Botanical Survey of Hartman Reserve Nature Center
including Hartman Bluff State Preserve
31 March 2006
William C. Watson
Cedar Falls, Iowa
Hartman Reserve Nature Center
Black Hawk County Conservation Board
Cedar Falls, Iowa
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.
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.
2) Mesic Hardwood Forest
This upland forest assemblage occurs on the slightly more moist, sheltered slopes containing north and east aspects. The canopy is dominated by A. saccharum, Tilia americana (basswood) along with Quercus borealis var. maxima (red oak). The subcanopy often contains a significant A. saccharum component. A diverse and often dense complement of spring ephemerals also can be found in this habitat. On some slopes a pronounced fern flora is present with species such as Adiantum pedatum (maidenhair fern) in fairly significant numbers. The summer herbaceous flora, as in the dry hardwood forest, appears less expressive. This is notable where the canopy and subcanopy are most dense. Experimental management involving removal of a small portion of the A. saccharum canopy/subcanopy primarily and monitoring the results may be warranted. This change would probably enhance all forest strata eventually.
Under a more historical regime of ecological processes such as drought and naturally occurring fires, a number of species were probably somewhat restricted to the more protected slope aspects. Some of these processes such as fire, however, have been suppressed for an extended period of time. This has most likely allowed the forest communities to become more intermixed as the mesic species expanded into the drier portions of the uplands. Some caution should be taken when interpreting this, however, as a significant amount of time has passed since early settlement changed the dynamics of the natural processes affecting the composition of the forest. Considering the relatively small area of the entire upland habitat, the interlaced proximity of the drainages and the ameliorating environmental effects of the nearby river, these factors probably always provided for a certain ebb and flow of species beyond strict boundaries and into what might be considered as secondary habitat.
The upland forest environments of HRNC face a unique problem of erosion along the course of some of the natural drainages. One of the larger drainages has its genesis at the River Hills School and parking lot. Water draining from this area is probably an important factor initiating some of the erosion and should be addressed. Soil erosion is occurring along the entire drainage system and will be a disturbance factor affecting the forest habitat and vegetation for some time to come. Limited control measures such as wooden planks installed at the Kay Romanin Bridge have been put in place. However, additional measures along the course of the drainage should probably be initiated.
Two remedial possibilities are partially in place along the ravine at the present time. The upper reaches of the ravine contain decaying piles of brush from the White Oak North and South forest thinning project. Unfortunately, in some places the density of the piles and the fact that most of the material is not in contact with the soil is probably adding to erosion by allowing run-off water from the parking lot to undercut the soil beneath. In addition, potential vegetation growth is being shaded out which would normally act as a further erosion control. At this time it may not be worth the effort to manipulate these piles as they are slowly decaying and sinking into the drainage and should eventually aid in erosion control.
There are a number of fallen trees across the ravine system which could be utilized for erosion control. Under ideal conditions these “dead falls” should be left in place as part of the natural cycle and wild aesthetic, however the potential value as erosion control may be more important. Portions of these down trees could be cut and dropped into the ravine slowing the flow of water and forming small retention barriers for soil accumulation and as an aid for potential vegetation growth. Some seeding of specific plants which grow well in this environment, such as Glyceria striata (fowl manna grass), may be warranted. Seed should come from native species found within HRNC.
3) Lowland Hardwood Forest.
This forest community occupies the majority of the alluvial terrace system in the lowland portion of HRNC. Old flood raceways (scrolls) and adjacent risers provide microhabitat partioning within the forest environment. The forest contains a diverse canopy with Gleditsia triacanthos (honey locust), Juglans nigra (black walnut), Ulmus Americana (American elm) among other species. Scattered mature Quercus macrocarpa (bur oak) were also found as part of the forest canopy. A rather dense subcanopy has formed over the years which include Celtis occidentalis (hackberry), Acer spp. (maples), Ulmus spp. (elms) and scattered Crataegus mollis (downy hawthorne). Surprisingly, a significant number of Q. macrocarpa were found scattered throughout portions of the forest subcanopy zone. It may be useful to actually map or acquire a set of global positioning coordinates for all of the canopy and subcanopy oaks within the lowland environments of HRNC. This could provide a better understanding of the actual oak distribution pattern in regard to future management decisions.
Two additional tree species of note occur, at least historically, within the lowland forest. A few Juglans cinerea (Butternut) are scattered throughout the forest. This species has become very rare throughout much of its range in Iowa due to an introduced disease which is killing many individual trees. Field observations this past season located approximately five living trees. There may be more but probably not many. Also Ulmus thomasii (rock elm) is another rarely encountered tree in Iowa. Van Norman (1987) reports this species from HRNC but it was not observed during the present study. To the uninitiated, this species looks like other elms and any prescribed tree cutting needs to take that into consideration. Further searches for this species may be warranted.
In some areas of the forest, the density of woody species has left the herbaceous flora as well as other strata somewhat depauperate. However, throughout the habitat as a whole and in areas such as canopy gaps and partial light environments, a diverse and representative flora exists. The overall herbaceous vegetation is dominated by a mix of graminoids - sedges and grasses plus a suite of native wildflowers. A number of sedges characteristic of a lowland forest/woodland environment, such as Carex amphibola var. turgida (narrow-leaf sedge), Carex conjuncta (soft fox sedge) and Carex grayii (Gray’s sedge) are relatively common within HRNC. Additional species were located including Carex muskingumensis (muskingum sedge) which is considered rare in the state (Eilers and Roosa, 1994). Notably, C. muskingumensis has not previously been reported from Black Hawk County (Van Norman, 1987) but is frequently encountered in the lowland forest at Hartman. Several other Carex spp. also occur within the habitat and as a whole may well have been one of the dominant groups of plants inhabiting the area during pre-settlement times.
