Impact of snow molds on conifers of
the ribbon forestMax Owens
EBIO 4100, Spring 2013
Winter EcologyMountain Research Station
University of Colorado-Boulder
IntroductionStructure of the ribbon forest: snow
accumulation has multiple effects on trees (Knight
1994)
Snow molds are specialized fungi that attack dormant plants under cover of snow (Pokorny 2009)
Many different species of cold-tolerant fungi are present under the snow during winter and disappear quickly after snowmelt (Schmidt et al. 2008)
IntroductionThese psychrophilic (cold-loving) fungi produce
mycelia during the severe conditions of winter. (Hoshino et al. 2009)
How?Spruce sapling growth is strongly inhibited by
presence of snow mold. (Cunningham et al. 2006)
IntroductionOpportunistic snow molds are insulated from
harsh climate of winter by the snowpack, and antagonists are practically absent (Matsumoto 2009)
For phytopathogenic fungi adapted to the cold, the subnivean environment is the perfect place to parasitize young trees
Question: How does the depth of snow contribute to the maintenance of the structure of the ribbon forest, as related to the presence of phytopathogenic snow mold?
Why it matters: Important factor in limiting growth of subalpine
trees?Maintenance of ribbon forest, a common structure in
subalpine forests near tree lineClimate change—precipitation on the rise at higher
elevations (Kittel 2013)
Hypothesis: The added insulative value of deeper snow creates a better environment for snow molds to parasitize trees.
Prediction: We would expect to see a greater incidence of snow mold in the glades of the ribbon forest, where snow is deeper.
SiteSubalpine ribbon forest above Mountain
Research Station at ~3,330m (10,930 ft.)
[Google 2013]
Methods 2 x 40m transect
crossing glade from ribbon to ribbon
Snow depth, tree heights, DBHs, and snow mold evidence were measured.
Snow was removed along transect to expose small trees, and snow was removed to base of each tree to expose any snow mold damage
MethodsIf present, height of snow mold/snow mold
damage extent was measuredTrees with a DBH of 8 cm or greater were
excluded, since trees this large generally did not have branches beneath the snowpack
Only one transect due to time constraintsUsed Excel and R to create plots, regressions
and t-tests
Results
Physical appearance of infected trees
• 2 main categories• Bundled needles with black
mold in between• Brown/black needles, not
bundled• Several trees with healthy
needles below snowpackBundled needles
Discolored needles, not bundled
Results
p-value: 0.268R2: 0.292
Regression
Resultsp-value: 0.0302
Bundled needles
Discolored, not bundled
Healthy needles
1 Engelmann spruce
1 Engelmann spruce
4 subalpine firs
2 subalpine firs
2 subalpine firs
T-test
Results
p-value: 0.326 T-test
ResultsRegression of snow depth and height of snow mold
was not significant, but trended towards higher extent of snow mold with greater snow depths
Significant difference in snow depths between trees with and without snow mold
Not enough data to differentiate snow mold presence/appearance between different tree species
No significant difference in tree size between trees with and without snow mold
DiscussionDeeper snow creates favorable environmental
conditions (insulation, moisture) for snow mold to infect treesPersistence of snow is critical (Matsumoto 2009)
Snow mold infection inhibits spruce growth, and one of the primary drivers of snow mold infection of saplings was snow duration (Cunningham et al. 2006)
Snow mold-tree interactions play at least some part in the complex maintenance of ribbon forest structure
DiscussionFurther research
Replicates of this study to create an accurate profile of snow mold height extent with snow depth (is there an optimal depth for infection?)A direct correlation between snow mold and snow
depth has implications for climate change.Snow depth and the maintenance of the ribbon
forest to determine the relative impacts of physical damage, shorter growing seasons, and infection by snow molds on trees
How much snow mold damage is too much for a conifer to survive?
ConclusionRibbon forest structure controlled by several
factors, including snow moldsFungi that infect plants underneath the snow; limits
growthDeeper snow makes snow mold infection more
likely InsulationAbundant moisture
Not enough data to determine pattern of snow mold damage extent in ribbon forest
Acknowledgements
Thanks to Tim Kittel for support and analysis help, and to Sebastian Baily, Jake Delfin, and Atty
Phleger for data collection help.
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