Disturbance and the tion. The latter was thought to generate “fragmentary successional cycles” or “heter- Successional Response of ogenous assemblages of pioneer species”3. Arctic Plants on The problem was later extensively reviewed by Churchill andHanson4 who pointed to Polar Desert Habitats the lack of quantitative data available on the rate and nature of replacementchanges in An important consideration in ecological communitiesand on communityvariation. research is to determine if conventionally ac- Their conclusions on successionalprocesses cepted ecological principlesoperate in similar in the Arctic were generated primarily from ways among the diverse environments of the descriptive correlative studies then available world‘s major biomes. One approach to an- for tundra communities. The lack of quantita- swering this question is to examine ecosys- tive data on successionalprocesses in the tems where physical environmentsare extreme Arctic remains as acute today as at the time by comparison with temperate or mesophytic of Churchill and Hanson’s review, and knowl- ecosystems. Barbowl, for example, has re- edge of the variation in community structure cently reviewed the evidence for three gener- on a broad geographical basis remains frag- ally-acceptedadaptive features of desert mentarys. These problems have recently taken vegetation (productivity, growth and pattern) on an addedapplied importance, since at- and found each to lack substantial factual tempts to establish restorative plant covers of basis, when contrasted with features of more non-arctic plant species are underway in the maic systems. His analysis points clearly to Canadian Arcticislands where disturbance the need for quantitative data to permit resulting from oil and gas exploration ac- correct interpretations about the adaptations tivities has occurrede. of organisms to extreme environments and, The present authors have observed during more importantly, in testing the universality several summer seasons disturbance-induced of widely-held ecological principles. succession on the Truelove Lowland of Devon The concepts ofsuccession and climax Island (76”N)in the Canadian Arctic Archi- vegetation have proved to have considerable pelago. In this paper are presented the results predictive value for ecologists. Numerous of observations of the successional response examples of the successionalprocess have of three vascular plant species on polar desert beendescribed from temperate and boreal microenvironments subjected to vehicle dis- ecosystems. Early work in the arctic tundras turbance. of North America, however, generated que- The study area is a post-Pleistocene strand tions about the validity of applying classical flat on the northeast coast of Devon Island. successional concepts in these regions? Ques- A pronounced series of raised beaches are in tionsfocused primarily on the short time evidence from the present coastline inland to periods available for equilibrium communities the upper marine hit (Fig. 1). These relict to become establishedand, more importantly, beachesprovide microsites of polar desert on the continuousinstability of most sub- conditions in the midst of a landscape domi- strates causedby widespread congeliturba- nated chiefly by hydric tundra meadows. As

FIG. 1. Aerialview of raised beach crestsas studied. Largearrows indicate locationsof vehicle-disturbed pavement. Smaller arrow denotes location of hand denuded plots. SHORT PAPERS 71

