Explaining Exposure and Phellum Pigment in the Cork Layer Oren Rabinowitz Vegetation Ecology CU EBIO 4100 Summer 2014 Introduction Populus tremuloides Michx is a well studied tree in the Rocky Mountains Scientists documented many aspects of the aspens physiological adaptation ID: 171252
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Slide1
Aspen Bark Coloration
Explaining Exposure and Phellum Pigment in the Cork Layer
Oren Rabinowitz
Vegetation Ecology, CU EBIO 4100
Summer 2014Slide2
Introduction
- Populus tremuloides
(Michx) is a well studied tree in the Rocky Mountains. Scientists documented many aspects of the aspen’s physiological adaptations to sub-alpine conifer forests (Pearson 1958, Schaedle et.al. 1967,Debyle 1985, Perala 1990)
- One aspect of the physiology of the aspen tree that remains understudied is the outward appearance of the bark as either greenish, orange or white.
- Various hypotheses have been proposed to explain the color variation in the tree bark.
Malpighiales
-Salicaceae
-PopulusSlide3
Prior hypotheses
Coloration in bark is readily observed but has never been properly described in the scientific literature as it pertains to the tree’s evolution.
- Marr (1947) noticed that early frost damaged white trees more than orange trees.
- Cottam (1954) observed that orange bark trees were found at higher elevations than white bark ones.
- Mitton (1980) suggested that the bark provided a distinguishing feature between male and female ramets, or small sapling suckers.Slide4
Preliminary Research
Microscopy in the Tripp lab and CU Herbarium revealed distinct layering of the cork cambium, subtended by the chlorenchyma and the vascular cambium.Slide5
Hypothesis and Prediction
H1 = Physical weathering is a factor in determining bark colorationH0
= Physical weathering has no effect on bark coloration
Initial tests on cork tissue - White at maturity
- Hydrophobic- Easily removed by physical force
- Burns quickly and completelySlide6
Experimental Design
- The Spot Test: performed on nine total trees from three different stands. Six spots drawn with a pen on the surface at breast height on a randomly selected tree. Microscale physical weathering simulation was used on test spots and color differences were recorded using a color scale.
-
Initial Color and Density
: density readings from canopy mirror and initial color from color scale were measured and recordedSlide7
Sample Areas
A= Elk Meadow, Mountain Research Station, CO.
B
= Mud Lake Open Space, Nederland, CO.
C= Hesse Trailhead, Eldora, CO.Slide8
Kruskal-Wallis H Test
Our Kruskal summary on the ranked data indicates that not all of our group means are the same, and this effect is due to the treatment on color change.Slide9
Density Correlation Test
Slight correlation between density and color. This is most likely due to a sampling error of small size. Insignificant p-value is recorded, but we hypothesize that an increase in sample size would give better workable data.Slide10
Results
Our statistical analysis reveals that the relationship between treatment type and coloration differed significantly for the spot test. Our initial box plot supports the Kruskal summary (p=.04).
Dense stands are protected from weathering and are expected to have whiter bark on appearance. Larger sample will most likely increase our statistical power in this correlation (
p=.19
).Slide11
Discussion and Findings
Fire is the most effective form of physical weathering that reduces accumulation of white bark tissue on cork layer. This phenomenon reveals the orange, immature, non-weatherable bark cells beneath. Water and wind are less effective. Marr and Cottam’s previous hypothesis also support this finding.
There may be a relationship between the
density
of an aspen stand and initial color
, highlighting the effect of dense stand resistance to weathering.
Based on our findings, we can
reject
the null hypothesis (
p=.04
) and say that physical weathering
has
an effect on aspen bark color, by removing layers of mature bark. We
fail to
reject
the null hypothesis that density has an effect on initial color(
p=.19
), but we
assume
that there may be a relationship.Slide12
Further Research
- The specific color of a tree could be more easily quantified using a field tool, or a universal color index for field biologists. Unfortunately these tools have not been invented yet.-Deeply orange/green stands could be reflective of past fire history of an area, but similar tests on coloration and burn history would need to be conducted.
- Aspens may contribute significantly to wildfire fuel load from continual shedding of flammable bark tissue. Slide13
Additional Questions
How long does an aspen take to replenish a white layer of outer bark tissue after a burn?Does sunlight, time or both bleach the initially orange bark cells?
Does the thickness of the cork cambium affect observable tree color?
At what age does smooth, photosynthetic bark become furrowed, inactive bark?
Does a lack of weathering hinder photosynthetic capabilities of the chlorenchyma?
Is chlorenchyma found in other high elevation deciduous species (Salix)?Slide14
Thanks!
Tim Kittel, Erin Tripp, Summer Sugg, Amy Concilio, and this guySlide15
Citations
Cottam, W.P (1954). Prevernal Leafing of Aspen in Utah Mountains. J. of the Arnold Arboretum. Vol. 35 #3 p 239 - 250.
Debyle, N.V., Winokur, R.P. (1985). Aspen : Ecology and Management in the Western United States.
USDA Forest Service General Technical Report
RM-119.
Marr, John W (1948). Frost Injury to Aspen in Colorado.
Ecological Society of America Proceedings.
Vol. 28 #4 p 60.
Mitton, Jeffry B. and Michael C. Grant (1980). Observations on the Ecology and Evolution of Quaking Aspen, Populus Tremuloides, in the Colorado Front Range.
American Journal of Botany.
Vol. 67, #2, pp 202 -209.
Pearson, L.C. and D.B. Lawrence (1958). Photosynthesis in Aspen Bark.
American Journal of Botany
. Vol 45, #5 pp 383 - 387.
Perala, Donald A.(1990), Populus tremuloides Michx. Quaking Aspen.
Aspen Bibliography.
Paper 2878, pp 555 - 569
Schaedle, M. P. Iannaccone, and K.C. Foote (1967). Hill Reaction Capacity of Isolated Quaking Aspen Bark Chloroplasts.
Forest Science,
Vol. 14, #2 pp. 222-223
Yau, Chi. (2004).Kruskal Wallis Test.
R Tutorial.
Web.(http://www.r-tutor.com/elementary-statistics/non-parametric-methods/kruskal-wallis-test)