DEVELOPING ENVIRONMENTAL INDICATORS FOR MINNESOTA

Forests

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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affect forests include land areasconverted to other uses, timberharvest by species, and introduc-tion of exotic species.

How does it affect us?Changes in forest health may dimin-ish the flow of benefits. Indicators ofhow we are affected include eco-nomic benefits of timber harvestand water quality in forestedwatersheds.

What are we doing aboutit?Societal strategies to maintain or restore

healthy forests include implementa-tion of forest managementguidelines, regeneration strate-gies, and forest resource monitor-ing.

In this chapter we outline importantbenefits from forest ecosystems, thekey ecological characteristics thatdetermine the health of forests, thepressures affecting forests today, thecurrent status and trends relating toforests, and the most significantpolicies and programs that affectMinnesota forests. Throughout thischapter we give examples of indica-tors that provide important informa-tion about Minnesota forests.

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

What is happening to ourforests?Environmental condition can be assessedusing indicators based on ecologicalcharacteristics of forests, includingextent and distribution of foresttypes, tree growth, and snag andwoody debris density.

Why is it happening?Indicators of human activities that

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HIGHLIGHTSBenefits of HealthyForests� Provide cultural heritage and

sense of beauty� Sequester carbon and regulate

changes in global nutrientcycles

� Contribute $7.8 billion inforest production to thestate�s economy

� Improve water quality bystabilizing soils andintercepting nutrients inrunoff

� Provide wildlife habitat� Regulate overland and

subsurface water flows� Provide recreation resources� Enhance the resort industry

Important EcologicalCharacteristics� Different forest types exist

across the state, each with uniqueattributes and services

� Forest types are influenced byclimate, landforms and soils,disturbance regimes, and land-use activities

� Size and number of canopylayers influence ecologicalfunction

� Disturbances affecting ecologicalfunction include fire, windthrow,grazing, pest outbreaks, andlogging

� Human pressures may alter thefrequency and intensity of naturaldisturbances

� Landscape patterns affect forestcomposition and wildlife

Pressures� Forest fragmentation� Diseases and pests (e.g., oak wilt,

spruce budworm, gypsy moth)� Timber harvesting� Atmospheric pollutants (acid

precipitation, ozone, greenhousegases)

� Land conversion (roads,agriculture and urbandevelopment)

� Exotic species (e.g., buckthorn)� Recreational activities

Status and Trends� Less than 0.02% of old-growth

maple-basswood forest remains� Extent of forest land increased

from 16.5 million acres in 1977to 16.7 million acres in 1990

� Aspen forests cover the largestpercentage (35%) of forestedlands in the state

� Reduced structural diversity offorest stands

� Projected wood harvestsvolume for the year 2000 arenearly double those of 1980

Major Policies andPrograms� Support for �no net loss of

forests� (Minnesota SustainableForest Resources Act)

� Comprehensive timberharvesting and forestmanagement guidelines

� White pine regenerationstrategies

� Landscape-based forestresources planning andcoordination

� Research, monitoring, andcontinuing education

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BENEFITS ofFORESTSForests are an integral part of ournatural and cultural heritage.Minnesota forests range from themixed conifer-hardwood forests inthe north, to the broadleaf forests inthe south, to the numerous parks andgreenways in urban areas. All ofthese forested areas provideMinnesotans with a variety ofessential goods and services(Figure 1).

Forest products are an importantpart of Minnesota�s economy andprovide wood for pulp, paper, andlumber. In 1995, the forest productsindustry (the third largestmanufacturing industry in the state)contributed 7.8 billion dollars to theeconomy and provided 57,000 jobs(MDNR 1997). The state�s forestsalso offer recreational benefits,providing hiking, camping, andhunting opportunities, and sites foreducation and scientific pursuits.These activities, in turn, bringsubstantial economic benefits tonearby communities. For example,most of the 1,300 privately ownedresorts are closely associated with thepine and hardwood forests in thecentral region of the state (MFRC1997a).

In addition to economic andrecreational benefits, healthy forestsprovide numerous benefits that areoften difficult to quantify (JaakkoPoyry 1992f). Aesthetic and spiritualforest values are of increasingimportance to society (Bengston andXy 1995), and forests provideessential ecosystem services (Johnson1988; Rolston 1990). A variety ofplants and animals depend on forestsfor habitat, including wildlife speciesof special concern such as the red-shouldered hawk, gray wolf, pinemarten, wood turtle, and bald eagle(Leatherberry et al. 1995). Healthyforests maintain the light,temperature, and moistureconditions that support the animalsand plants living there. Forestsregulate overland and subsurfacewater flows, thus maintaining year-round water flows rather than flood-and-drought regimes. They

contribute to healthy aquaticecosystems by stabilizingstreambanks and filtering sedimentand nutrients from water movingthrough the forest. For example, in1990 more than 200,000 acres ofwindbreaks and natural woodedstrips helped prevent soil erosion andimprove water quality (Leatherberryet al. 1995).

Forests also play a key role in cyclingessential elements such as oxygen andcarbon. We depend on forests andother plant communities forproduction of the oxygen that webreathe. They also trap carbondioxide from the atmosphere andstore it in leaves, trunks, and roots.Temperate forests worldwide maysequester about 0.7 billion tons ofcarbon annually, which wouldotherwise remain in the atmosphereand could contribute to globalclimate change (Dixon et al. 1994).

Minnesotans clearly depend onforests for a variety of importantecosystem goods and services. Suchbenefits are sustained only if wemanage forests to promote theirlong-term health. Unhealthy forestscannot provide a full range ofecosystem benefits. By monitoringand tracking the health of Minnesotaforests, we can better understandhow to manage forests so that theycontinue to provide benefits thatimprove our daily quality of life.

BenefitCategory Example

Aesthetic Beautiful scenery

Ecological Microclimate regulationErosion & floodcontrolMaintenance of habitat& biodiversity

Economic Timber productsNon-timber products(e.g., maple syrup)Recreational tourism

Health Clean airWater purification

Historic Historic and culturalsites

Public use Recreation (e.g., birdwatching, hunting,fishing, camping)

Spiritual Wilderness settingBequest for futuregenerations

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FOREST ECOLOGYGeneral patterns in foresttypesMinnesota has two major foresttypes: mixed conifer-hardwoodforests and eastern broadleaf forests.The location of these forests and thedifferences in dominant species aredetermined by patterns inprecipitation, temperature, underlyingsoils and landforms, and disturbanceregimes (MDNR EcologicalClassification System 1996, Figure 2).

