Journal of Environmental Management (2002) 64, 207–217doi:10.1006/jema.2001.0524, available online at http://www.idealibrary.com on

The response of two arctic tundra plantcommunities to human trampling disturbance

Christopher A. Monz

Sterling College, Craftsbury Common, VT 05827, USA

Received 24 December 2000; accepted 19 October 2001

A 4-year study was conducted to evaluate the consequences of human trampling on dryas and tussock tundra plantcommunities. Treatments of 25, 75, 200 and 500 trampling passes were applied in 0Ð75 m2 vegetation plots at a timeof approximately peak seasonal biomass. Immediately after and 1 and 4 years after trampling, plots were evaluated onthe basis of plant species cover, percent bare ground, vegetation height, and soil penetration resistance. One year aftertrampling, soils were collected for nitrogen analysis in highly disturbed and control plots. Immediately after trampling, 500trampling passes resulted in approximately 50% cover loss in the dryas tundra and 70% cover loss in tussock tundra,but both communities showed a substantial capacity for regrowth. Plots where low and moderate levels of tramplingwere applied returned to pre-disturbance conditions by 4 years after trampling, but impact was still evident in plotssubjected to high levels of disturbance. These results suggest that these tundra communities can tolerate moderate levelsof hiking and camping provided that use is maintained below disturbance thresholds and that visitors employ appropriateminimum-impact techniques. By utilizing this information in a visitor education program combined with impact monitoringand management, it is possible to allow dispersed camping and still maintain these vegetation communities with aminimum of observable impact. 2002 Elsevier Science Ltd.

Keywords: tundra, arctic, Alaska, wilderness, recreation, disturbance, visitor management.

Introduction

Managers of parks and protected areas worldwideare often faced with the challenge of maintaininga high level of resource protection while simul-taneously offering ample recreation opportunitiesfor visitors. These challenges come at a timewhen backcountry recreation is increasingly pop-ular. A recent analysis of recreation use trendsin wilderness areas in the US shows that visi-tation has steadily increased during the period1965–1996, with total use increasing nearly six-fold (Cole, 1996). Similar trends in visitation andassociated resource impacts have been reportedin protected areas worldwide, including the Euro-pean Alps, Indian Himalayas, Nepal and Patagonia(Denniston, 1995). Given these marked increases,it has been suggested recently that recreationand tourism activities could surpass the resource

Email: cmonz@sterlingcollege.edu

extractive economy as the single largest threatto the conservation of protected areas (Denniston,1995).

The overall trend of increased visitation can beexacerbated by the development of more conve-nient transportation access to a protected area, aphenomenon in which land managers often havelittle influence. In Alaska, access to many of thenorthern National Parks and protected areas waspreviously limited to air transportation. This hasrecently changed with the opening to the publicof the Dalton Highway along the northern extentof the Alaska pipeline, substantially improvingaccess to the region, and increasing the poten-tial for recreational disturbance. (Paul Salvator,personal communication).

Historically, the Alaskan Arctic remained rela-tively undisturbed by humans until the initiation ofpetroleum exploration in the 1940s (Walker et al.,1987). Since that time studies have been conductedon the impacts of oil field development (Walkeret al., 1986; Oechel, 1989), disturbance-induced

0301–4797/02/020207C11 $35.00/0 2002 Elsevier Science Ltd.

208 C. A. Monz

thawing of permafrost soils (Truett and Kertell,1992) and the consequences of vehicle trails insummer (e.g. Bliss and Wein, 1972) and in win-ter (Felix et al., 1992; Emers et al., 1995; Emersand Jorgensen, 1997). Similar studies of human-induced disturbance have been conducted in theCanadian High Arctic (Forbes, 1992a & b; Kevanet al., 1995). Other disturbances, such as the effectsof sand and dust on tundra adjacent to gravel roadshave also been examined in Alaska (Auerbach et al.,1997) and in Siberia (Forbes, 1995).

With the exception of work in the Canadian HighArctic (Forbes, 1992a; Kevan et al., 1995) there islittle specific information on the ability of arctictundra ecosystems to tolerate off-trail, dispersedrecreation use and few studies on trampling dis-turbance in the Alaskan north. In an unpublishedreport, Reid and Schreiner (1985) investigated theconsequences of low levels of trampling appliedthroughout the summer to three vegetation typesin Denali National Park. The alpine communityin this study, dominated by Dryas octopetala,was found to be relatively durable to human use.This implies that directing visitors to these areasand away from other vegetation types could be aviable management strategy for maintaining rela-tively undisturbed conditions. Information of thiskind on the relative tolerance of ecosystems tohuman trampling disturbance is useful to landmanagers seeking to provide opportunities for dis-persed recreation while preserving the ‘natural’ or‘pristine’ character of an area. (Hammitt and Cole,1998).

