EFFECTS OF TIMING OF PRECIPITATION AND ACORN HARVEST DATE ON EMERGENCE OF QUERCUS-EMORYI

Germination of semi-arid Quercus is strongly correlated with the rainy season. However, the timing and amount of summer precipitation in the southwestern United States is extremely variable. Ongoing and impendi ng changes in global and regional climates are likely to increase this variability. Specifically, anthropogenically induced changes in gener al circulation patterns may alter the seasonal distribution of precipi tation in a directional manner. In addition to climatic variability, t he inter-and intra-annual variability of Quercus emoryi Torr. (Emory o ak) acorn maturation also is high. Therefore, in light of existing cli matic variability and potential future climate change, we conducted a greenhouse experiment to investigate the effects of acorn maturation d ate and the timing of the onset of the 'monsoon' on emergence of Q. em oryi seedlings. Acorns were collected at weekly intervals in July of 1 995 and 1996, planted in a greenhouse, and subjected to different wate ring treatments. Watering treatments were (1) acorns watered the same day as planting; (2) acorns watered two weeks after planting; (3) acor ns watered four weeks after planting. Emergence in 1995 was significan tly greater in the last week of acorn maturation and decreased signifi cantly as time to the onset of the 'monsoon' increased. Emergence in 1 996 was very low, presumably because of soil moisture contents that we re lower than those observed in 1995. The dependence of e. emoryi on w ater for emergence has profound implications for Q. emoryi recruitment in the face of current climatic variability and future climate change . Summers with a delayed 'monsoon' and decreased soil moisture may sev erely constrain recruitment of this woody plant.