Holocene Timberline Fluctuations in Jasper National Park, Alberta

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Article in Science · August 1983 DOI: 10.1126/science.221.4607.261 · Source: PubMed

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Michael Kearney Brian Henry. Luckman University of Maryland, College Park The University of Western Ontario

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The user has requested enhancement of the downloaded file. M. Klibanov and E. D. Morris, Enzyme Microb. er gas, N2; flow rate, 20 mUImn), following ing to 2500 to 3000 m above sea level. Technol. 3, 119 (1981). centrifugation of the aqueous solution (after the 16. K. Kay, Environ. Res. 6, 202 (1973); "Polychlo- peroxidase treatment) and chloroform extrac- Climatic data are sparse (2). Rainfall rinated biphenyls, a report by the Committee on tion. increases with elevation and ranges from Assessment of Polychlorinated Biphenyls in the 19. B. N. Alberti and A. M. Klibanov, Biotechnol. Environment" (National Academy of Sciences, Bioeng. Symp. 11, 373 (1981). 500 to 1000 mm per year (1300 to 5000 Washington, D.C. 1979). 20. Supported by grants from the Environmental 17. D. Sissons and D. Welti, J. Chromatogr. 60, 15 Protection Agency (R808619) and the M.I.T. mm of snowfall). The mean annual tem- (1971); 0. Hutzinger et al., Chemistry ofPCB's Sea Grant. The views expressed herein do not perature for Jasper (elevation, 1061 m) is (CRC Press, Boca Raton, Fla., 1982). necessarily reflect the opinion of the Environ- 18. 4,4'-Dichlorobiphenyl and 2,4,5-trichlorobi- mental Protection Agency and no endorsement 2.8°C, with July and January means of phenyl were determined by gas chromatography of that agency should be inferred. 15.2°C and - 12.2°C, respectively. The (180-cm glass column packed with Analab's Super Pak 20M; oven temperature, 160°C; carri- I February 1983; revised 4 April 1983 Maligne and Athabasca valleys lie primarily within the subalpine forest zone and are dominated by varying propor- tions of Picea engelmanni Parry (Engel- mann spruce), Abies lasiocarpa (Hook.) Holocene Timberline Fluctuations in Nutt. (subalpine fir), and Picea glauca Jasper National Park, Alberta (Moench) Voss (white spruce). The sum- mits and upper reaches of valleys in the Abstract. Pollen, fossil logs, and macrofossils from three high-elevation sites in Maligne Range are mantled by alpine the Maligne Range, Jasper National Park, Alberta, provide the first detailed record tundra. All the sites reported here lie of timberline fluctuations in the Canadian Rockies during the last 8700 years. above present timberlines (Fig. 1) (3) and Timberlines were much higher than at present between 8700 to 5200 years ago but are surrounded by heath (Cassiope spp.) oscillated significantly in elevation, with a major episode of timberline recession tundra communities intermixed with punctuating two periods of high timberline between about 6700 to 5900 and about stands of Salix arctica Pall (arctic wil- 8700 to 7000 years ago. Since 5200 years ago, regional timberlines have generally low). Occasional dwarf subalpine fir receded with perhaps brief reversals, reaching their lowest recorded positions (Abies lasiocarpa krummholz) occurs in sometime after 500 years ago. the vicinity of the Watchtower Basin site. Past fluctuations in the alpine timber- berta. These results provide a clearer Pollen cores recovered from the line have proved to be sensitive indices definition of the Holocene climatic his- Watchtower Basin and Excelsior Basin of Holocene climatic changes in several area, the Hyp- sites (4) provide the most complete and tory of this particularly on June 8, 2015 areas of North America (1). We report sithermal, than has been possible before continuous records of past timberline the results of what we believe to be the now and are compared with data for oscillations in this area. We reconstruct- first detailed investigation of Holocene other sites in the North American Cordil- ed the direction and magnitude of past timberline changes in the Canadian lera. timberline changes from ratios of select- Rockies based on pollen, fossil logs, and The Maligne Range forms the inter- ed pollen taxa, using regression equa- macrofossils recovered from three sites fluve between the Athabasca and Ma- tions derived from the relation between above the present timberline in the Ma- ligne rivers (Fig. 1) and consists of clas- altitude and modern surface samples ligne Range, Jasper National Park, Al- tic Cambrian and Precambrian rocks ris- (Fig. 2) (5). When plotted against eleva- www.sciencemag.org

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Timberline

