Gulf of California

With the uplift of the Sierra Madre Occidental in the late Oligocene-early Miocene, tropical deciduous forest was isolated in northwestern Mexico. Thornscrub and then the Sonoran Desert formed during a drying trend in the middle Miocene. The opening of the Gulf of California at the same time dramatically influenced the vegetation and flora of the region. Today the transition from the New World Tropics to the Northern Temperate Zone is in Sonora with the northernmost tropical deciduous forest in the Sierra San Javier (28°N).

In island systems, nitrogen-rich seabird guano is a marine subsidy that can shape terrestrial plant communities. In zones of nutrient upwelling such as the Gulf of California, copious seabird guano is commonplace on bird islands. Several bird islands host regionally unique cactus forests, especially of the large columnar cactus, cardón (Pachycereus pringlei). We show that a chain of interactions across the land-sea interface yields an allochthonous input of nitrogen in the form of seabird guano, fueling the production of some of the densest cactus populations in the world.