Building baselines: Evaluating plant communities on the islands of Bahía de los Ángeles, Baja California, Mexico

Bahía de los Ángeles (BLA), located on the Baja peninsula on the Gulf of California, is known for impressive biodiversity, including several endemic plant and animal species, many of which live within bay’s archipelago of 16 near-shore islands. Because of these characteristics, BLA is part of a protected biosphere reserve, which is managed by the Mexican government agency Comisión Nacional de Áreas Naturales Protegidas (CONANP). For nearly three decades, our project has collected data on BLA’s island plant communities. CONANP uses these data to monitor the island flora and fauna in order to detect changes, such as in response to climate change or human disturbance. In 2018, we conducted an additional project to compare three sampling methods used to survey plants: 1) plant percent cover estimates using quadrats; 2) aerial imaging surveys using an Unmanned Aerial Vehicle (UAV); and 3) plant qualitative abundance estimates using a visual census. We then assessed the advantages and disadvantages of each method in terms of three main factors: 1) ability to measure plant diversity; 2) sampling effort, and 3) the relative sampling disturbance of each method to the island communities. We used each of the three sampling methods on a subset of three islands. Quadrats provided precise estimates of percent cover, but only for the most abundant taxa, and required the greatest sampling effort and disturbance. Visual censuses consistently identified the highest plant diversity, with a moderate sampling effort and disturbance. Aerial imaging cause the least disturbance to the islands, and the least sampling effort, but when using visible light imaging was only effective at identifying larger taxa (e.g., Pachycereus pringleyi (cardón) or Ferocactus gatesi (biznaga)). Broadly, we concluded that each sampling method had advantages depending on the sampling goal and constraints such as available time, funding, and personnel. Ultimately, a combination of techniques is necessary to establish broad baseline data on plant community structure. The continued sampling of BLA’s plant community, as well as the introduction of new techniques such as aerial imaging, will be important for monitoring plant community structure changes within this biosphere reserve.