Executive Summary - City of Des Moines

Natural Resource Inventory
Executive
Summary
3226 University Avenue Des Moines, IA 50311
515-237-1386
www.dmparks.org
PARKS AND RECREATION

NATURAL RESOURCES INVENTORY OF THE
CITY OF DES MOINES PARKS AND
CONSERVATION LAND
Report to:
City of Des Moines Parks and Recreation Department
3226 University Avenue, Des Moines, IA 50311
By:
Dr. Thomas Rosburg
Department of Biology, Drake University
2507 University Avenue, Des Moines, IA 50311
Or
Botanical and Ecological Consulting
73448 260 th St, Colo, IA 50056
May 2013

EXECUTIVE SUMMARY
The principal results of the natural resource inventory of the Des Moines park system are
summarized here. There are several central conclusions that can be made.
1) The conservation value and importance of the park system is demonstrated by the presence of an
impressive number of vascular plant species; the number of plant species supported is very high. The
651 species observed includes 459 that are native to central Iowa, which represents 30% of the native
flora of Iowa. In other words, nearly one third of the state's native plants inhabit the park system's
ecosystems. The 459 native species observed exceed the number of native plant species that have been
observed in the floristic surveys for several Iowa counties (much larger areas). It also exceeds the
number of native species observed in a similar study at Whiterock Conservancy in Guthrie County (a
similar amount of land area). The number of native and naturalized species observed in the park system
is 617, a measure of floral richness that exceeds the richness observed in Ledges State Park in a study
done in 1985. Ledges State Park occupies about one fourth of the land area as the Des Moines park
system, but it is considered to be one of the state's botanical jewels due to its topographic and edaphic
diversity.
Obviously many of these native plant species are common species that occur throughout Iowa.
Nonetheless, the high plant richness observed verifies the park system is providing important
conservation results ~ high plant richness helps to support high animal richness. A sensible approach to
conservation is summed up by the phrase "a goal of conservation should be to keep the common species
common". The high plant richness of the park system informs the park system of a paramount
responsibility - management should sustain and protect this high plant diversity.
2) The quality of the flora supported by the park system is substantial. This can be supported by three
types of evidence. First, there were 8 species observed that are endangered, threatened, or special
concern species in Iowa. One of these, the threatened species shining willow, is a tentative identification
and needs further investigation to verify identification. The
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other 7 species are listed as special concern species; 4 of them are especially notable in their importance.
Two of the four species (pale violet and frost grape) represent the first known observations for the
species in Polk County. The other two species (long-scaled green sedge and large seed dodder)
represent just the second observation for Polk County. It is clear that the park system is providing
habitat for several uncommon plant species in central Iowa.
The second line of support for the significant quality of the flora is based on the conservatism of plant
species. The 459 native species observed include 78 (17.0%) that have an Iowa Coefficient of
Conservatism of 7, 8, 9 or 10 (10 is the maximum coefficient). The range of 7-10 is used to indicate a high
level of conservatism, which means the species is conservative in its habitat requirements and therefore
mainly inhabits pristine and natural environments. Plant conservatism provides a way to distinguish
weedy, early successional, common species (low conservatism) from species that are more specialized,
infrequent, and dependent on later successional natural habitats. Relatively high numbers (or percentage)
of high conservative species indicate a higher ecosystem quality. Although the 17% of high conservatism
species in the park system is somewhat lower than some other sites chosen for comparison, those other
sites (e.g., Sylvan Runkel State Preserve with 23% and Whiterock Conservancy with 19%) are among
some of the highest quality botanical sites in Iowa, and they do not have a history of urbanization and
human disturbance. Given the urban environment of the Des Moines park system, the conservatism
observed is a positive feature that indicates high quality ecosystems are present.
The third source of evidence for substantial floristic quality is the occurrence of new records for native
plant species in Iowa. There were 6 species observed that are not included on the current checklist of
Iowa plants. One of these, spreading sand mat, is a new record for Iowa. Three of the species are new
records for Polk County. The absence of the other two species from the checklist can be explained by
different nomenclatural interpretations. Overall, these new records provide additional evidence of the
Des Moines park system supporting unusual and important plant species.
