Seasonal water source patterns in a northern Arizona pine forest

The relationships among stand density and seasonal plant water source patterns in ponderosa pine ( Pinus ) forests are important for informed management decisions a bimodal climate with increasing variability winter monsoon precipitation inputs. Winter recharges soil moisture, yet it has declined over the past 20 years southwestern United States, is becoming more variable both magnitude timing. Near Flagstaff, Arizona August 2013 (monsoon), October (post-monsoon), May 2014 (post snow melt), we measured δD at five depths, xylem Muhlenbergia montana (a perennial C 4 grass), Festuca arizonica 3 P. seedlings (< 2 old), saplings (2–5 cm basal diameter), mature trees (> 60 diameter breast height) treated (thinned burned) untreated (no thinning, no burning) stands. We found that moisture was higher all depths stands May, after melt, this pattern persisted through deepest (60 cm). also that, sampling months, of grasses indicated use shallower than trees, presumably due to differences rooting depths. Additionally, August, greater reliance on deeper stands, likely competition shallow Our isotopic data indicate used predominantly October, while during months. Importantly, our regenerating (seedlings saplings) sources, suggesting an increasingly role if inputs continue decline. Collectively, these findings demonstrate actions can benefit via increased overstory rely precipitation, herbaceous species younger, trees.