Grassland-shrub

Habitat Description

Habitat Crosswalk

Introduction

Grassland-shrub is a transitional grassland community that exists anywhere a grass-dominated field contains a light cover of scattered shrubs (Sample and Mossman 1997). It covers a wide moisture gradient and thus is considered to be a continuum of many grassland communities, including Dry, Dry-mesic, Wet-mesic, and Wet Prairies, Pasture, and Idle Cool and Warm Season Grasses and Forbs. As a result, the plant composition of Grassland-shrub closely resembles its associated grassland type and contains no characteristic herbaceous species. It does differ structurally, however, from other grassland communities due to the higher woody plant coverage. Native and non-native woody plants constitute 5-30% of the vegetative cover in Grassland-shrub; virtually all woody plants are <3 meters in height (Sample and Mossman 1997). Shrub species common to this community type include native common prickly-ash and smooth sumac, non-native honeysuckles and multiflora rose, and saplings of box elder, eastern red-cedar, and a variety of cherries. Willows and dogwoods also can be present under certain conditions, especially on wet sites. If these species grow beyond 3 meters in height and reach cover values >30%, however, the community shifts to a savanna or woodland system. Thus, Grassland-shrub can play a key transitional role in the conversion of grassland to woodland habitats (Lett and Knapp 2005).

Historical and Present-day Context and Distribution

Although more than 800,000 hectares of tallgrass prairie existed in Wisconsin prior to European settlement, less than 4,000 hectares (<1%) remain today (WDNR 2005). Agriculture and urban development destroyed most native prairies and left remnants severely fragmented and isolated. Grassland-shrub likely suffered a similar fate because of its close association with native prairies as well as oak savanna, another much reduced habitat. However, there is no documentation to confirm this. Even today, grassland-shrub habitats are not well-inventoried despite their importance to numerous priority bird species (Sample and Mossman 1997). Much of this habitat type exists on private lands, for example retired pastures and abandoned crop fields. Furthermore, few areas are actively managed for this habitat type because it has little or no economic value to landowners. Powerline corridors inadvertently create grassland-shrub habitat, but their long, linear shape makes them difficult to maintain (Knutson et al. 2001). Brooklyn Wildlife Area in Dane and Green counties is one example of a managed grassland-shrub complex and others occur in the following ecological landscapes, often resulting from an inability to keep up with management: Southeast Glacial Plain, Southwest Savanna, and Western Coulee and Ridges.

Natural Disturbances and Threats

Prairies were disturbance-prone and -dependent systems prior to settlement by Europeans. Different disturbance regimes (i.e., disturbance type, scale, frequency, severity, and timing) across the landscape resulted in a complex mosaic of successional or developmental stages and a broad range of patch sizes. In particular, frequent fires in either early spring or fall enhanced the productivity of warm-season grasses and restricted most woody plant growth to riparian areas, protected escarpments (Heisler et al. 2003, Briggs et al. 2005), or slopes with cooler, moister aspects. Less frequent fire regimes allowed for the development of a shrub and oak grub component in prairies and oak openings. Fire intervals equal to or greater than five years tend to favor increases in shrub cover, abundance, and species richness (Sample and Mossman 1997, Heisler et al. 2003). As native grassland ecosystems were converted to cropland and pastures, however, the resulting fragmentation reduced the frequency, intensity, and extent of fire. Additionally, the extensive fragmentation of remnant grasslands by fields, woodlots, roads, and other human developments has increased the availability of seed sources from surrounding woody vegetation (Steinauer and Collins 1996, Briggs et al. 2005). Invasive shrubs such as multiflora rose, glossy buckthorn, and exotic honeysuckles have dominated many areas and limited the recruitment of native woody and herbaceous species (Johnson et al. 2006).

One of the greatest threats to Grassland-shrub is a direct result of its ephemeral nature: the management challenge of maintaining this early-successional habitat on the landscape. Without regular but relatively infrequent disturbance, this habitat succeeds to a woodland system. Most of the grassland-shrub habitat currently found on Wisconsin’s private lands (e.g., recently retired pastures and crop fields) is an unintended consequence of the removal of disturbance and thus will only function as grassland-shrub for a limited time period. It is a dynamic and unstable habitat as it appears, disappears, and moves across the landscape and deliberate management is to needed it maintain it. Managers of public lands should re-introduce infrequent disturbance to establish or sustain this habitat type; it is not clear how to maintain Grassland-shrub on private lands.

Related WBCI Habitats: Wet Prairie, Wet-mesic Prairie, Dry-mesic Prairie, Dry Prairie, Pasture, Idle Warm Season Grasses and Forbs, Idle Cool Season Grasses and Forbs.

Overall Importance of Habitat for Birds

Grassland-shrub is an important habitat for priority grassland birds requiring woody vegetation such as Northern Bobwhite, Willow Flycatcher, Loggerhead Shrike, Brown Thrasher, Bell’s Vireo, Common Yellowthroat, and Field, Lark, and Clay-colored Sparrow as well as more generalist species such Song Sparrow, American Goldfinch, and Red-winged Blackbird. Obligate grassland birds not requiring woody vegetation also occur as breeding species in this habitat, including Northern Harrier, Short-eared Owl, Sedge Wren, Eastern and Western Meadowlark, Bobolink, Dickcissel, Vesper, Savanna, Grasshopper, and Henslow’s Sparrow. However, woody cover generally needs to remain below 20% to sustain these species (Sample and Mossman 1997) and thus obligate grassland birds are not included in the Priority Birds table.

