Revista Chilena de Historia Natural ISSN: 0716-078X [email protected] Sociedad de Biología de Chile Chile GARCILLÁN, PEDRO P.; VEGA, ERNESTO; MARTORELL, CARLOS The Brahea edulis palm forest in Guadalupe Island: A North American fog oasis? Revista Chilena de Historia Natural, vol. 85, núm. 1, 2012, pp. 137-145 Sociedad de Biología de Chile Santiago, Chile Available in: http://www.redalyc.org/articulo.oa?id=369944300011 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative THE BRAHEA EDULIS PALM FOREST: A FOG OASIS? 137 REVISTA CHILENA DE HISTORIA NATURAL Revista Chilena de Historia Natural 85: 137-145, 2012 © Sociedad de Biología de Chile RESEARCH ARTICLE The Brahea edulis palm forest in Guadalupe Island: A North American fog oasis? El palmar de Brahea edulis de Isla Guadalupe: ¿Un oasis de niebla en Norteamérica? PEDRO P. GARCILLÁN1, ERNESTO VEGA2 & CARLOS MARTORELL3, * 1Centro de Investigaciones Biológicas del Noroeste (CIBNOR), Mar Bermejo No. 195, Col. Playa Palo de Santa Rita, Apdo. Postal 128, La Paz, Baja California Sur 23090, México 2Centro de Investigaciones en Ecosistemas (CIEco), Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro No. 8701, Col. Ex-Hacienda de San José de La Huerta C.P. 58190 Morelia, Michoacán, México 3Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, 04510 México D.F., México *Corresponding author: [email protected] ABSTRACT Fog is a factor that affects deeply the structure of vegetation of coastal deserts. Guadalupe is an oceanic island located 260 km off the coast of Baja California, and is one of the few places of the Sonoran Desert coasts with scarped coastal topography and frequent fog. With the aim to identify the effect of fog on the community of the palm forest (palmar) of Brahea edulis located in the northern tip of the island: (1) we analyzed the richness and composition of vascular plants in the palmar compared to the remainder of the island, and (2) we analyzed the altitudinal variation of the abundance of palms, herbs and mosses to identify if there is altitudinal variation of the vegetation. Although species composition was not different between palmar and the rest of island, species richness and vascular plant cover were greater in the palmar. On the other hand, we found a clear altitudinal zonation of the vegetation in the palmar that is similar to that found in South American fog-driven plant communities such as the lomas. Thus, the palmar community of Guadalupe Island may be considered as a fog oasis, one of the very few that occur in North America. Key words: altitudinal gradient, coastal desert, fog effect, Sonoran Desert, vegetation. RESUMEN La niebla es un factor que afecta profundamente la estructura de la vegetación de los desiertos costeros. Guadalupe es una isla oceánica a 260 km de la costa de Baja California y constituye uno de los pocos lugares de la costa del Desierto Sonorense donde se reúnen una topografía escarpada próxima a la costa y una alta frecuencia de nieblas. Con el objeto de identifi car el efecto de la niebla sobre la comunidad del palmar de Brahea edulis presente en la ladera norte de la isla: (1) analizamos la diferencia de la riqueza y la composición de plantas vasculares del palmar respecto del resto de la isla, y (2) analizamos la variación altitudinal de la abundancia de palmas, plantas acompañantes y musgo para determinar si existe variación altitudinal de la vegetación. Encontramos que, aunque la composición de plantas del palmar no fue diferente del resto de la isla, la riqueza de especies y la cobertura fueron claramente superiores en el palmar. Finalmente, constatamos una clara zonación altitudinal de la vegetación en el palmar semejante a la encontrada en las comunidades dependientes de la niebla en Sudamérica, tales como las lomas. Por tanto, la comunidad del palmar de Isla Guadalupe puede considerarse como un oasis de niebla, uno de los pocos existentes en Norteamérica. Palabras clave: desierto costero, Desierto Sonorense, efecto de niebla, gradiente altitudinal, vegetación. INTRODUCTION fog because of cold ocean streams and the thermal inversion found inland (Rundel 1978, Water is the most relevant factor for arid Schemenauer & Cereceda, 1991, Leipper 1994). ecosystems. Its spatio-temporal availability Coastal deserts and Mediterranean scrubs affects deeply the structure of communities occurring in those latitudes are subject to high (Ehleringer & Mooney 1983, Polis 1991). water stress (Meigs 1966, Ezcurra et al. 2006). Between the latitudes 20º and 35º in the western In the extremely-dry coastal deserts of South coasts of most continents, a large proportion America, it is possible to fi nd genuine oases of the water available occurs in the form of known as lomas in the sites where a topographic 1111 GGarcillan.inddarcillan.indd 137137 112-04-122-04-12 15:1315:13 138 GARCILLÁN ET