Climatic and Ecological Implications of Shrub-Chronologies at Rock Glacier Sites of the Eastern Sierra Nevada Range, California, U.S.A.
AuthorFranklin, Rebecca Sara
AdvisorHughes, Malcolm K.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractHerb- or shrub-chronology, a technique adapted from dendrochronology, is the study of the annual growth rings in roots of certain perennial dicotyledonous plants. The presence of annual growth increments in high-elevation plants is significant as it highlights the applicability of herbchronology for climatic, ecological and geomorphologic applications in alpine and other extra-arboreal regions. For alpine sites along the eastern crest of the Sierra Nevada range I present the first shrub-ring chronologies of the species Linanthus pungens (Torr.) J.M. Porter & L.A. Johnson. L. pungens individuals were collected at, and are especially ubiquitous at rock glacier sites in north-east trending glacial-cirque valleys. Rock glaciers are an increasingly recognized and studied feature on the alpine landscape, supporting floristically diverse plant populations, distinct thermal regimes decoupled from the external air and perennial water sources fed by interstitial ice. These landforms are expected to be refugia for alpine flora and fauna in some regions for projected warmer and drier climates. To evaluate plant growth on rock glaciers as compared to adjacent talus slopes in the central Sierra Nevada range of California, USA, a series of five cirque basins were selected as sites for paired rock glacier- talus slope vegetation comparisons. Vegetation cover, species richness, diversity measures and plant functional traits were recorded at ten sites (five rock glaciers, five talus slopes) along a 100-kilometer latitudinal span of the eastern slope of the Sierra Nevada range. Canonical correspondence analysis was used to evaluate general patterns in cover, diversity and functional traits for the 10 sites and inform subsequent statistical analyses. Both vegetation cover and species richness were significantly greater on rock glacier sites than on adjacent talus slopes even though mean slope values for the rock glacier sites were higher. Significantly, for the present study, rock glaciers support a higher number of the species Linanthus pungens, a climatically sensitive, long-lived alpine sub-shrub, showing that these periglacial landforms are not only floristically distinct but are also habitats containing natural climate archives useful to the field of herbchronology. L. pungens shrub-ring chronologies are determined to be distinct from Pinus albicaulis chronologies growing at the same five sets of sites in the Sierra Nevada study location. P. albicaulis (PIAL) tree-ring chronologies and L. pungens (LIPU) shrub-ring chronologies were constructed for four cirque basin sites. Comparisons were made between chronologies based on growth form (shrub or tree) and site, and on chronology response to average monthly temperature, total monthly precipitation and April 1 snowpack values. Chronologies are significantly more similar to other chronologies of the same growth form (PIAL-PIAL or LIPU-LIPU) than are same-site chronologies of different growth form (i.e. PIAL-LIPU chronologies) (p < 0.05). This holds true for comparisons based on Pearson’s correlation coefficients or Gleichläufigkeit (GLK) values. Growth response to monthly temperature and precipitation values is highly variable for same-site chronologies and also for same growth form chronologies. Topographical position and proximity to treeline was held constant at all sites so differences in climate-growth response within sites and within species may be attributed to factors that are unrealized in the sampling design. Based on composite climate anomaly maps, wide ring widths in PIAL chronologies occur after average winter and spring precipitation and with warm growing seasons while narrow PIAL rings fall after wet springs and with average summer temperatures. Years in which all LIPU rings are wide are found to occur during warm dry springs and growing seasons while years in which all LIPU rings are narrow occur in conjunction with wet winters and springs. Investigation into the longest and most replicated chronology at the Barney Lake (BL) site allowed a climate-growth comparison over a longer period of time (the BL chronology is 112 years in length with sufficient sample replication (EPS > 0.85) to capture a robust common signal from 1952 through 2007). Marker years in the BL chronology correspond to drought (wide rings) and persistent snowpack (narrow rings). Response function analysis indicates significant correlations with July minimum temperatures and the previous year's November precipitation. Increase in the radial growth of the taproot of L. pungens at BL has not decreased over the past century and is more highly correlated to temperature (positively) and snowpack and precipitation (negatively) during the latter half of the chronology period. Predictions of decreasing snowpack and warming temperatures for the alpine Sierra Nevada could indicate increased shrub growth over the next century and possible shrub range expansion if unprecedented drought does not prove to limit growth in the future. Work at BL and the other four alpine L. pungens chronology locations demonstrate a potential for additional research on climate-shrub growth interactions and in particular for investigations into climate controls on upper shrubline growth and movement in the Sierra Nevada range in California.
Degree ProgramGraduate College