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