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2 Z 0.1 - cc Awe g% /WB a*LEB Curve 1 Y=1838.19-108.17 In X r=- 91 S.E.1= * 33.3 m Curve 2 Y=2114.46+148.21 In X r= .92 S.E.9: 62.7 m 0.01 I." 14 16I 18 20 22 Elevation (102 m) Fig. 2. Elevational changes in Abies/Pinus pollen ratios (dots) from modem surface samples collected on Mount Edith Cavell, approximately 10 km south of Jasper. The regression line defined by curve 1 includes all samples above the timberline; curve 2 is based on all samples below the timberline; r = correlation coefficient; S.E.5 = standard error of the estimated value of y. Abies/Pinus ratios (trian- gles) for surface samples of the Watchtower Basin (WB) and Excelsior Basin (EB) cores Fig. 1. Sketch map of a part of Jasper National Park, showing the site locations. are shown for comparison. 15 JULY 1983 261 Table 1. Characteristics offossil logs recovered from sites above tree lines. ago when the timberline approached its modem limits. The rise in Sam- Lnt Diam- Cdt Num- Mean sharp apparent 14 ber timberline elevations at both sites after pie ple GenusLength Detamere C date ring Com- (years) of width ments - No. (cm) (m 5900 years suggests a substantial low- rings (mm) ering of timberline elevation. Peat accu- Watchtower Basin mulation was much slower (- 0.5 to 1.0 Wl Picea 244 11 (base) 8060 ± 90 (GSC-2615) 120 0.46 Complacent cm per century) at both sites during the W2 Picea 30 40* 7910 ± 70 (GSC-3226) - 60 - 0.33 late Holocene. The better-dated Watch- W3 Picea 50 8 8770 ± 80 (GSC-3195) 31 1.32 Very com- tower placent Basin record indicates timberlines Maligne Pass close to present levels until - 1600 years MPI Abies 470t 22 5920 ± 100 (BGS-566) 91 1.12 Tilted stem ago. Thereafter considerable retreat oc- MP2 Abies 353t 13 5260 ± 70 (GSC-3147) 150 0.56 curred, punctuated by two brief rever- *Estimated from curvature of rings. tRootstock attached. sals - 1000 and 500 years ago. Timber- lines reached their lowest recorded elevation sometime after 500 years ago. The palynologic evidence of higher tion on semilogarithmic paper, the Abiesi indicates that the site was closer to the timberlines between - 8500 and 5900 Pinus pollen ratios exhibit two linear timberline than it is at present-that is, years ago is confirmed by the presence trends (6), increasing up to the vicinity of timberline advanced toward the site. of spruce and fir needles in this interval the timberline and thereafter decreasing Conversely, higher apparent elevations of the Watchtower Basin core (Fig. 3) above the tree line. Using elevation as indicate that the timberline had receded and by logs recovered from this site and the dependent variable, we determined down-valley relative to its present posi- Maligne Pass (Table 1). The dimensions by least squares that elevational changes tion. Apparent elevation curves for both of these logs, complacent ring width pat- in these ratios (X) are best approximated sites are shown in Fig. 3. Dating control terns, and the presence of rootstocks in by Eq. 1 for the curves is based on the radiocar- some cases indicate that they were well- Y= 1838.19- 108.171nX (1) bon dates shown, the Mazama tephra developed standing trees, not krumm- [- 6600 years ago (7)], and interpolation holz, and were growing on or adjacent to above the timberline and by Eq. 2 from other dated sedimentary records at the bogs under quite favorable condi- Y = 2114.46 + 148.21 ln X (2) the sites. These data indicate that the tions. Data for the oldest log from the basal peats of these pollen cores date Watchtower Basin site (W3, Table 1) below the timberline. from - 8100 (Watchtower Basin) to 8500 suggest that the initial timberline ad- Past timberline changes are expressed (Excelsior Basin) years ago. vance predated the recovered pollen rec- as variations in site "apparent eleva- The apparent elevation data indicate ords. tion" (6). Apparent elevation changes that timberlines were much higher than The well-documented strong correla- are based solely on Eq. 1. Although a at present between - 8500 and 5900 tions of timberline elevations with cer- particular Abies/Pinus ratio may be repli- years ago (8). Two major periods of high tain summer isotherms (commonly the cated above and below timberline, both timberline may be identified dating from July 10°C isotherm) have long favored a pollen sites are well above the general - 8500 to 7000 and - 6700 to 5900 years temperature-related threshold as the ma- tree line and none of the fossil pollen ago in the more detailed Watchtower jor control of timberline elevation (9). ratios exceed the maximum ratio value Basin curve. These are separated by a We would discount fire as a probable near timberline. For sites above the pres- brief but well-marked period of timber- cause of the trends in Fig. 3 as there is ent timberline a lower apparent elevation line recession culminating - 6900 years little evidence from the logs, the sedimentary record, or the age characteristics of the present vegetation cover (10) Excelsior Basin Watchtower Basin Elevation (m) Elevation {m) to support frequent major fire activity. 