DEVELOPING ENVIRONMENTAL INDICATORS FOR MINNESOTA

Prairies

The Environmental Indicators Initiative

State of MinnesotaFunded by the Minnesota Legislature

on recommendation of theLegislative Commission on Minnesota Resources

Sponsored byThe Environmental Quality Board

1998

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Citizens and decision makers useenvironmental indicators to helpeffectively manage and protectMinnesota�s prairies. Environmentalindicators answer four questions.

What is happening to ourprairies?Environmental condition can be mea-sured by the relative abundance ofnative, exotic, and weedy plantspecies, soil organic mattercontent, and percentage of prairieacreage managed with fire.

Why is it happening?Indicators of human activities thataffect prairies include the conver-sion of prairie to other uses, theexclusion of fire, and over-grazingby cattle.

How does it affect us?Changes in prairie health and extentmay diminish the flow of benefits.Indicators of how we are affectedinclude changes in the number ofnative plant and animal speciesfor scientific investigation andenjoyment, the availability ofareas for hunting grasslandwildlife, changes in foragequality, and changes in soilquality.

What are we doing aboutit?Societal strategies to maintain or restorehealthy prairie include the imple-mentation of best managementplans (that include grazing andprescribed burning), preservation

of remaining prairie through landacquisition and easements, andrestoration of permanent vegeta-tion.

In this chapter we outline importantbenefits from prairie ecosystems, thekey ecological characteristics thatdetermine the health of prairies, thepressures affecting prairies today, thecurrent status and trends relating toprairies, and the most significantpolicies and programs that affectMinnesota prairies. In this chapter wegive examples of indicators thatprovide important informationabout Minnesota prairies.

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HIGHLIGHTSBenefits of HealthyPrairies� Habitat for wildlife, especially

grassland birds and waterfowl� Fertile soils and erosion control� Opportunities for recreation,

including hunting and wildlifeviewing and scientific research

� Plant species with potential foragricultural and medicinal uses

� Sustainable forage for livestock� Cultural and historical

significance to Minnesotans

Important EcologicalCharacteristics� Underlying bedrock,

topography, soils, and moistureavailability determine prairieplant community composition

� Productive prairies contain adiverse assemblage of plants thatexploit nutrients and waterefficiently

� Nitrogen and water availabilityoften limit plant growth inprairie

� Fire, grazing, drought, andburrowing animals are naturaldisturbances that help maintainprairie ecosystems

Impacts on Prairies� Fragmentation of remaining

prairie habitat by agriculture,development, roads, and utilities

� Loss of prairie to mining andassociated road and buildingconstruction

� Conversion of prairie to otheruses (livestock production) viathe introduction of exotic speciesand agricultural chemicals andthe exclusion of periodic fires

� Isolation of small remnantprairies from other naturalcommunities

� Inadequate managementincluding elimination of fires,overgrazing, and recreationaloveruse

� Airborne deposition of nitrogen

Status and Trends� Less than 1% of original

Minnesota prairie remains� Little high-quality prairie is

available for preservation� The Red River region holds

most of the largest tracts ofprairie remnants in the state

� Increased public interest inprairie restoration and prairieplants for landscaping

Major Policies andPrograms� Scientific and Natural Areas

Program protects significantexamples of prairie

� Conservation Reserve Programreestablishes permanentgrassland cover

� Native Prairie Tax ExemptProgram assists landowners inpreserving prairie

� Reinvest in Minnesota (RIM)Native Prairie Bank allows theDNR to preserve prairie bypurchasing easements fromlandowners

� The Nature Conservancyprotects some of the highest-quality prairie tracts in the state

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BENEFITS OFPRAIRIESTallgrass prairies once covered athird of Minnesota in a zoneextending from the northwest to thesouth and southeast (Figure 1). Theprairie supported an enormousdiversity of plants, includingmembers of the aster, legume, rose,lily, and grass families, and dozens ofothers. These grasslands producedthe richest agricultural soil in theMidwest. The ecological, economic,scientific, and cultural values ofMinnesota�s tallgrass prairie areprecariously preserved in the lessthan 1% of the original tallgrassprairie that remains today.

Prairie provides food and shelter formany species of wildlife. About halfof the state�s rare species occur onprairies (MDNR 1990). Greaterprairie chickens and sharp-tailedgrouse depend on grasslands, andgrassland songbirds, including uplandplovers, bobolinks, meadowlarks,and longspurs, nest in prairievegetation. Prairie wetlands providehabitat for many species of water-dependent birds, including mallards,pintails, canvasbacks, blue-wingedteal, marbled godwit, and Americanbitterns. These wetlands are alsoimportant stop-over habitat formigrating waterfowl and sandhillcranes. Prairie plant communitiessupport a rich assemblage of small

rodents, which in turn supportmammals (badger, red fox, mink,and coyote) and raptors (red-tailedhawks, Swainson�s hawks, kestrels).

