Lodgepole Pine / Ponderosa Pine Ecotone

By Tyler Bieneman

Lodgepole Pine / Limber Pine Ecotone

VS.

Winter Ecology Winter Ecology – – Spring 2005Spring 2005

Mountain Research Station Mountain Research Station – – University of Colorado, University of Colorado, BoulderBoulder

Questions

• What are the key factors that determine ecotones and dominance?

• What are the elements involved in determining observed ranges of species?

• How do winter conditions play a role in separating species?

MeansWhat factors play a significant role?

• Elevation• Moisture• Soil contents

– Rocks– Clay– Silt– Sand

MeansHow does winter play a role?

• Problems of cold

conditions

– Difficulty finding liquid

water

– Transporting liquid

water throughout the

tree

- Cold temperature causes stress to plants and freezes water both inside and outside the tree

Lodgepole adaptations to cold

• Have very small conduit diameters compared to other non-conifer temperate trees

• Prevents freeze-induced cavitation inside the tree

• A portion of thaw runoff is able to be directly absorbed by stems and foliage

• Able to have liquid water at temperatures as low as -20C

• Freezing and thawing damage xylem and decrease conductivity of water

Two ecotones adressed

• From ponderosa pine to lodgepole pine

•From lodgepole pine to limber pine

Lodgepole/Ponderosa Ecotone

• Ponderosa pine sites were lower in elevation and has less surface rockiness and less steep slopes

• Lodgepole dominates on the steeper slopes and on slightly more rocky soils

• Inverse pattern of lodgepole pine below ponderosa pine stands in cold air drainages

• Rapid decrease in lodgepole pine basal area along ecotone gradient

• Ponderosa pine basal area decreased less than half as it moves into lodgepole pine stands

• Fires favor lodgepole, and fire suppression favors ponderosa growth. Lodgepole require fire to spread their seeds; ponderosa pines are indicative of older growth forests

Lodgepole/Ponderosa Ecotone

Lodgepole/Ponderosa Ecotone

The lodgepole pine dominates steeper slopes and slightly more rocky soils. It is evident that ponderosa pine is less adapted to dealing with extreme cold, demonstrated by lodgepole dominance in cold air drainages (even at low elevations), and ponderosa dominance at lower elevations and warmer areas. The ponderosa has the ability to survive in variable soil moistures but is limited fairly strictly by elevation. Fire is another important factor in determining which species will be dominant.

Limber/Lodgepole Ecotone

• Limber pine dominates at high-elevation sites with increased surface rockiness and decreased soil depth

• Upper limit of lodgepole pine in the ecotone with limber pine is correlated with increased surface rockiness, elevation and shallower soils

• The upper limit of lodgepole pine is more predictable than the lower limit of limber pine

• Limber pine dominated stands had a small number of lodgepole, whereas the lodgepole dominated areas have significant basal area of limber pine

• Elevation and surface rockiness were significantly lower in the lodgepole pine plots compared to the ecotone and limber pine plots

• Little difference in soil composition along the lodgepole/limber pine transect

Limber/Lodgepole Ecotone

Limber/Lodgepole Ecotone

Lodgepole pine has a more predictable upper limit because it is highly limited by surface rockiness and elevation. The cause of the limit for the limber pine is the moisture of the soil. The limber pine lower limit is less strict because the soil rockiness does not affect the limber pine as much as the lodgepole. Moisture/elevation gradient graph shows that lodgepole pine is greatly influenced by elevation. Lodgepole pines are more sensitive to the higher elevations and rockier soils. Lodgepole pines rely on thaws throughout winter to survive, and cannot survive the extreme kind of cold that the limber pine can.

DiscussionThe elevation gradient is the most significant factor in

determining the distribution of species. The percentage sand, clay, silt, and surface rockiness seemed to be the most important elements in determining the upper limit that the lodgepole pine can tolerate. The soil moisture also is important in establishing the limits of certain species. The lower limit of the lodgepole is less strict than the upper limit, and is determined by completely different factors. The lodgepole at the limber ecotone boundary is restricted by decreased soil moisture and increased soil rockiness, allowing the limber pine to dominate. The limber pine is out competed once soil moisture is within acceptable range for lodgepole pine. The lodgepole at the ponderosa ecotone boundary is restricted mostly by elevation, and soil properties are not as significant. The ponderosa can grow in variable soil moistures, but have trouble surviving in colder, higher environments. The lodgepole lower limit seems to be mostly controlled by competition with the ponderosa, where the ponderosa dominates in warmer areas. The cold air drainages allow for lodgepoles to descend lower than usual because they can dominate the ponderosa pine in this area. Fire disturbances create different landscapes and ecotones as well. Lodgepole are excellent pioneer species, so after a fire the area is dominated by lodgepole. The ponderosa pines represent an older, less disturbed, forest growth.

Sources

Sparks, Jed, Campell, G. and Black, R. Oecologia 127, 2001. Water content, hydraulic conductivity, and ice formation in winter stems of Pinus contorta: a TDR case study.

Stohlgren, Thomas and Bachand, R. Ecology 78(2), 1997. Lodgepole Pine (Pinus Contorta) Ecotones in Rocky Mountain National Park, Colorado, USA.

Stohlgren, Thomas, Bachand, R., Onami Y. and Brinkley, D. Plant Ecology 135, 1998. Species-environment relationships and vegetation patterns: effects of spatial scale and tree life-stage.