subalpine fir: snow, a ge/size, and b ark beetle i nteractions
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Subalpine fir: Snow, Age/size, and Bark Beetle
Interactions
Adam AlbrightWinter Ecology - 2012
Mountain Research StationUniversity of Colorado, Boulder
Outline.• Subalpine Fir, snow, and the Bark Beetle• The big question• A possible way to make the connection• Results Presentation• Discussion• Conclusions• Acknowledgments• References
Introduction• Subalpine fir – high
elevation species• Adapts to extreme
environment by heavily investing in needles over roots
• Drought stress – major cause of mortality (direct & contributing)
• Western Balsam Bark Beetle – USGS maps/data indicate major cause of Subalpine mortality
• Preferentially target older trees, more food/tree.
(Bleiker et al, 2003; Antos et al 2008; Bigler et al, 2007)
The Big Question
• Is there a connection between snow depth (water supply), tree diameter/age, and incidence of beetle attack in the subalpine fir?
Methods
• First, appropriate sites were chosen using USGS forest data.
• Once within a polygon (from the map) containing beetle-attacked subalpine fir, a random direction was taken for five, 50 X 2 meter belt transects.
• Within the transect, the following were recorded: DBH for each subalpine fir, snow depth, health (alive or dead/dying), and presence of beetle gallery.
Methods: Cont
• Key measurements were graphed for comparison. For four comparisons averages and standard errors were compared. One comparison is a scatterplot.
• Each graphed measurement was additionally subjected to a 2-tailed, t-test; this determines if there is a significant difference between the means.
• Assumptions:– Normal Distribution – Data sampled independently from the populations
being compared.
MSR
P 2 P
G.L.V.
Niwot Ridge
Credit: Teresa Chapman, Adam Albright
Octopus shaped
galleries
Results: Graphical
Healthy trees: 79 Galleries: 6 Dead: No Gallery: 38
Healthy Gallery Dead: No Gallery0
10
20
30
40
50
60
70
80
90
Number of Healthy vs Number of Dying/Dead
Number of Healthy vs Number of Dying/Dead
cm
T-Test Results comparing snow depth: 0.05712
Dead Galleries Snow Depth No Galleries Snow Depth110
112
114
116
118
120
122
124
126
128
130
Snow Depth: beetle vs no beetle
Snow Depth: beetle vs no beetle
cm
T-Test: Dead trees only, snow depth: Gallery vs no gallery: 0.008548
38 trees
6 trees
cm
T-Test: Dead trees only, DBH: Gallery vs no gallery: 0.005039
cm
40 60 80 100 120 140 160 180 2000
5
10
15
20
25
30
35Snow depth influencing DBH
Snow depth influencing DBH
cm
Discussion
• Correlations:– Snow depth beetle infestation: non-significant
correlation– Snow depth for dead trees - beetle to not beetle:
possibly shows water supply role in infestation– Dead DBH - Gallery to no gallery: Beetles prefer
larger trees.– Snow depth (water supply) influences DBH.
Roughly bell-shaped.
Discussion cont.
• Problems:– Number of healthy to number with galley– Data sampled in clusters– Small sample size: • Time• Place• Tree samples
Conclusion• Snow: – Water resources impact tree size and beetle
incidence• Beetles:– Within small transects not as prevalent as
depicted.– Data points toward less impact than water stress.
• Bigger picture: – Snowfall is projected to decrease in the Rockies– Subalpine fir surround many watersheds (Boulder,
Longmont, etc) – Future studies needed to further understand link
Acknowledgments
• Tim “Wintologist” Kittel• My research assistants: Kalin and Chris and
Tori• My overabundance of scientific Swag• The bio-geography department for loaning
gear
References• Antos, Joseph A., Parish, R., Nigh, G. D., (2008) Growth patterns prior to mortality
of mature Abies lasiocarpa in old-growth subapline forests of southern
British Columbia. Forest and Ecology Management. (225) 1568-1574.
• Bigler, Christof, Gavin, D. G., Gunning, C., Veblen, T. T., (2007) Drought induces lagged tree mortality in a
subalpine forest in the Rocky Mountains. Oikos. (116) 1983-1994.
• Bleiker, Katherine P., Lindgren, S. B., Maclauchlain, L. E., (2003) Characteristics of subapline fir susceptible to attack by western balsam bark beetle. Canadian Journal of Forestry. (33) 1538-1543
• Kegley, Sandra. (2006) Western Balsam Bark Beetle: Dryocoetes confusus Swaine. Online at: http
://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5188058.pdf• Student t-test: Unequal variances. http://en.wikipedia.org/wiki/Student%27s_t-
test#Unequal_variances
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