Stability and Instability of Natural and Modified Upper Timberline Landscapes in theColorado Rocky Mountains, USAAuthor(s): Jack D. Ives and Katherine J. Hansen-BristowSource: Mountain Research and Development, Vol. 3, No. 2, Workshop on the Stability andInstability of Mountain Ecosystems. Berne-Riederalp, 14-19 September 1981 [Part One] (May,1983), pp. 149-155Published by: International Mountain SocietyStable URL: http://www.jstor.org/stable/3672996Accessed: 09/10/2008 18:40

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Mountain Research and Development, Vol. 3, No. 2, 1983, pp. 149-155

STABILITY AND INSTABILITY OF NATURAL AND MODIFIED UPPER TIMBERLINE LANDSCAPES IN THE COLORADO ROCKY MOUNTAINS, USA

JACK D. IVES1 and Katherine J. Hansen-Bristow2

ABSTRACT The forest-alpine tundra ecotone of the Colorado Front Range is defined as the transition belt extending from the upper timberline (upper limit of closely-spaced, symmetrical trees) to the treeline (upper limit of tree species). Its dynamics and natural history are outlined.

It is postulated that treeline and the upper part of the ecotone were established several thousand years ago under climatic conditions much more favourable to seedling establishment than those of today. Because the tree forms of the ecotone are able to maintain themselves over long periods by layering, the ecotone is extremely stable despite significant climatic fluctuation. This same characteristic renders it highly vulnerable to human impacts. In the last decade a change has begun from natural long-term stability to progressive short-term instability. The implications of this for wilderness area management are discussed.

RESUME Stabilite et instabilite dans les paysages naturels et modifies de la limite superieure desforits dans les Rocky Mountains, Colorado, USA. On definit lecotone entre la foret et la toundra alpestre comme la ceinture de transition qui s'etend de la limite superieure des forets (a savoir: la limite superieure des arbres disposes de faon dense et symmetrique) a la limite superieure des arbres (la limite superieure des especes arborescentes). Les grandes lignes de la dynamique de l'ecotone ainsi que son histoire naturelle sont esquissees.

On part du principe que la partie superieure de 'ecotone et la limite des arbres se sont etablies il y a plusieurs millenaires dans des conditions beaucoup plus propices a la survivance des sauvageons que les conditions actuelles. C'est parce que cette vegetation arborescente s'est averee capable de se maintenir a travers de longues periodes par marcottage que s'est produite une ecotone d'une extreme stabilite en depit de fluctuations climatiques importantes. Cette meme caracteristique la rend eminement vulnerable a l'impact humain.

Cette derniere decennie a vu les debuts d'un changement progressif de la stabilite naturelle a long-terme vers une instabilite realisee a court-terme. On etudie les implications de ce changement en ce qui concerne la gestion des zones sauvages.

ZUSAMMENFASSUNG Stabilitdt und Instabilitdt von natiirlichen und von verdnderten Landschaften im Baumgrenzgebiet der Colorado Rocky Mountains, USA. Fur Colorado Bergketten (Front Range) wird das Gebiet von bewaldeter Zone bis zur alpinen Tundra als Ubergangsgiirtel zwischen der Waldgrenze (obere Grenze dicht stehender, symetrisch gewachsener Biume) und der Baumgrenze (obere Grenze aller Baumarten) definiert. Dynamik und Entstehungsgeschichte dieses Gebietes werden skizziert. Es wird angenommen, da1f die Baumgrenze und der obere Teil des Ubergangsgebietes vor einigen 1000 Jahren unter klimatischen Bedingungen entstanden sind, die zur Ansamung wesentlich giinstiger waren als die heutigen. Da die Baumarten des Giirtels sich iiber lange Zeit hinweg durch Ableger vermehren konnen, gilt das Gebiet als recht stabil trotz betrachtlicher, klimatischer Schwankungen. Andererseits ist es aber gegeniiber menschlichen Eingriffen besonders gefahrdet. Wahrend der letzten 10 Jahre ist ein Wechsel von natiirlicher, langfristiger Stabilitit zu progressiver Instabilitat eingetreten. Die daraus folgenden Konsequenzen fur die Verwaltung dieses Naturschutzgebietes werden diskutiert.