Experimental trampling of ground cover vegeta-tion has often been utilized to assess the toleranceof vegetation and soils to human use. Since Wagar(1964) first proposed this approach, many vegeta-tion types worldwide have been examined. Theseinclude, for example, mountain and riparian vege-tation in the United States (Cole, 1993; Monz et al.,2000), heaths in Scotland (Bayfield, 1979), sub-arctic and alpine areas in Canada (Gnieser, 2000),and sub-arctic vegetation in Finland (Tolvanenet al., 2001). A standard methodology, developedby Cole and Bayfield (1993), has been utilized inseveral of these studies and allows comparisonsto be made across different ecosystems (e.g. Cole,1995a & b).

The objective of this project was to investi-gate the consequences of human trampling ontwo common plant communities in arctic Alaska:the dryas dwarf shrub tundra and the cottongrass tussock tundra. Controlled levels of tram-pling were applied to these plant communities andinitial responses and subsequent re-growth were

measured. This information is important for sev-eral reasons. First, these tundra communities aregeographically widespread in Alaskan protectedareas where recreation use is prevalent, both inthe arctic and in sub-arctic areas at higher eleva-tions. Second, management objectives emphasizethe protection of their pristine character, devoidof permanent trails or campsites (e.g. Gates ofthe Arctic General Management Plan, 1986). Andfinally, backcountry travelers will undoubtedlytravel and camp on these communities, particu-larly the dryas tundra, which offers comfortablehiking and camping in an otherwise challengingenvironment. It is hoped that this informationwill provide guidance to managers in future visitorcapacity decisions and in the further developmentof appropriate minimum impact visitor practices.

Methods

Study site and plant communities

The study area was located in the Bureau of LandManagement (BLM) managed ‘utility corridor’which is accessible from the Dalton Highway(Alaska pipeline haul road) near the GalbraithLake Camp (68°270N 149°300W). This area is inthe north eastern foothills of the Brooks Rangeand lies approximately 15 km south of the ToolikLake research station. Although Gabraith Lakewas a work camp during the construction of theoil pipeline, the experimental plots were locatedapproximately 1Ð5 km from the old work site(vacant since 1978) and 3 km from the pipelinehaul road in an area of no known or observabledisturbance. Recreational use is increasing at thislocation as it is one of the few spots along thenorthern Dalton Highway where visitors can drivesome distance off the highway and camp. It alsoprovides one of the few easily accessible hikingpoints into Gates of the Arctic National Park andPreserve (Paul Salvator, personal communication).

Vegetation in the study area is similar to manytundra communities found in the region, and con-sists of two primary types; dryas tundra domi-nated by the mat-forming shrub Dryas octopetala(mountain avens) and a moist tussock tundra dom-inated by Eriophorum angustifolium (tall cotton-grass) and other graminoids. Across much of arcticAlaska, Dryas typically occupies sites along rivercorridors that are high and flat with well drained,stony soils while Eriophorum is common to thelower-lying areas on poorly drained, acidic soilswith shallow permafrost (Viereck et al., 1992). This

Trampling disturbance and arctic tundra 209

paper follows the nomenclature of Viereck et al.(1992) in that plant communities are referred towith common names (i.e. dryas tundra), whereasscientific names following Hulten (1968 and 1973)are used for individual plant species.

Experimental treatments

Trampling

Experimental design for the trampling treatmentsfollows the standard protocols described by Coleand Bayfield (1993). Four replicates of experimen-tal trampling lanes (1Ð5 mð0Ð5 m) were establishedin each of the two plant communities. Lanes wereselected within blocks on the basis of suitabilityof application of trampling and homogeneity of thevegetation. Treatments were randomly assigned toeach lane within blocks. Each replicate block con-sisted of five lanes; control (untreated), 25, 75, 200and 500 trampling passes. A pass is a one way walkconducted with at a natural gate along the lane bya person weighing 60–75 kg and wearing a lug soleboot. Treatments were applied once during earlyJuly, which is approximately the time of maximumseasonal aboveground plant biomass. For examina-tions of the overall ability of vegetation to toleraterecreational use, application of trampling at onetime has been shown to be equally as effective asmultiple treatments throughout the season. (Bay-field, 1979; Cole, 1985).

