Tree-ring climate response of Jeffrey pine in the Cascade Creek Watershed, Northern California

Understanding the forest response to ongoing climate change is crucial in forest management strategies under anticipated climate adversity. To understand the retrospective growth dynamics of Jeffrey pine (Pinus jeffreyi Grev. & Balf.), tree-ring chronology from the subalpine forest in the Lake Tahoe Basin, California was correlated with air temperature, precipitation, and Palmar Drought Severity Index (PDSI). The years 1757, 1782, 1886, 1859, 1876, 1920, 1929-30, 1977, 1988-89, 2001-02, 2008, and 2014 were some of the years with noticeable low growth. There was robust growth in 1747-49, 1792, 1828, 1866-68, 1913, 1969, 1984, 1998, and 2011. Ring width index (RWI) and basal area increment showed a recent growth increase. Climate-growth response analysis revealed the growth-inhibiting influence of the hot and dry summer. More pronouncedly, warm and wet winter was found to be conducive to tree growth in the following year. A significant growth correlation with the previous year climate (stronger with PDSI) and its absence in current spring may be suggestive of potential growth stimulation by predicted warmer and longer growing season in the future. However, since the RWI chronology consisted mostly of mature trees and because the old cambial age tends to have signal divergence, further studies incorporating younger trees and cohabitant species would provide deeper insights into the growth-climate response.