Natural Ecosystems

Background

Boulder Valley Natural Ecosystems are defined as places that support natural ecosystems of native plants and animals or possess important ecological, biological, or geological values.  Boulder Valley Natural Ecosystems may also contain features that are rare, unique, or sensitive to human disturbance and are essential to maintain the scientific and educational importance of places representing the rich natural history of the Boulder Valley. The Natural Ecosystems Map also identifies connections and buffers that are important for sustaining biological diversity and viable habitats for native species, for protecting the ecological health of certain natural systems, and to buffer potential impacts from adjacent land uses.

Designation as a Boulder Valley Natural Ecosystem does not supersede any other designation in the BVCP or any other designation.

The Boulder Valley Natural Ecosystems Map provides a comprehensive, valley-wide view of natural systems and baseline information for long-range planning purposes.  By providing a broad, qualitative overview of natural ecosystems in the Boulder Valley, the city and the county can continue to shape and further refine their efforts to protect the natural landscape.  As more quantitative data are gathered and compiled about biological resources in the Boulder Valley, more specific habitat management, protection, and restoration guidelines will be outlined in natural resource management plans. 

Planning and other city and county practices to help accomplish policies 3.03 Natural Ecosystems and 3.04 Ecosystem Connections and Buffers include: 

1. Public acquisition
2. Purchase of development rights or conservation easements
3. Promotion of private land conservation practices
4. Transfer of development rights
5. Rezonings
6. Mitigation of impacts through development review
7. Encouragement of designation of state natural areas through voluntary agreements with the Colorado Natural Areas Program
8. Land use designation changes and rezonings
9. Annexations and initial zonings
10. Service area boundary changes
11. Subcommunity and departmental master planning

Criteria for Boulder Valley Natural Ecosystems Designation

Group 1 criteria (below) were developed to designate core, high quality natural ecosystems.  Group 2 criteria were used to designate areas that may be important in providing ecosystem connections and buffers, and protecting large areas from being split apart.  Group 2 areas also may be human-altered landscapes that retain significant populations of species of concern or function to meet biological requirements for species of concern (e.g., reservoirs).  Generally, Group 2 areas provide a buffer between Group 1 areas and adjacent land uses. 

Group 1 and 2 designations reflect a qualitative difference in present habitat conditions.  The context of a particular site as well as its present habitat conditions are considered in making Group 2 designations.  As further data on a particular site are acquired, the Natural Ecosystems Map may be amended to reflect new information or changes in habitat quality.

(1) Group 1 Criteria:     

(a) For all areas:

• Relatively undisturbed natural communities composed mostly or entirely of native species and remnants of pre-settlement ecological conditions and functions or;

• Significant habitats supporting unique, native flora and fauna (e.g., county species of special concern, state or federal lists) or;

• Areas supporting relatively high diversity or density of native species (e.g., riparian areas, large areas, unique geologic substrates or formations, cliff-nesting bird habitat) or;

• Special habitats supporting significant concentrations of sensitive animal species populations for at least a portion of their life cycles (ground nesting areas, heronries, riparian areas, woody draws, travel routes, seasonal havens, winter ranges) or;

Areas having plant communities with well-developed, representative, or unique structural diversity (vertical, horizontal, aggregations).

(b) Additional criteria for wetlands and riparian areas:

• Wetlands or riparian areas meeting any of the above criteria or;

• Significant wetlands of high or very high wildlife habitat value (number and diversity of native species) according to city evaluation methods or;

• Wetlands identified as priority wetlands in Cooper, Advanced Identification of Wetlands in the Boulder Valley, May 1988, pp. 29-32 or;

• Significant wetlands that are adjacent to or functionally linked to other mapped natural ecosystems or;

• Riparian areas with potential for maintaining high wildlife habitat value (numbers and diversity of native species) and ecosystem functioning.