2 2062 2162 1942 2042 2142 2242 Extended timberline fluctuations such as those demonstrated at these sites must have been related to climatic conditions. The data in Fig. 3 suggest a maximum displacement of - 200 m for timberlines during the last 8100 years. The inferred postglacial timberline history ofthe Jasper area parallels available Holocene timberline records for other Mazama ash sites in the Cordillera (1). A mid-Holo- cene timberline high stand, occurring between 9000 and 4500 years ago de- pending upon locale, is generally well 8450 * 170 (GSC documented in these chronologies and provides the most compelling paleobo- Fig. 3. Changes in the apparent elevation of the Watchtower Basin and Excelsior Basin sites. tanical evidence for a mid-Holocene Vertical lines drawn through the curves indicate the present apparent elevations of the sites. warm period or Hypsithermal. This evi- The horizontal on curves bars the are the confidence limits (.95 level) of the reconstructed dence contrasts with many elevational changes. Dashed lines indicate equivalent peaks in the curves. We corrected the Cordilleran Abies/Pinus ratios for the presence of grains ofthe high-altitude pine species Pinus albicaulis by pollen profiles, particularly from the subtracting from the unidentified pine sum the proportion of these grains found in the identified Northern Rockies, where the signature sum. of a Hypsithermal is often equivocal or 262 SCIENCE, VOL. 221 absent (11). The onset of generally cool- 10. M. S. Kearney, Can. J. Bot. 60, 2283 (1982). Albion Complex (Center for Mountain Archaeol- 11. R. N. Mack, N. W. Rutter, V. M. Bryant, Jr., S. ogy, Ward, Colo., 1978). er summers after 4000 to 5000 years ago, Valastro, Ecology 59, 956 (1978). 15. Y. C. Lin, C. Y. Fan, P. E. Damon, E. J. 12. L. J. Maher's [Abstr. INQUA. Congr. 2, 227 Wallick, Proc. 14th Int. Cosmic Ray Conf. 1975, indicated by the overall decline in tim- (1973)] reconstruction of a rise in vegetation 995 (1975). berline elevations (12), is compatible zones during the last 5000 years in the Colorado 16. M. Stuiver and P. D. Quay, Science 207, 11 Rockies is out of phase with this interpretation. (1980). with the Holocene glacial record of the However, S. A. Hall lGeol. Soc. Am. Bull. 88, 17. This research was supported by grants from the Cordillera, which shows an increasing 1593 (1977)1 has suggested that Maher's inter- Natural Sciences and Engineering Research pretation of fossil PicealPinus ratios may be in Council of Canada and the Geological Survey of incidence of glacial activity culminating error since comparison with modem pollen Canada. We thank K. B. Cawker, D. Crann, E. in the "Little Ice Age" advances of the spectra of the area support a general lowering of Zweck von Zweckenberg, and F. F. Dalley for vegetation belts and cooler conditions since assistance in the field. W. E. S. Blake provided last few centuries (13). 5000 years ago. 14C dates GSC-2615, -3147, -3195, and -3226. 13. J. M. Grove, Prog. Phys. Geography 3, 1 (1979). The Hypsithermal remains one of the 14. J. B. Benedict and B. L. Olson, The AMount 12 December 1982; revised 17 March 1983 most striking features of late Quaternary climate, and evidence is mounting in support of rapid and complex changes in temperatures during this period in western North America. Archaic settlement Ages Estimated from a Diffusion Equation Model for data from the Colorado Front Range (14) Scarp Degradation indicate major discontinuities in the settlement record of this area between Abstract. The diffusion equation derivedfrom the continuity equationfor hillslopes - 7000 and 6500 years ago and - 6000 to is applied to scarp erosion in unconsolidated materials. Solutions to this equation 5500 years ago, perhaps as a result of allow direct calculation ofthe product ofthe rate coefficient and the age ofthe scarp prolonged severe droughts. Analyses of from measurements of scarp morphology. Where the rate coefficient can be the annual rings offossil bristlecone pine estimated or can be derived from scarps of known age, this method allows direct snags from New Mexico (15) reveal ma- calculation of unknown ages of scarps. jor fluctuations in atmospheric 14C between - 8000 and 5000 years ago, with a In the past 25 years many efforts have and n = 1 (7). Slope wash on the rela- substantial departure - 7500 years ago. been made to mathematically model the tively