suchthey represent the xeric portion of a logistic activities associated with maintenance typical arctic “mesotopographicgradient” and supply of the research station. The repeti- recently describedby Billings’. tive use of particular beaches along main Teeris has validated the desert-like quality travel routes resulted in what appears upon of these sites with respect to the water rela- casual inspection to be a virtual elimination tions of plant species establishedon them, and of the plant cover on the beach crests (Fig.2). Barr9 has constructedisostatic emergence Sice 1969 the use of tracked vehicles has curves for the area. In combination the data beenseverely restricted, and many beaches presented by the two writers suggestthat these have been essentially free of disturbance by locations have been both free from intensive heavyvehicles since that time. During the congeliturbation and available for plant colo- summer of 1973 the present authors analysed nization for a relatively long time period.The three beach ridges (Fig. 1) to ascertain in a beaches examined duringthe present studyare quantitative manner the differencebetween in the order of 5,000 to 6,000 years emer- those sites now in the process of recovering gente. The present writers interpret the and adjacent undisturbed communities. Qua- plant communities established on these sites drats 0.5 m x 5.0 m in size were placed at to be in equilibrium withthe present environ- 10-metre intervals along vehicle-disturbed ment and thus represent climax plant com- areas, and at three metres to the side at the munities. same intervals in undisturbed portions of the The phytosociology of this community is beach. Individual species were countedat each known in detaillo. The surface of the beach quadrat. Total cover valuesfor vascular plants crest is composed of a desert-like pavement and lichens were estimated visually by two of pebbles and cobble. Vascular plant cover observers and the averages of their respective is sparse. Only four species occur consistently estimates recorded. Results of these analyses andmay be dominant in terms of cover; are presented in Table 1. Data havebeen Saxifraga oppositifolia,Dryas integrifolia, included for only the three most consistently Salixarctica and Carexnardina. Abouta encountered species, since these made up the dozen other species are found sporadically, majority of vascular plant cover on the plots none showing more than trace cover in this analysed. Other vascularspecies occurred community. Lichens normally cover between only sporadically. Data from quadrats on the 40% and 50% of the ground surface. Most undisturbed portion of the beach show ex- of the lichen spzcies(56 taxa have beennoted) pectedvalues. Vascular plant cover is low, are of crustose or foliose genera. lichen cover dominates and Saxifraga oppo- These raised beach sites, because of their sitifolia and Dryas integrifolia are prominent xeric nature and hard surface pavement, pro- both in terms of numbers and cover.Minuar- vide the mostacceptable locations for the tia rubella, whileconsistently present is movement of tracked vehicles withinthe area. represented by only a few individuals on each During the period of establishment of the quadrat. The high count on plot 1 of beach A presentresearch facilities in 1960-61, and is due to a group of seedlings found beneath during the years of 1962 through 1969, a a singlemature plant. variety of tracked vehicles were utilized for Thevalues for total plant cover on the

FIG. 2. Vehicle track along the surfaceof a raised beach crest. Lighter colour results from sandy material exposed after removalof the lichen mat and vascular plant cover. 72 SHORTPAPERS

TABLE 1. Individual counts and overall cover valuesfor plants on undisturbed and vehicle-disturbed beach pavement.

Beach A B C z 4 Sample no. 12 3 4 59 8 7 6 101112 c Undisturbed beach pavement Vascularplant cover (x) 35 30 7 40 3628 25 45 27 33 40 26 31 Lichencover ( %) 50 53 55 5148 55 50 40 4543 37 33 47 Plant counts per 2.5m2: "Saxifragaoppositifolia 8959 37 127 90 7169 19 61 88 87 87 79 * Dryasintegrifolia 2024 7 4046 14 42 33 252528 15 27 M inuartia rubellaMinuartia 35342211 111 042 5 Vehicle-disturbed beach pavement Vascularcoverplant (x) 8 4 3 6 3 679 3 46 3 5 Lichen coverLichen ( %) unityless than Plant countsper 2.5rn2: +Saxifragaoppositifolia 4838 37 84 89 94 96 99 65 47 33 116 72 +Dryas integrifolia+Dryas 520768 1261 736 5 Minuartiarubella 3244 35 751614 51 29181978 44 .38 *Cushions of Saxifraga and Dryas were recorded as individual plants.

vehicle-disturbedpavement are, not unex- folia while prominent numerically was repre- pectedly,drastically reduced. More interest- sented chiefly by smaller seedlings and thus ing,however, are comparisonsof the three contributed substantially less to cover values. species in recolonization. Thetwo species Similar results were also obtained on small found most commonly in undisturbed com- quadrats artificially denuded of all vegetation munities show quite distinctive responses fol- in 1969 (Table 2). Counts of individuals on lowingdisturbance. Saxifragaoppositifolia four quadrats showed the presence of a num- seedlings yielded counts similar to those for berof invading Minuartia rubella seedlings undisturbed terrain, while Dryas integrifolia and occasional Saxifragaoppositifolia, but populationsremained severely reduced in after four years all plots still lacked Drym numbers. Minuartia rubella, onthe other integrifolia. hand, had.substantial1y increased its numbers Harper11 has suggested that the artificial in comparison with those for the species on creation of low-diversity communities in .the undisturbed terrain. Further, in the majority field may bea fruitful methodfor understand- of quadrats on disturbed areas Minuartia ing the way inwhich observed patterns in rubella was now the major contributor to the climax communitiesare established with time. total vascular plant cover. Saxifraga oppositi* Observations made during the present study

TABLE 2. Individual counts of three plant species from 40 x 40 cm plots which werecleared of vegetation by hand in the summer of 1969.