INTRODUCTION

The task of determining when a particular landscape is stable or when it is unstable is one of great complexity. This is because many different criteria can be used for defi- nition of stability and instability (see papers by Gigon; Messerli; Winiger; this issue). In a complex urban and industrialized landscape, with scattered recreation and wilderness areas, value judgements are inevitable: is the

stability/instability equation to be balanced from a socio- economic, cultural, political, or biological point of view? This is one of the more important questions for the work-

shop to consider. This paper discusses the question as it

relates to the transition belt or ecotone between the upper montane forest and the alpine meadow in the Colorado Front Range. Wardle (1974) has described the timberline areas of western North America as some of the most nearly natural in the world. Large-scale human impacts have been restricted to the last hundred years or so. Impact by Palaeo- Indian hunters and gatherers, however, while not easily determinable, must have occurred to some degree over the last 10,000 to 14,000 years (Husted, 1974; Benedict and Olson, 1978).

The montane forest-alpine meadow transition, hereafter

'Department of Geography, University of Colorado, Boulder, Colorado 80309, U.S.A. 2Department of History and Geography, Utah State University, Logan, Utah 84322, U.S.A.

150 / MOUNTAIN RESEARCH AND DEVELOPMENT

referred to as the forest-alpine tundra ecotone and equated with the subalpine belt (Love, 1970; Barry and Ives, 1974), of the Colorado Front Range, is very well developed, espe- cially on the eastern side of the Continental Divide. This is principally the result of extremely strong downslope winds, frequently exceeding 150 km per hour during the period from November to March (Barry, 1973). Until the last twenty years this ecotone has been a largely inaccessi- ble and little-used mountain wilderness, with the excep- tion of the mining boom during 1880-1920 when fire and some cutting of trees for fuel and construction occurred. The last twenty years have witnessed a remarkable and accelerated growth in recreational use, including four-wheel drive and snowmobile vehicles, cross-country skiing, hunt- ing, fishing, hiking, and back-packing. In 1978 and 1979, respectively, the Indian Peaks Wilderness and the Niwot Ridge Biosphere Reserve were established within a por-

tion of the Colorado Front Range. Much of the remaining area of the Front Range falls within Rocky Mountain Na- tional Park and the non-wilderness sections of the Roose- velt/Arapahoe National Forest (Ives and Dow, 1982; Baumgartner, 1983).

The purpose of this paper is to discuss the concept of stability/instability in the near-natural setting of the for- est-alpine tundra ecotone as it existed twenty years ago. For this period human impact was insignificant, with the exceptions noted above. The second purpose is to examine the actual and potential impacts from the recently accelerat- ing human recreational activities and to analyse to what extent this is causing a change from stability to instability, that is, the long-term (i.e., thousands of years) biological stability in the first instance, and shorter term (100 years) biological instability induced by human impact in the second.

THE FOREST-ALPINE TUNDRA ECOTONE OF THE COLORADO FRONT RANGE

The forest-alpine tundra ecotone of the Colorado Front

Range is defined as the forest-alpine meadow mosaic ex-

tending between timberline (upper limit of tall, symmetri- cal, closely-spaced trees of the montane forest) and the

upper tree-species limit or treeline. The vertical width of this subalpine belt varies with exposure, slope, and sub- strate, but is frequently as much as 200 m, with the species limit extending to about 3,500-3,600 m a.s.l. It is charac- terized by a gradual progression in the reduction in indi- vidual tree height and frequency with increased altitude, and from upright symmetrical forms, to upright flagged forms, and at highest elevations to prostrate mat shrub forms (Figure 1). The principal tree species are Picea engel- mannii, Abies lasiocarpa, and Pinus flexilis, with occasional stands of Pinus aristata Bailey in the southern part of the

range. Juniperus and Salix spp. occur frequently in close association with the flagged tree "islands" and mat forms.

Except where glacial troughs transect the landscape, slopes at the altitude of the forest-alpine tundra ecotone are

usually gentle, the product of long, continued periglacial mass movement without Pleistocene glacial disruption. The

contrasting periglacial and glacial landform elements, to-

gether with the special "edge effects" of tree island and

alpine meadow mosaic, are responsible for the high aesthe- tic value accredited to this mountain belt (Figures 2 and 3; Baumgartner, 1983).

