depths, slab size, and weak layer size. Chi-square analysis for comparing the compression testsSlide6
Results – Snow Depth
Dead Tree mean z = 102.25cm
Live Tree mean z = 79.5cm
T-test (2 tailed, paired)
p
value = 0.002365Slide7
Results - Stability
Dead Trees – Columns easily failed at the depth hoar layer
Live Trees – Columns were more difficult to get to fracture
Chi-square analysis:
p
– value: 0.049787Slide8
Results – Slab Size
Mean Dead tree slab size = 78.25cm
Mean Live tree slab size = 63.25
T-test (2 tailed, paired)
p
value = 0.05261Slide9
Results – Weak Layers
Dead Trees showed larger depth hoar/faceting layers
(avg. 28.75 cm) with larger grain sizesSlide10
Results – Weak Layers
Live Trees showed smaller faceting layers (avg. 16.5 cm) with smaller grain sizes
T-Test (2 tailed, paired)
p –
value = 0.038044Slide11
Discussion
Live and dead trees have significantly different influences on the snowpack in their immediate surroundings
Snow depth, Stability, Slab size, weak layer size
Dead trees create a less stable snowpack
Larger weak layers and slabs
Both can still act as trigger points (Viglietti
et al
., 2009)
Future Research: Temperature differences, different terrain, different speciesSlide12
References
Pugh, E., & Small, E. (2011). The impact of pine beetle infestation on snow accumulation and melt in the headwaters of the Colorado River.
Ecohydrology
,
5
, 467-477. Retrieved February 13, 2014, from http://dx.doi.org/10.1002/eco.239
Viglietti
, D.,
Letey
, S., Motta, R.,
Maggioni
, M., &
Freppaz
, M. (2009). Snow and avalanche: the influence of forest on snowpack stability.
International Snow Science Workshop
,
n/a
. Retrieved February 13, 2014, from http://
arc.lib.montana.edu
/snow-science/objects/issw-2009-0323-0327.
pdf