Trampling response variables

Standard indices of trampling effects (Cole andBayfield, 1993) were recorded in each lane inone 30ð50 cm subplot placed in the center of thelane by measurement from permanent markersplaced at the lane edge. Measurements consistedof (1) visual estimates of canopy coverage of eachvascular plant species (only green material) and ofmosses and lichens; (2) visual estimates of the coverof bare ground, which included mineral soil, organicmaterial and plant litter; and (3) determinationsof vegetation height, using a point quadrat framewith five pins 5 cm apart within the width of thesubplot, for a total of 50 pin drops. Every effortwas made to standardize and calibrate ocularcover estimates by using 100 random pin dropsper subplot as a baseline in initial trial runs,and then basing final ocular estimates on theseresults. Soil compaction was estimated using apocket soil penetrometer (Forestry Suppliers, Inc.Jackson, MS 39284-8397 USA) with two random

measurements per subplot. Measurements wereperformed approximately 10 days after tramplingto asses initial resistance to trampling (referredto hereafter as ‘immediately after’) and repeated1 year and 4 years after to evaluate regeneration(resilience). All measurements were taken at asimilar time during the growing season. Laneswere rated as to the extent of resemblance toa recognizable trail (1D ‘no discernable path’;2D ‘some evidence of a trail’; 3D ‘trail formationobvious’) after 4 years of recovery.

Soil analysis

After two growing seasons, soils were sampled to adepth of 10 cm in lanes of high trampling intensity(500 passes in dry and 200 in moist tundra) and incontrol plots. This was accomplished by excavationof a small area in the dry tundra with a troweland by using an Oakfield style slotted samplerin the moist tundra. Depth accuracy in the moisttundra was problematic due to high amounts oforganic material in surface horizons and resultingcompaction. Soils were kept cold after samplingand frozen immediately after transport from thefield site until analysis was performed. In thedryas tundra, the surface organic horizon wasseparated from the mineral horizon. Total Kjeldahlnitrogen (TKN) and 2M KCL extractable NHC4 andNO�3 were determined on soils from both sites bystandard laboratory techniques (Soils AnalyticalLaboratory, Montana State University, Bozeman,MT USA).

Data analysis

For the trampling results, analysis follows the sug-gested protocols of Cole and Bayfield (1993) wherea primary response variable for each vegetationtype is relative cover. This is a measure of theproportion of the original vegetation that survivestrampling and is adjusted for changes occurringon control plots over the same time period. It isdetermined in each plot by summing all of the indi-vidual species to obtain total plant cover and thencalculating relative cover as:

Surviving cover on trampled subplotsð cf ð100%

initial cover on trampled subplots

where:

cfD initial cover on control subplotssurviving cover on control subplots.

210 C. A. Monz

Relative cover was also calculated for a fewcommon species to examine individual speciesresponses. Relative height of the vegetation wascalculated by summing the heights and dividing bythe number of values greater than zero and thensubstituting the mean height values in the formulagiven above for relative cover. Calculations of resis-tance and resilience indices follow the proceduresoutlined by Cole (1995a). Species richness was cal-culated by counting the total number of individualplant species in each measurement subplot.

Many multivariate approaches have been iden-tified in the literature to assess changes in plantcommunities as a consequence of disturbance orenvironmental factors (e.g. Gauch, 1982; McCuneand Mefford, 1999). Here, a principal componentsanalysis (PCA) on the species cover data followed byanalysis of variance (ANOVA) on the factor scoreswas employed. This technique has the advantageof being a relatively straightforward approach thatallows treatment differences to be tested statisti-cally. The PCA was used to assign factor scoresto each subplot based on species cover and theANOVA tested for significant treatment differences

on these factor scores. Thus, subplots were ordi-nated in factor space by the PCA. This approachwas used for each of the three post-trampling sam-pling times within both tundra communities. Astandard varimax orthogonal rotation was per-formed on the factors derived in the PCA. Allstatistical tests throughout this study were per-formed using SPSS software version 6.1.1 for theMacintosh (SPSS, Inc., Chicago, IL, USA.).

Results

At the initiation of the experimental work thepre-trampling species abundance for experimentalplots in both sites (Table 1) was assessed. The plotsare typical of the dryas and tussock tundra foundin the region (Viereck et al., 1992).