Mixed conifer-hardwood forestsoccupy the north-central andnortheast portion of the state. (Figure2 refers to this area as the LaurentianMixed Forest Province.) Soils havedeveloped slowly in this region andare relatively nutrient poor. Foresttypes include coniferous uplandspecies such as white pine, red pine,jack pine, balsam fir, and whitespruce; hardwoods such as aspen,birch, and mixed oak; and lowlandspecies such as black ash, blackspruce, tamarack, and white cedar.

Eastern broadleaf forests occupy atransition zone between the mixedconifer-hardwood forests in thenorth and the agricultural land andtallgrass prairie in the south. A varietyof deciduous forest types areassociated with this transition zone.Maple-basswood forests are late-successional forests that occur inareas protected from fire. Oakforests occur most commonly in thesouthern and western edges of thetransition zone. And some aspenforests occur in the northern regions,between extensive forested peatlandsand grassland areas (MDNREcological Classification System1996).

Knowledge about the extent anddistribution of Minnesota�s foreststypes is a basic step to understandingour forest resources. In other words,we need to know what kinds offorests occur across the state, howmuch area they cover, and wherethey are located. Indicators of theextent and distribution of foresttypes provide this baselineinformation about general patterns inMinnesota�s forest ecosystems.

DiversityIn broad terms, biological diversity isthe variety of life. It describes thenumber of ecosystem parts, howthey are arranged, and the variousprocesses that occur among them.Forest diversity has several levels of

organization. Landscape diversityis the variation in forest types thatoccur within a large area (such aswhite pine, jack pine, and aspenforests). Habitat diversity is thevariation in habitat characteristicsoccurring within a forest (such as thepresence of dead trees that providenesting cavities for wildlife).Community diversity is the numberof different groups of plants andanimals and how they interact (suchas the associations among variousplants, the animals that consumethem, and the bacteria and fungi thatdecompose them). Speciesdiversity is the variation in speciesoccurring within a forest (such as thevariety of plants and wildlife livingwithin the fores). And geneticdiversity is the variation in the gene

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pool of forest species.Forest diversity is influenced by anumber of complex factors,including climatic condition; forestpatch size, shape and configuration;continuity of forest stands; frequencyand intensity of disturbance (fire,windthrow, pests); structuralvariability (tree age diversity, canopyopenings, vertical layers); and humanactivities that alter these factors. Forexample, the diversity of forest typesin a landscape depends in part on thecontinuity of forest stands and thepattern of fire regimes in that region.

Habitat and community diversitywithin a forest depend in part onchanges in the structure of treecanopies. For example, the presenceor absence of forest canopyopenings influences the microclimateon the forest floor; this in turnaffects plant species composition.Forests with dense canopy layerssupport understory plant species thattolerate low light. When disturbances(human and natural) occur that openup the canopy layer, more lightreaches the forest floor, and otherplant species that have higher lightrequirements begin to thrive. Thus,forested areas with occasional gapscreated by fire, high wind, and sometypes of logging allow a diversity ofplant communities to thrive at astand level. Extensive gaps occurringthroughout the forest, however, maybe detrimental to biodiversity at aregional level (Jaakko Poyry 1992b).

Animal species diversity in forestsdepends in part on the physicalstructure of forest vegetation and thecomposition of plant species. Forestswith several vertical layers (such asherbs, shrubs, trees of different ages

and sizes, and downed logs) andspatial variability (such as canopygaps and openings) provide a varietyof habitat for wildlife species. Forexample, some song birds nest invegetation near the ground, whileothers nest high in the canopy.Various mammals and birds live inthe hollowed-out cavities of deadtrees. And some mammals requireforest openings for browse. Forestrypractices that allow dead trees anddowned logs to remain in place andthat manage for stands withdifferent-aged trees improve thequality and diversity of the availablehabitat (Jaakko Poyry 1992d).

When measuring and discussingforest diversity, it is essential to definethe level of organization and spatial scale being addressed(Zumeta 1991). Indicators ofdiversity should span multiple levels.For example, the extent anddistribution of forest types and theproportion of forest in each ageclass provide a broad measure offorest diversity at a landscape level.Snag and woody debris densityand foliage height diversityprovide some measures of habitatdiversity. The distribution andabundance of key plant species(e.g., long-lived late-successionalherbs) are indicators of communitydiversity. And the ratio of�vulnerable� species to total�forest-dependent species� is oneway to assess changes in speciesdiversity.

Biological productivityForest productivity includes thegrowth of plants via photosynthesisand the growth and reproduction ofanimals. Minnesota�s deciduous

forests are generally more productivethan its northern coniferous forests(Tester 1995) due to a combinationof warmer temperatures, higherprecipitation, and more fertile soils.Tree growth in northern mixedconifer-hardwood forests is oftenlimited by low soil fertility and theshort growing season. Because soilproductivity is the foundation forplant productivity in forests,management practices that promotehealthy soils are essential formaintaining the productivity andsustainability of these systems(MFRC 1997c).

Disturbances that influence nutrientlevels, available water, light on theforest floor, or temperature affectlevels of productivity. Thesedisturbances can be natural, such asfire or pests, or may be human-related events, such as clearing forestlands. Maintaining biologicalproductivity in forests is importantnot only for numerous resourceproducts (e.g., timber, pulpwood)but also for maintaining ecosystemfunctions (e.g., hydrologic cycles).

Indicators help assess the ability of aforest to maintain its productivecapacity over time. Tree growth (e.g.,number, volume, and diameter ofgrowing stock) is one indicator offorest plant productivity. Whencoupled with indicators of harvestingtrends, this indicator givesinformation about the ability of aforest to maintain the production oftimber resources. Populationtrends of key animal speciesrepresenting various trophic levelsare an indicator of animal

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productivity. Indicators of animalproductivity help assess trends acrossmultiple trophic levels, which givesbroader insight into overall foresthealth.

