Vegetation of Pike’s Peak State Park
Pike’s Peak State Park is located along the bluffs of the Mississippi River in northeastern Clayton County, Iowa. Physiographically, it is contained in the eastern portion of the Paleozoic Plateau Landform Region, commonly known as the “Driftless Area” (Prior 1992). The varied topography of the park, including steep bluffs, deep ravines, and flat to rolling uplands, is typical of this landform region and provides diverse habitats for plant species and plant communities. As will be seen, a diversity of rock formations and land uses also contributes to floristic diversity of the park.
Forests
Historically, as revealed by compilation of General Land Office (GLO) plat maps originally drawn between 1837 and 1849, the vegetation in and around the park was predominantly forest (Fig. 1). In fact, based on the GLO maps, Clayton County was the most extensively forested county in Iowa, with 70% of its land surface mapped as “timber” (Anderson 1996). Additional woody vegetation types-“grove”, “thicket” and “barren”- occupied small areas of upland in the county, less than 0.1% each. Islands in the Mississippi River also provided additional forest cover (about 0.8%). Today, forest cover in Clayton County is still the highest among all counties in Iowa, with 21% of its surface covered with forest (Brand and Walkowiak 1991). The difference between 71% forest cover in the “presettlement” era and 21% forest cover today largely reflects extensive clearing and deforestation by agriculture and urbanization since 1850 (Fig. 2). However, differing precision between the coarsely drawn GLO maps and finely delineated photo-interpretations by modern forestry surveys may also account for a portion of the disparity.
The forest vegetation of northeast Iowa has been classified differently by various researchers. On a national atlas of potential natural vegetation, Kuchler (1966) depicted all of the Paleozoic Plateau plus the easternmost section of the Southern Iowa Drift Plain as “Maple-Basswood Forest (Acer-Tilia)”, a classification first assigned to the area by E. Lucy Braun (1950) in her classic book The Deciduous Forests of Eastern North America. This classification emphasized the potential of the forest vegetation to become dominated by shade-tolerant sugar maple (Acer saccharum) and basswood (Tilia americana) trees if natural succession were uninterrupted by disturbance. Alternatively, Shantz and Zon (1924) classified northeast Iowa as part of a larger “Oak-Hickory (Quercus-Carya)” forest. This classification was based on the existing prevalence of shade-intolerant oaks and hickories, especially white oak (Quercus alba), red oak (Quercus rubra), and shagbark hickory (Carya ovata), despite their seemingly successional status. The presence of numerous small stands of conifers in the region, especially eastern white pine (Pinus strobus), led Tolstead (1938) and Shimek (1948) to classify northeast Iowa as a western unit of the mixed coniferous-deciduous forest of the Great Lakes region.
In contrast to sweeping classifications of broad geographic areas, Cahayla-Wynne and Glenn-Lewin (1978) studied the upland forest vegetation of the northeast Iowa by inventorying 35 study plots distributed among eight public forest reserves. Eight of the 35 plots were established in Pike’s Peak State Park. (The other seven areas were Merritt Forest State Preserve, Retz Woods State Preserve, Effigy Mounds National Monument, Yellow River State Forest, Brush Creek Canyon State Preserve, Backbone State Park, and White Pine Hollow State Preserve.) Overall, they quantitatively described five major “dominance-types” among the forests of the region:
Acer- communities dominated by sugar maple (Acer saccharum) with basswood and white oak of secondary importance,
usually found in the most mesic (moist and shaded) and oldest sites.
Tilia- communities dominated by basswood (Tilia americana) with bitternut hickory (Carya cordiformis), sugar maple, and red oak of minor importance, usually found in mesic sites.
Quercus rubra- communities strongly dominated by red oak with sugar maple of minor importance, usually found in mesic sites.
Quercus alba- communities dominated by white oak (Quercus alba) with red oak as a secondary species and sugar maple and basswood as minor components, usually found on drier sites.
Pinus- communities dominated by white pine (Pinus strobus) with white oak an important secondary species and red oak and sugar maple as minor components, usually found on xeric (very dry) sites.