Many workers have attempted to determine the relation-

ships between upper timberline and environmental con- trols on tree growth throughout the world (Tranquillini, 1979) and in the Colorado Front Range in particular (Wardle, 1968, 1974; Marr and Marr, 1973; Ives, 1973a, 1978; Hansen-Bristow, 1981, 1982). Holtmeier (1981) has discussed the use and misuse of the term krummholz with

respect to the Front Range and the Alps. Some of the gen- eral and specific conclusions are relevant to the present dis- cussion. The major controls are: (1) a short, cool growing season, restricted by late-lying snow, frozen soils, and both

early and late frosts; (2) the absence, or rarity, of seedling establishment and survival within the upper ecotone; (3)

inadequate winter hardiness acclimatization in needles which leaves tissues subject to extensive damage from mild autumn frosts; (4) widespread winter desiccation occurring in a high radiation environment where frozen ground and frozen root systems, inadequately protected by a shallow snow cover or wind-blown surfaces, prevent water replace- ment. Tranquillini (1979) discusses these factors in detail.

PI 4S4,0

8 tit0

(% O~~~~9~~~~;s~ ~~~I" :~ ?Q"/ \ )s?n

Mat

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ig

Width of belt and decreasing tree deformation

FIGURE 1. A schematic diagram of the forest-alpine tundra ecotone showing the transition from upright, symmetrical trees to prostrate mat forms.

J. D. IVES AND K. J. HANSEN-BRISTOW / 151

FIGURE 2. Low-level oblique air photo- graph looking onto Niwot Ridge, Colo- rado Front Range, showing the transi- tion from the upper montane forest to the treeline.

Reproduction throughout much of the ecotone is vege- tative, by layering on the downwind side of tree islands where boughs are pressed down against the soil surface by the lee-side snowdrift (Figure 4). There exists a mat island/snowdrift interaction whereby the individual tree is killed off on the windward west side as it migrates down- wind through layering on the east or lee-side (Marr, 1977). Over wide areas, very few seedlings are found in the upper two-thirds of the ecotone. This, together with a calculated age of individuals of 800-1,000 years (Ives, 1978) would indicate that the species limit was established at least a thousand years ago. By extrapolation from the upper eco- tonal prostrate forms and the dynamics of mat island/snow- drift interaction, it was concluded by Ives (1973a, 1978) that an individual may survive several thousands of years. This situation of almost indefinite survival requires a uni- form slope of several hundred metres. Tree migration onto a convex slope segment will tend to deprive it of snowdrift

protection, leading to eventual death, whereas a concavity will result in too-deep snow, shortened growing season, and attack by snow mould.

Much more detailed work by Hansen-Bristow (1981) provided extensive support for the foregoing interpretation. From this it was hypothesized that the treeline must have been established several thousand years ago, probably during a post-glacial warm period. Treeline and the entire

upper ecotone have survived the vicissitudes of climatic

change over the past several thousand years. New trees are

only recruited in fortuitous circumstances where seedlings become established and survive in micro-habitats, such as in the lee of large rocks or clumps of Salix spp., or other trees.

Eight transects along various slope aspects on Niwot

Ridge indicate that conifer seedling establishment and sur- vival are rare within the upper sub-belts of the forest-alpine tundra ecotone (Hansen-Bristow, 1981). Figure 5 indicates

the altitudinal distribution versus the year of establishment and species of seedlings, saplings, and small trees along a south- to southeast-facing slope of Niwot Ridge. Although treeline extends to 3,530 m along the transect no small trees were found above 3,410 m. This is 120 m below the upper limit of present-day treeline.

It has been hypothesized by Hansen-Bristow (1981) that warm periods would encourage a rise in altitude of the tim- berline, the conversion of mat forms into mat and upright flagged trees, and so on, but a significant increase in the altitude of the treeline itself would be unlikely. More severe

periods would reduce the flagged trees in the mid-section of the ecotone and deplete the timberline but probably not

significantly affect the altitude of the treeline. Thus in favourable periods the ecotone would be constricted in

FIGURE 3. The tree island and alpine meadow mosaic are responsi- ble for the high aesthetic value accredited to the forest-alpine tundra belt.

152 / MOUNTAIN RESEARCH AND DEVELOPMENT

vertical extent; during severe periods it would be extended. At present the upper ecotone appears heavily stressed.

The discussion concerning the stability of the forest-

alpine tundra ecotone has a possible flaw (pers. comm., Slatyer and Wardle, 1982). Because of the very long life-

span of individual tree-islands, recruitment of new mem- bers into the population, as chance establishment of seed-

lings in the lee of rocks and pre-existing trees, need occur

only at long time intervals to maintain the upper ecotone. In this sense, the authors' hypothesis may have been over- stated. A systematic analysis of rate of recruitment of indi- viduals over a period an order of magnitude greater than that demonstrated in Figure 5 is required. Nevertheless, this qualification does not significantly affect the conclu- sion drawn here. This defines biological stability in rela- tion to the much shorter period of average human life ex-

pectancy, and short-term environmental impacts resulting from human disturbance of the ecotone.