Nutrient cyclingNutrient cycling is the movement ofessential elements, such as nitrogenand carbon, through living andnonliving materials. Elements movefrom the atmosphere, through livingplants, animals, and decomposers,and back to soil, water, and air.

Cycling within a forest is essential forcontinued growth and productivity.Plant growth and the subsequentbreakdown of forest litter (deadleaves and other plant material)ensure that soils contain essentialnutrients to support new generationsof forest growth. Forest litterdecomposition is caused by theactivity of numerous organismsincluding birds, mammals, insects,worms, soil bacteria, and fungi, aswell as physical processes such aswind and water erosion. Throughthis continual growth andbreakdown of organic matter,healthy forests create soil, which isimportant for maintaining biologicalproductivity within a forest(Leatherberry et al. 1995).

Forests play a crucial role in thecycling of elements among systems.For example, forests intercept anduse nitrogen that is deposited fromprecipitation and erosion. Whennitrogen is trapped by plant material,it remains in the forest system ratherthan being transported downslope towater bodies. This retention slowsthe introduction of nutrients intorivers, streams, lakes, and wetlands,

and helps to maintain the quality ofthose systems. Activities thattemporarily remove plant cover ordisturb soils (e.g., timber harvesting)may increase erosion and nutrientloss to adjacent ecosystems. BestManagement Practices (BMPs),which are widely used in Minnesota�sforests today, reduce these impactswhile maintaining the benefits oftimber harvesting (Jaakko Poyry1992g). However, activities thatpermanently remove forest cover(e.g., road construction, residentialdevelopment) can greatly alter thecycling of nutrients within andthrough a landscape.

Forests also have a significant impacton nutrient cycling at a global scale.Trees use carbon dioxide from theatmosphere for new growth; thus,forests act as a storage area, or�sink,� for carbon. This storage ofcarbon may offset some of thecarbon released by increasing fuelemissions and thus diminish theeffects of global climate change(Myers 1997).

Indicators of nutrient cycling areoften difficult to measure but doprovide important informationabout the health of a forest system.For example, the percentage ofland with significant soil erosionprovides information about hownutrients may be flowing out offorested systems into nearby waterbodies. Other physical changes insoils (such as thickness,compaction, bulk density) giveinsights into the ability of a forest tomaintain productivity. More specificmeasurements, such as the area andpercentage of forest wherenutrient depletion exceeds

replenishment (of potassium,calcium, magnesium), also giveforest managers information aboutthe ability of a forest to maintainproductivity over time.

HydrologyForests play a key role in regulatingoverland and subsurface water flowswithin a watershed. They interceptrainfall and slow surface runoff, thusdecreasing excessive and costlyerosion. Forests slowly releasecaptured water back to theatmosphere via evapotranspiration,and to streams and rivers within awatershed, thereby serving as acritical component in the hydrologiccycle and regulating the quantity andquality of water supply. Forestedwatersheds are more likely toprovide a constant flow of cleanwater. In contrast, large deforestedwatersheds are more likely toexperience flood-and-droughtregimes, and water quality will likelybe diminished due to erosion (Myers1997).

At a more site-specific scale, theability of forested areas to regulatewater flow may be altered due todisturbances along vegetatedwaterways. The flow of water maychange following the loss of riparianvegetation caused by natural events(e.g., fire) or human activities (e.g.,harvesting).

Indicators that track changes instream flow provide usefulinformation about how well forestsare maintaining hydrologic cycleswithin a watershed. It is especiallyimportant to compare theseindicators to historic ranges ofvariability in stream flow. In

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managed areas the area andpercentage of stream miles withvegetated buffer strips also givesinsight into how well aquatic systemsmay be protected from the excessflow of nutrients from uplandterrestrial systems.

Natural disturbanceregimesDisturbance regimes are recurringevents that help maintain healthyecosystems. While disturbances maysometimes seem temporarilycatastrophic, over the long run theymaintain natural cycles that areessential for healthy ecosystems.Important natural disturbances inforest ecosystems include fire,windthrow, insects and diseases, andanimal grazing.

Differences in the frequency,intensity, and type of disturbancehave shaped the composition ofMinnesota�s forests (Mladenoff andPastor 1993). Before Europeansettlement, areas in the transitionalzone that were exposed to frequentfires from adjacent prairie weredominated by oak savanna, whileforests in wetter areas near rivers andlakes were often dominated bylowland hardwoods. Areasprotected from fire werecharacterized by old-growth �maple-basswood� forest, which wascomprised mostly of elm and thenbasswood and maple (Grimm1984). In northern forests, wildfirewas a major factor determiningspecies composition. Intensewildfires kill many species, butMinnesota�s three pine species-red,white, and jack pine-are adapted tofire. Before European settlers arrivedin the state, wildfires burned a pine

forest every 13 to 38 years, withmore intense fires every 150 to 200years (Tester et al. 1997). Theserelatively frequent fires contributedto the dominance of fire-adaptedpine trees.

Windstorms create gaps in the forestcanopy in both conifer forests anddeciduous forests. The gaps createspaces where more sunlight reachesthe forest floor, allowing species thatneed more light to becomeestablished. In northern forests,windstorms often remove the olderand taller red and white pines,leaving spruce, fir, maple trees, andyoung pines standing (Tester et al.1997). Some kinds of timberharvesting can also create gaps in theforest and thus influence the amountof light reaching the forest floor.

Animal activities have significantimpacts on the functioning andcomposition of the forest ecosystem.Beaver affect forest stands byremoving trees and altering waterflows. Herbivory by insects, such asthe spruce budworm, and mammals,such as deer, affects the growth andreproduction of certain forestspecies. High deer populationsstrongly influence plant speciescomposition in Minnesota�s forests.