In terms of initial resistance, low to moder-ate levels of trampling disturbance (25–75 passes)had little effect on the dryas tundra (Figure 1a).Higher levels of trampling resulted in significantdecreases in relative cover, with the highest levelof trampling (500 passes) leaving only 19% relative

Table 1. Initial frequency and mean percent cover of all species in both tundra vegetation types.Standard errors are shown for all species with mean cover greater than 1%. ‘C’ indicates relativecover less than 1%

Species Vegetation type

Dryas tundra Tussock tundra

Freq. Cover Freq. Cover

Androsace chamaejasme subsp. Lehmanniana 2 CArctostaphylos rubra 31 1Astragalus umbellatus 33 CCarex spp 83 C 31 CCassiope tetragona subsp. tetragona 19 CDryas integrifolia subsp. integrifolia 97 6š0Ð8Dryas octopetala subsp. octopetala var. 100 33š1Ð8 3 CoctopetalaEriophorum angustifolium subsp. subarticum 100 7š0Ð8Eriophorum spp 22 1š1Ð7Geum glaciale 29 CHierochloe alpina 27 CLedum palustre 69 1lichens 100 28š1Ð1 81 1Minuartia artica 2 Cmosses 90 2 100 16š1Ð4Oxytropis nigrescens subsp. bryophilia 69 1Pedicularis spp 27 C 13 CPolygonum bistorta subsp. plumosum 63 C 59 CRhododendron lapponicum 21 C 22 CSalix reticulata subsp. reticulata 52 2 94 5š0Ð9Salix rotundifolia 23 CSilene acaulis subsp. acaulis 15 CSalix lanata subsp. Richardsonii 6 CVaccinium uliginosum subsp. microphyllum 8 CVaccinium vitis-idaea 2 C

Trampling disturbance and arctic tundra 211

0500

140(a)

Rel

ativ

e ve

geta

tion

cov

er (

%)

25

20

40

60

80

100

120

200750

500

140

Number of passes

(b)

25

20

40

60

80

100

120

20075

After trampling1 year after4 years after

Figure 1. The relationship between vegetative cover and trampling intensity in the (a) dryas tundra and (b) tussocktundra plant communities. Values are means š 1SE.

0500

160(b)

25

20

40

60

80

100

120

20075

140

Rel

ativ

e ve

geta

tion

hei

ght

(%)

Number of passes

After trampling1 year after4 years after

0500

160(a)

25

20

40

60

80

100

120

20075

140

Figure 2. The relationship between vegetation height and trampling intensity in the (a) dryas tundra and (b) tussocktundra plant communities. Values are means š 1SE.

cover remaining. In tussock tundra (Figure 1b),substantial vegetation loss occurred with only 75passes and the highest level of trampling resultedin only 10% cover remaining. Both vegetationtypes demonstrated a substantial ability to recover(resilience), but at the high level of disturbance,regeneration was not complete in either pant com-munity even after 4 years. For example, relativecover for the 500 pass level was 77% in the dryastundra and 78% for the tussock tundra, indicat-ing that regeneration was not complete in theseplots. Immediately after trampling, relative heightof the dryas tundra was largely unaffected by tram-pling, while the high level of trampling resulted inonly approximately 40% relative height in the tus-sock community (Figure 2). Both vegetation typesexhibited an increased height after regeneration atall levels of trampling.

In both vegetation types, analysis on only themost abundant individual species was possible dueto overall cover and frequency in plots (Table 2).In the dryas tundra, Dryas octopetala was moder-ately resistant, with 58% relative cover remainingafter 200 passes. Vegetation regeneration was sub-stantial after 1 year and nearly complete after 4years, but loss due to trampling remained at thehigher disturbance levels. At moderate and highlevels of trampling, lichens did not fully recovereven four years after disturbance. In the tus-sock tundra, after a significant initial decline incover due to trampling, Eriophorum angustifoliumrebounded substantially after 1 year, but reducedcover was still observable at the 500 pass leveleven after 4 years. Mosses were initially sensi-tive to moderate and high levels of trampling withregeneration being complete after 4 years in all

212 C. A. Monz

Table 2. Relative coverŁ of abundant species after trampling and after 1 and 4 years of recovery