AL. barrier intercepts the horizontal movement of Martorell & Ezcurra 2002). However, there is the fog. Because this water source occurs in one area where a high frequency of fogs occurs the form of an altitudinal belt, vegetation in the altogether with a scarped terrain: Guadalupe lomas shows a strong structure with a clear Island (Fig. 1). Steeply rising 1298 m from differentiation among plants with different the sea in just 1.5 km, this island constitutes growth forms and phenology occurring at a barrier that intercepts thick and recurrent separate elevational strata. In general, the fogs coming from the northwest. In contrast, portions of the elevational gradient that receive the annual rainfall is just 133 mm, making the less water are dominated by cryptogams, while climate at Guadalupe very similar to that of herbs, shrubs and even trees characterize belts South American coastal deserts. with increasingly fog availability (Lydolph 1957, Ever since the first naturalist, Edward Rundel 1978, Rundel et al. 1991). Palmer, visited Guadalupe in 1875, the presence In North America, only the Baja California of fogs and their effect on the vegetation in the coastal desert is found in the latitudes (20- northern tip of the island have been repeatedly 30º) where fog oases are found in other reported, (e.g., Watson 1876, Bryant 1887, continents. Nevertheless, the effect of coastal Franceschi 1893, Sutliffe 1933, Weber 1993, fogs is diluted gradually as it is blown inland Moran 1996, Oberbauer 2005). Furthermore, by because of the absence of a steep topography looking at the potential vegetation map by León that intercepts the humidity near the shore de la Luz et al. (2003) it is possible to notice an (Rundel & Mulroy 1972, Nash III et al. 1979, intriguing paralelism between the altitudinal Fig. 1: Location of Guadalupe Island in the Pacifi c island corridor of the California Floristic Province. The inset shows location of palmar of Brahea edulis (gray circle) in the island. Ubicación de la Isla Guadalupe en el corredor de islas del Pacífi co de la Provincia Florística de California. El recuadro muestra la localización del palmar (círculo gris) en la isla. 1111 GGarcillan.inddarcillan.indd 138138 112-04-122-04-12 15:1315:13 THE BRAHEA EDULIS PALM FOREST: A FOG OASIS? 139 zonation of Peruvian lomas (Rundel 1978, Rundel 1996). It contains a remarkable small-scaled replicate et al. 1991) and the south-north vegetation of the mainland transition between Mediterranean and desert scrubs (González-Abraham et al. 2010). The gradient of the island: In its southern third, palmar is located in a northwestern-facing, very steep which has a very low fog input, the landscape is (45 %) hillside found in the northern tip of the island. dominated by succulent plants and rupicolous The substrate is largely covered by large rocks. The vegetation is composed mostly of herbs and palms, but lichens; herbs and small shrubs characterise some scattered pines (Pinus radiata var. binnata) occur the island’s center, and forests dominated by near the hilltop. The large number of fallen trunks and either Pinus radiata D. Don, Callitropsis forbesii rotting stumps suggest that a pine forest once developed in the higher portions of the area until it was cleared (S. Watson) D. P. Little, and Brahea edulis (H. by two centuries of extreme overgrazing by goats. Wendl) are present at the foggy northern third Nomenclature follows Moran (1996), and Little (2006) of Guadalupe. Moreover, these fog-dependent for C. forbesii. In May 2004, we set 23 transects 30 × 2 m each along forests are also similar to the relictual fog- the northern slope of the island. Transects were located dependent rainforest patches found at similar following intervals of 30 m in altitude, encompassing an latitude (30º S) in northern Chile (del Val et al. elevational range from 430 to 1090 masl. Below 430 m there was a vertical cliff reaching down to the ocean. In 2006). They are also relict populations of tree every transect, we recorded the vascular plant species species located several hundreds of km away present, and estimated visually the vegetation cover. from their current range distribution or of their Botanical vouchers were deposited at the BCMEX (Universidad Autónoma de Baja California, Ensenada, closest relative species, and persist in a matrix of B.C., Mexico) herbarium and identifi ed with the help of arid land thanks to the fog. Steve Junak and José Delgadillo. In the center of each The palmar, a community dominated by transect, in a 2 × 2 m quadrat, we estimated visually the cover of mosses occurring over the stones. We used this an open monospecific grove of the palm cover as a proxy for atmospheric humidity because it Brahea edulis, occurs in some 20 ha in the would not be greatly affected by run-off or sub-surface northernmost slope of the island.