Botanical Survey of Hartman Reserve Nature Center


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Botanical Survey of Hartman Reserve Nature Center

including Hartman Bluff State Preserve

Final Report

31 March 2006

William C. Watson

Biological Consultant

Cedar Falls, Iowa
for
Hartman Reserve Nature Center

Black Hawk County Conservation Board

Cedar Falls, Iowa

INTRODUCTION

Hartman Reserve Nature Center (HRNC), which includes Hartman Bluff State Preserve, is located in the northeastern portion of the state of Iowa within Black Hawk County. HRNC is situated directly south of the Cedar River within the incorporated boundaries of the cities of Cedar Falls and Waterloo. The overall size of HRNC is 295 acres owned and managed by the Black Hawk County Conservation Board.. Of that total, 46 acres are included within the recently designated state preserve.

HRNC occurs on the Iowan Surface which is one of the major landform regions within the state. Prior (1991) describes this landscape in part as “having multileveled or stepped surfaces” which “though subdued, occur in a gradual progression from the major stream valleys outward toward the low crests that mark their drainage divides.” The topography of HRNC incorporates a floodplain, adjacent river terrace, valley bluffs and subsequent uplands farthest from the river. The area contains a number of habitats dominated by lowland and upland hardwood forest habitats as well as more open environments which are a result of or influenced by the course of the river and past cultural activities.

Eilers (1971) produced a floristic inventory of the Iowan Surface which formed the botanical foundation of this region of the state. Smaller and more targeted botanical/floristic inventories of protected areas including preserves are few in number and nonexistent for forested habitats within this landform. This is in contrast to adjacent landscapes, particularly the Paleozoic Plateau in northeast Iowa. In this region of the state, numerous botanical/floristic surveys have been accomplished within forested natural areas including White Pine Hollow State Preserve (Thorne, 1964) and Brush Creek Canyon State Preserve (Eilers, 1974). A survey of HRNC including the state preserve should help fill a knowledge gap of Iowa's diverse forest resources. This may offer a better understanding of the transition from the central Iowa forests to those on the Paleozoic Plateau.

During the 2004 and 2005 field seasons, a botanical survey of HRNC was conducted to document the vegetation present at this site. The inventory had three objectives: 1) compile a comprehensive checklist of the vascular plant taxa, 2) identify the existing plant communities and 3) provide habitat management recommendations.

METHODS

Fieldwork pertaining to the botanical survey of HRNC commenced in June 2004 closely following the announcement of funding provided for the project. One complete growing season was to be dedicated to the survey. Therefore, fieldwork continued into spring and early summer 2005 to fulfill the contract requirements. The author then continued additional survey visits for the remaining 2005 field season in an attempt to produce more complete results.

Over the course of both field seasons, surveys were accomplished at scattered time intervals in an attempt to document the vegetation within the study area. Survey dates for 2004 included June 26, 27 and 30; July 7, 8, 19, 22, 25, 26 and 27; August 10, 11, 12, 19, 21, 22 and 30; September 3, 4, 12, 13, 18 and 19; October 31. Survey dates for 2005 included April 9, 10, 15, 27 and 29; May 3, 5, 6, 19 and 21; June 4, 9, 10 and 20; July 2, 12, 28 and 30; August 7, 12 and 28; September 3, 7, 23 and 30; October 17.

During the surveys, all of the identified plant communities/habitats within HRNC were visited and walked through. All vascular plant taxa observed were recorded. Those which were not readily identifiable in the field were collected and processed for later identification. The identification process involved use of numerous floristic manuals and comparative studies of specimens housed in the University of Northern Iowa herbarium in Cedar Falls and to a lesser degree, the Iowa State University herbarium in Ames.

From the surveys, the author compiled a comprehensive checklist of all vascular plant taxa documented to occur within the boundary of HRNC. The only exclusions were those species under direct horticultural management. This included the vegetation within ornamental stone or wood planters. These planters are found adjacent to the nature center and other nearby buildings as well as at the east end of the parking lot and nearby flagpole. Also excluded was the vegetation surrounding the small, artificial pond in front of the nature center and the recently installed water garden behind the nearby program building.
RESULTS AND DISCUSSION

A comprehensive checklist of vascular plants from HRNC is presented in Appendix I. The checklist includes all of the native or naturalized vascular plant taxa encountered during the field study. Also included were those taxa which either appear to be leftover nursery stock from when part of the study area was owned by private business or the result of county sponsored prairie seed mix plantings. It was felt that inclusion of both these latter categories was important due to ongoing and potential future management of the overall botanical resource of HRNC. Checklist nomenclature for all plant taxa previously reported in Iowa follows Eilers and Roosa (1994) except for the genus Rubus L. which follows Widrlechner (1998). A small number of taxa not included within Eilers and Roosa (1994) follows either Wetter et al. (2001) or Voss (1985, 1996).