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3) Much of the park systems conservation value comes from the diversity of ecosystems that are
supported, which are identified by the plant associations that were delineated and mapped. There are 80
natural or semi-natural plant associations supported by park system and they account for about 53.6% of
the total area (the remaining acreage is parkland, the term used to reference the highly managed areas in
the park, water, and non-vegetation areas). Among these natural plant associations, 21 are
herbaceous/grassland types, 4 are shrubland types, 2 are savanna types, 11 are woodland types, 23 are
forest types and 19 are wetland types. Among the natural/semi-natural associations, forest associations
account for the greatest area (64.6%), followed by herbaceous associations (22.8%), woodlands (6.0%)
and wetlands (5.8%).
Oak-dominated associations account for 14% of all forests and woodlands in the park system. They also
represent the extant communities that have the highest remnant value and potential for ecological
restoration. For the most part, they represent highly degraded oak savanna and oak woodland, which are
two native plant associations that were originally a large part of the native landscape in central Iowa, but
nowadays are essentially gone from the landscape due to decades of woody encroachment and urban
development. The Des Moines Park system is in a unique and significant position in that it can make an
important contribution to the restoration of oak savanna and oak woodland through renovation of these
degraded remnants. Oak savanna and woodland restoration is possible in several parks, including
MacRae, Pioneer, Prospect, Grandview, Ewing, Greenwood, Ashworth and Waveland Golf Course.
Tallgrass prairie reconstruction and cool season grass-forb associations account for 38% of the area of the
herbaceous communities. Although additional tallgrass reconstruction could be done by utilizing the cool
season grass-forb communities (which are dominated by non-native grasses), it is important to consider
the landscape and habitat diversity created by maintaining some of the park lands in cool season grass
associations. The increased landscape diversity that comes from greater numbers of different plant
associations within a park provides higher habitat diversity and heterogeneity that translates into higher
wildlife value. There certainly could be more tallgrass prairie reconstruction accomplished in the park
system. Prairie occupied the second largest share of the native landscape of the park system (35.3%), but
now
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only represents 1.2% of the park system. There is ample cool season grass parkland, which has very low
wildlife value, that could be utilized for prairie reconstruction. In converting it to tallgrass prairie, not
only is there more native vegetation and wildlife habitat (which increases the park's value for wildlife
viewing, photography, nature observation, environmental education), there is less mowing maintenance
to do once the prairie is established. Any new prairie reconstructions should utilize a seed mix that is
entirely comprised of species native to central Iowa. Three prairie species have been planted in the parks
that are not native to central Iowa, two in an ecosystem restoration (wild quinine and purple coneflower),
one in a prairie garden (prairie smoke) and one in lawn (buffalo grass).
There is also good opportunity to accomplish wetland restoration in the park system. Although wetlands
comprise a very small part of the park's ecosystems, they support an inordinately large number of plants.
Nearly a third (31. 7%) of the plant species observed have a wetland affinity of-2 or lower (occur in
wetlands 67% or more of the time), and nearly a fifth (18.9%) have a wetland affinity of -4 or lower
(occur in wetlands 89% or more of the time). Among the 78 high conservative species observed, 25
(32.1%) are wetland species (wetland affinity ≤ -2). Wetlands not only increase the botanical diversity
and quality of the park system, but they also increase the function of the park system in providing
essential ecosystem services like cleansing water of sediment and nutrients, controlling flooding, storing
carbon and replenishing groundwater.