From the foregoing discussion it is concluded that the

forest-alpine tundra ecotone, and specifically the treeline, is extremely stable in a biological time-frame. Within this time-frame individual forms have a life-span of several thousand years which greatly exceeds the periods of post-

Elevation (m) Individua

-_-^~~~~3550 ~* AbiE 3550 ~~~~~3540 X~~x PicE

./ Pint 3530-treeline Pin 3520 3510 3500 3490 3480 3470 3460 3450 3440 3430 3420 3410 X 3400 * x 3390 3380 3370 * x x x x 3360 x x

x x x x 3350 *x ?x x 3340 3330-timberline

FIGURE 4. Winter setting of a wind-swept tree island with lee snowdrift accumulation. The snowdrift assists in the layering process which results in downwind migration and longevity of the tree.

glacial climatic fluctuation. The forest-alpine tundra eco- tone of the Colorado Front Range, therefore, may be re-

garded as an extreme case of mountain ecosystem stability.

I Tree Species es lasiocarpa ea engelmannii us contorta

x

x x

x x 0 A

x

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x x

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Year c) I)-, 0) 0) ) 0) 0) )0 ) ) 0) a) a) a0,) I- I- 0)0 >0> , o0 0> 0> 0 O Q , FIGURE 5. Altitudinal distribution versus year of establishment and species of seedlings, saplings, and small trees along a south- to southeast-facing slope on Niwot Ridge.

J. D. IVES AND K. J. HANSEN-BRISTOW / 153

RECREATION IMPACTS

The Colorado Front Range lies within a few hours driv- ing and hiking time of an urban population of more than two million people -the so-called Front Range Urban Cor- ridor. Within about two hours from Boulder, Denver, Fort Collins, and other centres it is possible by car to reach alti- tudes in excess of 3,500 m at about six different locations. By a combination of car and hiking, it is possible to reach treeline at many points within three hours and the Conti- nental Divide within five hours. Rocky Mountain National Park and Trail Ridge Road, which extends above timber- line for about 18 km, attract more than two million visi- tors a year. Until recently, however, this massive human impact has been confined to within a few metres of auto- mobile access (Willard and Marr, 1970). Rapid increase in hiking, back-packing, four-wheel drive and snowmobile use over the last twenty years has resulted in extensive back-country environmental degradation. Concern for the preservation of the beautiful mountain terrain extending southward from the southern boundary of Rocky Moun- tain National Park led to the formal establishment of the Indian Peaks Wilderness. This area, covering both sides of the Continental Divide, is about 300 km2 and contains alpine, subalpine, upper and lower montane ecosystems. According to United States law, formal designation of "wilderness" places severe restrictions on types of use. Specifically motor vehicles and permanent structures are excluded. When former President Carter signed the Indian Peaks Wilderness Act into law in November 1978, the Citi- zens Committee that had been created to help ensure for- mal designation of the Indian Peaks Wilderness was dis- banded since its task was assumed to be complete. While intensity of use in the wilderness area hardly approaches that experienced by many areas in the European Alps, in the last few years it has become apparent that day hikers and back-packers in sufficient numbers can degrade the

very area that they had actively campaigned to "preserve." Water pollution from too many and too close camp sites, trampling of vegetation, soil compaction, damage to trees, and scavenging of fallen wood for camp fires, have become

widespread phenomena (Hansen-Bristow et al., 1981). This discussion is limited, however, to the forest-alpine tundra ecotone, first because its special aesthetic characteristics attract high concentrations of recreation impact (Baum- gartner, 1983), and second because its very ecological sta- bility prompts conversion to instability with the introduc- tion of a new species in large numbers -Homo sapiens.

In the Colorado Front Range, the forest-alpine tundra ecotone is usually located at upper mid-slope on a moun- tain. It is precisely at this position that the middle and dis- tant views are especially attractive to the human eye; at higher levels the landscape perspective flattens out, while at lower levels views are restricted by the dense stands of coniferous forest. Less energetic visitors also can much more easily reach treeline than the summits of the high moun- tains. Also, within the ecotone the near view is especially attractive, given the pleasing alternation of tree cluster and open meadow, while some of the wind-deformed elfin wood

(Holtmeier, 1981) offer fantastic shapes (Figure 6). Where

small lakes are present the ecotone provides excellent camp sites with shelter, water, abundant camp-fire fuel, and mag- nificent distant views.

