Forests

Conifer forests occupy the majority of South Park's mountain slopes from treeline to the floor of South Park (figure 3.3). Upper treeline in the interior of western North America is thought to be controlled by low summer temperatures (Billings, 1988), whereas lower treeline, such as at the foothills of the Mosquito Range, is controlled by summer soil drought table 3.2

Plant Species Characterizing the Main Vegetation Types in South Park

Ecosystem Common Name Scientific Name

Alpine tundra

Fell field

Dwarf clover

Trifolium nanum

Moss campion

Silene acaulis

Snowbed

Tufted hairgrass

Deschampsia cespitosa

Parry's clover

Trifolium parryi

Meadow

Elk sedge

Kobresia myosuroides

Alpine avens

Acomastylis rossii

Dryad

Dryas octopetala

Sedge

Carex scirpoidea

Forest

Engelmann spruce

Picea engelmannii

Subalpine fir

Abies bifolia

Douglas-fir

Pseudotsuga menzesii

Blue spruce

Picea pungens

Limber pine

Pinus flexilis

Aspen

Populus tremuloides

Bristlecone pine

Pinus aristata

Lodgepole pine

Pinus contorta

Ponderosa pine

Pinus ponderosa

Wetland

Peatland

Spikerush

Eleocharis quinqueflora

Arrowgrass

Triglochin palustre

Triglochin maritimum

Elk sedge

Kobresia simpliciuscula

Kobresia myosuroides

Porter's feathergrass

Ptilagrostis porteri

Wet meadow

Nebraska sedge

Carex nebraskensis

Arctic rush

Juncus arcticus

Shrubby cinquefoil

Pentaphylloides floribunda

Riparian

Plainleaf willow

Salix planifolia

Barrenground willow

Salix brachycarpa

Mountain willow

Salix monticola

Salt flat

Alkali grass

Puccinellia airoides

Saltgrass

Distichlis stricta

Glasswort

Salicornia europea

Sea-blight

Suaeda calceoliformis

Mustard

Thellungiella salsuginosa

Salt marsh

Three-square

Schoenoplectus pungens

Alkali bulrush

Bobloschoenus maritimus

Arrowgrass

Triglochin maritimum

Sea milkwort

Steppe

Blue grama grass Sedge

Fringed sage Lichen

Arizona fescue Mountain muhly

Chondrosum gracilis Carex stenophylla ssp. eleocharis Artemisia frigida Xanthoparmelia chlorochroa Festuca arizonica Muhlenbergia montana

FIGURE 3.8 Wet meadow (foreground) dominated by sedges is important pasture for domestic livestock in South Park. On the hills in the background are large clones of aspen and two strips of conifer forest. The lower strip of bristlecone pine traces a bedrock outcrop, and mixed-conifer forest dominated by Douglas-fir is present on the mountaintop. The hill slopes around the forests are dominated by Arizona fescue grassland.

FIGURE 3.8 Wet meadow (foreground) dominated by sedges is important pasture for domestic livestock in South Park. On the hills in the background are large clones of aspen and two strips of conifer forest. The lower strip of bristlecone pine traces a bedrock outcrop, and mixed-conifer forest dominated by Douglas-fir is present on the mountaintop. The hill slopes around the forests are dominated by Arizona fescue grassland.

(Daubenmire, 1974). Six main forest types occur in South Park, dominated by the following:

1. Engelmann spruce and subalpine fir at the highest elevations in mature stands.

2. Lodgepole pine forests in recently burned sites and on drier slopes.

3. Aspen as successional stands on burned slopes and persistent stands on rocky, low-elevation ridges and hogbacks.

4. Bristlecone pine on windblown ridges on the floor of northern South Park, and near treeline in other areas.

5. Mixed-conifer upper montane forests dominated by Douglas-fir and blue spruce in the foothills of the southern portion of South Park.

6. Ponderosa pine forests at low elevations in the southern portion of South Park.

Most notable among the forests are distinctive aspen stands that occur as oval-shaped patches on ridges near lower tree-line in the foothills and on hogbacks within South Park (figure 3.8). These patches are most likely clones of genetically identical trunks. The clonal growth of aspen is well known (Barnes, 1966), and clones can be very large, covering many hectares (Grant et al., 1992). Stem suckers emerge from root systems after disturbances such as fire (Mitton and Grant, 1996). Baker (1925) hypothesized that only during the late Pleistocene were conditions suitable for the establishment of aspen seedlings, so it is possible that some clones are 10,000 or more years old. Aspen seedlings are occasionally found after large fires, such as the Yellowstone fires of 1988 (Romme et al., 1995). Many of South Park's stands of aspen occur as isolated clones at the lower treeline separated from continuous forests, so they may be little influenced by forest fires. Long-lived clones may also be limited to rocky outcrops, such as the hogbacks, owing to herbivory of tree roots by pocket gophers in areas with more finely textured soils (Cantor and Whitham, 1989).

Also notable are stands of bristlecone pine on dry ridges and hills on the margins of South Park and on hogbacks throughout the park (figure 3.8). Bristlecone pine is most common in windy environments near upper treeline, for example on the Mount Goliath area of Mount Evans, at the northern end of South Park. However, bristlecone pine is also the most common low-elevation tree in the northern and central portions of South Park. Several bristlecone pine trees on Black Mountain in the southern portion of South Park are more than 2100 years old, and one was 2435 years old at the time of analysis, making them the oldest known trees in the Rocky Mountains (Brunstein and Yamaguchi, 1992). The old bristlecone pines and aspen clones demonstrate the great stability of many South Park habitats. The dry, rocky environment of bedrock hilltops creates substrate stability that limits biological productivity, reduces the potential for fire, and limits herbivory by rodents.

Upper montane forests, occurring between high-elevation spruce and fir forests and low-elevation ponderosa pine forests, are dominated almost completely by Douglas-fir in northern Colorado. However, in southern Colorado, including South Park, this ecosystem is a true mixed-conifer forest containing Douglas-fir with ponderosa pine, subalpine fir, limber pine, Engelmann spruce, aspen, white fir, southwestern white pine, and lodgepole pine. In northern Colorado blue spruce is confined to the riparian zone. However, where monsoon rains occur, as in South Park, blue spruce expands out of the riparian zone and up onto mountain slopes.

The unglaciated eastern portion of South Park, including the Tarryall Mountains, is characterized by spruce and fir forests that in places have an understory of the reindeer lichen Cladina stellaris at its only location in the western United States. This is one of the most abundant understory plants, lichen or otherwise, in the boreal forests that stretch from

FIGURE 3.9 The steppe in the foreground is dominated by blue grama grass, with flowering paintbrush (Castilleja integra) and other herbaceous dicots. On the valley bottom, the dark areas are wetlands, with shrubby cinquefoil (Pentaphylloides floribunda) prominent. In the middle distance, a hogback supports patches of aspen and bristlecone pine forests.

FIGURE 3.9 The steppe in the foreground is dominated by blue grama grass, with flowering paintbrush (Castilleja integra) and other herbaceous dicots. On the valley bottom, the dark areas are wetlands, with shrubby cinquefoil (Pentaphylloides floribunda) prominent. In the middle distance, a hogback supports patches of aspen and bristlecone pine forests.

Scandinavia across Russia, Canada, and Alaska. This fruticose lichen can be up to 10 cm tall and forms continuous mats. The unglaciated mountains also provide habitats for large populations of other widely disjunct boreal and mountain plants, such as the sedge Carex tenuiflora at its only location south of Minnesota, cottongrass (Eriophorum gracile), and bog saxifrage (Hirculus prorepens) in quaking peatlands.

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