Roots of prairie plants are extensiveand deep. The intertwining rootsoften form sod, which holds the soiland slows erosion. Decaying roots,soil organisms, and other organicmaterial improve water and airpenetration, and increase fertility.Fertile soils, a long growing season,and sufficient rainfall make thetallgrass prairie a very productiveecosystem (Tester 1995). Highagricultural productivity promotedthe conversion of tallgrass prairie tocropland. Native prairie grasses,which once supported vast herds ofbison and elk, now providedependable forage for livestock.

Prairie species have potential as cropplants and as medicines. NativeAmericans in North Dakota plantedred-, white-, and black-seededvarieties of sunflower developedfrom wild species, one of the firstimproved crops developed fromnative prairie species (Wilson 1987).Jerusalem artichoke, the root ofanother prairie sunflower, can befound in supermarkets. Other nativespecies, such as eastern gama grassand Illinois bundleflower, arepotential agricultural perennials (Piper1993). Native Americans used manyprairie plants as medicines. Purpleconeflower was used against colds,has anti-inflammatory and painkillingproperties, and stimulates theimmune system (Chadwick 1995).New drugs and medicines may awaitdiscovery in prairie species.

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Prairie has enormous scientific valueto ecologists, wildlife biologists, soilscientists, and agronomists. Studyingthe genetic structure of wild grassesand forbs helped crop breedersdevelop new disease- and drought-resistant strains of hybrid grains. Soilscientists are interested in the abilityof native prairie grasses to improvesoil fertility. Because intact prairie inMinnesota is rare, scientific study ofhow prairie ecosystems function andthe potential benefits they hold for usis imperative.

The use of prairie plants in low-maintenance landscapes for parks,corporate headquarters, roadsides,and other public areas is increasing inpart because prairie plants controlsoil erosion effectively.

As a driving factor in our state�shistory and economy, prairie is aculturally significant landscape forMinnesotans. Native Americansdepended on prairie buffalo andother wildlife and plants for foodand medicines. Immigrants farmedthe rich prairie soil, built houses fromits sod, and created Minnesota�sagricultural economy.

ENVIRONMENTALINDICATORSWhat are environmental indicatorsand how can they help us measurethe health of prairie ecosystems?Indicators are selected measures thathelp us understand environmentalconditions, alert us to potentialproblems, and suggest actions thatprevent or fix problems before theybecome crises. The followingscenario shows how environmentalindicators can be used to improveenvironmental decision making inprairie ecosystems.

Frank and Mary are third-generationfarmers. The pasture on theirproperty has never been plowed, butover the past few years, the quality of

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forage has decreased, substantialsupplemental feed was required fortheir cattle, and shrubs werebecoming more common upslopefrom the stream than on the streambank. In dry summers, weedyspecies, such as Canada thistle,reduced the amount of forageavailable. In addition, because cattleconcentrate along the stream, thebank has eroded significantly. Thestream is muddy and often full ofalgae. Although Frank and Marydepend on the pasture to providehigh-quality forage for their cattlenow, they want their children toinherit land that is productive and ingood condition.

Working in partnership withconservation agencies, their localwatershed coordinator, and theDNR, Frank and Mary developed avoluntary conservation plan toimprove forage for cattle andenhance the native prairie. The planincluded vegetation managementpractices, rotational grazing, andsteps to stabilize the stream bank.They planted native switchgrass, bigbluestem, and Indian grass and builta fence to exclude cattle from thestream banks. Prescribed burninghelped the native grasses andremoved weedy species from thesite. Some of these activities wereeligible for cost sharing through localagencies.

Under the plan Frank and Marycontinue to cut hay and grazelivestock on the pasture. Improvedforage results in better cattle weightgain. The steam bank is stabilizing,and the water quality is improving.

The prairie scenario is representativeof the complex issues affectingprairies. The EII frameworkprovides insights into therelationships between humanactivities and environmental changeand helps select indicators thatmeasure progress toward solvingcomplex problems. Some humanactivities adversely affect ecosystemhealth and diminish the flow ofbenefits. In the prairie scenario,indicators of human activities includeheavy livestock grazing and fireexclusion. These activities arepressures that cause changes inenvironmental condition. Indicators ofenvironmental condition include therelative abundance of native andweedy plant species, stream-bankerosion, and sediment,phosphorus, and nitrogen contentof stream water.

