Dendrochronological assessment of springs effects on ponderosa pine growth, Arizona, USA

Abstract Tree rings have been widely used to reconstruct environmental history, especially water availability, because historical records of streamflow are often limited. In the semiarid southwestern USA, springs provide critical water resources and support biodiversity hotspots, but spring flows are poorly documented and spring effects on tree-ring growth are not well studied. Our project was designed to measure the effect of spring adjacency on ponderosa pine tree growth and drought response. We sampled trees adjacent to springs (“near”) and farther away (“away”) that were similar in latitude, slope, soil characteristics, height and stem diameter, so we inferred that differences in ring width were due to the springś influences. We gathered cores from a total of 50 ponderosa pine trees at ten different springs around Flagstaff, Arizona. We crossdated and measured the tree rings and developed chronologies of near and away trees. We compared absolute growth of trees in each category using basal area increment (BAI; mm 2 /year), which ranged from 806 to 2511 mm 2 tree − 1 year −1 near springs and between 503 and 2125 mm 2 tree − 1 year −1 away from springs. Near trees had consistently higher BAI growth over the past 66 years, the common period of analysis, although the difference was not statistically significant. Mean tree-ring sensitivity from the chronology near springs was 0.323, while the chronology away from springs was significantly higher, 0.366. Drought sensitivity index was significantly higher for away trees, indicating that years of severe drought had a greater negative impact for away than for near trees. Drought recovery index, however, showed inconsistent results. The findings indicate that ponderosa pine growth is responsive to spring settings, even in severe drought. Given that small springs are abundant in semiarid regions, they may provide valuable ecological buffers for warming climate. Further investigation to quantify springs perenniality and variability is needed.