(2) Group 2 Criteria:
(A designated Group 2 area must meet one primary and at least one secondary criterion)

(a) Primary

Buffers or connections

• Undeveloped areas that provide important connections between Group 1 areas or;

• Undeveloped areas adjacent to Group 1 areas that provide important buffering functions or;

• Undeveloped areas adjacent to Group 1 wetlands or riparian areas which provide important buffering functions.

(b) Secondary

Proximity

• Undeveloped areas close to critical habitats where restoration can provide linkages between habitats, reduce fragmentation, increase necessary habitat size, improve habitat quality, or buffer habitat from nearby development or;

Restoration potential

• An area with high availability of surface or groundwater, intact soil and geologic structure, presence of non-native species is relatively low, and presence of native seed sources is relatively high or;

• An area capable of maintaining ecosystem functions or recovering from human-associated uses or;

• An ecological community that significantly illustrates the process of succession and restoration to a natural condition following disruptive change or;

Size

• A relatively large area capable of maintaining natural ecosystem functions, with minimal fragmentation from various human land uses (building structures, roads, and trails) or;

• Undeveloped floodplains and upland areas surrounding significant wetlands necessary for the protection of wildlife habitat and ecosystem functions or;

Habitat for populations of special species

• Special habitats supporting sensitive animal species populations for at least a portion of their life cycle (ground nesting areas, heronries, riparian areas, woody draws, travel routes, seasonal havens, winter ranges).
Area Descriptors for Boulder Valley

Natural Ecosystems Map

The numbers below correspond to the area descriptions on the Natural Ecosystems map.

1. Great Plains Mixed Grass Prairie - North Boulder Valley
This area is primarily characterized by native shortgrass and midgrass prairies on the mesas and outwash plains and tallgrass in the drainage swales and bottomlands.  Significant wetlands occur in areas with seasonal moisture.  The Boulder Reservoir supports numerous wetlands, including sedge meadows, cattail marshes, and lacustrine shorelines.  The area supports extensive prairie dog colonies providing the prey base for more than ten species of raptors including nesting northern harriers and historical occurrences of burrowing owls.  Wintering and migrating bald eagles use the perch and roost opportunities in the area as well.  Rare plants occur on the Pierre shale outcrops along the mesas.  Several woody draws support high densities of small mammals and birds.

2. Foothill Shrublands and Woodlands - North Boulder Valley
This area north of Boulder represents the rich merger of Great Plains grasslands with the woodlands and shrublands of the Front Range foothills.  Tallgrass and mixed-grass prairies blend into ponderosa pine savannahs and foothill shrublands of chokecherry, three-leaved sumac, and wild plum in woody draws.  The steep gradient causes abundant biological diversity.  The number of different kinds of habitats found in these areas support high numbers of native plants and animals.  Rare plants occur on Pierre shale outcrops.  Large predators (mountain lion and black bear) use the woody draws and rocky outcrops.  Numerous mule deer are the principal prey species in this area.  The grassy swales, woody draws, and streams and ponds are particularly important wildlife habitats.  Rare reptiles and amphibians (e.g., prairie rattlesnake, tiger salamander) also occur in this area.

3. Montane Woodlands/Great Plains Mixed Grass Prairie
This area is one of the largest, relatively intact (i.e., few roads) areas in the county that preserves the transition from Great Plains grasslands to ponderosa pine savannahs, ponderosa pine forests, and ponderosa pine/douglas fir forests.  The elevational gradient again supports abundant biological diversity.  This area has one of the highest breeding bird densities in the state (98th percentile for breeding birds).  Given the worldwide declines in numbers of neo-tropical migrant birds (birds which migrate to the tropics during the winter), this area has added importance for the birds which breed here.  There is also a high density of nesting raptors (e.g., golden eagles, prairie falcons, and the federally-listed peregrine falcon) which are found nesting on craggy rock outcrops.
A high concentration of rare plants exists in this area.  The federally-listed Ute ladies’-tresses orchid is found unobtrusively flowering in wet riparian meadows.  Several unique or representative geologic features such as the Flatirons, Red Rocks, Echo Rocks, Boulder Canyon, and Eldorado Canyon exhibit the geological history of the Boulder Valley.  Large predator habitats supporting black bear and mountain lion link with habitats on county and State lands to the west.