As part of a major study of the Indian Peaks area, with the objective of producing an environmental atlas (Ives and Dow, 1982), Ketchin (1980) made an intensive study of four of the most popular drainage basins. One aspect of this study involved determination of the existing physical impacts of recreational use. This involved assessment of

degree of trampling, effects of collection of wood for camp fires, mapping the total number, and variation in density, of fire pits according to popularity of camping sites, and the overall effects of recreational use on water purity. The study confirmed the earlier speculation, noted above, that where sections of the forest-alpine tundra ecotone contain small lakes, the impact of camping was severe and fire pits caused unsightly damage. At these altitudes the total stand-

ing and fallen dead tree biomass is much less than within the closed crown forest at lower elevations. In addition, removal of this material for camp fires is ecologically much more significant than removal of even greater amounts of dead wood from within the forest. This is largely because the dead wood in the ecotone serves the purpose of protect- ing living tissues downwind from wind blast, both directly by reducing the amount of abrasion from wind-blown ice and snow particles, and indirectly from inducement of lee- side snow drifting. Once the ecologically unaware, or un- concerned, camper has burned the fallen dead wood from within easy reach of his chosen camp site, the windward dead boughs on the elfin wood tree islands come under attack from the axe. Even green wood has been extensively cut in some of the more popular localities. An additional form of impact is the collection of some of the more fan-

tastically shaped dead boughs of elfin wood to adorn private gardens. This is particularly true of the few high-altitude stands of bristlecone pine (Pinus aristata) in the southern

part of the Indian Peaks area, and this is especially regret- table because these stands are between 1,000 and 2,000 years old in their present form, and much older when the

"migration factor" is taken into account.

FIGURE 6. The wind-deformed elfin wood offers fantastic shapes which are highly attractive to the human eye.

154 / MOUNTAIN RESEARCH AND DEVELOPMENT

It will be obvious from the foregoing discussion, from the estimate of the age of the tree islands, and from an understanding, albeit imperfect, of the dynamics and history of the forest-alpine tundra ecotone, that continua- tion of such practices by recreationalists will permanently impair the upper part of the ecotone. Even the lower part, where seedlings survive more frequently, and the upper- most section of the montane forest, will require a very long period for recovery from present human impacts. Also, as individual trees are lost, the rate of recovery will be further reduced since wind abrasion will be intensified. In effect, alpine environmental conditions will penetrate to lower alti- tudes. Since this entails heavy wind and drifting snow conditions for much of the year, re-establishment of forest, or tree island, conditions will be difficult. This situation is exemplified by the forest fire that occurred in about 1901 and swept through the ecotone on the south side of Niwot

Ridge. The upper part of the ecotone has experienced almost no seedling establishment in the intervening 80 years; even within the area originally occupied by closed forest, regrowth has been very limited.

Additional impacts from excessive recreational use include trampling, cutting, and loss of sections of the alpine tundra plant communities that form the other part of the ecotonal mosaic in conjunction with the tree islands. Damage to the vegetation mat at these altitudes, the low- est limit for occasional patches of permafrost (Ives and Fahey, 1971; Ives, 1973b), causes an acceleration of needle- ice development. This process produces a form of frost churning of the soil mantle which tears the roots of plants and severely inhibits revegetation. Thus an increase in bare soil cover can be predicted which will result in a reduction in alpine flowering species and an increase in source area for blowing sand.