Indicators can describe desiredconditions (stable stream banks, cleanwater, soil retention, productivenative grasses). They also can be usedto guide restoration efforts bymonitoring progress in returning thepasture to a healthier state. Strategiesfor improvement may includemanagement activities thatrestore and maintain native plantspecies (rotational grazing,exclusion of cattle from stream-bank areas, prescribed burning,seeding with native species). Suchstrategies help restore and maintainthe health of the prairie and ensurethat the benefits (sustainable, high-quality forage, weight gain incattle, erosion control, nativegrasses) we look for from prairiesare . Table 1 shows how prairieindicators are organized within theEII framework.

PRAIRIE ECOLOGYIn Minnesota, tallgrass prairie hasexisted for centuries in a shiftingbalance with forests to the east. Forexample, prairie expanded to the eastduring a dry period 8,000 years agoand then retreated during coolingperiods as forests expanded to thewest. Fire was (and is) essential inmaintaining tallgrass prairie. Althoughcurrent rainfall amounts in the easternprairie can support trees, prairieplants are better adapted to fire.Where fire is frequent, trees areeliminated, and grasses flourish.

Compared to many forests, prairie isstructurally simple. In Minnesota, afew woody shrubs, includingwolfberry, wild rose, and smoothsumac, are native to tallgrassecosystems (Chadwick 1995).However, Minnesota prairies consistlargely of grasses (over 30 species)and nongrass, herbaceous plants(several hundred species; MDNR1993). Historically, fires and bisoncreated a patchy environment thatsupported a wide variety of plantsand animals. Native prairie wasproductive and colorful, rich ininsects, birds, and small and largemammals with varied environmentaland habitat requirements (Figure 2).Deep, fertile soils, gentle topography,and a favorable climate madetallgrass prairie especially suitable foragriculture. Today, the tallgrassprairie region is the Midwest�s cornbelt, and native tallgrass prairiepersists only in small, scatteredremnants. Approximately 150,000acres of Minnesota�s 18 million acresof prairie remain (Figure 3; Wendt1984).

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Plant communitiesUnderlying bedrock, topography,soils, and moisture availabilitystrongly influence plant communitycomposition in Minnesota prairies(see text box; MDNR 1993) Grassesdominate in Upland Prairies, with tallgrasses (big bluestem and Indiangrass) more common on moist sites,and midheight grasses (littlebluestem, sideoats grama, porcupinegrass, and June grass) common ondrier sites. Forb species compositionvaries with soil moisture, but forbstypically are abundant and may belocally diverse. Several shrub or sub-shrub species (e.g., leadplant) arecommon, but trees and tall brush aregenerally absent. The presence ofabundant shrubs, small aspen, balsampoplars, and bur oaks distinguishesUpland Brush-Prairies from UplandPrairies.

Biological productivityPrairies are very productiveecosystems, in part because hundredsof plant species exploit soil nutrientsand water in diverse ways (Weaver1954). For example, some speciesare adapted to cool, moistconditions (blue-joint reed grass,cordgrass, meadow rue, goldenalexanders), while others tolerate heatand drought (grama grasses, needlegrass, big bluestem, sage). Somespecies have shallow, fine roots tomaximize collection of rainwater(little bluestem, June grass), whileothers have long taproots (compassplant, pale purple coneflower,upland boneset) to extract waterfrom deep in the soil (Figure 4). Inmesic tallgrass prairie in Wisconsin,annual production may reach 7,000to 9,000 lbs/ac/yr. Average

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MINNESOTAPRAIRIE TYPES

Wet prairie occurs mainly in southernand western Minnesota, and occasionallywithin the deciduous forest zone, in lowareas where the water table remains withinthe plant rooting zone for several weeksduring the growing season but whereinundation occurs only infrequently andbriefly. Wet prairie is especially commonin the Glacial Lake Agassiz Interbeacharea, where artesian seepage occurs.Dominant wet prairie grasses includeprairie cordgrass and blue-joint. Sedgesand rushes are also importantcomponents of the plant community.Although forbs are abundant in wetprairie, fewer forb species occur in wetprairie than in mesic prairie. Commonforbs include panicled aster, New Englandaster, meadow ragwort, giant goldenrod,and sawtooth sunflower. Small willowsare also common.