After trampling After 1 year of recovery After 4 years of recovery

Number of passes Number of passes Number of passes

25 75 200 500 25 75 200 500 25 75 200 500

Dryas TundraDryas octopetala 73 83 58 14 100 116 95 82 100 112 89 98Lichens 104 89 42 20 100 83 61 25 98 103 55 35

Tussock TundraEriophorum angustifolium 100 90 35 9 131 96 92 44 98 89 92 77Dryas integrifolia 112 63 16 7 112 117 52 39 101 79 60 32Mosses 96 100 55 12 86 109 121 70 103 97 106 64

Ł Relative cover is the proportion of original cover that survives trampling, adjusted for changes on control plots. Relative covers werecalculated following Cole and Bayfield (1993). This procedure reduces the variation between replications by calculating mean pre- andpost-treatment cover estimates on all replications and then calculating relative cover from these means. As such, confidence intervalscannot be calculated.

treatments except the 500 pass level. Visual rat-ings of the degree of trail formation after 4 yearsof recovery revealed no observable trail formationin the dryas tundra, but in the tussock commu-nity, trail formation was greater at the 500 passlevel (MD3Ð0) compared to control plots (MD1Ð0,FD24Ð25, P<0Ð0001).

Immediately after trampling the percent bareground increased significantly in the dryas tundraat the 200 and 500 pass level, but there was nosignificant increase in soil penetration resistance(an index of surface soil compaction) (Table 3). Asimilar trend was observed in the tussock com-munity in terms of bare ground, but soils weremore susceptible to compaction, with just 75 passesshowing a significant increase in penetration resis-tance compared to the control plots. Penetrationmeasurements were highly variable however, andcould have been possibly been improved by takingmore measurements per subplot. In both commu-nities, no significant differences in bare ground orpenetration resistance were observed after 4 yearsof recovery. At this time bare ground estimateson all plots approximated pre-disturbance lev-els. Indices of resistance, resilience and tolerance(Table 4) indicate that the dryas tundra was some-what more resistant to initial disturbance whilethe tussock tundra was of high resilience. Inter-estingly, despite the observable changes in the soiland plant communities, soil nitrogen (NHC4 , NO�3and TKN) did not differ significantly in compar-isons of control and highly disturbed plots afterone year of recovery (Table 5).

Overall plant species composition seemed to berelatively unaffected by trampling as examined bythe PCA-ANOVA approach since few statisticallysignificant differences were found (Table 6). Inaddition, observations of the plots over the course

of the experiment suggested that little if anyreplacement of species occurred.

Discussion

Although there is a significant literature on theresistance and resilience of plant communities(e.g. Cole, 1993; Monz, 2000, and others) and thisinformation has been synthesized across ecosystemtypes (Cole, 1995a & b), site-specific information onthe response of plant communities to human distur-bance is desirable for management decisions. Thisspecific information is particularly useful for landmanagers developing use regulations and educa-tional practices. Applied trampling studies do notexactly mimic disturbance from actual visitor use,but do provide an effective means for examiningthe responses to recreational disturbance whilecontrolling or evaluating the influence of extrane-ous variables. This approach can therefore providean index by which to base visitor use managementdecisions (Cole and Bayfield, 1993).

The degree to which a plant community cansupport human use is a combination of its ability toresist the initial disturbance of trampling and itssubsequent capacity for re-growth. The propertyof withstanding initial disturbance is most oftenreferred to as resistance (Sun and Liddle, 1991;Cole and Bayfield, 1993) though Grime (1979)called this property inertia. In this experiment,resistance was determined by measuring plantproperties approximately 10 days after the appliedtrampling. A post-disturbance waiting period isneeded before assessing resistance to accuratelydiscern viable plant tissue from damaged material.

Resilience has been used commonly in theliterature (Grime, 1979; Cole and Bayfield, 1993)

Tram

pling

disturb

anceand

arctictund

ra213

Table 3. Exposure of bare ground, changes in soil compaction and species richness due to tramplingŁ

Treatment After trampling After 1 year of recovery After 4 years of recovery

Bare Soil Species Bare Soil Species Bare Soil Speciesground penetration richness ground penetration richness ground penetration richness