Humans can alter the frequency andintensity of some natural disturbancesin forests by preventing forest fires,harvesting timber, and influencingpopulation numbers of browserssuch as deer. Some disturbances,including the introduction of exoticspecies and broad changes inlandscape patterns, are very differentfrom the disturbances that historicallyshaped forests because they typically

involve faster changes, are of greaterintensity, and affect larger areas thando natural disturbances. Extremechanges in natural disturbanceregimes can have detrimental effectson the health of Minnesota�s forests.Humans also help restore naturalcycles that have been altered overtime. For example, forest managersmay implement prescribed burns oruse harvesting techniques that striveto mimic disturbance cycles. Suchefforts to work with nature�s cycleshelp maintain healthy forests.Mimicking natural spatial patternsand disturbances is one of the mosteffective ways to conserve forestdiversity (Jaakko Poyry 1992b).

Knowledge about the historic rangeof variation is important to interpretindicators of disturbance cycles. Forexample, acres of forest burnedannually is an important indicatorthat gauges the extent and frequencyof forest fires. This indicator isespecially important in coniferousforests, where some forest typesrequire fires for regeneration andrenewal (e.g., jack pine). Knowingthe historic range of variation for firein jack pine forests helps interpretthis indicator so that managers candevelop appropriate firemanagement plans. The frequencyof pest and disease outbreaks isanother indicator of disturbancecycles that provides informationabout how forest health may bechanging over time.

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PRESSURES ONFORESTSLand conversionThe largest changes in Minnesota�sforests over the past 150 years haveresulted from clearing land forsettlement, agriculture, and harvestingtimber (Ahlgren and Ahlgren 1983).During the late 1800s and early1900s, much of the state�s forestswere cleared for settlement andfarming. Timber harvesting ofvaluable trees also contributed to aloss of forest land. Following whitepine harvests in the late 1800s andearly 1900s, much of the land wasnot replanted or managed; rather, itwas left for settlement and farming(White Pine Regeneration StrategiesWork Group 1996). While dramaticchanges following Europeansettlement reduced Minnesota�sforest extent by approximately 20million acres (Leatherberry et al.1995), regrowth and changes inmanagement practices have resulted

in an increase statewide from 12million acres in 1900 to 17 millionacres today (MDNR 1997).

Today�s loss of forested land isgreatly affected by developmentpatterns. Currently urbandevelopment, includingtransportation corridors, accountsfor most of the loss andfragmentation of forest in theprairie-forest transition region (TNC1995), particularly around the TwinCities metropolitan area (MDNR1995; Figure 3). In the northern lakesregion, lakeshore development is acause of loss and fragmentation offorests.

Indicators that track land use andconversion provide some of themost basic assessments of ecosystemstatus and trends. For example, thepercentage of forest land areaconverted to other uses isparticularly relevant considering thegrowing desire for �no net loss� of

forested land (1995 MinnesotaSustainable Forest Resources Act).When coupled with indicators ofecosystem functions, such ashydrology, these indicators giveinsight into how land conversionmay be affecting flood and droughtregimes in a watershed.

FragmentationForest fragmentation is simplydefined as the disruption in thecontinuity of a forest habitat (Lordand Norton 1990). Within this broaddefinition, various types offragmentation can be distinguished(Harris and Silva-Lopez 1992; Figure4). Relatively permanentfragmentation, such as that createdby development and land conversion(Figure 4a, b), differs from moretemporary types, caused by timberharvest and land management(Figure 4c, d; Jaakko Poyry 1992b).Fragmentation also occurs indifferent spatial forms. �Isolating�fragmentation reduces the existingforest to small patches surroundedby another land use (e.g., small forestpatches surrounded by agriculture[Figure 4a]) or another age class (e.g.,old-growth patches surrounded byyounger forests [Figure 4c]). �Gap�fragmentation is less extensive andcreates gaps within continuous forestcover (e.g., openings for lake homes[Fig. 4b], or patches of clear-cut in acontinuous forest [Figure 4d]).

Forest fragmentation can significantlyalter ecological functions in someforested landscapes (Jaakko Poyry1992b). Relatively permanent,isolating fragmentation caused byagriculture and extensivedevelopment (Figure 4a) can

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profoundly affect the landscape byaltering microclimate, water flows,nutrient cycling, and forest patchregeneration. It also has detrimentaleffects on animal and plant speciesthat require large patches of forestedland for survival and reproduction.Small patches of forest have moreedge habitat relative to interior foresthabitat than do large patches offorest. This situation createsconditions that hinder some nativeplants and animals in favor ofdisturbance-tolerant species. Forexample, smaller forest fragmentsfavor common species, like thebrown-headed cowbird and the bluejay, at the expense of birds preferringinterior forest conditions, like theovenbird (Table 1).

Isolating fragmentation caused by

widespread timber harvest can alsohave an impact on forestcomposition and function. Forexample, old-growth pine standsonce covered a larger portion ofMinnesota�s landscape, but manyremaining pine stands are nowseparated, or fragmented, by otherforest types. This condition mayaffect mature-forest dependentspecies that require certain types ofhabitat, such as the pine warbler,which requires a minimum patch sizeof 25 acres of mature pine (Green1995).

The effects of gap fragmentation,however, are not well understood.Forest gaps caused by certainsilvicultural techniques can be similarto natural disturbances such aswindthrows, and are beneficial to

wildlife species that prefer youngforest patches. Many forest harvestshave been designated for this veryreason. At a local scale these gapsmay be desireable because theyenhance or create habitat forimportant gamebird and otheranimal species. When considered at alarger scale, however, theimplications may differ (JaakkoPoyry 1992b). For example, gapscaused by harvesting may be of adifferent size or frequency than theopenings historically created bywindthrow or fire. Like other formsof fragmentation, clear-cut gaps willincrease �edge� habitat and reducethe overall extent of mature forest,which may have a negative effect onsome area-sensitive bird species(Manolis et al. in review). Ongoingresearch should help increaseunderstanding of how gapfragmentation affects the diversityand functions of forested systems.

Indicators can also play an importantrole in better understanding forestfragmentation. Indicators such as theratio of forest interior to totalforest area provide measures offragmentation. Also, mapping thedistribution of forested areas inthe landscape is particularly usefulfor tracking trends in forestfragmentation. When coupled withindicators that track key ecosystemproperties (such as songbirdpopulation trends), these indicatorsgive insight into how forestfragmentation may be affectingforest functions over time.

