Biodiversity is a term that describes the total number of living species found in an area. That concept has gained importance and exposure because of the expansion of the human population and the reduction of pristine natural areas on Earth. In 1988 Norman Myers developed a method for designating places on Earth that contain significant numbers of unique plant species, but that were experiencing significant habitat loss. He termed these areas biodiversity hotspots and identified them as supporting at least 1,500 species of plants that were unique to the area (aka endemic) and that had lost at least 70% of its original area. There are now 36 such areas recognized globally, and while they represent just 2.3% of the Earth’s land surface, they contain about 50% of the world’s endemic plant species and 42% of all terrestrial vertebrate species.
One of these hotspots, called the California Floristic Province, is found along the Pacific Coast of North America extending from a portion of northern Baja California through most of California and into a portion of extreme southwest Oregon. It is one of only five areas in the world with a Mediterranean-type climate, all of which are biodiversity hotspots. Like the other Mediterranean climate areas, the California Floristic Province is typified by hot, dry summers, and cool, wet winters. For those of us living in Southern California, we can appreciate the wet aspect of some of our wetter winters.
The California Floristic Province once covered over 113,000 square miles (293,000 km2), but now only a little more than 28,000 square miles (73,000 km2) of vegetation remain. Within this area are over 2,100 species of plants that uniquely evolved there. Much of the area has been lost to agriculture development, urbanization, road construction and pollution.
The California sycamore (Plantanus racemosa), as seen in today’s photo, is a tree species native to the California Floristic Province that is highly emblematic of plant communities found along streams and other water courses. The presence of this species is a clear indication of the presence of the perennial occurrence of near-surface ground water. Lacking ground water in the root zone, this species cannot survive.
In places like California’s Central Valley where ground water had been depleted by more than a century of agricultural withdrawal, very few younger sycamore trees are to be found in areas they once dominated. With almost no new individuals adding to the population, as the older trees age and die, these once thriving ecosystems are undergoing drastic changes because of the human impact on them. Unfortunately, stories like this are playing out all over the California Floristic Province, a place more than worth saving.