Mesic prairie occurs primarily insouthern and western Minnesota onmoderately well-drained to well-drainedloamy soils. Once the most widespreadtype of grassland in the state, mesic prairiecovered gently rolling glacial landforms.Mesic prairie is dominated by grasses: bigbluestem and Indian grass on all site; littlebluestem and porcupine grass on dryersite, and switchgrass and prairie cordgrasson wetter sites. Forbs (purple prairieclover, prairie turnip, rough blazing star,goldenrod, smooth aster, wood lily,leadplant, prairie rose, purple coneflower)are also abundant, with speciescomposition varying locally with soilmoisture. Most of Minnesota�s mesicprairie has been plowed, providing themost productive agricultural soils in thestate. Northwestern Minnesota containsmost of the state�s mesic prairies.Elsewhere only small remnants remain,many along railroad rights-of-way (Wendt

1984). Kentucky bluegrass is present atmost sites indicating post-Europeansettlement disturbance.

Dry prairie occurs on undulating torough topography. Soils range fromalmost pure sand with little profiledevelopment to mollisols (prairie soils),but with a much thinner organic-richsurface horizon than soils of the mesicprairie. Soils are well drained toexcessively drained. Dry prairies aremaintained by fires but requires lessfrequent fires than mesic and wet prairiesbecause droughty conditions slow thegrowth of woody species. Dry prairiesvary considerably in species composition.Midheight and short grasses and sedges(porcupine grass, little bluestem, side-oatsgrama, and sun-loving sedge) usuallydominate, but forb composition isvariable (blazing star, prairie golden-aster,goldenrod, narrow-leaved puccoon, prairiesmoke, prairie larkspur).

The Barrens subtype of Dry prairieoccurs on dry to somewhat moist standson outwash plains, old dune blankets,and alluvial deposits along rivers andstreams. These prairies occur in thenorthwest, central, and southeasternportions of the prairie zone, often asinclusions with Oak Savanna or OakWoodland. Community compositionand structure are determined by the lownutrient level, low levels of organic matter,and poor water-retaining capacity of sand.Distinctive forbs that occur in thissubtype include prairie sagewort, large-flowered beard-tongue, hairy puccoon,and silky prairie-clover.

The Sand-gravel subtype of Dry prairieoccurs on gently to steeply sloping sitesthroughout the prairie zone including theformer shorelines of Glacial Lake Agassiz,with scattered occurrences in thedeciduous forest-woodland zone.Prominent species include needle grass,

prairie dropseed, blue grama, prairiesagewort, small white beard-tongue,plains paintbrush, and milk-vetch.

Upland brush-prairies generally occur onsomewhat poorly drained to well-drained,sandy clay loam to loamy fine sand soil,with mollisols predominating. Thedominant vegetation is a mixture ofprairie grasses (big bluestem and prairiedropseed on all sites; little bluestem,junegrass, and porcupine grass on driersites; prairie cordgrass and mat muhly onmoister sites) and shrubs. Shrub speciesinclude slender willow, pussy willow, bogbirch on wet-mesic sites; hazel, sakatoonand chokecherry on dry-mesic and mesicsites; and prairie willow and leadplant onbetter drained, sandy sites. Quakingaspen suckers and stunted bur oak treesmay be common on dry sites. Forbspecies are those common to mesicprairie.

Savannas are transitional communitiesbetween prairie and the forest. Insavannas, fire-adapted trees coexist withprairie plants in an open, park-likelandscape. Bur oak, protected by thickbarks, survives fire and desiccation. Jackpine, in the north-central portion of thestate, is adapted to poor soils and requiresfire to open its cones, In the northwestportion of the state, quaking aspen formsclonal clumps interspersed with wetprairie and sedge meadow. BeforeEuropean settlement, the savannaecosystem covered 5 million acres of theMinnesota landscape (Wendt 1984).Today, less than one-tenth of 1 percent ofoak savanna remains (MDNR 1977b).

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productivity of temperate grasslandworldwide (8,000 lbs/ac/yr;Whittaker 1975) compares favorablyto that in temperate deciduous forest(10,800 lbs/ac/yr) and tropical dryforest (14,400 lbs/ac/yr; Whittaker1975).

Indicators of productivity includemeasures of plant production andthe abundance of grassland-dependent animal species (e.g.,greater prairie chicken and sharp-tailed grouse). Fluctuations in thenumber of animals may also indicatechanges in the amount of habitat dueto fire management and increasedarea of grassland. On grazed prairies,long-term trends in forageavailability and livestockproduction are also measures ofprairie health.

