What are the effects of Exposure on the treeline ecosystem?

Brian SchleckserWinter Ecology spring ’09

Mountain Research Station, University of Colorado, Boulder

Established Literature and How it Guided me

• “Facilitation and Competition on Gradients in Alpine Plant Communities” Choler, Michalet and Callaway

-shed light on gradients, and competition

• “Influences of Wind and Snow on Northern Tree-Line at Manitoba, Canada” SCOTT, HANSELL and ERICKSON

- discussed how wind and snowdrifts effect an ecosystem

• “Predicting Vegetation Types at Treeline Using Topography and Biophysical Disturbance Variables” Brown

- was a highly advanced study, but in detail explained the variables of choice, possible pitfalls, as well as vegetation types along the gradient

Thought ProgressionHow does the treeline ecotone behave with

regard to exposure?

What variables can I study in a timely manner; but will be properly representative?

Can my predicted results possibly occur based on past casual observation?

Can I even make it to treeline with daylight when I start at noon???

Experimental Design

• Study 3 zones: Exposed Semi-Exposed Protected

• Gauge the sample’s: overall growth grouping strategy

observable characteristics

• Set sample goals large enough to be statistically robust, but appropriate for time.

MethodsSample five trees in three zones: -Full exposure-Partial exposure-Full protection

Variables of Interest:-Height-DBH-Density-Flagging-Grouping shape

•Each variable measured or characterized the tree groupings in an important way.

Exposed

Protected

HeightMeasuring height (meters) of primary tree in grouping.

Circumference (DBH)Circumference of primary tree in grouping.

Measured at Chest level

Important for assessing max growth.

• Bunch Cluster Krumholz

• Group w/ neighbors Consolidated Forest

Density (Grouping)

Density

• Trees within 5 meter reach from primary tree

5m

Flagging

The Data: obvious and curious

Exposed Semi Exposed Protected0

2

4

6

8

10

12

Height by Exposure Zone

Zone AveragesPolynomial (Zone Av-erages)

Exposure

Met

ers

Relating to Height..

1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

5

10

15

20

25

30

35

40

45

50

DBH

Centi

met

ers

Exposed Semi-Exposed Protected

A Bit of a Curveball…

0

2

4

6

8

10

12

Average Density by Zone

Aver

age

# Tr

ees

Exposed Semi-Exposed Protected

Distribution of Tree Sizes, by Zone

1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

5

10

15

20

25

30

35

40

45

50

Tree make-up

SaplingsSecondary TreesPrimary Trees

# Tr

ees

Exposed Semi- Exposed Protected

Newly Understood Relationship

• Increased Specimen Density goes hand in hand with Increased Exposure.

0

2

4

6

8

10

12

Average Density by Zone

ExposedLinear (Exposed)Semi-ExposedProtected

Aver

age

# Tr

ees

Example of lower exposure, lower density Example of high exposure, high density

Implications/Conclusions

• Does exposure affect treeline mechanics?

YES• In what ways?1. Height limitation2. Circumference limitation3. Density4. Grouping strategy

Future research?• Presence and impact of scrub willow in semi-exposed

zone-what allows it to grow?

• Summer repetition of study-include wind scouring, re-tally density counts, lingering

snowpack

Works Cited

• Predicting Vegetation Types at Treeline Using Topography and Biophysical Disturbance Variables Author(s): Daniel G. Brown Source: Journal of Vegetation Science, Vol. 5, No. 5, Applications of Remote Sensing and Geographic Information Systems in Vegetation Science (Nov., 1994), pp. 641-656 Published by: Opulus Press Stable URL: http://www.jstor.org/stable/3235880 Accessed: 01/03/2009 12:25

• Influences of Wind and Snow on Northern Tree-Line Environments at Churchill, Manitoba, Canada, PETER A. SCOTT,’ ROGER I.C. HANSELL’ and WILLIAM R. ERICKSON*I (Received 26 August 1992; accepted in revised form 19 January 1993 http://pubs.aina.ucalgary.ca/arctic/Arctic46-4-316.pdf

• Facilitation and Competition on Gradients in Alpine Plant Communities Author(s): Philippe Choler, Richard Michalet, Ragan M. Callaway Source: Ecology, Vol. 82, No. 12 (Dec., 2001), pp. 3295-3308 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/2680153 Accessed: 01/03/2009 12:35

• Special thanks to Phil McDonald for field assistance

Protected zone

Semi exposed zone

Tracks from the exposed zone

Research Assistant