4. Great Plains Shortgrass and Mixed Grass Prairie Complex - South Boulder
This expanse of primarily public land provides today’s Boulder Valley resident with the feeling of the sweeping prairie expanses that existed prior to European settlement more than 150 years ago.  Rolling topography supports complexes of short and mixed grass prairies.  Several small streams carve the landscape, identified by their signature thin, narrow green ribbons of riparian forests.  The numbers of plants and animals living in native prairie grasslands is truly astounding, and we’re only just now finding out how important these areas are for maintaining healthy numbers of native plants and animals.  The prairie dog is now recognized as a true “keystone” species for this area, as more than 160 different animals are known to depend upon thriving prairie dog colonies.  Our chances of restoring and maintaining native prairies are probably best accomplished here due to the size of the area and the variety of ecological conditions.

5. South Boulder Creek Floodplain
Plains streams in the Boulder Valley received the greatest amount of disturbance and development during the past 150 years from damming, channelization, grazing, mining, and irrigation. Although this area has been similarly impacted, the South Boulder Creek floodplain is the best remaining example of a natural riparian corridor in the Boulder Valley.  Historic meanders support extensive complexes of tallgrass prairie, sedge-dominated wetlands, and wet meadows.  Floodplains of streams exiting the mountains are the real “wet environments” in this semi-arid climate.  The South Boulder Creek floodplain provides habitats for many rare species — Ute ladies’-tresses orchid and Preble’s meadow jumping mouse are among the rarest.  The best examples of native tallgrass prairies in the Boulder Valley are located along South Boulder Creek.

Alteration of the hydrology of floodplains is the single most important impact of development on these areas.  Historic wetlands which occurred throughout these extensive floodplains have largely disappeared due to grazing, development, irrigation, damming, and agriculture.  Several floodplain areas of South Boulder Creek, however, have an inherent capacity for restoration, given the proximity to water and the relative lack of development impacts.

6. Boulder Creek Floodplain and Associated Uplands
Boulder Creek is the main tributary to the South Platte River in Boulder County.  Boulder Creek has many of the riparian attributes of South Boulder Creek, although impacts from hydrologic alteration and floodplain development are much greater in the Boulder Creek watershed.  Boulder Creek is a classic plains riparian system that retains some restoration potential east of the city.  Many native wildlife species continue to depend on plains riparian systems.  This area has seen extensive restoration from historic gravel mining operations (particularly Walden and Sawhill Ponds) and now provides habitat for a high concentration of aquatic bird species of special concern.  The floodplain of Boulder Creek supports several rare plants (e.g., prairie gentian), important ecosystems (wetlands and tallgrass prairie remnants) and rare birds (one of the largest great blue heron nesting localities in Colorado).  Several unique geological formations such as the Valmont Dike and the White Rocks are located in this area and provide important habitat to several native species of plants and animals.

7. Great Plains Mixed Grass Prairie-Northeast Boulder
This area is one of the last remaining, relatively undeveloped remnants of the association of shortgrass and mixed grass prairie in eastern Boulder County.  Although the impacts from development, grazing, and cultivated farming are extensive in this area, enough remnants of native prairie ecosystem exist to make restoration possible.

8. Wetlands and Riparian Areas with High Ecological Value
Several wetlands and riparian areas within the Boulder Valley have high value due to the complexity and health of their habitat or because of their relative uniqueness to the valley.  Sombrero Marsh is one of the best remaining prairie wetlands in Boulder County due to its large size and diversity of biological communities.  Stretches of Fourmile Canyon Creek, Dry Creek, and several of the reservoirs also exhibit high quality habitat for native plant and animal species.

Last Updated on Friday, 14 December 2012 11:36