Additionally, they qualitatively described one more community-type on exposed, xeric sites such as crags and bluffs dominated by eastern red cedar (Juniperus virginiana) and chinquapin oak (Quercus muhlenbergii). Communities of this type were always too small in area to be sampled with their standard plot size of 0.1 hectare (20m X 50m). (This interesting community type is discussed below as a “glade”.)
The woody understory of the major forest types was generally dominated by ironwood (Ostrya virginiana) and blue beech (Carpinus caroliniana) trees. The herbaceous layer was typically populated with Virginia creeper (Parthenocissus quinquefolia), sweet cicely (Osmorhiza claytoni and O. longistylis), wild geranium (Geranium maculatum), and enchanter’s nightshade (Circaea lutetiana), among others. Seedlings and saplings of sugar maple were the most common species encountered in the lower strata of the forest throughout their plots.
Of the five major dominance types identified
by Cahayla-Wynne and Glenn-Lewin (1978) for northeast Iowa, two (white oak and
red oak) were well-represented in their sample of Pike’s Peak State Park
(Cahayla-Wynne 1976), reflecting the placement of their plots on ridgetops and
gentle slopes in the park. Other community-types
were present, but remained unsampled until Christiansen (1980) conducted a comprehensive
inventory and mapped the vegetation of the entire park. Using a combination of small plots, linear
transects, and qualitative reconnaissance, he documented the occurrence of communities
dominated by white oak, by red oak, and by sugar maple. Basswood occurred as a secondary species in
many samples, but was never observed as solely dominant. Although scattered individuals of white pine
were found in the park, communities dominated by this tree species were
determined to be absent.
Because of the comprehensive nature of his study, Christiansen (1980) documented the occurrence of a variety of forested and non-forested vegetation in Pike’s Peak State Park (Fig. 3). Approximately half of the park contains natural vegetation, primarily on the steep bluffs and deep ravines along the Mississippi River. The natural vegetation is mostly forest, but small prairie and glade communities are also present. The other half of the park, primarily on flat to rolling uplands away from the river bluffs, contains a complex of non-natural vegetation, including old fields, mowed lawns, and a pine plantation.
Christiansen (1980) identified six natural forest community-types in the park. Three of them form an intergrading complex on steep, rocky slopes dominated by a variable mixture of sugar maple, red oak, basswood, and white oak. They were mapped as occurring extensively on bluffs along the Mississippi River and in three large ravines (named, from north to south, “Schade Glen”, “Weir’s Glen”, and “Pictured Rock Glen”). The “sugar maple-basswood” community was restricted to the steepest bluffs facing the Mississippi. The “red oak-sugar maple” community was the single most extensive forest type in the park, mapped mainly in large ravines. The “red oak-sugar maple-white oak” community occurred at the head of a single large ravine (Weir’s Glen). Except for the central portion of Schade Glen (once cleared for use as a vineyard, now in an advanced stage of woody succession), this community occupies most of the mesic habitat suitable for its development. The sugar maple-dominated communities correspond to the “southern mesic forest” recognized by Curtis (1959) for Wisconsin while the red oak-dominated communities correspond to his “southern dry-mesic forest”.
A fourth forest type, termed “Oak-Hickory” by Christiansen (1980), was dominated by white oak and shagbark hickory and occurred only on the gently sloping, loess-covered summits of ridgetops between major ravines. This type corresponds to the “dry southern forest” of Curtis (1959). The largest expanse of this community is located on the broad ridge in the northernmost part of the park (the “Point Ann” area). Small areas of this community can also be found on long, narrow divides between Pictured Rock Glen and Weir’s Glen in the southern part of the park and between Weir’s Glen and Schade Glen in the east-central part. The existing stands within the park are remnants of a formerly more widespread community that was largely converted for use as agricultural fields in the past. (Following establishment of the park, these areas were retired from production and are now old fields). Christiansen (1980) also recognized a disturbed variant of the Oak-Hickory community that he called “open woodland”, sites where the area under the trees was maintained as a lawn for visitor use (such as the picnic area, campground, and the Indian mound area on the ridge between Pictured Rock Glen and Weir’s Glen).