Plot no. 1 2 3 4 Year of mapping 19711973 19711973 19711973 19711973 Plant counts (40 cm x 40 cm) Saxifraga oppositifoliaSaxifraga 1 1 1 1 00 1 0 Dryas integrifolia 00 00 00 0 0 Minuartia rubella 5 8 18 12 69 28 SHORT PAPERS 73

indicate that, for these habitats at least, im- 4Churchill, E. D. and Hanson H. C. 1958. portant shifts in the numerical relationships The concept of climax in Arctic and alpine betweenspecies occur followingvehicle vegetation. BotanicalReview, 24 129-91. disturbance (andsubsequent reduction in Kambert, J. D. H. 1973. Terrestrial environ- community diversity). The sharp increases in ments:vegetation and permafrost. In: populations of Minuartiu rubella and the dis- Pimlott, D. H., Vincent K. M. and tinctive recolonization rates of Saxifraga McKnight, C. E. (eds.),Arctic Alternatives, oppositifolia and Dryas integrifolia popula- Ottawa: Canadian Arctic Resources Com- tionsmay be easily viewed as disturbance mittee. inducedsuccession. The causal reasons for these population responses are not known. All 6Anonymous. 1973. No lawnmowen are three species appear to produce substantial needed yet, though Arctic grass is growing. amounts of seed in the field. These observa- Oilweek, 24(31): 42. tions do serve to emphasize,however, that ‘Billings, W. D. 1973. Arctic and alpine our present understanding of the population vegetations:similarities, differences, and dynamics of Arctic tundra plants may be in- susceptibility to disturbance. Bioscience, adequate for predictivepurposes. It is un- 23: 697-704. likely, for example, that in selectingnative *Teeri, J. A. 1972. Polar desert adaptations of plants for restoring vegetation on disturbed a High Arctic plant species. Science, 179: xeric tundra Minuartiarubella wouldhave 496-7. been favoured over Dryas integrifolia if we gBarr, 1971. Postglacialisostatic move- were to rely solelyon our observations of W. ment on northeastern Devon Island: a re the two species in undisturbed communities. appraisal. Arctic, 24: 249-63. The study of responses of vegetation to current land manipulations in the Arctic may loBarrett, P. E. 1972. Phytogeocoenoses of a provide valuable clues to the Understanding of coastal lowland ecosystem, Devon Island, the successional process in this region. It is N.W.T. (Doctoral dissertation, Department the authors’ belief that existing data on suc- of Botany, Universityof British Columbia). cession in tundra in the High Arctic are in- IlHarper, J. L. 1969. The role of predation adequate for the long-range planning of land in vegetationaldiversity. Diversity and use in many tundra habitats, and that greater Stability in EcologicalSystems, Brook- emphasisshould be directed towards this haven Symposiumno. 22,48-61. problem in the future.

ACKNOWLEDGEMENTS This work was financed in part by the Arc- tic Institute of North America and by the ALUR Program of the Department of Indian and Northern Affairs, The authors, however, assume full responsibility for all information presented.They would particularly like to thank Mr. Fred Alt of the Polar Continental Shelf Project, which provided logistic support. Paul Barrett Ronald Schulten Department of Botany University of Massachusetts Amherst, Ma. 01002, U.S.A.

REFERENCES IBarbour, M. G. 1973. Desert dogma re- examined: shoot productivity and plant spacing. AmericanMidland Naturalist, 89: 41-57. ZGriggs, R. F. 1934. The problem of Arctic vegetation. WashingtonAcademy of Science Journal, 24 153-75. sBritton, M.E, 1957. Vegetation of the Arctic tundra. In:Hanson, H. P. (ed.), Arctic Biology, Corvallis: Oregon State University Press.