CONCLUSION

The discussion presented above strongly supports the contention that while the timberline and forest-alpine tundra ecotonal landscapes of the Colorado Front Range remained little affected by human activity they were very stable on the scale of several thousands of years. Once human activity, in the present instance recreational activ- ity, develops to a significant degree instability replaces sta- bility. This takes the pattern of: (1) removal of tree forms from the upper ecotone which, under existing environ- mental conditions, survive largely by asexual or vegetative reproduction, and therefore, by definition, cannot replace themselves; (2) timberline being subjected to stronger winds and harsher environmental conditions which were once buffered by the ecotonal belt; and (3) cutting and removal of the intervening alpine tundra vegetation mat, thus causing increased needle-ice activity. For the alpine meadow communities the required time for recovery is dif- ficult to estimate. Willard and Marr (1970) estimate from 100 to more than 500 years, depending upon plant com- munity type (these estimates are based on studies of the effects of trampling along Trail Ridge Road but are ade- quate for the present discussion). Thus damage with a 100-year recovery interval can be defined as permanent since it far exceeds the average human life-span. Recovery from damage incurred within the ecotone and upper part of the montane forest will be at least as slow. Re-establish- ment of tree islands in the upper part of the ecotone, how- ever, will be virtually impossible under existing climatic conditions. A significant reduction in aesthetic qualities can be assumed. These remarks, however, infer recovery rates following cessation of impact. Where the impact is con- tinuing, and uncontrolled, the stage is set for extensive environmental instability.

While it is easy to overstate the case for fragility, or low resiliency (Webber and Ives, 1978) of the forest-alpine tundra ecotone and alpine tundra, more precise data and model- ling experiments are required (Marchand and Chabot, 1981). It would seem appropriate, however, to adopt the term resistance (Gigon, this issue, pp. 95-102) and conclude

that the forest-alpine tundra ecotone has become signifi- cantly less resistant as a consequence of stress imposed on an ecosystem (forest) that is close to its upper limits under natural conditions. The authors here are presently determining the timing of climatic change within the ecotone as well as mapping the macro-fossil evidence of a more extensive ecotone in the past. Nevertheless, damage to the upper ecotone tree forms can be predicted as termi- nal, and to the intervening tundra communities as long- lived.

Without awaiting the results of more detailed research there are certain immediate implications for wilderness area management. First, systematic mapping of degree and dis- tribution patterns of physical impact and long-term moni- toring would be an invaluable management tool. Second, some form of recreational use zoning should be considered whereby certain areas are allowed to become recreationally fallow for specific periods of time. Third, abolition of camp fires from the ecotone should become part of an immediate adjustment to the present management policy. Fourth, the careful selection of ecotonal sites with a view to total long- term protection from impact of any form should be ini- tiated. Thus some of these unique and especially beautiful areas could be preserved and enjoyed without the need to enter them on foot.

It is also necessary to be practical, in view of the fact that the United States Forest Service, custodians of the Indian Peaks Wilderness, are inadequately staffed either to undertake the proposed research or to police new policy such as that proposed here. Two complementary approaches are available to help reduce this problem. Policy which can be shown to have a rationale based upon scientific fact will be much more palatable to a significant proportion of wilderness area users. It follows from this that the facts and comments in this paper should be prepared for widespread communication among the user groups. Second, as in many mountain areas of the United States and other coun- tries, recreational organizations exist which have strong conservationist interests. With advice and encouragement

J. D. IVES AND K. J. HANSEN-BRISTOW / 155

they can be expected to make a large contribution toward moderation of the present trend toward instability, and the development of a form of sustained recreational use with-

out reduction in aesthetic qualities below a tolerable mini- mum.

ACKNOWLEDGEMENTS

The general views expressed in this paper evolved dur- ing field work in the Colorado Front Range over the last fifteen years. This work was in part supported by National Science Foundation grants under the auspices of the Inter- national Biological Programme-Tundra Biome and espe- cially by a NASA-PY grant to the first author (NGL-06- 003-200). In addition, special thanks are due to Messrs. Jim Ficke and Whitney Lerer, former District Forest Rangers, and their staff in Boulder, for their understand-

ing and encouragement, and to many members of local

REFERENCES Barry, R.G., 1973: A climatological transect along the east slope

of the Front Range, Colorado. Arctic and Alpine Research, 5(2): 89-110.

Barry, R.G. and Ives, J.D., 1974: Introduction. In Ives, J.D. and Barry, R.G. (eds.), Arctic and Alpine Environments. Methuen & Co. Ltd., London, pp. 1-13.

Baumgartner, R., 1983: The visual landscape of the Indian Peaks Area, Colorado Front Range, U.S.A. Mountain Research and Development, 3(1): 13-25.

Benedict, J.B. and Olson, B.L., 1978: The Mount Albion Complex. Research Report No. I, Center for Mountain Archeology, Ward, Colorado.

Gigon, A., 1983: Principles and typology of ecological stability and instability. Mountain Research and Development, 3(2): 95-102.

Hansen-Bristow, K.J., 1981: Environmental controls influencing the altitude and form of the forest-alpine tundra ecotone, Colo- rado Front Range. Doctoral Dissertation, Department of Geography, University of Colorado, Boulder, Colorado. 245 pp.