A total of 451 vascular plant taxa representing 83 families are reported from HRNC during the present study. Within this total, three distinct vegetation categories are identified. 1) Vegetation native to Iowa and occurring naturally in HRNC account for 331 of 451 taxa (74%). 2) A total of 33 plant taxa (7%) are native to North America (30 of 33 are native to Iowa) but apparently do not occur naturally in HRNC. 3) An additional 87 plant taxa, originating from the old world, are non-native/exotic and account for 19% of the total. A large majority of the latter category has become naturalized and is part of the HRNC flora. However, a small number of planted ornamental trees and shrubs recorded on the checklist do not appear to have spread from their point of origin. The present study added a total of 37 native Iowa plant taxa naturally occurring within HRNC which were previously unrecorded for Black Hawk County (Van Norman, 1987).

No naturally occurring populations of vascular plants reported from HRNC during the study appear on the state of Iowa endangered/ threatened/ special concern plant list. However, three species have been proposed for listing: Carex assiniboinensis (assiniboiboine sedge), Poa sylvestris (woodland bluegrass) and Uvularia sessilifolia (sessile-leaved bellwort). Two additional species, Allium cernuum (nodding wild onion) and Echinacea purpurea (purple coneflower), are presently on the state list but are not native to HRNC. Both were brought in with seed mixes or otherwise planted. The geographic origin of these two species cannot be ascertained and may well be from sources outside of Iowa. All five species are further discussed within the text of the report.

In addition to creation of a comprehensive vascular plant checklist, field work identified 10 plant communities present within HRNC. These habitats were not only surveyed for vascular plants, but also in regard to potential threats and management needs in an effort to better understand and enhance the botanical resource present within HRNC. Recommendations are incorporated under a general description and discussion of each plant community that follows.

1) Dry Hardwood Forest.

This community occurs on the higher and drier uplands of Hartman. The area is bordered by the bluff system to the north and includes the more level topography running to the south and southwest away from the bluff. The area is dissected by several drainages which flow out of the uplands and ultimately into the nearby Cedar River. The dry hardwood forest also occupies the well developed west facing upper slopes of these drainages.

One of the representative canopy species of this community is Quercus alba (white oak). The drier portions of the uplands farthest from the bluffs still support a preponderance of Q. alba in the canopy as was probably the case in pre-settlement times. Other canopy species commonly associated with this habitat include Carya ovata (shagbark hickory), Fraxinus americana (white ash) and Prunus serotina (black cherry). Within the understory, Ostrya virginiana (ironwood) is present as is Acer saccharum (sugar maple) which is commonly encountered. The herbaceous zone includes a well developed spring ephemeral flora where adequate light is available.

A rare sedge, C. assiniboinensis, can be found in the herbaceous layer of this forest type. A localized but very dense population of this species was observed near River Hills School. Evidently part of the population occurs on school property and part is located on HRNC property within the recently recognized state preserve. The density of the population is striking as this species is excluding most other herbaceous growth in the immediate vicinity where it occurs. While not observed elsewhere, certainly a small number of plants could be overlooked. At present, the area should simply be monitored and not significantly manipulated.

The forest subcanopy as well as the canopy has filled in with more mesic and fire intolerant species, particularly sugar maple. Certainly this has hindered oak regeneration, but additional aspects of the forest vegetation particularly the herbaceous zone have very likely been adversely impacted as well. In portions of the forest the dense stands of young A. saccharum have intercepted much of the available light resource. This has resulted in a rather depauperate summer herbaceous zone where these stands are most dense.

In response to some of the perceived changes affecting the forest environment, county conservation personnel initiated a thinning program beginning in 1999. The goal was to remove selected canopy and subcanopy trees from four areas of the forest to enhance oak regeneration (V. Fish, pers. comm., 2004). The three largest thinning zones included White Oak North and South and Red Oak II. White Oak North and South are located on the level uplands north of Grand Boulevard on either side of a drainage ravine which begins at the River Hills School parking lot. Red Oak II occurs along a steep, west facing slope of the same drainage ravine farther along its course toward the lowland portion of HRNC.