Biological diversityAlthough a few species of tall andmidheight grasses dominate, thenorthern tallgrass prairie contains alarge number of nongrass plantspecies (Turner and Knapp 1996)and is one of the most diversehabitats in the Midwest. Its animalcommunity is also very diverse. Inmany cases prairie species haveadapted well to landscape changesand are abundant in pastures andwoodlots near prairie remnants.Populations of other species withmore restrictive habitat needs,however, have declined (Tester1995). For example, monarchbutterflies adapt well to agriculturallandscapes, while Dakota skippersand regal and fritillary butterflies donot, and are found only on prairieremnants.

Indicators of biological diversity

should measure species, habitat, andlandscape diversity. Plant communityindicators include the relativeabundance of exotics and nativespecies, the abundance oflegumes, and the relativeabundance of grazing-tolerantand grazing-intolerant plants. Theabundance of prairie chickensand sharp-tailed grouse and otherspecies that require open habitatscharacteristic of prairies are alsouseful indicators. The abundance ofadult butterflies and moths(Dakota and other skippers, regal,fritillary) that are dependent onprairie help track plant communitycomposition and habitat diversity.Landscape diversity indicatorsinclude indices of landscapefragmentation and connectivityand the acreage and distributionof prairie.

Nutrient cyclingIn prairies, the primary storage areasfor carbon, nitrogen, phosphorus,and other nutrients are soils, livingplant material, and plant detritus.Nutrient cycling is relatively fast forsome nutrients, compared to that inforests, as prairies do not store vastreserves of nutrients in above-ground dead material (Tester 1995).Once nutrients become fixed inorganic form by plants andmicrobes, they tend to be retained,and little is exported out of thesystem. Slow decay processes(including decomposer insects andmicrobes, and leaching) releasenutrients from aboveground andbelowground plant material. Somenutrients volatilized by fire arecarried away by wind, while othersare deposited in mineral rich ash.

Low nitrogen and phosphorusavailability often limits plant growth.Big and little bluestem, however,have low nitrogen requirements anda competitive advantage over plantsthat need more nitrogen (Tester1995). Air-deposited nitrogencompounds (produced when fossilfuels are burned or in windborneparticles of agricultural fertilizer) maychange species composition in favorof nitrogen-loving plants (Wedin andTilman 1992). Many prairie plantsobtain nutrients through associationswith bacteria or fungi. The roots ofmany grasses and forbs formmutualistic associations withmycorrhizal fungi that greatly

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increase the plant�s uptake ofphosphorus, other scarce minerals,and water (Chadwick 1995).Nitrogen-fixing bacteria associatedwith prairie legumes enrich the soilwith nitrogen (Magers 1992).Grasslands store twice as muchcarbon per acre as do forestsbecause of the rapid turnover ofplant material in prairies.Approximately two-thirds of theplant tissue in prairies is locatedbelowground in roots and rhizomes.In the course of three to four years,the roots of prairie grasses nearly alldie and are replaced by new roots(Weaver 1954). Maintaining thisdynamic root system removescarbon dioxide from the atmosphereand stores it as dead organic matterin the soil. Thus, prairie soils maycontribute significantly to slowingclimate change (Chadwick 1995).

Comparisons of soils from prairiesand agricultural areas providevaluable information on nutrientcycling. Soil aggregate size,nutrient-holding capacity,organic matter content, and levelof soil disturbance, including soilcompaction and erosion, measureprairie soil quality and prairie health.

Natural disturbanceregimesNatural disturbances (i.e., fire,drought, grazing) help maintainprairie ecosystems. Native prairieperennials have strong, deep rootsystems and energy reserves anddormant buds that lie below the soilsurface, which allow them to surviveand recover following fires andperiodic droughts. Plant and animaldiversity is highest in tallgrass prairies

where fire, grazing, and burrowinganimals interact.

FirePresettlement prairie fires, started bylightning or set by Native Americans,probably burned every 3 to 10 years(MDNR 1990). Frequent fires (anddroughts) restrict woody plants torefuges near streams and ponds. Inthe absence of fire, dead plantmaterial builds up, soils retainmoisture, and the prairie is moresusceptible to invasion by trees andshrubs (Curtis 1959). Fire alsodiscourages exotic species by creatingconditions more favorable to thesun-loving native species with whichthey must compete. Litter buildupincreases shade, reduces soiltemperature, and slowsphotosynthesis, resulting in a moresignificant reduction in growth ofnative species than of more shade-tolerant exotics (Parenti 1978;Weaver and Rowland 1952; Olds1969; Rice and Parenti 1978; Knappand Seastedt 1986).