Two other forest types described by Christiansen (1980) occupied very small areas of land in the park. The “streamside” community, corresponding to the “wet-mesic forest” of Curtis (1959), occurred on the banks of the lower reaches of Schade Glen and Weir’s Glen; its dominant trees were basswood, red elm (Ulmus rubra), and walnut (Juglans nigra). The “floodplain” community, corresponding to the “southern wet forest” of Curtis (1959) and located on small deltas along the banks of the Mississippi River at the mouths of Weir’s Glen and Pictured Rock Glen, is dominated by silver maple (Acer saccharinum) and willows (Salix).
Prairie openings and glades
Christiansen (1980) identified a non-forested natural community-type in Pike’s Peak State Park, the “prairie opening”. He mapped two small occurrences on the east side of Schade Glen, but only one of them (on the spine of a rocky ridge) is probably a natural occurrence. The other (on an eroded lower slope once cultivated as a vineyard) is most likely an old field that was partially colonized with prairie plant species spreading from the nearby natural community. Big bluestem (Andropogon gerardii) and little bluestem (Schizachyrium scoparium) are dominant grasses in this community, with several other typical prairie species such as purple coneflower (Echinacea pallida), spiderwort (Tradescantia), azure aster (Aster azureus), and flowering spurge (Euphorbia corallata) also present. This community corresponds to the “dry prairie” community of Curtis (1959).
Although not specifically recognized or mapped by Christiansen (1980), another prairie-like opening is found on a narrow bedrock ridge on the east side of Pictured Rock Glen (the “Crow’s Nest” area). The vegetation here is a mixture of scattered stunted trees of eastern red cedar and chinquapin oak, an herbaceous understory with several prairie species, and exposures of bare rock and ledges. Sometimes termed a “cedar glade” (Curtis 1959) or simply “glade”, this is an example of the “crags and bluffs [dominated by] Juniperus virginiana and Quercus muhlenbergii” as described by Cahayla-Wynne and Glenn-Lewin (1978). In addition to prairie species, this site also contains cliff goldenroad (Solidago sciaphila) and blueberries (Vaccinium angustifolium and V. myrtilloides). The goldenrod occurs on bare rock of the Galena Limestone while the blueberries occur in sandy soil weathered from the St. Peter Sandstone.
Old fields
Christiansen (1980) mapped a complex of old fields on flat topography in the west-central and southwestern parts of the park. These fields were retired from cultivation following acquisition of land parcels by the park in 1968. Christiansen (1980) recognized several variants that reflected the degree of invasion of woody plants into these formerly cultivated areas:
“Grassy” fields dominated by Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), quackgrass (Agropyron repens), redtop (Agrostis gigantea), Canada goldenroad (Solidago canadensis), and late goldenrod (S. gigantea).
“Early Woody” fields similar to the grassy old fields except that the tree saplings, including Siberian elm (Ulmus pumila), boxelder (Acer negundo), and white mulberry (Morus alba), were taller and well established, although scattered.
“Advanced Woody” fields dominated by young trees forming a complete canopy. Principal trees were boxelder, Siberian elm, American elm (Ulmus americana), white ash (Fraxinus americana), walnut, bitternut hickory, and black cherry (Prunus serotina).
He also pointed out that one old field in the southwest corner of the park had been densely planted with conifers, mainly white pine, Scotch pine (Pinus sylvestris), and Austrian pine (Pinus nigra). The latter two species are not native to North America.
Comparison with Wyalusing State Park, Wisconsin
In The Vegetation of Wisconsin (1959, pp. 88-89), ecologist John Curtis provided a map and brief descriptions of natural forest communities in Wyalusing State Park, which is located in Wisconsin at the mouth of the Wisconsin River, directly across the Mississippi River from Pike’s Peak State Park. Of the nine communities mapped in Wyalusing, six were directly comparable to vegetation types in Pike’s Peak:
cedar glade, on a southwest-facing slope at the tip of a narrow ridge above escarpment of Prairie du Chien dolomite
dry-mesic forest of white oak and red oak, on high upland
dry-mesic forest of nearly pure red oak, on steep slope
dry-mesic forest of red oak and basswood, on north-facing slope and in ravine
southern mesic forest of maple and basswood, largely confined to the steepest portion of the north face of the hill [overlooking the Wisconsin River]
lowland hardwood forest of silver maple, American elm, and green ash, in floodplain of Wisconsin River
In fact, four communities in Wyalusing State Park were used as “typical examples” of their types in Curtis’ classic book The Vegetation of Wisconsin: cedar glade, mesic forest, wet-mesic forest, and wet forest. Thus the examples of these communities in Pike’s Peak State Park are probably very similar to what is widely used as a standard reference (or “type-locality”) throughout the Midwest.