, 1982: Environmental factors influencing growth within the forest-alpine tundra ecotone, Colorado Front Range. Asso- ciation of American Geographers National Convention Abstracts, April, San Antonio.

Hansen-Bristow, K.J., Flack, J.E., and Plam, M., 1981: Bac- terial densities within recreational stream waters during sum- mer holiday weekends, Indian Peaks study area, Colorado Front Range. Great Plains-Rocky Mountain GeographicalJournal, 10.

Holtmeier, F. K., 1981: What does the term "Krummholz" really mean? Observations with special reference to the Alps and the Colorado Front Range. Mountain Research and Development, 1(3-4): 253-260.

Husted, W.M., 1974: Prehistoric occupation of the alpine zone in the Rocky Mountains. In Ives, J.D. and Barry, R.G. (eds.), Arctic and Alpine Environments. Methuen & Co. Ltd., London, pp. 857-872.

Ives, J.D., 1973a: Studies in high altitude geoecology of the Colo- rado Front Range: a review of the research program of the Institute of Arctic and Alpine Research, University of Colo- rado. Arctic and Alpine Research, 5(3, pt. 2): A67-A75.

,1973b: Permafrost and its relationship to other environ- mental parameters in a mid-latitude, high altitude setting, Front Range, Colorado Rocky Mountains. In: Permafrost, The North American Contribution to the Second International Conference, National Academy of Sciences, Washington, D.C., pp. 121-125.

wilderness groups. Much of the field work was based on the University of Colorado Mountain Research Station

during the first author's tenure as director of the Institute of Arctic and Alpine Research (1967-1979). Most recently, support for a continuing forest-alpine tundra ecotone study has been obtained from NSF Long-Term Ecological Re- search Project, grant no. DEB 8012095, to Dr. P.J. Web- ber. Thanks are due to Drs. Ralph Slatyer and Peter Wardle for valuable field discussions on the authors' forest-

alpine tundra ecotone hypothesis during May 1982.

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Issue Table of ContentsMountain Research and Development, Vol. 3, No. 2, Workshop on the Stability and Instability of Mountain Ecosystems. Berne-Riederalp, 14-19 September 1981 [Part One] (May, 1983), pp. 77-193Front Matter[Illustration][Illustration]Preface [pp. 77 - 78]Official Opening of the Workshop Address of Welcome [p. 79]Stability and Instability of Mountain Ecosystems: Introduction to a Workshop Sponsored by the United Nations University [pp. 81 - 94]Typology and Principles of Ecological Stability and Instability [pp. 95 - 102]Stability and Instability of Mountain Ecosystems: Definitions for Evaluation of Human Systems [pp. 103 - 111]Key Processes for Stability and Instability of Mountain Ecosystems: Is the Bottleneck Really a Data Problem? [pp. 113 - 119]Unstable and Vulnerable Ecosystems: A Comment Based on MAB Research in Island Ecosystems [pp. 121 - 123]Rural Development in Mountainous Areas: Why Progress Is So Difficult [pp. 125 - 129]Soil Erosion and Soil Formation in Agricultural Ecosystems: Ethiopia and Northern Thailand [pp. 131 - 142]Land Resources and Agricultural Utlization in Xizang Autonomous Region, China [pp. 143 - 148]Stability and Instability of Natural and Modified Upper Timberline Landscapes in the Colorado Rocky Mountains, USA [pp. 149 - 155]The Impact of Hydroelectric Power Plants on a Mountainous Environment: A Technique for Assessing Environmental Impacts [pp. 157 - 175]Mountain ChroniclesRenewable Resource Development in the Mountain Areas of the World Mohonk Mountain Seminar, 5-10 December 1982: An Interim Report [p. 177]Mohonk Mountain Seminar Resolutions [pp. 177 - 181]Photographs and Notes on Tourism and Deforestation in the Solu Khumbu, Nepal [pp. 182 - 185]ICIMOD: A New Centre for South-Central Asian Mountain Development [p. 186]MAZINGIRA: The International Journal for Environment and Development [p. 186]

Reviewsuntitled [pp. 187 - 188]untitled [pp. 188 - 189]untitled [p. 189]untitled [pp. 189 - 190]untitled [p. 190]untitled [p. 190]Books in Brief [p. 190]

Correspondence [pp. 191 - 193]Back Matter