Prairie burning often results in amosaic of burned and unburnedpatches. Wet areas, brushy areas, andstreams retard fires, and grazing mayreduce amounts of grass (fuel)enough to prevent the spread of fire.The resulting patchy landscapeprovides a diversity of habitat andnutrient resources that supports highplant and animal species diversity.

Annual late-spring burning increasesthe growth of warm-season grasses(Abrams et al. 1986; Gibson andHulbert 1987; Kucera and Koelling1964; Sims 1988) and slows thegrowth of forbs (Towne andOwensby 1984). Midsummer and

late-fall fires favor spring bloomingforbs. Forbs that bloom inmidsummer are not harmed by fireany time of year (Lovell et al. 1982).

Fire also affects the distribution ofsmall mammals (Collins and Wallace1990), birds (Tester and Marshall1961), and insects. Some rodentsbenefit from the removal of thetangled mat of stems. Deer micecolonize burned prairie fromsurrounding unburned areas. Westernharvest mice, meadow voles, andsouthern bog lemmings, however,are less common on burned prairie.Savannah sparrow populations aresmaller in years immediately afterfire, while LeConte�s sparrows aremore numerous after a burn.Extensive fires may reducepopulations of insects and otherarthropods on small, isolated prairieremnants. Insect species that aremore sensitive to fire, whosepopulations are small, or that arepoor dispersers may be unable torecolonize isolated prairies (Reed1997). A prairie landscape containingsites at different successional stagesand sites that are burned with varyingfrequencies tends to support thehighest number of arthropodspecies.

Grazing animalsHistorically, prairies were grazed byelk, pronghorn, and large herds ofbison. Grazing created structuraldiversity in the vegetation andinfluenced the relative abundance ofplant species (MDNR 1990). Forexample, selective grazing of warm-season grasses allowed other plantsto increase and typically resulted inhigher overall plant diversity (Collins1987; Collins and Barber 1985).

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Bison wallows, patches of firm-packed earth where bison rolled andstamped, held water and remainedmoist into the dry summer season(Grinnell 1970). These wallows wererefuges where moisture-loving plantsand annual species could survive fireand drought (Collins and Uno 1983).

DroughtMost tallgrass prairie plants are welladapted to drought (Sims 1988;Vankat 1979). Some wait outdrought as seeds or belowgroundstorage organs and increase innumber in wet years (Shelford 1963;Weaver 1954). In many species, rootsstore carbohydrates and growrapidly after a drought. In addition,close-set hairs (pubescence), warm-season photosynthesis, and leaf shape(thin and divided leaves, common inprairie plants, give off heat fasterthan thick, nondivided leaves) areexamples of structural adaptationsthat minimize water loss.

Burrowing animalsBurrowing mammals, such as pocketgophers, badgers, and groundsquirrels, loosen and aerate soils andaffect the distribution and density ofplant species as they feed (Tester1995). Burrowers create smallmounds of bare soil where seedsgerminate more readily than incompetition with established plants.Some annuals are most common onold burrow sites (Estes et al. 1982).Bare areas around burrows and theburrows themselves are refugesfrom fire and summer heat for smallanimals. Mima mounds, hummocksof soft soil rising 1 to 2 feet abovethe surface of northwesternMinnesota prairies, are created by

prairie burrowers and are remixedyear after year by toads diggingwinter burrows (Tester 1995).

Indicators of natural disturbanceregimes in prairie that help measureprairie health include the percentageof prairie area managed usingfire, prairie litter density, therelative abundance of warm- andcool-season grasses, and grazingintensity.

PRESSURES ONPRAIRIESFragmentationRoads, fields, woodlots, anddevelopment have fragmented theprairie ecosystem into small, isolatedremnants (Figure 5). Fragmentationcreates barriers to dispersal ofwildlife and recolonization by plantsand creates opportunities for invasive

exotic species. In addition, manygrassland birds nest only in largetracts of grassland and avoid smallpatches that otherwise seem to begood habitat (Herkert 1994). Oneconsequence of fragmentation is thatbirds and mammals that use edgehabitat (raccoons, fox, white-taileddeer, and cowbirds) have increased,while species requiring largeunbroken grasslands, such as prairiechickens and marbled godwits, havedeclined.

Prairie remnants are more vulnerableto chance events than are large areasof prairie. Small populations ofplants or insects often do notrecover following disturbances aseasily as do larger populations(Gilpin and Soule 1986). The Dakotaskipper, for example, is a prairiebutterfly endemic to northerntallgrass and mixed-grass prairies anda pollinator of prairie plants (Licht

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1995). In large prairies, skippersrecolonize burned areas fromunburned areas. In small fragmentsof prairie, however, fire may reducea population of skippers, leavingthem vulnerable to otherdisturbances that could eliminatethem.