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Timber harvestingTree removal can affect foreststructure and function at local sites oracross large regions depending onthe intensity and frequency ofharvesting methods. For example,logging may affect forest soilresources by removing nutrientsfrom the site and compacting anderoding soils; the magnitude of thisimpact varies with soil type, treespecies, and time between harvest(MEQB et al. 1993).

In general, activities such as roadconstruction, skidding practices, andyarding (log storage) have thegreatest potential to cause soilcompaction and erosion, which inturn may diminish long-term forest

productivity (Government ofCanada 1991). In addition, removalof vegetation along water bodiesincreases the potential for erosionand flooding.

Thus, timber harvesting in riparianareas can have impacts on the waterquality of adjacent streams and rivers,many of which support importantrecreational fish species, such as troutand bass. Timber harvesting also hasthe potential to affect forest habitatand wildlife. Changes in thecomposition and structure of aforest influence the diversity anddistribution of wildlife species. Theymay also influence the degree andintensity to which pest or diseaseoutbreaks occur (MEQB et al. 1993).

At a landscape scale, harvesting mayperpetuate forests that arecompositionally and structurallysimplified because stands of short-lived species, usually in pure cultures,are readily used by the pulpwoodindustry (Kotar 1997).

Forest managers use a variety ofpractices to mitigate adverse effectsof timber harvesting (Jaakko Poyry1992a). Compliance with BestManagement Practices maintains thequality of nearby water bodies anddependent fish communities (JaakkoPoyry 1992g). Nutrient loss, soilcompaction, and soil erosion can belessened by keeping as much organicmaterial as possible on site, timingthe harvest during winter or dryperiods, and considering soil typeand topography (MEQB et al. 1993).

Managers can mimic naturaldisturbance regimes by matching theappropriate silvicultural system to a

given forest area (e.g., creating gapsfrom harvesting that are similar tothose historically caused bywindthrow or fires). A variety ofsilvicultural and managementpractices also help restore foresttypes that are currently difficult toregenerate naturally, such as red oakand white pine (Kotar 1997; JaakkoPoyry 1992e). These approaches helpensure the maintenance of diverseforest conditions and functions.

In recent years timber certificationprograms have developed to identifyand promote the use of timber fromwell-managed sources. For example,in 1997 more than 555,000 acres offorest land in Aitkin County werecertified as being sustainablymanaged by the SmartwoodProgram (MOEA 1998).

Indicators that track harvestingtrends and application ofsilvicultural practices providebaseline information on possibleimpacts to forested areas. Theactual and projected timberharvest by species (million cords/year) gives general information aboutdemands on forest resources.Indicators like the percentage offorest land area lost to forestharvest infrastructure (e.g., roadsand trails for large equipment) alsotrack pressures on forested areas.Coupling indicators that measureharvesting trends and ecologicalfunctions (e.g., soil productivity)provides insight into how harvestingmay affect long-term forest health.Efforts to understand suchrelationships were part of the task ofMinnesota�s Generic EnvironmentalImpact Statement on TimberHarvesting and Forest Management

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(GEIS) (Jaakko Poyry 1992a).

Recreational activitiesThe increase in the number ofvacation and second homes in andaround Minnesota�s forests hasresulted in forest land conversionand fragmentation and increasedrecreational demands in forestedareas. New homes, roads, andsupporting commercial facilitiesfragment the forest and increase thepotential for non-native ordisturbance-tolerant species to moveinto the forest. In addition,management decisions for forestsbecome more socially andecologically complex. For example,fire is important for maintaining thelong-term health of mixed conifer-hardwood forests. However,increasing numbers of people livingor recreating in these forests make itmore difficult to allow natural firesto burn, or to implement prescribedburn regimes.

In recent years, use of off-highwayvehicles (OHVs) in Minnesota�sforests has increased. As OHVs areused to access larger and moreremote areas, there are increasedconcerns that this activity mayaugment soil compaction anderosion, harm understory shrubs andherbs, and disturb animalpopulations that depend on large,contiguous forests. Plans that willmanage use of OHVs to sustainforest health while allowing desiredhuman use are currently underconsideration by stakeholder forums.Finally, increased use of wildernessarea forests for motorized andnonmotorized activities has resultedin conflicting opinions about land useand management needs, a situation

that further illustrates the complextrade-offs that forest managers mustaddress.

A variety of tools are necessary tohelp manage the complexitiesinvolved with forest lands andrecreation. The RecreationOpportunity Spectrum (ROS) is onetool that sets standards for forestconditions and classifies forest landsaccording to the kinds of recreationalexperiences that people want toenjoy. For example, urban forestsprovide parks and resort areas, semi-primitive motorized forest landsprovide a predominantly natural-appearing environment while stillallowing for motorized recreation,and primitive areas allow for agreater wilderness experience (USFS1990). Maintaining a full spectrum offorest lands ensures that Minnesotanshave access to a variety ofrecreational opportunities (MSDI1994).

Indicators that track trends inrecreational demands andactivities on forested areas (suchas OHV use and other trail use)provide information about whereand how these activities may affectforest ecosystems. It is important tolink these indicators to trends inecological properties (such as soilcompaction, plant communitycomposition, and distribution ofwildlife species) to betterunderstand to what degree theserecreational activities may affect thehealth of forested systems. Thisinformation is useful in developingrecreational management plans forMinnesota�s forests. Recreationalbenefits are appreciated byMinnesota�s citizens; managing for

healthy forests helps ensure that thesebenefits will be maintained for thelong term.

Biological pressuresBiological pressures on forestecosystems include exotic species,pests, diseases, and grazers. Exoticspecies compete with native forestspecies and may eliminate importantfood and nesting resources. Forexample, the Tatarian honeysuckleand European buckthorn wereintroduced as ornamental shrubs andhedges but have spreaduncontrollably and now dominatethe understory in many forests at theexpense of native species that areimportant animal food and habitat(TNC 1995).

Pests and diseases occur in all forests;they are natural change agents andplay an important part in forest foodwebs and forest succession(Mladenoff and Pastor 1993). Athigh levels or unnatural frequencies,however, they can disrupt forestfunctions. Pests in Minnesota�sforests include the forest tentcaterpillar, spruce budworm, whitepine weevil, two-lined chestnutborer, and the gypsy moth. Diseasesinclude trunk rot, white pine blisterrust, Dutch elm disease, and oak wilt(Jaakko Poyry 1992c; MDNR1995a).

