Late-Glacial and Postglacial Vegetation and Climate of Jackson Hole and the Pinyon Peak Highlands, Wyoming

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1 University of Wyoming National Park Service Research Center Annual Report Volume 11 11th Annual Report, 1987 Article Late-Glacial and Postglacial Vegetation and Climate of Jackson Hole and the Pinyon Peak Highlands, Wyoming Cathy W. Barnosky Carnegie Museum of Natural History Follow this and additional works at: Recommended Citation Barnosky, Cathy W. (1987) "Late-Glacial and Postglacial Vegetation and Climate of Jackson Hole and the Pinyon Peak Highlands, Wyoming," University of Wyoming National Park Service Research Center Annual Report: Vol. 11, Article 10. Available at: This Grand Teton National Park Report is brought to you for free and open access by Wyoming Scholars Repository. It has been accepted for inclusion in University of Wyoming National Park Service Research Center Annual Report by an authorized editor of Wyoming Scholars Repository. For more information, please contact

2 Barnosky: Late-Glacial and Postglacial Vegetation and Climate of Jackson Ho rate-glacial AND POS"roo.ACIAL VEnErATION AND CLIMATE OF JACKSON HOLE AND '!HE PINYON PEAK HIGHlANDS, WYOMING Cathy W. Barnosky Carnegie Museum of Natural History Pittsburgh, PA Objectives 'Ibe objective of this study has been to describe the late-q.laternary vegetation of the Jackson Hole region and vicinity in order to clarify the nature and composition of ice-age communities, the rate and direction of plant migration during the recession of glaciers from the region, and the long-term stability of connnunities in the Park to envirormental changes in the postglacial period. 'Ibis information is necessary to assess the sensitivity of the Park's comrmmities to envirormental change and fill a critical gap in our understanding of the vegetational, climatic, and glacial history of the north-central Rocky Mountains as a Whole. Methods A detailed discussion of the nethodology for this study is included in the UW-NPS Research proposal and therefore will not be repeated here. Continuous pollen records from dated lake-sediment cores are the primary data base in this project. 'Ibese records have been obtained from a transect of lake sites extending from the southern margin of the former Yellowstone ice field to the ice divide (see Table 1 for site information). Pollen percentages, pollen accumulation rates (when possible), and the presence of plant macrofossils are used to trace the developmnt of forest within the deglaciated area. Radiocarlx>n age determinations of the sediment and petrographic identification of known ash layers within the cores provide a chronologie fram\\ork to help correlate the pollen profiles between sites. Central to the paleoenvironmental reconstruction is a knowledge of the rocxlern pollen rain and its relation to the present-day vegetation and climate. Accordingly, a second goal of the research has been to study the pollen rain from different vegetation types and at a variety of elevations in the GTNP region. These results sqpplernent those published from Yellowstone Park (Baker 1976) and the Snake River Plain (Iavis t981). Many studies of regional pollen rain have suffered from the fact that different types of sites (e.g. lake sediments, soil, moss polsters) were sampled and compared, even though their pollen-trapping characteristics are known to vary greatly. In the current project, only lake surface sediments were collected, so that the results could be co~red directly with the fossil record Published by Wyoming Scholars Repository,

3 University of Wyoming National Park Service Research Center Annual Report, Vol. 11 [1987], Art Table 1. Information on Fossil Pollen Sites Site Location Water depth Length of 14C dates/depth Volcanic/Depth and at coring site c ore (yr B.P.) (m) ashes /(m) elevation (m) (m) (m) Mariposa Lake, 48 09'N,110 17'W ,458_!90 I Glacier Pk B I 4.32 Yellowstone N.P , I ,570I110 I Emerald Lake, 44 04'N,110 17'W , I Mazama I 3.30 Teton National , I Glacier Pk B I 5.20 Forest 10,700I110 I Divide Lake, 43 46'N,l10 14'W ,970_!80 I Glacier Pk B I 3.05 Teton National ,800_!90 I Forest 11,840_!110 I * Fallback Lake, 43 58'N,110 26'W , I Glacier Pk? I 4.69 Teton National ,o1oi120 I * Forest 12, I * 15,640I160 I * I U1 0\ I Two Ocean Lake 43 54'N,110 32'W o.o ,330_!120 I Fen, Grand 2124 Teton N.P. Lily Lk 46 12'N,110 19'W , 720_!70 I Mazama I ,010_!50 I I Lily Lk Fen 46 12'N,110 19'W o.o ,170.±.170 I Mazama I ' 10, I Glacier Pk B I ,130I110 I ,370.±.120 I ,040.±.220 I Hedrick Pond, 43 45'N,110 36'W , I Glacier Pk B Grand Teton N.P ,210+8o , I * 14,580I150 I * 17,160_!210 I * *Judged too old because Glacier Pk 8 (ca yr B.P.) lies stratigraphically below sample. 2