4) The most critical management task needed in the park system is invasive species control. The
integrity of the entire park system, its ability to provide habitat for native organisms, recreational
experiences for users, and sustainable ecosystem services is compromised by the threat of invasive plant
species. It is imperative that the Des Moines park system take an aggressive approach to controlling
invasive species. Every tract of park land has an invasive species problem. Among the 180 non-native
species encountered in the park system, 45 could be labeled invasive (approximately 25%). The
invasive species with the highest potential for causing loss of biodiversity include:
• Ailanthus altissima (Tree of heaven)
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• Alliaria petialata (garlic mustard)
• Berberis thunbergii (Japanese barberry)
• Bromus inermis (smooth brome)
• Celastrus orbiculotus (oriental bittersweet)
• Cirsium arvense (Canada thistle)
• Conium maculatum (poison hemlock)
• Caronilla varia (crown vetch) .
• Elaeagnus species (Russian and autumn olive)
• Lespedeza cuneata (sericea lespedeza)
• Lonicera species (Honeysuckle species)
• Morus alba (white mulberry)
• Pastinaca sativa (wild parsnip)
• Phalaris arundinacea (reed canary grass)
• Polygonum cuspidatum (Japanese bamboo)
• Populus alba (white popular)
• Rhamnus cathartica (common or European buckthorn)
• Robinia pseudoacacia (black locust)
• Rosa multiflora (multiflora rose)
• Trifolium species (red and alsike clover)
Pollution is also an important threat to park biodiversity and function. The most conspicuous form of
pollution observed is the illegal dumping of many kinds of discarded items. Many parks have degraded
habitats due to dumping. In some cases it appears to be of recent origin and in other cases it appears to be
historic. Some of the most blatant examples were observed at McHenry, Prospect, Greenwood, Gray's
Lake and in the North Des Moines River Open Space along Morningstar Drive. Water pollution, evident
from very discolored water, is present in the stream along Morningstar Drive.
5) Three species of ash trees are present in the park system - green ash, white ash and black ash. All
are susceptible to the emerald ash borer. Green ash is a ubiquitous species on park
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lands. It was the most abundant species in the plant inventory of the extant plant associations identified
and delineated. It was also the most abundant species in the tree mapping survey that was done on much
of the parkland habitat in the park system. Its presence throughout many of the ecosystems on park lands
suggests that its demise (due to the borer) could cause a substantial ecological disturbance. White and
black ash are much less abundant than green ash. White ash occurs in a few parklands where it has been
planted and as a natural member of several plant communities. Black ash is less common than white ash
and only present as a natural member of a few plant communities. The low occurrence of both white and
black ash means that their loss from parks and natural areas is not likely to be devastating as green ash.
However, both white and black ash are more conservative than green ash, so their removal may have
important unknown effects.
6) Ecosystem restoration should be a priority for park management. Oak woodlands and savanna should
be the first priority since they were historically very important but nowadays are among the most
threatened of ecosystems. They are also the only ecosystem present in the park system that occurs as a
remnant, albeit very degraded. Mac Rae, Greenwood, Prospect and Pioneer offer opportunities for oak
woodland and savanna restoration. Prairie reconstruction should be the second highest priority, and the
goal of placing a prairie example in every park is doable. Parkland and cool season grass habitats occur
in nearly every park site, and they provide a good starting point for reconstruction. It is important to
design seed mixes that are appropriate for Polk County (paying attention to species biogeography) and
for the habitat (paying attention to ecology). Wetland reconstruction is the third priority, since there are
fewer good sites and the logistics of wetland reconstruction are usually more difficult than prairie.
Identifying a site for a wetland reconstruction is the first important step and an understanding of the site's
hydrology is imperative. One site that appears to have potentially good sites is Cownie Soccer Open
Space, especially for wetlands that would support wetland wildlife.
Another important strategy that this ecosystem inventory can support is a policy of best-use
management. Basically this means that each park or unit of park landscape should be
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evaluated to determine what types of use are possible or currently in practice. In this way uses that are not
compatible can be identified, and a process to determine which use is the best with regards to meeting
park system objectives can be completed. The concept is basically that some parks may be better suited to
protection of biodiversity, while other parks are better suited to recreational opportunities that are often
not compatible with biodiversity and environmental protection.
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Natural Resource Inventory
Des Moines Parks and Recreation
3226 University Avenue Des Moines, IA 50311
515-237-1386
www.dmparks.org