short, steep slopes of scarps seems These variations in atmospheric 14C are evolution of hillslopes (1, 2). These mod- likely to conform to these values. Where thought to be proxy data for fluctuations els are constrained by the diversity and m = 0 and n = 1 the rate of downslope in solar activity (16) and therefore possi- complexity of natural hillslopes and by transport is simply proportional to the bly for climatic changes. We believe that difficulties in determining the ages of surface gradient. the complex and apparently episodic os- many landforms. Scarps in unconsolidat- Most models of hillslope evolution are cillations in summer temperatures exhib- ed materials are common landforms that based on continuity considerations and ited by the Jasper timberline record sup- are simpler than other kinds of hill- assume no change in density of the surfi- port the picture of a multiphase Hypsi- slopes. They often have specifiable ini- cial material (1, 2). This requires that the thermal. tial conditions, and they change fast change in elevation of a point be equal to M. S. KEARNEY enough to test the temporal predictions the difference between the amount of Department of Geography, University of mathematical models. Recent studies material transported to the point and the of Maryland, College Park 20742 of scarps (3-6), especially fault scarps, amount of material transported away B. H. LUCKMAN have produced many measurements of from it, or Department of Geography, scarp morphology (Fig. IA). The pur- ay_ as University of Western Ontario, pose of this report is to explicitly solve (2) London, Ontario N6A 5C2, Canada the diffusion equation for scarp bound- at ax ary conditions and to demonstrate how Combining the continuity equation (Eq. References and Notes the solution can be used to estimate 2) with the dependence of downslope 1. V. C. LaMarche, Quat. Res. (N. Y.) 3, 632 scarp age. transport on surface gradient (Eq. 1 with (1973); L. J. Maher, Jr., ibid. 2, 531 (1972); J. T. Andrews, P. E. Carrara, F. B. King, R. Stuck- Changes in the morphology of scarps m = 0 and n = 1) gives the diffusion enrath, ibid. 5, 173 (1975). in unconsolidated deposits are controlled equation 2. B. Janz and D. Storr. The Climate ofthe Contig- uous Mountain Parks: Banff, Jasper, Yoho, by transport-limited processes, primarily ay a2y Kootenay (Canadian Atmospheric Environment soil creep, raindrop impact, and slope Service, Toronto, 1977). at = Cd 2 (3) 3. Excelsior Basin (elevation, 2150 m) and Maligne wash. For these processes the supply Pass (elevation, 2300 m) are approximately 100 m above the present timberline, whereas Watch- rate of loose debris is not a controlling This equation is well known as a descrip- tower Basin (elevation, 2200 m) is about 125 m factor, and process rates are generally tion of many processes in chemical diffu- above the present limits. All three sites are located in closed bedrock depressions. proportional to powers of the slope dis- sion, conductive heat flow, and flow 4. The cores were recovered with Hiller (Excelsior tance and the sine or tangent of the slope through porous media. Equation 3 has Basin) and Livingstone (Watchtower Basin) cor- ers. angle (2): also been derived for a variety of slope 5. M. S. Kearney, in preparation. models (1, 2), including several for scarp 6. L. J. Maher, Jr., Geol. Soc. Am. Bull. 74, 1485 (1963). evolution (4, 8). For scarp boundary 7. J. A. Westgate, Can. J. Earth Sci. 14, 2593 axn (1) finite (1977). conditions it has been solved by 8. Although these two curves correspond closely where S is the rate of downslope trans- difference methods (4) and by analytical in shape, the apparent elevations are relatively lower throughout the Excelsior Basin record. port, c is a rate constant, x is horizontal methods (8) similar to those presented This probably reflects slight differences in the distance, and y is elevation. For raindrop here. configuration of the valleys. Greater emphasis is- placed on the more detailed and better-dated impact and creep processes, which are The diffusion equation applied to Watchtower Basin core in the discussion. the dominant processes on many scarps, scarps implies that the change in eleva- 9. P. W. Wardle, in Arctic and Alpine Environ- ments, J. D. Ives and R. G. Barry, Eds. (Methu- m = 0 and n = 1 are generally accepted tion of a point is proportional to the en, London, 1974), p. 371; W. Tranquillini, at Thus Physiological Ecology of the Alpine Timberline (1, 2). For slope wash m and n may vary profile curvature that point. with (Springer, Berlin, 1979). considerably, but in some cases m = 0 time the crest and the toe become round- 15 JULY 1983 263

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