Dendroclimatic Analysis of Sierra Nevada Mixed Conifer Species between Different Diameter Size Classes

Climate change is expected to lead to higher temperatures in the Mediterranean region of northern California in the Sierra Nevada. Dendroclimatic studies typically focus on large, old trees, but there relatively limited understanding on how climatic sensitivity can vary with trees of different size classes. We collected tree increment cores and compared radial growth responses of small (20.32 to <= 40.64 cm), medium (40.64 to <= 60.96 cm), and large (>60.96 cm) diameter mixed conifer species in the Sierra Nevada to different climate variables (temperature, precipitation, and climate moisture index (CMI)). The most common tree species encountered were white fir (Abies concolor (Gord. & Glend.) Lindl.), followed by sugar pine (Pinus lambertiana Dougl.), ponderosa pine (Pinus ponderosa Dougl. Ex P. & C. Laws), and incense cedar (Calocedrus decurrens (Torr.) Florin). One of the most coherent responses from all diameter groups and across all species was the positive response to increasing minimum winter temperatures. All diameter groups and species also responded positively to precipitation and CMI at some point in the analysis period, which is the seasonal window of April of the prior year to October of the current year of ring formation. Perhaps the most notable difference when comparing the three diameter groups to climate was the higher occurrence of negative responses to the temperature of the previous year from the largest diameter group, as well as the higher number of negative responses to temperature in general. These results suggest that larger trees may be more sensitive to future climate projections compared with smaller trees and they may carry those effects into the next year. The use of dendroclimatology to assess how mixed conifer species in the Sierra Nevada responded to past climate is a key resource that can be used to infer how trees may respond to a future changing climate.