(%) resistance (%) resistance (%) resistance.kg/cm2/ .kg/cm2/ .kg/cm2/

Dryas tundracontrol 35Ð0š2Ð9 a 0Ð7š0Ð2 a 9Ð0š1Ð3 a 37Ð5š2Ð5 a 0Ð6š0Ð3 a 9Ð8š1Ð4 a 30Ð0š4Ð1 a 1Ð3š1Ð3 a 11Ð0š1Ð5 a25 passes 40Ð0š4Ð1 a 0Ð8š0Ð2 a 8Ð5š0Ð7 a 36Ð0š12Ð4 a 0Ð8š0Ð3 a 10Ð0š0Ð7 a 37Ð5š4Ð8 a 2Ð5š1Ð4 a 11Ð5š0Ð9 a75 passes 42Ð5š4Ð8 a 0Ð8š0Ð2 a 8Ð5š1Ð3 a 47Ð5š2Ð5 a 0Ð8š0Ð3 a 9Ð3š0Ð5 a 40Ð0š5Ð8 a 1Ð5š0Ð2 a 10Ð5š0Ð3 a200 passes 67Ð5š7Ð5 b 1Ð6š0Ð3 a 8Ð8š1Ð0 a 53Ð0š4Ð8 a 1Ð1š0Ð3 a 8Ð8š0Ð3 a 40Ð0š7Ð8 a 1Ð5š1Ð2 a 9Ð8š0Ð8 a500 passes 87Ð5š2Ð5 b 1Ð6š0Ð3 a 6Ð3š0Ð6 a 65Ð0š6Ð4 a 1Ð8š0Ð9 a 9Ð0š0Ð7 a 35Ð0š5Ð0 a 2Ð8š1Ð3 a 10Ð3š0Ð8 a

Tussock tundracontrol 62Ð5š4Ð8 a 0Ð5š0Ð1 a 7Ð0š1Ð0 a 52Ð5š4Ð8 ab 0Ð5š0Ð1 a 8Ð8š1Ð0 a 60Ð0š4Ð1 a 0Ð1š0Ð0 a 9Ð0š1Ð3 a25 passes 65Ð0š8Ð7 a 0Ð9š0Ð3 a 7Ð8š0Ð5 a 55Ð0š2Ð9 ab 1Ð1š0Ð3 ab 10Ð3š1Ð0 a 67Ð5š6Ð3 a 0Ð3š0Ð1 a 9Ð8š1Ð0 a75 passes 70Ð0š4Ð1 a 1Ð9š0Ð3 ab 7Ð5š0Ð5 a 42Ð5š2Ð5 ab 1Ð2š0Ð3 ab 10Ð3š0Ð8 a 62Ð5š2Ð5 a 0Ð4š0Ð2 a 10Ð5š1Ð0 a200 passes 85Ð0š5Ð0 ab 2Ð9š0Ð3 b 6Ð5š0Ð5 a 52Ð5š2Ð5 ab 2Ð1š0Ð3 b 9Ð3š0Ð8 a 62Ð5š9Ð5 a 0Ð5š0Ð2 a 9Ð0š0Ð8 a500 passes 97Ð5š2Ð5 b 3Ð0š0Ð3 b 7Ð8š0Ð8 a 65Ð0š6Ð5 ab 2Ð3š0Ð3 b 8Ð8š1Ð7 a 65Ð0š11Ð8 a 0Ð3š0Ð1 a 8Ð8š1Ð4 a

ŁMeans not followed by the same letter are significantly different using the Scheffe test at aD0Ð05.

214 C. A. Monz

Table 4. Indices of resistance, resilience, and tolerancefor the two vegetation typesŁ

Dryas Tussocktundra tundra

ResistanceMinimum number of 200 200passes that causeapproximately a 50%cover loss

(48% Loss) (55% Loss)

Mean relative cover after0–500 passes

64Ð3 58Ð2

ResilienceMean increase in cover1 year after 0–500passes, as a percent ofthe damage caused bytrampling

69Ð6 105Ð1

Mean increase in cover4 years after 0–500passes, as a percent ofthe damage caused bytrampling

75Ð8 86Ð7

ToleranceMaximum number ofpasses that leave atleast 75% relative cover1 year after trampling

200 >500

Mean relative cover 1year after 0–500 passes

89Ð2 102Ð1

Maximum number ofpasses that leave atleast 75% relative cover4 years after trampling

500 >500

Mean relative cover fouryears after 0–500passes

91Ð4 94Ð4

Ł Calculations follow Cole and Bayfield (1993).

