Recruitment Patterns and Mature-Tree Growth Response of High-Elevation Pines to Climatic Variability, 1883-2013, Western Great Basin, USA

Abstract:

We monitored recruitment (trees less than 131 years old in 2013) of subalpine Pinus flexilis(PiFl) and P. longaeva (PiLo) along ecotones at upper, mid, and lower treelines in 7 western Great Basin mountain ranges. Recruitment is greatest near and above current treeline, but only in scattered, highly localized locations, and predominantly in PiFl , which is leapfrogging 300 m above PiLo. Recruitment occurred consistently throughout middle and low elevations. At middle elevations, recruitment is extending beyond forest borders into sage meadows; at low elevations, recruitment is extending below the 20^th century lower treeline in north-aspect, narrow ravines. Recruitment for both species was episodic, with a dominant pulse in the interval 1970-2000. This period is associated with wet autumns and warm growing-season minimum temperatures. Spectral analyses of limber pine recruitment birth year densities resolved strong primary peaks at 5 years. These peaks occurred at all elevations, but were strongest for high-elevation transects and weakest for low elevations. Radial growth from four limber pine chronologies (analyzed for the years 1883 to 2013) showed greatest growth during the same period as the recruitment pulse, with significant declines in growth since 1990 at all sites.