Persistent and cumulative impacts of drought on forest growth: a Douglas fir case study (reescheduled)

Circulation models forecast changes in global temperature and precipitation that will likely alter forest function. North America is expected to experience increases in intensity and frequency of hot days and nights, and is already experiencing severe and frequent drought and forest fires. Current forest dieback has been attributed to climate change, however forest resilience to climate variability is not well understood. Tree ring records can be used to assess this resilience. In particular, trees exhibit ecological memory: delayed, persistent, and cumulative responses to disturbances. This is attributed to physiological feedbacks, which exacerbate disturbance impacts. Quantifying ecological memory will improve insight about tree growth response to disturbance. This is important for forecasting growth under future climate scenarios; the impact of frequent and severe droughts will likely be cumulative and persistent. North American Douglas fir is drought tolerant, and in its distribution covers a large latitudinal gradient in North America. It is an ideal candidate for understanding impacts of drought. Previous work shows that Douglas fir trees in the southern range exhibit greater drought tolerance than in the northern range, suggesting adaptation to drought consistent with the latitudinal moisture index gradient. Ecological memory to drought events has not been quantified. We quantify both the ecological memory of Douglas fir to drought using tree ring records from the International Tree Ring Data Bank, and relevant climate data. This work advances understanding of impacts of disturbance on tree growth, improving predictions of forest function.