Christopher WhiteEBIO 4100 – Winter Ecology

Spring 2012

Variables Affecting Tree Well Formation

http://www.steamboattoday.com/news/2008/jan/17/hidden_dangers/

Tree Well Formation• The tree wells that form at the

bases of trees in the winter are a result of radiative balance within the tree.

• As the tree absorbs short wave radiation from the sun, it then emits long wave radiation to preserve this radiative balance.

• This long wave radiation melts the snow at the base of the tree, creating a depression in the surrounding snow.

http://www.skimaven.com/post/single-chair-rides-and-powder-turns-at-vermonts-mad-river-glen/

Tree Wells, Who Cares?

• These tree wells create lots of variation in snow depth within a region:- Can affect which animals, plants, and microbes are present- A dense forest can collectively alter the snowpack surrounding the trees

• Recreational Accidents:- Many people die each year by falling into tree

wells- Tree wells can be deceivingly large, and if a

skier or a snowboarder falls into them, it can be an extremely dangerous situation

For safety information: http://www.treewelldeepsnowsafety.com/index.php

http://www.skiwhitewater.com/store/images/treewell.jpg

Question

• What are the relationships between DBH, tree height, surrounding tree density, and tree species on the size of tree wells? Which are most important, and which have no significance?

Hypotheses

• DBH: The wider the tree, the larger the well• Tree Height: The taller the tree, the larger the

well• Surrounding Tree Density: The denser the

transect, the smaller the wells• Species: The darker the bark, the larger the

wells (proportional to size)

Previous Studies• Lot’s on tree well influence, not much on formation:- “The net effect of forest canopies is a snowpack with spatially

heterogeneous depth and snow water equivalence (SWE)”- “In Northern Vermont, Hardy and Albert [1995] measured

approximately one third less snow at the time of peak SWE beneath the canopy as found in the open. In the boreal forest, Pomeroy and Schmidt [1993] observed snow beneath jack pine canopy equal to 55% of the undisturbed snow, while in Alaska’s taiga, Sturm [1993] found snow depths at the tree trunks equal to approximately 20% of the undisturbed snow.”

Methods

• Identify the tree species• Measure:- Tree Well Radius and Depth- DBH- Tree Height• Measure 25 m2 transect (5x5) – count trees to

determine density

http://media.lonelyplanet.com/lpi/15169/15169-3/681x454.jpg

RESULTS

DBH

0 50000 100000 150000 200000 25000005

1015202530354045

f(x) = − 6.2457962921459E-10 x² + 0.000263991446006249 x + 13.1478864987938R² = 0.520956824403615

DBH vs. Tree Well Volume

DBH (cm)Polynomial (DBH (cm))

Tree Well Volume (cm^3)

DBH

(cm

)

n 20

R^2 0.521

p(t) 0.000327334

Significant Relationship!

Tree Height

NO Significant Relationship!

0 5000 10000 15000 20000 25000 30000 35000 40000 450000

5

10

15

20

25

f(x) = − 4.42597702572201E-09 x² + 0.000229648709499509 x + 8.93850935465823R² = 0.0332069417274513

Tree Height vs. Tree Well Volume

Tree Height (m)Polynomial (Tree Height (m))

Tree Well Volume (cm^3)

Tree

Hei

ght (

met

ers)

n 20

R^2 0.033

p(t) 0.441904197

Surrounding Tree Density

0 50000 100000 150000 200000 2500000

5

10

15

20

25

30

f(x) = 3.80884648537568E-10 x² − 0.000159743070112237 x + 18.0092754907397R² = 0.283155236366994

Surrounding Tree Density vs. Tree Well Volume

Surrounding Tree DensityPolynomial (Surrounding Tree Density)

Tree Well Volume (cm^3)

Tree

Den

sity

(per

25m

^2)

n 20

R^2 0.283

p(t) 0.015730325

Significant Relationship!

Tree Species

Lodgepole Subalpine Fir Aspen0

5000

10000

15000

20000

25000

30000

35000

Tree Species and Tree Well Volume

Tree Well VolumeDBH

Species

Mea

n Tr

ee W

ell V

olum

e (c

m^3

)

?

Tree Species

Lodgepole Subalpine Fir Aspen0

5000

10000

15000

20000

25000

30000

35000

Tree Species and Tree Well Volume

Tree Well VolumeDBH

Species

Mea

n Tr

ee W

ell V

olum

e (c

m^3

)

Lodgepole Subalpine Fir Aspen0

5000

10000

15000

20000

25000

30000

35000

0

5

10

15

20

25

Tree Species and Tree Well Volume

Tree Well VolumeDBH

Species

Mea

n Tr

ee W

ell V

olum

e (c

m^3

)

Ratios (Volume/DBH):Lodgepole Pine: 1457.46

Subalpine Fir: 1235.65Aspen: 184.62

Discussion

• DBH: Significant Relationship (Confirms Hypothesis) – Why?

- The wider the tree, the more surface area exposed to the sun, the more short wave radiation, the more long wave radiation emitted

• Tree Height: Not Significant (Rejects Hypothesis) – Why?- Radiation received at the top of the tree does not have a

large impact on radiation emission at the base of the tree. Other factors are inhibiting – tree bark heat transmission.

Discussion

• Surrounding Tree Density: Significant relationship (Confirms Hypothesis) – Why?

- Competition for light in dense areas of the forest limit the amount of short wave radiation exposure – as a result, tree wells are generally smaller

• Tree Species - ????????

Tree Species

Lodgepole PineSubalpine Fir

Aspen

Due to lack of proper equipment (radiometer to actually measure longwave radiation coming from the tree), I’m going to make the assumption that

Lodgepole Pine has the largest tree wells (proportional to DBH) due to its darker bark color in comparison with Subalpine Fir and Aspen. A darker bark color will

absorb more solar energy, and as a result, the tree will emit more long wave energy, melting more snow and creating larger tree wells.

Sources of Error

• First day of data collection followed precipitation event – may have filled tree wells

• Assumed perfectly geometric shapes (when calculating volume of the tree well)

• Tree selection wasn’t exactly “random” – looked for trees with prominent/measurable tree wells (lots were filled in with snow)

Future Experiments

• Microbial respiration rates vs. tree well depth• Animal activity around tree wells• Use a radiometer to actually measure

longwave emissions

http://www.erdc.usace.army.mil/pls/erdcpub/docs/erdc/images/Measuring_spatial_variability_of_longwave_radiation.jpg

References

• Hardy, J.P., 1998. Snow Ablation Modeling in a Mature Aspen Stand of the Boreal Forest. Hydrologic Processes 12, 1763- 1778

• Hardy, J.P., 2004. Solar Radiation Transmission Through Conifers Canopies. Agricultural and Forest Meterology 126.

• Pomeroy, John. 2009. The Impact of Coniferous Forest Temperature on Incoming Longwave Radiation to Melting Snow. Hydrological Processes.