A total of 32 native grass species have been identified from HRNC. A number of these are found within the lowland forest including Elymus virginicus (Virginia wild rye), Cinna arundinacea (wood reed), Diarrhena americana (American beak grass) and Muhlenbergia bushii (nodding muhly). Both D. americana and M. bushii appear to be at the northernmost edge of their distributional range within the United States and have most likely migrated up the Cedar River corridor. The wildflower or forb component includes a number of species also present in the upland habitat as well as those restricted to the lowlands such as the rare Arisaema dracontium (green dragon). The spring ephemeral flora is well developed and contains a number of species similar to the uplands as well as those more commonly associated with lowland forests such as Mertensia virginica (bluebell).
The process of cutting and girdling selected trees for oak regeneration and creation of an oak savannah has begun in the lowland forest. As in the uplands, county personnel are removing a portion of the existing forest canopy and subcanopy. This is occurring near the west boundary of HRNC, south of the Riverside Recreation Trail in an area referred to as Lucy’s Meadow. The affected area is easily observed from the nearby overlook platform. Within the limited cutting zone already completed, no naturally occurring oaks are present. However, in the adjacent forest to the east which is slated for cutting, naturally occurring oaks are present. Approximately 20 oaks occur in this area, the majority around Turtle Pond. As such, perhaps further thinning should take a more measured approach similar to recommendations in the upland forest. Cutting could be centered around or in conjunction with oaks already in place. Less cutting or girdling would also produce a more transitional thinning pattern as the western boundary of the newly dedicated state preserve is nearby. This buffer may yield a less stark and more aesthetically pleasing environment as well.
In addition, this area also appears to contain a significant population of P. sylvestris commonly found growing under the existing canopy. At this time it is unknown what effect continued thinning of the canopy and attempts to convert the area to oak savannah may have on this rare species. Eilers and Roosa (1994) state the habitat for P. sylvestris is moist woods; alluvium.
Within the area already thinned, a number of oak saplings have been planted under supervision of county personnel. Several of these are Quercus bicolor (swamp white oak). This species does not otherwise occur in HRNC although it is found naturally along the Wapsipinicon River in the northeastern corner of the county (Van Norman, 1987). These trees probably should be removed and if plantings are continued, it is recommended that native species to HRNC be used.
Field study observations of the lowland forest clearly support a measured and thoughtful opening of the forest canopy to increase growth of all species and strata present. The difficulty comes in finding the optimum degree and pattern of cutting to enhance the vegetation diversity as well as wildlife which uses the forest. Norris et al. (2003) state that while some bird species were more diverse in frequently disturbed, successional forests, neotropical migratory birds of high conservation concern to the U. S. Fish and Wildlife Service are more diverse in mature, undisturbed forests than in successional forests in northeast Iowa. The overall general recommendation is to err on the side of conservation. This is most obvious in the realization that additional trees can always be cut but it may take several decades to replace them. Smaller cutting zones which mimic natural canopy gaps may be the best pattern to follow.
The creation of scattered canopy gaps throughout the lowland forest could be staggered over time. This would allow a wider range of age classes and successional stages of all woody species as well as a denser and more diverse herbaceous layer to form. Eventually, additional small canopy gaps may coalesce into larger blocks of restored habitat within the lowland forest. These scattered sites should be restored only with hartman ecotype seed if needed.
The lowland forest offers the potential habitat for the only recommended restoration effort using an outside seed source at HRNC. This effort would involve Napaea dioica (glade mallow) which is a very rare species in Iowa. At one time, this species was a federal candidate for protection and is presently on the state list of endangered/threatened/special concern vascular plants. While not actually located within HRNC, a small colony was found just outside the boundary during the field study. This is one of several small colonies located along or near the Riverside Recreation Trail in Cedar Falls (Watson, 1993). Unfortunately, some colonies are already extirpated and others are in jeopardy. To protect the local N. dioica population, it is recommended that seed be collected, grown under supervision and reintroduced into the appropriate habitat(s) within HRNC. Preferred habitat in Iowa is moist lowland forest openings with partial to full sunlight, riverbanks and perhaps some wetland habitats. If this is attempted, state permission is required and the introduced plants should be monitored.
A complication in this restoration effort is the fact that a small number of N. dioica plants were found growing around the pond by the nature center. This artificial habitat contains several rare species which have no historical or biological tie to HRNC or the surrounding landscape. It is recommended that all of the N. dioica plants in the pond setting either be destroyed or perhaps given to the University of Northern Iowa greenhouse for possible incorporation into their collection of plants. This would prevent the escape of this species into natural habitats at HRNC and possibly interbreeding with the native population.
There is a significant number of native plants which occur in the lowland forest. Restoration efforts which affect the forest should concentrate on using these local species. Not only are they adapted to the area but they represent the original native vegetation which is the natural heritage of HRNC.