Tree-ring growth response of Pinus Ponderosa (PIPO) to climatic variability in Prescott National Forest, Arizona

Abstract:

A tree-ring growth response study was conducted in Prescott National Forest, Arizona to determine the climatic variables that may be altering the growth patterns of Pinus Ponderosa (PIPO). Final findings include a constructed species chronology to understand growth variations in response to past and ongoing climate conditions and possible weather phenomena attributed to the region, such as El Nino/La Nina events. Data collected from four sites in Prescott National Forest include two tree cores from thirty mature individuals, tree diameter at breast height, tree height, tree canopy, and GPS location. The data collected was compared between individual study plots to determine how the plots differ in age classes and ring width variations to define the overall age structure of the different sites within Prescott National Forest. We also analyzed the changes in growth variability in response to climatic variables.  Palmer Drought Severity Index (PDSI) values as well as Mean Temperature and Mean Precipitation were used to correlate years of growth with monthly and seasonal climatic variables. This was done by studying Ring Width Index (RWI), which enabled us to infer how changes in climate have altered the historical success of Ponderosa Pine in Prescott National Forest. The 244 tree core samples were measured using the dendrochronology program Cdendro and crossdated using COFECHA. The final stages of research involved using the dplR program in R to construct RWI chronology graphs to highlight pointer years of low growth and correlate them with known drought years in the region.

Keywords: dendrochronology, forest ecology, climate change

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