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