Vegetation in the Vicinity of Porcupine Cave

The southern portion of South Park is a rolling landscape of forested hills and grassland slopes with small streams or marshes in the valley bottoms (figure 3.14). The area around Porcupine Cave is undulating, with ponderosa pine, Douglas-fir, and aspen forests on the tops and north-facing slopes of hills. Some of this forest area has clearly developed only during the twentieth century, owing to fire suppression. Thus the forested areas of today are probably larger than those that existed prior to human settlement in the nineteenth century. Few older trees are evident in these forests, and most trees are quite young. However, the presence of stumps indicates the cutting of older trees in many areas.

The steppe communities are similar to those in the northern part of South Park. Blue grama grass, sedge (Carex steno-phylla ssp. eleocharis), and fringed sage dominate with numerous other grasses, herbaceous dicots, and lichens. It is a rich assemblage of plants adapted to mammalian herbivory.

FIGURE 3.11 Tussocks of elk sedge (Kobresia simpliciuscula) dominate the calcareous peatland in the foreground. Each plant is approximately 40 cm tall and 30 cm in diameter.

FIGURE 3.11 Tussocks of elk sedge (Kobresia simpliciuscula) dominate the calcareous peatland in the foreground. Each plant is approximately 40 cm tall and 30 cm in diameter.

FIGURE 3.13 Map showing the circumpolar distribution of Ptilagrostis porteri in North America and the closely related P. mongholica in central Asia. Shaded areas encircled by dark lines indicate the regions within which the species are currently known.

FIGURE 3.12 Map showing the circumpolar distribution of Kobresia simpliciuscula, one of the many boreal species abundant in South Park. Shaded areas encircled by dark lines indicate the regions within which the species is currently known. Note the wide distribution of this species in northern North America and Eurasia, and the presence of populations far to the south in the Rocky Mountains of Colorado (South Park) and central Asia.

FIGURE 3.13 Map showing the circumpolar distribution of Ptilagrostis porteri in North America and the closely related P. mongholica in central Asia. Shaded areas encircled by dark lines indicate the regions within which the species are currently known.

Grasses and sedges have their meristems (growing points) below the ground surface, instead of at the top of each branch, allowing the leaves to be repeatedly eaten without damaging the meristems. The leaves of these plants also have high silica content, which grinds down the teeth of herbivores. Both of these adaptations allow grass and sedge steppe plants to better deal with herbivory by large ungulates, as well as by smaller mammals such as rabbits and mice and by insects such as grasshoppers.

Wet meadows in the valley bottoms are the product of shallow groundwater tables, and sedges such as Nebraska sedge and arctic rush are most abundant, along with a wide range of herbaceous dicots. These wetlands are highly productive, with both abundant forage and perennial water in many areas.

FIGURE 3.14 A wet meadow-steppe-conifer forest complex in the southern portion of South Park. Forests are mixed aspen, ponderosa pine, and Douglas-fir. The steppe is largely dominated by blue grama grass, whereas the meadow is dominated by arctic rush, with flowering Geyer's onion (Allium geyeri, the light-colored and most abundant flowering plant) and louseworts (Pedicularis groenlandica and P. crenulata, the darker flowers in long spikes).

FIGURE 3.14 A wet meadow-steppe-conifer forest complex in the southern portion of South Park. Forests are mixed aspen, ponderosa pine, and Douglas-fir. The steppe is largely dominated by blue grama grass, whereas the meadow is dominated by arctic rush, with flowering Geyer's onion (Allium geyeri, the light-colored and most abundant flowering plant) and louseworts (Pedicularis groenlandica and P. crenulata, the darker flowers in long spikes).

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