Conversion to other usesConversion of prairie to agriculturalland is the major cause of thecontinuing loss of prairie. Since 1837,when the steel moldboard plowallowed the sod to be turned easily,prairie has been fenced and plowed.Prairie loss was also extensive in the1970s (MDNR 1990). OfMinnesota�s original 18 million acresof prairie, only 150,000 acres remain.Economic pressures and agriculturalpractices that may make it moreprofitable to plow or develop openland than to keep it in nativevegetation continue to threatenprairie remnants.

Overgrazing and exclusion of firedecrease the abundance of nativespecies and promote exotics. Whereherbicides, pesticides, or fertilizersare applied to increase forage yields,and where domestic pasture speciessuch as red clover, brome, andtimothy grass (MDNR 1990) areinterseeded with native species, plantcommunities and the animals theysupport are altered.

Invasive speciesTo obtain fence posts and firewood,settlers planted trees and encouragedthe expansion of forest from riparianareas. Invasive species (such as birds-foot trefoil and crown vetch) andtrees (such as hybrid poplar) displace

native species and reduce the valueof prairie pasture. In addition,introduced trees provide perches forhawks and attract cowbirds andmammalian predators, all of whichthreaten populations of prairie birds.

Fire suppressionWhile managers recognize theimportance of fire in maintaininghealthy prairie, burning of prairierefuges may be constrained by lackof resources, local fire ordinances, orthe danger of fire and smoke to

adjacent residential or livestockoperations. In the absence of fire,invasive woody plants displace nativespecies.

Gravel miningThe beach ridges of Glacial LakeAgassiz in northwestern Minnesotacontain some of the state�s highest-quality prairie remnants (MDNR1997a). About 14,290 acres of prairieof high or medium significance,approximately 10% of all the prairieremaining in the state, are located inthe eighteen eastern townships ofClay County (Figure 6).Approximately 3,960 of these acresoverlie valuable gravel deposits.Citizens of the beach ridges regionare attempting to balance the use andpreservation of these resources (ClayCounty Beach Ridges Forum 1997).

Air pollutionEven remote prairies are subject toairborne pollutants. Nitrogencompounds�fallout from fossil fuelcombustion and agricultural fertilizeruse�are of particular concern.Increasing nitrogen levels encouragethe invasion of nitrogen-lovingplants, such as quack grass (Wedinand Tilman 1996), Kentuckybluegrass, and reed canary grass.

Off-highway vehiclesOn some prairie preserves, improperor excessive use of off-highwayvehicles (OHVs; all-terrain vehiclesand snowmobiles) compacts the soil,leaves large ruts, and destroys nativevegetation. Potential consequences ofthese activities include increased soilerosion, changes in plant speciescomposition, and interference withground-nesting birds.

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Environmental indicators helpdemonstrate the relationshipsbetween human activities and thehealth of prairies. For example, theratio of edge to total prairie areaand the distribution of prairie landacross the landscape measurefragmentation of prairie ecosystems.The percentage of prairie landconverted to other uses, thepercentage of prairie acreage inbest-grazing management,pesticide and herbicideapplication rates, abundance ofexotic species, and the extent ofwoody plant cover help measurethe effect of human activities onprairie health.

PRAIRIE STATUSAND TRENDSLand conversion andfragmentationLess than 1% of Minnesota�s prairieremains, and most occurs in small,isolated patches. The little high-quality prairie that remains occurs onhilly or marginal sites that escapedthe plow. Railroad right-of-waysharbor many prairie remnants. Theseremnant prairies, maintained byperiodic burning to clear vegetation,are valuable as wildlife habitat andsources of seed for prairierestoration (MDNR 1986). Whilethese areas have unique ecologicalvalue, we are missing large areas ofmesic prairie, once the state�shallmark prairie ecosystem.

Minnesota�s remaining prairie isvulnerable to further fragmentationand conversion to other uses as landis subdivided or plowed. Conversionof lands in permanent vegetative

cover (pasture, woodlands) into rowcrop production continues inMinnesota. For example, over 40%of non-Conservation ReserveProgram (CRP) grasslands in theGlacial Lake Agassiz area ofnorthwestern Minnesota have beenconverted in the past 10 years(Natural Resources ConservationService, USDA, 1992 NaturalResource Inventory data). Theimpact of grassland habitatconversion and fragmentation isreflected in trends in grassland birdpopulations (Table 2).

