Climatic and ecological implications of shrub-chronologies at rock glacier sites of the eastern Sierra Nevada range, California, U.S.A

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 rock glacier sites in north-east trending glacial-cirque valleys. 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 and frequency, diversity measures, and plant functional traits were recorded at five rock glacier and five talus sites along a 100-kilometer latitudinal span of the range. 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. Pinus albicaulis (PIAL) tree-ring chronologies and L. pungens (LIPU) shrub-ring chronologies were constructed for the five 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. Investigation into the longest and most replicated chronology at the Barney Lake site (112 years in length with EPS > 0.85 for 1952–2007) allowed a climate-growth comparison over a longer period of time. Marker years in the Barney Lake 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.