Paleoecology of a Late Pleistocene Monterey Pine at Laguna Niguel, Southern California

Abstract

Twenty-five ovulate cones of Pinus radiata, entombed in a Late Pleistocene (ca. 30,000 B.P.) landslide at Laguna Niguel, coastal southern California, are about as long as fossils from Carpinteria but are much shorter than cones of the modern Año Nuevo and Cambria populations. The fossil record shows that cone size of P. radiata increased since the Late Miocene (6-7 Ma [million annum]). This need not mean that the small-coned pine trees at Monterey are older than the large-coned trees at Año Nuevo and Cambria. Allozyme differentiation among the three modern California populations indicates that the Cambria and Año Nuevo populations diverged earlier than the Monterey. This suggests that the ``new'' small-coned Monterey population probably results from the colder climate there, a relation shown by P. radiata cones of glacial age and also by modern ecotypes of P. flexilis and other taxa. The Laguna Niguel fossils indicate that (1) rainfall was ca. 580-635 mm, or twice that of today; (2) mean annual temperature was fully 2 C cooler; (3) the annual range has increased 1.5-1.8 C; (4) warmth (W) has increased from W 13.7 to W 15 C today; and (5) the growing season was 1.3 mo (40 days) shorter than at present. The postglacial development of marked differences in the mean winter (<12 C) and summer (<17 C) temperatures of central and southern coastal California appear to account for the present major differences in the flora.