4 Barnosky: Late-Glacial and Postglacial Vegetation and Climate of Jackson Ho Results Pollen ~tra from surface ~les collected at different altitudes in the GTNP region correlate fairly well with the broad vegetation zones. The stronjest discrimination is between sites in open vegetation and those in closed forest, but within the forest the pollen signatures from upper- and lower-elevation communities are distinctive. Certain pollen types are good indicators of local plant presence, including Pseudotsuga and Populus. Other types are suggestive of particular vegetation types (e.g., Polygonum bistortoides-type pollen is indicative of subalpine vegetation) Fossil _percentage data for Lily Lake and Lily lake Fen, Divide lake, Emerald Lake, Mariposa, Hedrick Pond, and Fallback lake reveal a stratigraphy record that is similar, although variable in detail: Herb phase (>11,200 yr B.P.). This pollen assemblage is characterized by high percentages of Artemisia, Gramineae, and Cyperaceae pollen. Nonarboreal pollen accounts for most of the pollen. Artemisia percentages exceed 40% at many levels, Gramineae accounts for 5-15% of the pollen, and Cyperaceae for 2-10%. Salix is present in small percentages, as is Juniperus pollen. The sediments containing the herb phase are inorganic silts and clays, deposited when the productivity of the lake was low. Conparison with nodern pollen data suggests that this phase \\as a period of alpine parkland and rooadow couummities with few trees in the vicinity of the lake. Birch-Juniper phase (ca. 11,200-ca. 11,100 yr B.P.). '!his pollen phase is characterized by high percentages of Betula and Juniperus and a decline in the abundance of Artemisia, Gramineae, Cyperaceae, and other nonarboreal pollen. Macrofossils in this phase identify Betula glandulosa as the likely contributor of birch pollen. At Lily lake Fen, Divide lake, and ~rald Lake, Juniperus pollen precedes the increase in Betula pollen: at Mariposa Lake, Fallback lake, and Hedrick Pond, these ~ies appear concurrently. Spruce phase ( <11, 100-ca. 10,000 yr B.P.). Picea becorres irrportant at the errl of the birch-juniper phase. Its percentages rise sharply from 15-40% at all sites and associated needles of Picea engelmannii were found at several sites. Selaginella densa spores 1.nply dry cpen ground, but the persistence of Betula and Salix pollen suggests unstable wet substrates as well. S ruce-fir Ha lox lon ine hase (<10,000-ca r B.P.>). Percentages of Abies and Pinus (haploxylon-type increase toward the end (top) of the spruce phase, reaching values of 5-15%. Whitebark pine is the likely contributor of haploxylon-type pine, although limber pine may have been present as well. The pollen assemblages suggest the establishnent of a subalpine forest similar to the Spruce-Fir-Whitebark pine forest at high elevations in GTNP today Published by Wyoming Scholars Repository,

5 University of Wyoming National Park Service Research Center Annual Report, Vol. 11 [1987], Art. 10 Diploxylon pine-ibuglas-fir phase (<ca yr B.P., >6700 yr B.P.). Percentages of diploxylon pine pollen increase to 45% at many sites and are attributed to lodgepole pine. Percentages of Pseudostuga, Populus, Cyperaceae, and Shepherdia are significant at some sites. The vege tation was probably closed lodgepole forest at all sites, with Douglas-fir and Populus present at Lily Lake, Hedrick Pond, and possibly Divide lake. Diploxylon pine phase ( <6700 yr B.P.) The final phase shows increasing values of diploxylon pine pollen at most sites and records the developnent of the nodern pine forest. At Emerald and Divide lakes, Abies and haploxylon pine percentages increase along with diploxylon pine and suggest the spread of subalpine fir, lodgepole pine, and whitebark pine locally. Conclusions The results of this study bear directly upon our understanding of the relation between pollen rain and vegetation, as well as on past vegetation and climate in the north-central Rocky Mountains. The main points of the fossil study can be summarized as follows: 1. Radiocarbon dates from Lily Lake Fen, Errerald Lake, Divide Lake, and Mariposa Lake suggest that retreat of the ice from the Pinyon Peak Highlands began as early as 60,000 yr B.P. and was conpleted before 11,200 B.P. 2. The major conifer species in the Pinyon Peak Highlands apparently migrated into the region from the south, after 11,200 yr B.P. Engelmann spruce arrived first at ca. 11,100 yr B.P. and was present at all sites within about 500 years. Whi tebark pine and subalpine fir were present as early as 10,400 yr B.P. and spread throughout the region in an equally short tine. 3. The pollen data indicate that the early Holocene climate was warner and drier than that of today. Under this climatic regine, Douglas-fir, lodgepole pine and Populus were able to grow above their current elevational limits. This inte~retation is s~ported ~ paleoclimatic model simulations that show that the Subtropical High, which typifies presentday summer circulation, was enhanced between 12,000 and 8000 yr B.P. The response in the north-central Rocky r-buntains was summer temperatures warner than tcxlay' s and decreased effective moisture. 4. A return bo cool relatively moist conditions is registered i n the middle Holocene by the increase in Picea, Abies, and haploxylon pine pollen. Fbrests in the Pinyon Peak Highlands becarre more open in the late Holocene, perhaps as a result of

6 Barnosky: Late-Glacial and Postglacial Vegetation and Climate of Jackson Ho changing fire frequency or climate. Literature Cited Baker, R. G Late Quaternary vegetation history of the Yellowstone Basin, Wyoming. u.s. Geol. Surv. Prof. Paper 729-E. Davis, 0. K Vegetation migration in southern Idaho during the Late Quaternary and Holocene. Ph.D. Diss., Univ. of MN, Minneapolis Published by Wyoming Scholars Repository,