Other indicators suggest positivechange. Between 1985 and 1995,farmers enrolled 1.8 million acres offarmland in the ConservationReserve Program. The CRP reduceserosion, protects soil resources, andprovides habitat for wildlife byestablishing permanent vegetativecover on highly erodible or

environmentally sensitive croplands(Figure 7). Native prairie vegetationhas been established on some CRPlands. In addition, a PrairieStewardship Partnership promotessound and sustainable economicdevelopment, while protecting theproductivity and diversity of naturalecosystems in the tallgrass prairieregion.

Protection andrestorationFederal (National Park Service,National Wildlife Refuge), state(Native Prairie Bank, Scientific andNatural Areas), and privateorganizations (The NatureConservancy preserves) are workingto protect and restore Minnesotaprairie. Approximately 34,800 acresof Minnesota prairie is protectedthrough these types of initiatives(Figure 8). In cities and suburbs,there is growing interest in

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landscaping with native species, andsome large prairie tracts have beenrestored around corporateheadquarters.

Restoration efforts that re-createnatural disturbances, including fireand grazing, are often mostsuccessful. Although prescribedburning is vital to long-termmaintenance of prairie, mowing cansimulate both fire and grazing andcan be used on many more sites.Restored prairie, however, is not asubstitute for native prairie. Manyfunctional elements of natural prairie,including insect species, soil fungi,and nematode worms and thecomplex ecological relationshipsbetween plants, pollinators,herbivores, and predatorscharacteristic of intact prairies are noteasily restored (Chadwick 1995).

EXISTING POLICIESAND PROGRAMSSeveral statewide programs protectMinnesota�s prairie from conversionto other vegetation types or otherland uses. Some permit selectedagricultural uses of the prairie, suchas grazing and hay cutting, whileothers manage prairie solely for itsscientific and habitat value.

Scientific and Natural Areas (SNAs)are managed by the DNR solely forthe protection of Minnesota�s rarestand most endangered naturalfeatures. Prairie SNAs are managedto preserve and enhance their nativeplant and animal communities.

The Native Prairie Tax ExemptionProgram exempts eligible nativeprairie lands from property tax. Tobe eligible for tax abatement, theprairie must be at least 5 acres in size(in most counties), and livestockgrazing is not allowed. In most cases,farmers can hay lands enrolled in theexemption program.

Designed to protect prairie fromconversion to cropland or otheruses, the Reinvest in MinnesotaNative Prairie Bank program allowslandowners to sell easements onprairie acres to the DNR. Easementsmay be permanent or of limitedduration with priority given topermanent easements. Easementsmay allow grazing or hay cuttingunder guidelines agreed to by boththe DNR and the landowner.

The Prairie Wetland HeritageConservation Initiative, funded by agrant from the federal MigratoryBird Conservation Commission,

preserves high-quality prairie insouthern Minnesota. The initiativewill purchase 2,380 acres of prairiesand adjacent lands, obtain easementson 225 acres, and restore wetlandson 500 acres. Acquired lands will bemanaged by the DNR or the U.S.Fish and Wildlife Service as wildlifemanagement areas.

The DNR�s Section of Wildlife andDivisions of Parks and Recreation,Forestry, and Trails and Waterwaysprotect prairie where it occurs onwildlife management lands and instate parks. Prairie is managed for itsvalue to wildlife and its aesthetic andrecreational value. The U.S. Fish andWildlife Service protects and restoresprairie on its wildlife refuges,waterfowl production areas, andother lands. The Fish and WildlifeService recognizes that prairieprovides cover for nestingwaterfowl and other wildlife, andhas a program to re-seed formercropland to native warm-seasongrass cover.

The Nature Conservancy (TNC), aprivate nonprofit organization,acquires and preserves areas ofundisturbed natural habitatsupporting rare and endangeredplants and animals. TNC protectssome of the highest-quality prairietracts left in the state. Its preservesare open for scientific use and havebeen burned in regular rotation since1962. Eleven of TNC�s preserves areleased to the DNR under theScientific and Natural Areasprogram.

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EXAMPLEINDICATORSTable 3 collects the indicators used inthis chapter. The indicators areorganized within the EII framework,which helps illustrate relationshipsamong human activities,environmental condition, the flow of

benefits, and strategies for sustaininga healthy environment. The indicatorsused in this chapter are examples thatillustrate how indicators may helpassess prairie health. The process ofdeveloping a comprehensive set ofindicators that assess prairie healthand inform environmental decisionmaking is ongoing. Developing

indicators will require collaborationwith stakeholders interested in theiruse, testing, refinement, andstandardization of measurementtechniques.

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