A Fog-Induced Lichen Community in Northwestern Baja California, with Two New Species of Desmazieria

Abstract

A coastal zone of luxuriant fog-induced lichen growth is present in northwestern Baja California. The combined effects of frequent conditions of high atmospheric humidity and strong sea breezes restricting vascular plant vegetation allow a remarkable lichen community to develop. The vegetation on volcanic cinder cones in the vicinity of Bahia de San Quintin is dominated by species of Desmazieria. Two new species of this genus, D. josecuervoi and D. pulchribarbara are described. A gradual transition from coastal sage scrub to Sonoran Desert vegetation occurs in northwestern Baja California between Bahia de San Quintin and El Rosario, 300 and 360 km by road south of Tijuana, respectively (Shreve, 1936). The coastal zone in this region remains dominated by coastal sage scrub elements, but many desert species are present. Conditions for lichen growth appear to be almost ideal along the immediate coast here. Although precipitation records for small villages in this area indicate a mean annual rainfall of only 93-138 mm (Table 1), frequent overcast and fogs with associated high humidity are a characteristic aspect of the environment. Strong sea breezes restrict vascular plant growth markedly, reducing spatial competition for saxicolous lichen species. The luxuriant occurrence of species of Desmazieria, not only on rock surfaces but on loose volcanic cinders, soil, and sand as well, indicates the optimal growth conditions. Dense clumps of lichens are important parts of the vegetation on wind-swept coastal beach terraces. Shrubs are often literally smothered by accumulations of lichens on their branches. Field studies on the ecological relationships of the luxuriant lichen vegetation were carried out on the slopes of Colina del Sudoeste, Bahia de San Quintin, Estado de Baja California (Fig. 1). Colina del Sudoeste, one of a dozen small cinder cones which form the San Quintin volcanic field (Woodford, 1928), is a small basaltic cone rising from the base of a narrow peninsula which forms the western margin of Bahia de San Quintin. The cone rises to an elevation of 116 m from the sand dunes at the base of the surrounding lava flows. The crater rim is rounded for about 8 m before dropping steeply 50-60 m to the floor of the crater. Both inner and smooth outer cinder walls of the crater slope at 30-350. Fragments are vesicular, and range in size from 2-10 cm in diameter at the crater rim to 1 cm or less at the base of the cone. This study 1 Field expenses were partially supported by a NIH Training Grant. 2 Department of Population and Environmental Biology, University of California, Irvine, California 92664. This content downloaded from 157.55.39.235 on Fri, 07 Oct 2016 06:21:41 UTC All use subject to http://about.jstor.org/terms 502 THE BRYOLOGIST [Volume 75 TABLE 1. Climatic data for stations in the coastal sage scrub to desert transition zone in northwestern Baja California. Data from Hastings and Humphrey (1969). (W, winter; Sp, spring, S, summer; F, fall). Elevation Precipitation (mm) Mean Temperature ( C) Elevation) W Sp S F W Sp S F (m) Sp S W Sp S F Santa Maria del Mar 30?25'30N, 115?53'30W 30 95.2 24.8 1.0 16.9 14.9 16.6 20.1 20.1 El Socorro 30030'00N, 115049'00W 10 70.9 22.2 0.9 22.6 14.4 15.8 19.2 18.1 El Rosario 30?03'30N, 115?43'30W 15 63.1 16.3 0.9 13.1 14.7 16.6 21.0 19.0