A Winter Comparison Study of A Winter Comparison Study of Dominant Alpine Plant Dominant Alpine Plant

Communities in the Southern Communities in the Southern Rocky Mountains and the Rocky Mountains and the

Chugach Mountains of Southern Chugach Mountains of Southern AlaskaAlaska

What factors control treeline and What factors control treeline and species distribution?species distribution?

Kyle CunninghamWinter Ecology – Spring 2006

Mountain Research Station – University of Colorado, Boulder

QuestionsQuestions

How does treeline change with How does treeline change with Latitude?Latitude?

What factors control winter treeline What factors control winter treeline communities?communities?

Are latitude and elevation predominant Are latitude and elevation predominant controls?controls?

What other factors are involved?What other factors are involved? Which factors are most likely to influence Which factors are most likely to influence

sub-alpine and treeline communities?sub-alpine and treeline communities?

Physical SettingPhysical Setting Southern Rocky Southern Rocky

Mtns.Mtns. Northern HemisphereNorthern Hemisphere Latitude : 40 degrees NLatitude : 40 degrees N N/S tending rangeN/S tending range Over 4830 km. long (for Over 4830 km. long (for

entire range)entire range) Width Range : 150- 650 km.Width Range : 150- 650 km. Elevation Range : 1500 m Elevation Range : 1500 m

(plains) – 4399m(plains) – 4399m Highest Peak : Mt. Elbert – Highest Peak : Mt. Elbert –

4399m (14,400 ft.)4399m (14,400 ft.)

Physical SettingPhysical Setting

Chugach Mtns.Chugach Mtns. Northern Northern

HemisphereHemisphere Latitude : 61 degrees Latitude : 61 degrees

NN E/W tending rangeE/W tending range Over 482 km longOver 482 km long Average Elevations : Average Elevations :

2438m – 3353m2438m – 3353m Highest Peak: Mt. Highest Peak: Mt.

Marcus Baker – Marcus Baker – 4016m.4016m.

**Coastal Mountain **Coastal Mountain Range**Range**

ClimateClimate

Southern Rocky Southern Rocky Mtns.Mtns.

Avg. Winter Temperature: Avg. Winter Temperature: -2 - +3 degrees C.-2 - +3 degrees C.

Avg. Annual Precipitation: Avg. Annual Precipitation: 36cm36cm

Snow Cover: 25cm - Snow Cover: 25cm - 152cm (depth)152cm (depth)

Chugach Mtns.Chugach Mtns. Avg. Winter Avg. Winter

Temperature: -6 - +2 Temperature: -6 - +2 degrees C. (would be degrees C. (would be colder, but insulated colder, but insulated by the ocean)by the ocean)

Avg. Annual Avg. Annual Precipitation: 41cm – Precipitation: 41cm – 177cm (coastal 177cm (coastal influence)influence)

Snow Cover: 152cm – Snow Cover: 152cm – 203cm (depth)203cm (depth)

Treeline ElevationTreeline Elevation

Rocky Rocky MountainsMountains

Average Treeline Average Treeline Elevation: 3,400 – Elevation: 3,400 – 4,000m4,000m

Chugach Chugach MountainsMountains

Average Treeline Average Treeline Elevation: 300 – Elevation: 300 – 500m500m

What’s the Point?What’s the Point?Treeline change with Treeline change with

elevationelevation How does treeline elevation vary with How does treeline elevation vary with

latitude?latitude? General rule of thumb: Treeline decreases General rule of thumb: Treeline decreases

with increasing latitudes at a rate of with increasing latitudes at a rate of 100m/degree of latitude. (Sveinbjörnsson)100m/degree of latitude. (Sveinbjörnsson)

Maximum treeline of 4000m in MexicoMaximum treeline of 4000m in Mexico Minimum treeline of 400-800m at Minimum treeline of 400-800m at

Canadian/Alaskan border.Canadian/Alaskan border. *Values are calculated for the Rocky *Values are calculated for the Rocky

Mountains Mountains They can be interpreted to other ranges world They can be interpreted to other ranges world

wide, but with a degree of error.wide, but with a degree of error.

