Dendroclimatology of Torrey pine (Pinus torreyana Parry ex Carr.)

Torrey pine (Pinus torreyana Parry ex Carr.) has one of the most limited geographical ranges and population size in the Pinus genus: it is present only on Santa Rosa Island and on the coast between San Diego and Del Mar. Because the survival of Torrey pine within its limited natural distribution depends on the health and climatic sensitivity of the adult tree population, we performed a dendroclimatological study to quantify the long-term response of dominant trees to climate. A 168-yr tree-ring chronology (1827-1994) was developed using a total of 28 increment cores extracted from 17 trees at Torrey Pines State Reserve, San Diego, California. Tree-ring samples were visually and numerically crossdated to assign accurate calendar years to each growth increment. Annual tree growth was highly and directly related to precipitation falling between the previous November and the current April. Temperature was not a significant predictor of tree growth. At seasonal scale, tree growth was highly and directly related to winter and spring precipitation, and was also significantly correlated to summer fog. However, when combined with winter and spring precipitation in multiple regression models, summer fog was not a significant predictor of tree growth. Total November through April precipitation explained a larger amount of variance after 1900 (64% in 1900-1949, 70% in 1950-1994) than before 1900 (48% in 1850-1899). The spatial correlation with western North America winter and spring precipitation, as well as with published tree-ring chronologies, reveals a link with the American Southwest. Global correlation maps with winter sea level pressure and sea surface temperature indicate that Torrey pine growth benefits from a southerly displaced North Pacific storm track and from warmer ocean water further south, suggesting a connection with increased transport of lower latitude moisture.