The Albedo of Selected Subarctic Surfaces

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The Albedo of Selected Subarctic SurfacesAuthor(s): D. E. Petzold and A. N. RenczSource: Arctic and Alpine Research, Vol. 7, No. 4 (Autumn, 1975), pp. 393-398Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1550183 .

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Arctic and Alpine Research, Vol. 7, No. 4, 1975, pp. 393-398 Copyrighted 1975. All rights reserved.

THE ALBEDO OF SELECTED SUBARCTIC SURFACES

D. E. PETZOLD* AND A. N. RENCZt

ABSTRACT

Dominant plant communities and exposed ed in the surface classification are sites in various earth surfaces of an eastern Canadian subarctic stages of regeneration after disturbance. The locality are classified and sampled with respect results of sampling exposed earth surfaces follow to shortwave radiative albedo. The physiologi- certain predictable patterns in that progression cal significance of the albedo variations of the from visual darkness to lightness corresponds to dominant lichen, Cladonia alpestris, with differ- increasing reflectivities. The mean albedo of all ent habitats is discussed. The albedos of the natural surfaces near Schefferville, Quebec, is major vegetation types are summarized. Includ- estimated to be 0.166.

INTRODUCTION

The term albedo, a, is used to denote the characteristic surface reflectivity of radiation in the range 0.3 to 3.5 microns (visible through infrared) and is expressed as the decimal frac- tion of reflected to incident global solar radiation. In general, the albedo of a surface depends upon its color, moisture condition, density and distribution of its components, leaf orientation (in the case of a vegetated surface), and solar elevation. Albedo generally increases with the visual brightness of the surface and decreases with the darkening effect caused by moistening.

Knowledge of such a surface property is fundamental to the determination of energy and moisture budgets of macroscale studies, which may involve the entire earth or any large geo- graphical unit, down to microscale investigations of plant communities or, indeed, individual plants. Differences in water use by plants may be explained in part by differences in their

physical properties, such as albedo (Fritschen, 1966). The total radiant energy available at the earth's surface for meteorological processes, termed net radiation, is a function of albedo by definition.

In the past, considerable albedo data has been collected for agricultural surfaces, forests, soils, snow, and ice. Because we know of only a few broadscale investigations in eastern subarctic Canada (Jackson, 1960; Davies, 1962), detailed microscale studies of the albedo of common surface types were undertaken in the Scheffer- ville, Quebec, area (54043'N, 67?42'W) from July 24 to August 5, 1974. A classification of the vegetation was devised and albedo measurements were then taken on representative surfaces within the vegetated types and on exposed nonvegetated surfaces, a major component of the Schefferville area.

SAMPLING TECHNIQUES

Representative surfaces were selected accord- ing to their frequency of occurrence and ease of identification. Usually between 15 and 20 sites representing one surface were chosen to derive

*Department of Geography, McGill University, Montreal, Quebec.

tDepartment of Biology, McGill University, Montreal, Quebec.

a mean albedo for that surface. A portable, hand-held apparatus was constructed to sup- port the equipment used to measure albedo. Two recently calibrated Lintronic Dome Solarimeters, sensitive to shortwave radiation in the range 0.3 to 3.5/u, were mounted level to the end of a 4.5-ft (1.38-m) long wooden dowel, one facing up to the sky, the other facing down. The other end of the timber was held and maintained level

D. E. PETZOLD AND A. N. RENCZ /393



with a small hand level so that the sensors were approximately 1 ft (0.3 m) above the surface. The output from the sensors was measured on a multichannel Comark millivoltmeter. Once a constant sky condition was attained, pairs of readings were taken until close agreement was reached. To minimize observation error associ- ated with instantaneous readings, measurements were taken on either completely overcast or clear

days. To eliminate albedo variations due to changing solar elevations, all measurements were taken within 1 hr of solar noon (approximately 1230 EDT).

Two quadrats of 2.5 sq. ft. (0.25 m2) were used to estimate plant cover. The species were subjectively given a percentage cover by looking straight down at the vegetation.

TABLE 1

Vegetation classification by habitat, species, and common name

Vegetation type Surface type (% cover) Common Name

I. Lichen tundra-Xeric community of bare rock and lichen above the tree line; stunted black spruce occasionally present.

1. Cladonia alpestris (~ 100%) 2. Cetraria ericetorum (,- 100%) 3. Stereocaulon paschale (100%) 4. Dicranum fuscescens (100%) 5. Picea mariana (100%)

II. Heath lichen tundra-similar to lichen tundra except that increased moisture allows for complete vegetation cover and invasion of heath shrubs.

1. Alectoria ochroleuca (42%), A. nigricans (4%), Cetraria cucullata (9%), C. ericetorum (3%), C. alpestris (38%), Vaccinium vitis-idaea (4%).