Dominant Sub/Alpine Dominant Sub/Alpine Winter Plants in the Winter Plants in the

Southern RockiesSouthern Rockies Riparian: Willow, Alder, Riparian: Willow, Alder,

*Aspen, (deciduous *Aspen, (deciduous dom.)dom.)

Sub-Alpine: Aspen, Sub-Alpine: Aspen, *Sub-Alpine Fir, *Sub-Alpine Fir, Engelmann Spruce, Engelmann Spruce, Lodgepole Pine, Limber Lodgepole Pine, Limber Pine (mixed aspen/fir Pine (mixed aspen/fir dom.)dom.)

Treeline (3400-4000m): Treeline (3400-4000m): *Englemann Spruce, *Englemann Spruce, Limber Pine, Lodgepole Limber Pine, Lodgepole Pine (Spruce dom.) Pine (Spruce dom.)

Dominance with Dominance with increasing elevation: increasing elevation: AspenAspen Fir Fir Spruce. Spruce.

Aspen

Englemann Spruce

* = Most dominant species

Dominant Sub/Alpine Dominant Sub/Alpine Winter Plants in the Winter Plants in the Chugach MountainsChugach Mountains

Riparian: *Black Riparian: *Black Cottonwood, *Paper Birch, Cottonwood, *Paper Birch, *Balsam Poplar, Aspen, *Balsam Poplar, Aspen, Lodgepole Pine (only pine in Lodgepole Pine (only pine in Alaska), willows. (deciduous Alaska), willows. (deciduous dom.)dom.)

Sub-Alpine: *Sitka Alder, Sub-Alpine: *Sitka Alder, Balsam Poplar, *Pacific Balsam Poplar, *Pacific Silver fir, Mtn./Western Silver fir, Mtn./Western Hemlock (mixed fir/alder Hemlock (mixed fir/alder dom.)dom.)

Treeline (300-500m): *Sitka Treeline (300-500m): *Sitka Spruce (south facing Spruce (south facing slopes), *White Spruce slopes), *White Spruce (north facing), Black (north facing), Black Spruce, Mtn. Hemlock Spruce, Mtn. Hemlock (spruce dominated)(spruce dominated)

Dominance with increasing Dominance with increasing elevation: elevation: Birch/poplar/cottonwood Birch/poplar/cottonwood Alder/fir Alder/fir White/Sitka White/Sitka SpruceSpruce

Sitka Spruce* = Most dominant species

What’s the Point?What’s the Point?Why do we find certain species in Why do we find certain species in

certain areas?certain areas? Can elevation and latitude be and accurate predictor of Can elevation and latitude be and accurate predictor of

winter plant communities?winter plant communities? Much more complicated than just two factorsMuch more complicated than just two factors Other factors include : *annual precipitation (coastal influences), Other factors include : *annual precipitation (coastal influences),

*sunlight exposure (highly variable in Alaska), *ecological ranges *sunlight exposure (highly variable in Alaska), *ecological ranges (native species/established population), depth of snow pack, seed (native species/established population), depth of snow pack, seed dispersal, geographical isolation, disturbances.dispersal, geographical isolation, disturbances.

Conclusion :Conclusion : There is some correlation, but altitude and There is some correlation, but altitude and elevation are not the predominant controls on winter tree elevation are not the predominant controls on winter tree populations.populations.

ConclusionConclusion :: Temperature tolerance (killing temperature) is a Temperature tolerance (killing temperature) is a main control on species distribution. Aspen, Poplar, and main control on species distribution. Aspen, Poplar, and White/Black spruce can tolerate -80 degree C temps, but do not White/Black spruce can tolerate -80 degree C temps, but do not respond well to warm temps (respiration exceeds respond well to warm temps (respiration exceeds photosynthesis). (Marchand)photosynthesis). (Marchand)

Conclusion :Conclusion : Increased precipitation and larger winter Increased precipitation and larger winter snowpack due to coastal inputs, mean high water content for snowpack due to coastal inputs, mean high water content for ChugachChugach. . More deciduous trees. More deciduous trees.

Conclusion : Conclusion : Less ppt. and snowpack means less available Less ppt. and snowpack means less available water for tree species in the water for tree species in the RockiesRockies. . More coniferous trees. More coniferous trees.

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