The Succulent Scrub of San Martín Island, Baja California, Mexico

Abstract

Baja California, Mexico, is home to enormous floristic diversity (Rieman & Ezcurra 2005; Peinado et al. 1995; Wiggins 1980) including a wealth of cacti and succulents. Readers may have accompanied CSSA trips to Baja California or may have read articles about the plants seen on those trips. On the Pacific Coast, near the southern edge of the California Floristic Province (which California shares with Oregon and Baja California), lies Greater San Quintin, a diverse and relatively unspoiled region (Howell 1957; Thorne 1993). The area includes eleven extinct volcanic cones with elevations up to 260 m, one of which is the island of San Martin that lies 5 km (3 mi) off shore. Island floras are of particular interest to botanists due to their isolation from mainland source populations which, in the context of variation in dispersal abilities among plant groups, results in unique plant communities (Carlquist 1974). San Martin Island is the southernmost of the Pacific Channel Islands on the continental shelf; it is also amongst the smallest, being only 0.9 square mile (2.3 square kilometers) in area ( Junak & Philbrick 1994). San Martin is unusual never having had large introduced animals such as goats and pigs, which have seriously impacted most of the California Channel Islands at some point in their history. Thus despite the small size of San Martin Island, it remains home to several endemic vertebrates (Samaniego-Herrera 2007). Although rabbits and cats were reported on the Island historically, today the largest non-native inhabitants are a few chickens that forage in the area around the fishing camp. San Martin Island is a cindercone, mostly composed of sharp volcanic lava rock, often with a dense covering of foliose lichens. There is relatively little soil buildup across most of the island, and the plants of the succulent maritime scrub grow among the rocks. There are also small areas