In many cases the worst pests anddiseases are those that are introducedfrom Europe and Asia. Forexample, Dutch elm disease, whitepine blister rust, and gypsy moths areintroductions that in some cases havesignificantly altered forest functionsin this region (Mielke 1997). Pestsand diseases decrease forest

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productivity by reducing growthrates and increasing incidences ofmortality and decay. Monoculturesor trees that are under stress due toother reasons, such as pollution ordrought, are most susceptible toattack (Mielke 1997). A variety ofmanagement practices are used toreduce the impacts of thesebiological pressures on Minnesota�sforests (Jaakko Poyry 1992c).

Browsers, such as deer, also placepressure on some forests by limitingregeneration of certain kinds of trees,such as white pine. Minnesota�swhite-tailed deer populations onceoccurred mostly in woodedtransitional areas, and occurred inlarger numbers in northern forestsonly after timber harvesting andclearings created ideal browse habitat(White Pine Regeneration StrategiesWork Group 1996). While deer arean important game species and anintegral part of Minnesota�s forests,they now occur at a much greaterdensity than they did historically, andthus exert a new kind of pressure onour forests.

Human activities indirectly alter thefrequency and intensity of biologicalpressures. In some situations,biological pressures that historicallyplayed a role in disturbance cycleshave now become more extremeand threaten the long-term health offorest ecosystems. For example, pestpopulations play a natural role inforested systems (Mladenoff andPastor 1993). At low levels, pests,such as spruce budworm, may notcause problems because theirpopulations are limited by naturalfactors, such as forest songbirds thatconsume them. Thus, human

activities that reduce forest songbirdpopulations, such as fragmentationand deforestation in tropicalbreeding grounds, can indirectlyincrease a pest�s population.Understanding the complexrelationships between humanactivities and biological pressures is achallenging but important task.

Monitoring trends in exoticspecies, pests, diseases, andpopulation trends of importantbrowsers (e.g., deer) gives forestmanagers early warning aboutpotential changes in forestproductivity and overall forest health.Linking population trends of pests(e.g., forest tent caterpillar) to treemortality (e.g., in aspen) mayillustrate how biological pressurescan affect long-term productivity. Iflong-term data are available, theseindicators show whether biologicalpressures are occurring morefrequently and intensely than theirhistoric cycles. This information mayprovide early warnings of negativechanges in Minnesota�s forests and isessential for identifying preventivestrategies to maintain healthy forests.

Atmospheric pollutantsSeveral kinds of atmosphericpollutants can have wide-rangingimpacts on forest systems. Acidprecipitation is not currently a majorproblem in Minnesota but hascaused extensive degradation ofeastern forests. Ozone, a primarycomponent of smog, causes directphysical damage to trees. Globalincreases in fixed nitrogen fromfossil fuels and agricultural fertilizersresult in chronic nitrogen depositionand may have long-term implicationsfor forest health (Foster et al. 1997).

Increases in greenhouse gases such ascarbon dioxide will likely causewarmer temperatures, influenceprecipitation patterns, and mayreduce soil moisture (MEQB et al.1993). These changes in globalclimate patterns are likely to altergrowing conditions (Stearns 1987)and the range and distribution offorest species (Government ofCanada 1991). For example, somescientists who have researched theimplications of climate change forMinnesota believe that many forestedareas will not be able to sustain rapidclimate changes; rather, over timevegetation patterns will shift in anortheastward direction, and currentforests may convert to brush andgrasslands (reported by Dawson andMarcotty 1997).

Monitoring trends in airbornepollutants and greenhouse gasesprovides necessary baselineinformation about changes in theatmosphere. Forest indicators canillustrate how these pressures may beaffecting the long-term health ofterrestrial systems. For example,trends in sensitive species (e.g.,mosses and lichens) indicate thedegree to which airborne pollutantsmay be affecting forested areas andmay serve as an early warning toforest managers.

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FOREST STATUSAND TRENDSMinnesota�s landscapebefore EuropeansettlementBefore European settlement, forestscovered about 60% of the land areain Minnesota (Leatherberry et al.1995). Forests were most extensivein the northern and south-centralregions of the state; the southwesternregion of the state was dominated byprairies. The mixed conifer-hardwoods in the northern region ofthe state included a mosaic of pineforests, extensive conifer bogs, andupland hardwoods (Stearns 1987).The central transitional region of thestate included a patchwork of easternbroadleaf forests, prairie, savanna,and wetlands. The south-centralregion of the state was dominated bythe �Big Woods� maple-basswoodforest, and the southeastern regionwas dominated by oak forest(Leatherberry et al. 1995).

Changes followingEuropean settlementThe extent and character ofMinnesota�s forests have undergonemany changes since Europeansettlement (Table 2). During the late1800s and early 1900s, many ofMinnesota�s forests were cleared forvarious purposes. Mature pine treesprovided a rich resource forMinnesota�s lumbering industry,which reached its peak in productionin 1905. In addition, forests acrossthe state were rapidly cleared foragriculture and settlement (Stearns1987). The U.S. Land Office Surveysrecorded that the total land area ofMinnesota�s forests decreaseddramatically from 31.5 million acresin 1850 to a historical low of 11.9million acres in 1895 (Leatherberry etal. 1995).

The composition of Minnesota�sforests also changed followingEuropean settlement. In particular,areas that were once pine forests

converted to aspen or shade-tolerantspecies such as spruce and fir(Ahlgren and Ahlgren 1983). Foreststhat were dominated by white andred pines that once occupied about3.5 million acres before Europeansettlement now occupy only about0.5 million acres, and most aresecond-growth (Frelich 1995).