III. Bog-hydric lowland feature with thick peat layer and carpets of sedge and moss. a. String bog 1. Raised edge: Carex sp. (90%), Eriophorum sp.

(4%), Moss sp. (5%), Betula glandulosa (2%). 2. Depressed interior: Carex sp. (22%), Kalmia

polifolia (2%), Aulacomnium palustre (31%), Smilacina trifolia (2%), Standing water (42%).

b. Sedge moss bog 1. E. russeolum (60%), Standing water (40%). IV. Meadow-mesic habitat with abundant sedge and moss growth; frequently

adjacent to lakeshores. 1. Sedge moss meadow: Polytrichum juniperinum

(73%), Carex kelloggii (19%), S. paschale (8%). 2. Sedge moss shrub meadow: Carex sp. (25%), B.

glandulosa (12%), Vaccinium uliginosum (13%), Moss sp. (50%).

3. Moss sedge meadow: C. lenticularis (83%), Sphagnum sp. (17%).

V. Woodland-coniferous forests with moss or lichen understory. 1. Black spruce lichen foresta: C. alpestris (85%),

C. mitis (4%), S. paschale (2%), Shrubs (9%). 2. White spruce moss forest-Not sampled. 3. Tamarack spruce sphagnum forest-Not sampled.

VI. Disturbed areas-man-made and natural disturbances. 1. Fire

(i) 1-year-old burn: Shrubs (2%), Ash and soot (98%).

(ii) 28-year-old burn: V. angustifolium (17%), Cladonia sp. (32%), S. paschale (2%), Festuca ovina (2%), Ash surface (2% ).

2. Graded surface: Epilobium angustifolium (77%), Calamagrostis canadensis (23%).

Reindeer moss Lichen Lichen Moss Krumholz

Lichens

Lichen, cranberry

Sedge, cottongrasses, moss, birch Sedge Bog laurel, moss, Lily, water Cottongrass, water

Moss Sedge, lichen Sedge Birch, blueberry Moss Sedge Sphagnum moss

Reindeer moss Lichens, shrubs

Shrubs, ashes

Billberry Lichens Grass, ashes Fireweed (in bloom) Grass

alncludes species composition of only understory vegetation.

394 / ARCTIC AND ALPINE RESEARCH



CLASSIFICATION OF SURFACE TYPES AND RESULTS

Since Schefferville lies within the boreal forest, the dominant vegetation type is coniferous woodland. Although forests dominate the landscape, there is a diverse assortment of plant communities due to the wide range of habitats. Above 2,400 ft (738.5 m) a.s.l., continuous tree growth ceases, giving rise to alpine tundra environments.

In the present study six vegetation types which are representative of the area were identi- fied for albedo measurements. Within each of the broad vegetation types, several surfaces have been sampled. Table 1 describes the physiog- nomy and species composition of the vegetation types and Table 2 lists the mean albedo and its standard deviation for the same surfaces.

Due to the extensive documentation of forest and water albedos (Jackson, 1960; Davies,

1962; Sellers, 1965; Reifsnyder and Lull, 1965; Nunez et al., 1971; and others) readings were not taken for woodland spruce or lakes.

Mention should be made of the various conditions of C. alpestris sampled in this study (surface types I.la, b, c, d, and V.lc). Three habitats were discerned: tundra, woodland, and tundra within the dust fallout of a nearby open pit mine. The areas sampled at the latter site were stained pinkish brown and the thalli (lichen bodies) near the bottom of the mat were probably dying. Due to the extremely hygroscopic nature of this lichen and the physical changes as- sociated with water absorption, a series of measurements was taken during and after rainy periods for comparison to that of the dry state.

Readings were also taken from disturbed en-

TABLE 2

The albedo of vegetated surfaces

Predominant Sites Standard Vegetation type Surface type color sampled 'a deviation

I. Lichen tundra la. C. alpestris (dry)a off-white 19 .223 .037 b. C. alpestris (tinted,

dry)a pink/brown 26 .167 .027 c. C. alpestris (wet)a pale green 24 .221 .029 d. C. alpestris (tinted,

wet) a dull light brown 16 .176 .008 2. C. ericetorum (dry) dull black 16 .121 .012 3. S. paschale (dry) gray 10 .256 .003 4. D. fuscescens dark green 5 .147 .007 5. P. mariana green 8 .158 .009

II. Heath lichen tundra 1. Total site sampled pale green 12 .209 .010 III. Bog

a. String bog 1. Raised edge green 16 .178 .009 2. Depressed interior light green (water) 16 .125 .010

b. Sedge moss bog 1. Total site sampled green (water) 16 .109 .015 2. Water surfaceb .071

IV. Meadow 1. Sedge moss bronze, green 14 .155 .010 2. Sedge moss shrub green 11 .182 .010 3. Moss sedge green 16 .181 .002

V. Woodland 1. Black spruce lichen .122 forest (total site)c

la. B. glandulosad green 34 .168 .013 b. Salix sp. green 16 .214 .009 c. C. alpestris (dry)a off-white 25 .264 0.20

VI. Disturbed sites 1. Fire- (i) 1-yr-old burn black 16 .069 .006

(ii) 28-yr-old burn green 16 .189 .015 2. Graded surface green, purple 16 .219 .011

aDwarf birch nearby. bNunez et al. (1971, p. 62), for solar elevation of 52 to 55?. eDavies (1962, p. 37), integrated value for trees and lichen mat. dC. alpestris beneath shrubs.