Flora and rare species
Over 250 species of vascular plants were observed by Christiansen (1980) for Pike’s Peak State Park during his community-level inventory of the vegetation. Although an impressive number, this is probably an underestimate of the total number of plant species that could be detected with an intensive floristic inventory. For example, a detailed, multi-year inventory of Backbone State Park focusing specifically on the flora yielded over 600 species of vascular plants (Bill Norris, personal communication).
Several rare plants (Eilers and Roosa 1994) have been documented at Pike’s Peak:
Jeweled shooting star (Dodecatheon amethystinum), shaded limestone cliffs, first documented by Mark Leoschke circa 1986
Shining clubmoss (Lycopodium lucidulum), found only on sandstone outcrops in forested areas; listed by Christiansen (1980)
Rice grass (Oryzopsis pungens), originally reported by Hartley (1962) from dry sandy woods
Sullivantia (Sullivantia sullivantia), found on moist, shaded cliffs; listed by Christiansen (1980)
Low sweet blueberry (Vaccinium angustifolium) and velvet-leaf blueberry (V. myrtilloides), in sandy upland woods and on sandstone ledges; collected by Robert Thorne, cited by Hartley (1962), listed by Christiansen (1980)
Summer grape (Vitis aestivalis), originally collected by Hartley (1962)
Literature Cited
Anderson, P.F. 1996. GIS research to digitize maps of Iowa 1832-1859 vegetation from General Land Office township plat maps. Iowa Department of Natural Resources, Des Moines, IA.
Brand, G.J. and J.T. Walkowiak. Forest statistics for Iowa, 1990. Resource Bulletin NC-136, North Central Forest Experiment Station, USDA Forest Service. 100 pp.
Braun, E.L. 1950. Deciduous forests of eastern North America. Blakison Company, Philadelphia, PA. 596 pp.
Cahayla-Wynne, R. and D.C. Glenn-Lewin. 1978. The forest vegetation of the Driftless Area, northeast Iowa. The American Midland Naturalist 100(2):307-319.
Christiansen, P. 1980. Vascular plant inventory, in Natural resources of Pikes Peak/Point Ann State Park. Iowa Conservation Commission, Des Moines, IA.
Curtis, J.T. 1959. The vegetation of Wisconsin. University of Wisconsin Press, Madison, WI. 657 pp.
Eilers, L.J. and D.M. Roosa. 1994. The vascular plants of Iowa: an annotated checklist and natural history. University of Iowa Press, Iowa City, IA. 304 pp.
Hartley, T. 1962. The flora of the “Driftless Area”. Dissertation, University of Iowa, Iowa City, IA.
Kuchler, A.W. 1966. Potential natural vegetation. Map, 1:7,500,000. National Atlas, U.S. Department of the Interior, Geological Survey, Washington, D.C.
Shantz, H.L. and R. Zon. 1924. Atlas of American agriculture. Part 1, Section E. Natural Vegetation. U.S. Department of Agriculture, Washington, D.C.
Shimek, B. 1948. The plant geography of Iowa. University of Iowa Studies in Natural History 18:1-178.
Tolstead, W.L. 1938. A flora of Winneshiek and Allamakee counties and Clayton County in the vicinity of McGregor, Iowa State College Journal of Science 12:321-384.
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from
Anderson,
R.R. (ed.), 2000, The Natural History of
Pikes Peak State Park, Clayton County,
Iowa:
Geological Society of Iowa Guidebook 70,
p. 43-48.