Table 5. Soil nitrogen in highly disturbed plots after 1year of recovery

NH4 NO3 TKN.mg kg�1/ .mg kg�1/ (%N)

Tussock tundraControl 11Ð5š2Ð3 0Ð13š0Ð2 2Ð4š0Ð1500 Passes 12Ð8š2Ð3 0Ð45š0Ð2 2Ð3š0Ð1

Dryas tundraOrganic horizon

Control 3Ð8š2Ð5 1Ð2š0Ð8 1Ð3š0Ð2500 Passes 8Ð1š2Ð5 1Ð0š0Ð8 1Ð2š0Ð2

Dryas tundraMineral horizon

Control 2Ð7š0Ð9 1Ð8š0Ð8 0Ð7š0Ð2500 Passes 3Ð5š0Ð9 1Ð2š0Ð8 0Ð6š0Ð2

to describe the ability of an ecosystem to recoverfrom disturbance. Here, resilience was assessedby comparing the relative cover after disturbancewith the relative cover after one and four years ofregeneration. Tolerance is another useful measureemployed by Cole and Trull (1992) and Coleand Bayfield (1993), that characterizes the abilityof vegetation to both resist and recover fromdisturbance. Tolerance was assessed in this studyby comparing vegetation cover after 1 and 4 yearsof regeneration with the initial pre-disturbancecover.

The results presented here indicate that thedry tundra is more resistant to trampling thanthe tussock community, though only slightly so(Table 4). Both communities exhibit approximatelya 50% cover loss with 200 passes and the dryastundra has an overall mean relative cover (across

Table 6. Results of principal components-analysis of variance (PCA-ANOVA) procedure on plant communitiesŁ

Analysis Immediately after trampling After 1 year of recovery After 4 years of recovery

MS F P MS F P MS F P

Dryas tundraFactor 1 by tramplingtreatment

0Ð802 0Ð762 0Ð566 1Ð62 1Ð96 0Ð153 1Ð78 2Ð24 0Ð112

Factor 2 by tramplingtreatment

8Ð27 2Ð06 0Ð058 0Ð476 0Ð417 0Ð793 2Ð22 3Ð31 0Ð039

% variation explained byfactors 1 and 2

36Ð8 31Ð5 34Ð4

Tussock tundraFactor 1 by tramplingtreatment

0Ð147 0Ð119 0Ð974 0Ð147 0Ð120 0Ð974 0Ð856 0Ð826 0Ð528

Factor 2 by tramplingtreatment

0Ð821 0Ð783 0Ð553 0Ð821 0Ð783 0Ð554 1Ð09 1Ð12 0Ð386

% variation explained byfactors 1 and 2

35Ð0 35Ð0 35Ð0

Ł A PCA was performed on species cover data for each of the two plant communities at each sampling time. ANOVA was used to testfor treatment differences on the factor scores of the first two components determined in the PCA.

Trampling disturbance and arctic tundra 215

the 0–500 passes) of 64Ð3% compared to 58Ð2%in the tussock tundra. Modeling work by Cole(1995b) suggests that resistance to trampling islargely a function of plant stature and whether theplants were graminoids, forbs or shrubs. Mattedgraminoids were found to be highly resistant, whileerect forbs the least. Dryas is a unique shrubthat forms dense low growing mats in most areas,and our results indicate that it is of moderateresistance. The tussock community, composed oferect graminoids is also of moderate resistance ascompared to the results reported from of a widerange of vegetation types (Cole, 1993).

Both communities demonstrate a substantialresilience, especially the tussock community, whichshows nearly full regeneration 1 year after distur-bance. Rapid regeneration of graminoids in tussockcommunities has been previously observed (Emerset al., 1995 and Chapin and Shaver, 1981) as a con-sequence of the disturbance of the surface organiclayers and the release of nutrients following distur-bance. Our results indicate modest stimulation ofgrowth in tussock tundra after 1 year with moder-ate levels of disturbance (e.g. 75 passes), followedby a return to conditions more closely approxi-mating pre- disturbance levels at 4 years. It is,however, unclear as to if this is due to a release ofsoil nutrients or a direct response to disturbance onthe part of the plants. Interestingly, at the 500 passlevel, there was little change in relative cover afterthe initial re-growth, and cover did not return topre-disturbance levels after 4 years (Figure 1). Soilnitrogen showed no apparent trends, however, incomparisons of control and highly disturbed plotsafter 1 year of recovery (Table 5). The dryas tundraregenerated more slowly at trampling intensitiesof 200 passes and above (Figure 1). In contrast tothe lower trampling intensities, the 500 pass leveldid not recover completely, with just 77% relativecover even after 4 years.