D. E. PETZOLD AND A. N. RENCZ/ 395



vironments that are now being revegetated. Findlay (1966) estimates that 55% of the land area around Schefferville has been burned in the last 25 years. This observation is also valid for subarctic regions of Ontario (Rouse and Ker- shaw, 1971) and Saskatchewan (Pruitt, 1959). The present study has sampled a 1-year-old burn and a 28-year-old burn with a regenerating forest floor. There is also a significant percentage of the landscape that is in various stages of regeneration after mining exploration which is accounted for by surface VI.2.

In addition to vegetated surfaces, nonvegetated surfaces were also sampled since an extensive amount of the landscape is scarred by open pit iron ore mines. Albedos of the most common ore colors were sampled in both the west and dry

states and the colors have been recorded accord- ing to standard Munsell notation. The results of these measurements appear in Table 3 under the classification of exposed earth surfaces. This category also includes three naturally occurring exposed surfaces that are also easily discernible: mud (silt), exposed slate bedrock, and frost scars.

To complete the study, two values have been added to Table 2 from previous work. One is for water surfaces with a solar elevation of 52 to 55?, which corresponds to the solar angle at solar noon during the period of the present study. The other is Davies's (1962) value for an open woodland calculated from airplane flights over various woodland densities.

DISCUSSION Although the primary purpose of this study

was to present a table of representative subarctic albedos, several points of interest have emerged. In particular several of the results illustrate the unique composition of lichens. The lichen thal- lus consists of an outer fungal layer in a symbi- otic relationship with an inner layer of fungi and algae which is the photosynthetic component of the organism.

In its natural state C. alpestris is quite a de- ceiving surface to the human eye. From the air, thick mats of this lichen could easily be mistaken for snow. However, the recorded albedos indicate that this species absorbs a relatively high percentage of incident solar radiation. Natural, dry C. alpestris on the tundra and in the woodland exhibit albedos of 0.223 and 0.264, respec- tively. This compares favorably to a few spot readings taken by Davies (1962) which yielded a mean value of about 0.21 for C. alpestris in an unspecified area. These values are very close indeed to that for any short green vegetated surface of 0.25 as concluded by Monteith (1959).

These results indicate that light conditions are only slightly less favorable for lichens compared to other green plants; that is, there are almost equal amounts of light energy available for photosynthesis in both cases. Ertl (1951) con- cludes that light absorption of lichen pigments is equal to that of pigments in the leaves of green plants. It is probably these pigments that im- part the low albedo readings to this species.

Table 2 also shows that the reflectivities differ from tundra to woodland environments. These results may be the consequence of the more favorable growing conditions in the woodland since the amount of decaying (dark colored) matter in the lichen mat would be decreased.


The results may also be a response to the increased sunlight in the tundra environment in the following way. Quispel (1959) reports that the production of lichen acids increases with an increase in sunlight. Since these acids are effec- tive in increasing light absorption (Hale, 1967), there is less solar radiation that can be absorbed by the inner algal layer. This serves as an im- portant adaptive advantage as the inner algal component of the lichen may be very sensitive to high sunlight (Kappen, 1973). In the open environment where the inhibitory effects of high sunlight to the photosynthetic process would be maximized, there is a higher percentage of light being absorbed by the outer cortical layer. This adaptation will decrease the amount of sunlight that is available for absorption by the algal component.

Another point concerning C. alpestris is the consistency in albedos between a wet and dry mat. A slight darkening in color is noticed in the transition from the dry to wet state; however, a large decrease in reflectivity did not occur.

The presence of standing water in depressed areas of a string bog definitely has a lowering effect on the albedo of the whole surface. The sedge growing in standing water was noticeably lighter in color than that growing in raised areas of the bog. however its albedo was relatively more than 30% lower. These results contradict Davies's (1962) hypothesis that although "a relatively continuous water layer covered the surface layer of the bog, the grass growth shaded it, thus the effect of the water surface is not great." Of course, the albedo of bog areas will greatly depend upon the amount of water present, a condition that varies considerably from month to month.



