Tree-ring growth response of Jeffrey Pine to climate in northern California

The forest ecosystem is responding to climate change worldwide by advancing to higher altitudes, increasing recruitment, and changing radial growth pattern. To understand how the sub-alpine forest ecosystem of northern California is responding, we collected tree-ring cores from Jeffrey Pine ( Pinus jeffreyi ) sub-alpine forest in the Lake Tahoe Basin, California. We used the standard dendrochronological procedure to surface, cross date, measure, and detrend tree-ring cores samples. Monthly and seasonal climate data of Tahoe city were applied to assess climatic variables controlling ring growth. We developed a 374 year-long (1645-2018) chronology from 48 cores (24 trees). The chronology was truncated to 244 years (1775-2018) based on subsample strength and sample depth. The years 1757, 1782, 1886, 1859, 1876, 1920, 1929, 1977, 1988, 2001, 2002, 2008 exhibited low growth (narrow ring) and years 1747, 1749, 1792, 1828, 1866, 1868, 1913, 1969, 1984 exhibited robust growth (wider ring). No recent increasing trend of ring width was observed in 10 years moving average of ring width index (RWI). However, the transformation of ring width to basal area increment (BAI) showed an increasing growth trend in recent decades. BAI also indicated that 1928-30, 1987-1989, and 2013-2014 were low growth periods associated with extreme drought events. BAI presents a better spatial correlation with monthly climatic variables than RWI. Thus, BAI has an advantage over RWI in studying tree-ring growth and climate response.