Subalpine Forests

Foxtail pine growing near treeline in the upper Kern area of Sequoia National Park.

NPS photo

Subalpine forests define the upper limit of tree growth in the Sierra. Trees in these forests can range from over 75 feet in height to the stunted and gnarled growth forms known as krummholz ("crooked wood" in German). Although occasionally found intermingling with the lodgepole and red fir forests below, the subalpine species are typically found between about 9500 to 12,000 feet in the southern Sierra. Trees you may encounter in the subalpine zone include mountain hemlock, whitebark pine, and foxtail pine, and occasionally western white pine, limber pine, and western juniper.

Three of these tree species can grow at the upper edge of forest (or "treeline") in the southern Sierra. They include whitebark pine, foxtail pine, and limber pine. Trees at these high elevations must be able to withstand harsh conditions, including cold temperatures, severe wind, and short growing season. Because these pines are the only trees in the upper subalpine zone, they play an important role regulating snowmelt and stream flow and providing habitat and food for birds and mammals. Below are photos and more information about these special trees.

 

Whitebark pine in the Evolution Basin area of Kings Canyon National Park. Whitebark pine can grow as an upright tree form as well as a shrubby krummholz form - an adaptation to difficult growing conditions created wind, ice, and  persistent snow.

Photo courtesy of Peggy Moore

Whitebark Pine

Whitebark pine has a wide geographic range in the west, including in the Rocky Mountains, the Cascades, and the Sierra Nevada, where it reaches its southern limit near Mt. Whitney in Sequoia National Park. Whitebark pine occurs on both the west and the more arid east side of the Sierra crest in scattered treeline stands. The seeds of whitebark pine provide an important food source for many seed-eating birds and mammals. Whitebark pine is entirely dependent upon Clark’s Nutcracker (a medium-sized relative of the crow) for dispersal of its large wingless seeds. While severe declines in whitebark pine are occurring range-wide, Sierra Nevada populations are still relatively healthy. However, in recent years that has been changing. In 2021, local scientists and park staff began observing branch dieback and death of whitebark pine trees in some areas. This has often been associated with bark beetles or occasionally with signs of white pine blister rust infection.

On December 15, 2022, the U.S. Fish and Wildlife Service (FWS) listed whitebark pine as threatened with potential extinction under the Endangered Species Act. FWS determined that the primary stressor driving the status of whitebark pine is white pine blister rust, a fungal disease caused by the nonnative pathogen Cronartium ribicola. Whitebark pine is also negatively affected by the mountain pine beetle, altered fire regimes, and the effects of climate change.

 

Backpacker hikes through a stand of foxtail pine near Little Claire Lake in Sequoia National Park.

Photo by Linda Mutch

Foxtail Pine

In contrast to whitebark and limber pine, foxtail pine has a limited distribution. It is endemic to California and is confined to two discrete regions: the Klamath Mountains of northwestern California and the southern Sierra Nevada. Foxtail pine always grows as an upright tree (not a shrubby krummholz form), even on the highest, most windswept and exposed sites. These trees are limited to high-elevation slopes, ridges and peaks, typically growing in open stands that are almost purely foxtail pine with little other vegetation. Like the whitebark pine, foxtail pine provide important habitat and food for birds and mammals. The oldest known foxtail is over 2,000 years old. Both live and dead wood of this species can be dated to produce multi-millennial tree-ring records used to reconstruct long-term variations in climate.

Foxtail pines, like whitebark pine, are starting to show dieback in some parts of the parks. In 2022, a National Park Service forest monitoring crew documented branch dieback and mortality of foxtail pine in or just outside of Sequoia National Park. They found signs of mountain pine beetles as well as signs of blister rust infection.

 

To withstand harsh growing conditions on windy, exposed slopes and ridges, the limber pine often has a low growth form, sprawling along rocks instead of growing upright.

Photo courtesy of Connie Millar

Limber Pine

Limber pine has a large distribution across western mountain ranges and occurs in a wide range of environments from lower elevation sites to treeline. It is uncommon in Sequoia and Kings Canyon National Parks, but extensive stands occur east of the Sierra crest in the Inyo National Forest and in the White Mountains of eastern California. It is a spreading or sprawling tree of high windy ridges and dry slopes. Limber pine is a pioneer on severe sites, moderating the environment to facilitate establishment of other species. Near its upper limits, the trunks of limber pine often arch over like a crescent and the treetop touches the ground as a result of centuries of harsh winds. Its seeds are food for numerous birds and mammals and are dispersed by Clark's Nutcrackers and small rodents.

 

Threats

All three of these treeline species, in addition to western white pine that also occurs in the subalpine zone, are threatened by a non-native pathogen that causes the disease white pine blister rust. This disease has caused severe declines in whitebark pine in other parts of its range, but local populations are still in good condition. Other threats include mountain pine beetle outbreaks and the warming temperatures and changes in timing and type of precipitation from climate change. By conducting long-term monitoring of whitebark and foxtail pine, scientists will be able to help managers plan for short- and long-term changes in these forests. Watch the video below to learn more about the importance of these iconic trees, where they grow, and how they are monitored.

 

Duration:

6 minutes, 53 seconds

Join field biologists as they monitor beautiful whitebark pine and foxtail pine forests in areas of Sequoia and Yosemite national parks that are at the rugged upper limits of where trees can survive.