Logging, fire suppression, andbiological pressures from deer anddiseases caused most of thesechanges in the composition ofMinnesota�s forests (White PineRegeneration Strategies Work Group1996). Before European settlement,areas occupied by white and red pineforests were maintained by a naturaldisturbance regime; periodic fireskilled invading hardwoods andshade-tolerant species while allowingmature pines to survive. Variability inthe frequency and intensity of firesresulted in a shifting mosaic of pinesinterspersed with other conifer andhardwood species. With intensivelogging at the turn of the century,however, vast numbers of pine treeswere removed from the landscape.A lack of seed sources combinedwith destructive postlogging firesinhibited the return of these pineforests (Ahlgren and Ahlgren 1983).Since then, suppression of low andmoderate intensity fires has limitedthe ability of the remaining pines tooutcompete and survive otherinvading species. Increased deerpopulations also have exertedsignificant pressures on pines becausedeer browse on seedlings, which canprevent reestablishment of pinestands at many locations. In addition,white pine blister rust contributes tothe difficulty of maintaining andregenerating white pine stands (White

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Pine Regeneration Strategies WorkGroup 1996). The changes in thecharacter and composition ofnorthern forests over the pastcentury illustrate how biologicalfactors and human activities canintermingle to dramatically alter alandscape.

Extent of today�s forestsRegrowth of trees and forestmanagement efforts includingprotection, reforestation, andconservation helped forests expandtheir total land area since the turn ofthe century (Figure 5). The ForestResource Inventory recorded 16.7million acres of forest in 1990(Leatherberry et al. 1995), with themajority of forested area occurringin the northern region of the state(Figure 6). The number and volumeof growing stock trees has increasedas well; inventories between 1977and 1990 showed a 10% increase innumber and a 22% increase involume (Leatherberry et al. 1995).Today a number of land-use factorsaffect the extent of Minnesota�sforests. While forests cover much ofthe northern part of the state, forestsin the south and central regions arepatchy and heavily fragmented(Figure 7). Large areas once coveredby eastern-broadleaf forest werepermanently converted to agriculturalor developed areas throughout thepast century (Figure 8). The maple-basswood forest of the Big Woodsonce covered 3,420 square miles insouth-central Minnesota; today itcovers a few thousand acres andincludes only a few hundreds acresof old-growth forest (Rusterholz1990). Other ecosystem types werepermanently converted as well; for

example, less than 0.1% of pre-European settlement oak savannaremains in south-central Minnesota(MDNR 1996).

In recent years, however, the ForestResource Inventory reports that thenumber of forest land acres hasremained more stable. For example,in the Central Hardwood Unit thepercentage of forested land area hasslightly increased since the 1977Forest Resource Inventory (Table 3);conversion to agriculture hasdecreased, and efforts at treeregeneration have increased.Programs that take highly erodiblelands out of agricultural productionand regenerate trees help maintainthese forested areas (Leatherberry etal. 1995). But in many areas, such asthe Big Woods, loss of forested landto agriculture is being replaced by

loss to urban growth. Encroachingdevelopment is now the greatestthreat to the extent of many forestedareas (Big Woods Project n.d.; TNC1995).

Composition, structure,and function of today�sforestsIncreases in forest acres during thetwentieth century have increasedbenefits such as erosion control,habitat for certain kinds of wildlife,nutrient uptake, removal ofatmospheric pollutants, andcontinued production of timberresources. Regrown forested acrescan be quite different, however, incomposition, structure, and function;in many cases they are notcomparable to presettlement forestsin terms of forest type, age class, and

16

overall biodiversity. For example,large areas of pine forests have beenreplaced by boreal conifer-hardwood forests composed largelyof aspen (Figure 9).

Aspen accounts for 35% of thestate�s timberland area. Lowlandconifer types, such as black spruce,northern white cedar, and tamarack,make up 18% of the state�stimberland. Many of these forestsoccur in the extensive bog areas ofnorthern Minnesota. In thetransitional region of the state otherhardwoods make up significantportions of the forested landscape.The 1990 Forest Resource Inventoryshows that oak-hickory, maple-basswood, and elm-ash-mapleforests occur frequently in theforested landscape of the CentralHardwood Unit, and have slightlyincreased since the last inventory(Leatherberry et al. 1995).In addition to changes incomposition, many of Minnesota�sforests have undergone significantage-class and structural changes(Stearns 1987). In 1990 the medianage of the state�s timberlands was 50

years (Figure 10). Young, early-successional hardwoods occurfrequently throughout today�s forestsalong with maturing even-agedstands. Many of these are single-ageaspen stands. Frequently these standshave less structural diversitycompared to older forests; forexample, there are fewer snags and

downed logs, which provide habitatfor wildlife. Old-growth forests thatsupport greater structural diversityare now much less common. Abouthalf of the forest before Europeansettlement was old growth. Innorthern forests, only 1.6% of pre-European settlement old-growthpine forests remain (Tester et al.1997).

In general, reductions in forestacreage, changes in speciescomposition from presettlementlandscapes, and shifts in forest agestructure have reduced the biologicaldiversity of Minnesota�s forests(Jaakko Poyry 1992a). This reductionof biodiversity may occur atdifferent scales, ranging fromlandscape diversity to speciesdiversity. Today hardwood forestsare the primary habitat for 51 of thestate�s 287 plant and animal speciesthat are now listed as endangered,

17

threatened, or of special concern(Pfannmuller and Coffin 1989). Inrecent years, management practicesthat target two of these species, baldeagles and timber wolves, haveresulted in significant increases intheir populations. Because forestswith a greater variety of species andhabitats are generally thought to bebetter able to tolerate and recoverfrom a disturbance, achieving similarsuccesses with other rare andendangered plants and animals is animportant challenge for today�sforest managers. Yet, a species-by-species approach is ecologically andeconomically impractical over thelong term; thus, managers arechallenged to consider holisticapproaches to maintaining the overallintegrity and diversity of forestedsystems (Jaakko Poyry 1992b).

Current trends andpracticesHarvestingDemand for forest productscontinues to increase, and woodharvest in Minnesota is expected toincrease into the year 2000 (Figure11). Minnesota�s wood harvest willcontinue to be dominated by aspen,followed by species harvested atmuch lower levels, such as pine,balsam, fir, spruce, birch, and oak.However, the GEIS predicts thataspen harvest will decrease in 10 to15 years, and that the harvest ofother hardwoods will increase.Minnesota�s timber harvest is mostlyused for pulp and paper (35%),waferboard and oriented strandboard (32%), and lumber (16%)(MDNR 1997).