The results of this study contrast somewhat withthe work of Reid and Schriener (1985) in that theprevious work found dryas tundra to be of lowresistance and high resilience. Direct comparisonsof the two studies are difficult due to method-ological differences, particularly in the timing andapplication of trampling treatments. However, theoverall conclusion, that the dryas tundra can toler-ate a moderate amount of dispersed use, is similarin the two studies.

Since Dryas octopetala has a low, mat-forminggrowth form, relative height (Figure 2) of the veg-etation was largely unaffected by trampling. Itwas, however, difficult to obtain accurate assess-ments of height in the field by standard methods,

so measurement error may have confounded anysubtle changes. In the tussock tundra, vegetationheight was significantly reduced with 500 passesimmediately after trampling (Figure 2). Due to themorphology of this vegetation type (collectively tallgraminoids in the 30 cm range), plants can be eas-ily flattened by intensive human use. This may notbe an important management consequence, giventhe degree of resiliency we observed. However, itcould be problematic since areas of disturbancemay become visually obvious to visitors. Disturbedareas could attract more use and reach levels ofdisturbance exceeding the ability of the ecosystemto recover.

Cole (1995a) in an analysis of the relative cover-trampling intensity curves of 18 vegetation types,concludes that the most durable vegetation typeswere not necessarily those with the highest initialresistance, but rather ones with a high tolerancefor a complete cycle of disturbance and recovery.Also, many vegetation types have thresholds ofvulnerability, beyond which complete recovery isat best very slow, and in some cases impossible.In general, both of the tundra communities andmost of the individual species examined wereable to recover to pre-disturbance conditions in alltreatments except the 500 pass level. If disturbanceis maintained at or below the 200 pass threshold,regeneration is possible fairly rapidly, even asquickly as one or two growing seasons.

It appears from this study that there is littleeffect on plant composition as a consequence of theapplied trampling (Table 6), though it is possiblethat these effects are very subtle, and our statisticaland sampling methods not sufficiently sensitive.Moreover, standard protocols for trampling studieswere followed (Cole and Bayfield, 1993) wheremosses and lichens are not identified by species.Some research indicates that these species maybe important indicators of disturbance in theseecosystems (Forbs, 1992a). It is also possible thatadditional cycles of disturbance and recovery overseveral years would result in plant communitylevel changes as has been demonstrated in otherresearch (Liddle, 1997).

In many protected areas in Alaska, managementplans call for the maintenance of resource condi-tions with as little observable human impact aspossible, that is, without the formation of per-manent trails and campsites (e.g. Gates of theArctic, 1986). A dispersal camping strategy, wheretotal use is limited but visitors are free to chooseplaces to camp is typically used to accomplishthis management objective (Leung and Marion,2000). This strategy contrasts with a containment

216 C. A. Monz

strategy, where visitors are required to travel onexisting trails and camp in designated or exist-ing campsites. Dispersal techniques have provenproblematic in some areas of moderate to highvisitation and have resulted in greater overallimpact compared to containment strategies in simi-lar environments (Leung and Marion, 2000). Giventhe tolerance observed to moderate disturbance inthese tundra communities, effective dispersal ofuse seems possible, but only if use remains belowthreshold levels and if visitors are proficient inminimum-impact camping. Observations at DenaliNational Park, an area where dispersal strategiesfor backcountry camping have been utilized forsome time, suggest that dispersal can be effectivein tundra ecosystems (Leung and Marion, 2000,Marion personal communication) and the findingsof this work support these observations.

This work provides a basis to develop prescrip-tive visitor management strategies for these tundracommunities, but cannot replace a thorough visitorcapacity decision process. By combining this infor-mation with monitoring and assessment programsand active visitor management, the maintenanceof pristine conditions in many areas is possible.It is especially important to manage and moni-tor the dryas tundra carefully, since visitors areoften attracted to these areas which offer dry, levelcampsites and easier hiking than the tussock com-munity.

Acknowledgements

The author thanks David Cole and Jeffrey Welker formany helpful suggestions, Gretchen Meier, Wendy Loya,Sharon Kehoe, Ralf Buckley and Stephanie White forassistance during the three field seasons, and JeffreyMarion, Glenn Haas, David Swift, George Wallace andDon Rodriguez for reviews of this manuscript. Thisproject was generously funded and supported by theNational Outdoor Leadership School’s Research Programand NOLS Alaska.

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