The present field study does not include an in-depth evaluation of vegetation dynamics in response to the tree cutting and opening of the canopy, however, some observations may be warranted. One of the more obvious changes due to the opened canopy is the vegetation response affecting the herbaceous zone. This layer of the forest would be the first to show substantive change and is the location where oak regeneration will meet initial challenges. Some natural oak regeneration was observed on the steep west facing slope of Red Oak II which is a positive sign. However, the number and distribution of these seedlings is unknown. This is the most open of the three thinning zones, receiving significant light at ground level.

Many species inhabiting the herbaceous layer have responded positively to the added sunlight. This has increased the diversity and vegetation density of this forest layer. Several species could probably be considered as dominant. Eupatorium rugosum (white snakeroot) appears to have increased exponentially throughout the thinning zones and is very common. Other species such as Podophyllum peltatum (mayapple) and Aralia nudicaulis (wild sarsaparilla) have produced large, rather dense patches due to their rhizomatous growth pattern and were commonly observed on the west slope of Red Oak II. These species in combination are probably intercepting significant light resources.

Numerous other species can be found throughout the thinning zones. The rare Uvularia sessilifolia (sessile-leaved bellwort) occurs on the west facing slope of Red Oak II. This is the only location in HRNC where this species was observed and may prefer an open habitat. Voss (1972) states this species and the closely related Uvularia grandiflora (large bellwort) which is more common in HRNC “seem to thrive in openings and borders of woods.” Directly adjacent to the small population of U. sessilifolia is a second species of interest. A single stem/ramet of Trillium recurvatum (red trillium) was observed. This species while fairly common in southeast Iowa woodlands is not known to occur naturally in Black Hawk County (Van Norman, 1987). A small population of T. recurvatum does occur extremely close to the HRNC boundary near a residence on private property. This species may have been planted sometime in the past and escaped into HRNC. T. recurvatum is freely available from the horticultural plant trade.

Within a significant portion of the three thinning zones previously mentioned, an apparent growth spike of Rubus alleghaniensis (blackberry) and Rubus occidentalis (black raspberry) is evident. These armed, shrubby species are having an effect on the herbaceous layer and probably oak regeneration. Due to their woody nature and seasonal growth pattern, these thicket forming plants have produced a rather dense impenetrable zone in significant portions of the thinning stands. While it is generally accepted that some tree removal is necessary for substantial oak regeneration, one unforeseen consequence may be this immediate response affecting the herbaceous layer. While Baughman and Jacobs (1992) state that seedling oaks will probably emerge from dense herbaceous vegetation, they go on to say that “plants that overtop oak seedlings eventually will eliminate them.” Growing through the Rubus spp. thickets may be an added impediment threatening oak regeneration as well as some conservative herbaceous species and should be monitored. The removal of slightly fewer trees may have been beneficial in retarding the Rubus spp. growth, particularly along the west facing ravine slope in Red Oak II which by its nature would have received significantly more incidental light even before any cutting occurred.

The selective cutting was to be followed by occasional prescribed burning to mimic historical conditions within the oak forest (V. Fish, pers. comm., 2004). However, the extensive Rubus spp. growth may actually be suppressing somewhat the process of fire management. These shrubby thickets are not primary carriers of fire and may be shading out native herbaceous species which are. It is also possible that additional moisture or humidity retention beneath these thickets may also inhibit fire.

A smaller forest thinning area occurs at Red Oak I which is located just back from the bluff area near the east boundary of Hartman. At this site the canopy was also opened substantially beginning in 1999 allowing more light to reach ground level. Both

R. allegheniensis and R. occidentalis as well as E. rugosum are present but not at the levels observed in the previous management zones. However, there is more woody growth including shrubs and young trees. The herbaceous layer is diverse and appears to have been stimulated by the additional sunlight.

Hopefully, the tree thinning and subsequent opening of the canopy of these four areas will provide the desired goal of oak regeneration over time. If future thinning cuts are planned, it is recommended that effects on, and restoration of, all strata of the forest environment be a primary focus. Perhaps a series of smaller and more measured cuts could be initiated. These areas may imitate more closely the naturally occurring canopy gaps which are found in all forests. If these canopy gap sites are initiated where significant amounts of shade now exist, it may be desirable to sow collected seed from the surrounding forest habitat. This need may be most pronounced for the herbaceous and shrub layers. Sowing this hartman ecotype seed would probably accelerate growth and restoration of these areas, as well as being in place to compete against the colonization of less desirable exotic species. Ideally, each potential canopy gap cut should be surveyed for invasive non-native species which would be removed before manipulation begins. Monitoring of these sites for the desired results would also be of value. One fairly simple and quick measure would be a series of before and after photo points. This would allow at least a gross comparison of the selected sites over time.
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