Drought stress signals in modern and subfossil Quercus laurifolia (Fagaceae) leaves reflect winter precipitation in southern Florida tied to El Niño-Southern Oscillation activity

In the present study, structural xeromorphic features in modern and subfossil Quercus laurifolia leaves from southern Florida were quantified to reconstruct past precipitation changes in sensitive terrestrial settings. Absolute cell numbers/mm2, quantified as epidermal cell density (ED) have been analyzed on leaves from herbarium collections as well as the leaves accumulated during the past 125 years in peat deposits. The results reveal a common principal correlation between the measured ED and winter precipitation (November through March, NDJFM: Herbarium r = - 0.74; peat profiles FAK98 r = - 0.72, FAK02 r = - 0.53) providing a measure of seasonal drought stress. In Florida, the amount of winter precipitation depends on El Niñ o-Southern Oscillation (ENSO) activity, where El Niñ o years produce wet and cold winters, while La Niñ a winters are dry and warm. The negative correlation between cell numbers and winter precipitation has the potential to record precipitation variability from subfossil leaves on near-annual to decadal time scales. In subtropical, terrestrial environments, where traditional paleo-proxies are limited, systematic analysis of leaf morphological characteristics can provide important information on precipitation changes through time. © 2010 Botanical Society of America