TABLE 3

The albedo of exposed earth surfaces

Wet Dry

Color Munsell Standard Color Munsell Standard Surfacea number a deviation number a deviation

Mud (silt)b red black 10R2/1 .066 .016 Boulders (ore) various .086 .010 Slate bedrock various .120 .005 Gravel (<2cm) dark red brown 2.5R3/3 0.98 .007 orange 2.5YR6/8 .170 .016 Frost scare various .139 .012

Ore/Ore Dumps

Structure Size <4 cm very dark red brown 7.5R2/3 .098 .005 <4 cm dark red 7.5R3/6 .111 .008 dull red brown 7.5R4/3 .127 .009 <4 cm bright red brown 5YR5/8 .115 .005 bright brown 2.5YR5/6 .158 .004 <4 cm orange 5YR6/8 .120 .008 orange 75YR7/6 .181 .002 <3 cm bright yellow brown 10YR6/8 .153 .012 <4 cm gray white N8/0 .201 .006 gray white N8/0 .273 .011

a 16 sites sampled unless noted. bl 1 sites sampled. c15 sites sampled.



The results of the ore sampling followed certain predictable patterns. The progression from visual darkness to lightness of the soil surface corresponds well with the progression from lowest to highest albedos, in both the wet and dry states. In every case, a marked relative increase, in the order of 15 to 74%, occurred on drying. These results correspond well with those presented by Geiger (1966) and Idso et al. (1975).

Findlay (1966) estimates the natural surfaces in the Schefferville area are comprised of the following: woodland (63%), lichen tundra (13%), bogs (1%), and lakes (23%). Mea- dows are relatively uncommon and regenerating areas disturbed by fires would be classified as tundra. For peak radiation hours in summer,

ACKNOWLEDGMENTS The field work for this study could not have

been completed if it were not for the patience and steady hand of Mr. S. Kelly. Funds for the study were provided in part by the Province of Quebec Department of Education.

REFERENCES

Davies, J. A., 1962: Albedo measurements over sub-arctic surfaces. McGill Sub-Arctic Res. Pap., 13: 1-86.

Ertl, L., 1951: utber die Lichtverhaltnisse in Laub- flechten. Planta, 39: 245-270.

Findlay, B. F., 1966: The water budget of the Knob Lake area. McGill Sub-Arctic Res. Pap., 22: 1-96.

Fritschen, L. J., 1966: Evapotranspiration rates of field crops determined by the Bowen ratio method. Agron. J., 58: 339-342.

Geiger, R., 1966: The Climate Near the Ground. Harvard Univ. Press, Cambridge. 611 pp.

Hale, M., 1967: The Biology of Lichens. Arnold, London. 176 pp.

Idso, S. B., Jackson, R. D., Reginato, R. J., Kim- ball, B. A., and Nakayama, F. S., 1975: The dependence of bare soil albedo on soil water content. J. Appl. Meteorol., 14: 109-114.

about 80% of the incident solar energy would be absorbed by tundra areas (due to the predomin- ance of surface type II.1) and 93% for lakes. The value for woodlands would be approximately 88%, however the value may vary with tree density and amount of lichen on the forest floor. Bogs in the area are mainly type III.a, indicating a mean absorptivity of about 85%. Applying these values to the frequency of occurrence of the surface types results in a mean absorptivity of 83.4% for this region (or a mean albedo of 0.166). Mining areas are characterized by pre- dominantly red colors, gray-white minerals are relatively uncommon. This indicates 85 to 89% shortwave absorptivity depending on the moisture conditions of the surface.

Jackson, C. I., 1960: Estimates of total radiation and albedo in sub-arctic Canada Arch. Meteorol. Geophys. Bioklimatol., 10: 193-199.

Kappen, L., 1973: Response to extreme environments. In Ahmadjian, V. and Hale, M. E. (eds.), The Lichens. Academic Press, New York, 311- 380.

Monteith, J. L., 1959: The reflection of short-wave radiation by vegetation. Quart. J. Roy. Meteorol. Soc, 85: 386-392.

Nunez, M., Davies, J. A., and Robinson, P. J., 1971: Solar radiation and albedo at a tower site. Can. Dept. Environ., Great Lakes Div., Rep. 3. 82 pp.

Pruitt, W O., 1959: Snow as a factor in the eco- logy of caribou. Arctic, 12: 159-179.

Quispel, A., 1959: Lichens. Encyclopedia of Plant Physiology, 2: 577-604.

Reifsnyder, W. E. and Lull, H. W., 1965: Radiant energy in relation to forests. U. S. Dep. Agric. Tech. Bull., No. 1344, 111 pp.

Rouse, W. R. and Kershaw, K. A., 1971: The effects of burning on the heat and water regimes of lichen-dominated sub-arctic surfaces. Arct. Alp. Res., 3: 291-304.

Sellers, W. D., 1965: Physical Climatology. The University of Chicago Press, Chicago. 272 pp.

Ms submitted February 1975




Documents

The Albedo of Selected Subarctic Surfaces