The type and arrangement of woody vegetation are important factors in determining habitat occupancy. For instance, thorny shrubs and low trees are important to Loggerhead Shrikes for nesting, perching, and impaling prey. However, shrikes as well as Field Sparrow and Lark Sparrow prefer woody vegetation that is either isolated or widely spaced. Conversely, Bell’s Vireo and Brown Thrasher favor dense thickets of shrubs, particularly common prickly-ash, American plum, and American hazelnut. In both circumstances, irregular patterns of woody vegetation are more beneficial to breeding birds than hard, linear edges because of reduced negative edge effects (Sample and Mossman 1997).

Priority Birds

Species Status Habitat and/or Special Habitat Features
Mallard B A generalist species that will nest in grassland-shrub. Appropriate open water for breeding pairs and broods must be available nearby.
Sharp-tailed Grouse B, w Formerly common nesting species but largely extirpated from this type.
Northern Bobwhite B, w Requires shrubs or brushy areas for escape cover and roosting.
American Woodcock B, m  
Barn Owl f Very rare resident in southern and central Wisconsin.
Short-eared Owl b, m, w Formerly common nesting species but largely extirpated from this type.
Willow Flycatcher b, m  
Loggerhead Shrike b, m Prefers isolated trees or large shrubs.
Bell’s Vireo b, m Prefers dense thickets of shrubs.
Brown Thrasher b, m Prefers moderate to dense shrub cover.
Blue-winged Warbler b, m  
Common Yellowthroat B, M Prefers a shrub component or tall, dense herbaceous cover.
Clay-colored Sparrow B, M Prefers scattered shrubs and a high litter layer.
Field Sparrow B, M Prefers scattered shrubs and a high litter layer. Most typical of upland sites.
Lark Sparrow b, m Scattered small red cedars are favored. Occurs in areas with bare soil and a high grass:forb ratio.

Objectives

Management Recommendations

Landscape-level Recommendations

  1. Create or support state and federal programs that manage, enhance, or restore grassland-shrub habitats on private lands. Develop cooperative agreements with private landowners to prevent habitat fragmentation and conversion in areas critical for grassland bird conservation.
  2. Partner with farm agencies to maximize benefits of agricultural practices focusing on grassland-shrub habitats.
  3. Identify areas appropriate for grassland-shrub management that will not conflict with other grassland priorities. Build public-private partnerships to conserve and restore grassland-shrub habitats in designated areas.
  4. Educate land managers about habitat requirements for high-priority shrub-nesting species (Knutson et al. 2001).

Site-level Recommendations

  1. Assist managers and conservation planners in recognizing sites where it is desirable to retain and manage for a grassland-shrub component.
  2. Institute longer burning rotations in areas designated for grassland-shrub management. Rotations equal to or greater than five years tend to maintain grassland-shrub communities (Sample and Mossman 1997).
  3. Reduce movement corridors for nest predators by planting and managing for woody vegetation in irregular patterns rather than hard, linear edges.
  4. Manage powerline corridors, abandoned agricultural fields, and other areas with existing shrub cover to support grassland-shrub species. Selective cutting and herbicidal treatment of trees may be needed to maintain grassland-shrub habitats.
  5. Develop property-specific plans to control invasive species on grassland-shrub habitats, such as glossy buckthorn, exotic honeysuckles, and multiflora rose.

Ecological Opportunities

Ecological Landscape Opportunity Management Recommendations
Southeast Glacial Plains Major All
Southern Lake Michigan Coastal Major All
Southwest Savanna Major All
Western Coulee and Ridges Major All
Western Prairie Major All
Central Sand Plains Important All
Central Sand Hills Important All
Forest Transition Present All
North Central Forest Present All
Northern Highland Present All
Northeast Sands Present All
Northwest Lowlands Present All
Northwest Sands Present All
Superior Coastal Plain Present All

Research Needs

  1. Quantify the availability and rate of loss of grassland-shrub habitats in Wisconsin.
  2. Monitor grassland-shrub management to assess its wildlife value and adaptively refine strategies.
  3. Continue to collect information on the structure and composition of native grassland-shrub habitats to better inform management efforts.
  4. Determine the most beneficial arrangement of grassland-shrub habitats within high-grass landscapes.
  5. Evaluate predation and cowbird parasitism rates associated with different woody cover configurations, i.e., linear vs. non-linear patterns, in grassland-shrub habitats.
  6. Determine the value of grassland-shrub habitats for migrating passerines (Knutson et al. 2001).
  7. Investigate adverse impacts of toxic chemicals to grassland birds nesting in or adjacent to agricultural fields (Vickery et al. 1999). 

Implementation

Key Sites

Key Partners

Funding Sources

Information Sources

References

Contact Information

Kreitinger, K. and A. Paulios, editors. 2007.
The Wisconsin All-Bird Conservation Plan, Version 1.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.