Forest managers use a variety ofapproaches to maintain and restorehealthy forests and mitigate adverse

effects of harvesting. Landscape-levelplans help managers develop harvestrotations that take into accountbroader spatial and time scales, thuspromoting the long-term health ofthe forested landscape. Suchlandscape-level efforts are notintended to reestablish the exactpresettlement pattern of forestvegetation, but they may help includesome of the structural andcompositional elements that werelost following extensive lumbering atthe turn of the century (Kotar 1997).At the site level, harvesting techniquesthat follow Best ManagementPractices (BMPs) help protect waterquality in lakes and streams. ForestResource Council technical teams aredeveloping more comprehensiveforest management guidelines toaddress critical areas such as forestsoil productivity, riparianmanagement, wildlife habitat, andcultural and historical resources(MFRC 1997a). In addition,

18

programs such as the ForestStewardship Program helplandowners meet individualized goalsand needs while at the same timeusing guidelines to ensure soundharvesting techniques. Programs thatfocus on planting and regenerationalso strive to ensure long-term forestproductivity.

Although these approaches areintended to mitigate potentiallyadverse effects of harvesting and tomaintain the long-term health ofMinnesota�s forests, to what degreethese practices are implemented andhow effective they are at protectingMinnesota�s forest resources is notalways clear. Thus, it is important todevise monitoring strategies thatevaluate the success of theseprograms. The Minnesota ForestResource Council is currentlydeveloping compliance andeffectiveness monitoring to trackhow well various mitigationstrategies are protecting the long-term health of Minnesota�s forests(MFRC 1997a).

OwnershipStatewide, almost 50% of forestland is in private ownership (Miles etal. 1995). In some areas of the state,however, a greater percentage of theforest is privately owned; 80% of theforested land in the CentralHardwood Unit is owned byfarmers, corporations, andindividuals, with farmers holding themajority of the land (Figure 12).These patterns have significant

implications for forest managementand monitoring because of the needto work cooperatively acrossownership boundaries.

Traditionally, forest harvestmanagement has been applied on astand-by-stand basis (stands are 1-50acres), with only one owner involvedin management decisions. But at thissmall scale, it is difficult to conservebiological diversity and providerecreational opportunities whileaccommodating production needs.Today management decisions areincreasingly based at the larger,landscape scale (100s to 1,000s acres)and require the cooperation ofnumerous agencies, stakeholders, andlandowners (MDNR 1997;Workshop Summary 1996).

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EXISTING POLICIESAND PROGRAMSThe 1995 Minnesota SustainableForest Resources Act (SFRA) fosters�no net loss� of forests and themaintenance of forest diversity withnew policies and programs thatencourage sustained management,use, and protection of the state�sforest resources (MFRC 1997b). TheSFRA legislation culminated aprocess during which diversestakeholders worked together tolearn about Minnesota�s forestresources and to make wide-rangingforest policy recommendations. TheGeneric Environmental ImpactStatement on Timber Harvesting andForest Management (GEIS) was amajor part of this process; itexamined the status of timberharvesting in Minnesota, assessedpotential impacts associated withdifferent levels of harvest, anddeveloped mitigation strategies.Following the GEIS, representativesof different stakeholder groupsworked to reach consensus onimplementation strategies. Now, theMinnesota Forest Resources Council

(MFRC), created from the 1995SFRA legislation, will use what waslearned from this process to developforest policies and facilitate theirimplementation. In addition, theMFRC will help integrate thenumerous policies and programs thatcurrently exist in Minnesota. Keyareas of focus include (MFRC1997a):

Site- and landscape-levelplanning.Efforts to manage across politicaland ecological boundaries are criticalto sustaining healthy forests. TheMFRC will provide landowners withsite-level assistance through thedevelopment of voluntary timberharvesting and forest managementguidelines that focus on forestriparian zones, wildlife, soilproductivity, and historical andcultural resources. In addition, theMFRC is developing a landscape-based planning process to betterintegrate site- and landscape-levelobjectives into broader regionalforest resource goals.

Continuing educationand outreach.The MFRC encourages educationprograms to keep Minnesota citizensinformed about forest issues. Forexample, the Minnesota LoggerEducation Program and the Centerfor Continuing Education of NaturalResources Professionals help forestprofessionals stay up to date on thelatest scientific information,technologies, and issues.

Improved coordinationand collaboration.The MFRC represents a range offorest interests in Minnesota. TheMFRC also recognizes and workswith existing programs thatimplement forest policy andmanagement. For example, theUSDA Forest Service revisesNational Forest Plans every 10 to 15years in accordance with the NationalForest Management Act (NFMA) of1976, the American Forest and PaperAssociation promotes sustainableforestry principles through itsSustainable Forestry Initiative, andthe DNR Old-Growth ForestIdentification and ProtectionGuidelines provide policy directionwhile landscape-level planning isunder development.

Research and monitoring.Managing for healthy forests requirestimely scientific information. Inaddition to promoting basic researchand the availability of forest resourceinformation, the MFRC calls forthree types of monitoring: �1) forestresource monitoring, to assess broadtrends and conditions in forestsresources at statewide, landscape and

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site levels; 2) practices andcompliance monitoring, to monitorthe actual use of certain timberharvesting and forest managementpractices; and 3) effectivenessmonitoring, to provide informationon the ability of various timberharvesting and forest managementmitigation practices to achieve theirintended objectives� (MFRC 1997a).The EII and MFRC are working todevelop a comprehensive set ofindicators for Minnesota�s forestecosystems.

EXAMPLEINDICATORSTable 4 collects the indicators used inthis chapter. The indicators areorganized within the EII framework,which helps illustrate relationshipsamong human activities,environmental condition, the flow ofbenefits from the environment, andstrategies for sustaining a healthyenvironment. The indicators used inthe chapter are examples that

illustrate how indicators may helpassess the condition of Minnesota�sforests. The process of developing acomprehensive set of indicators thatassess forest condition is ongoing.Developing indicators will requirecollaboration with stakeholdersinterested in their use, testing,refinement, and standardization ofmeasurement techniques.

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