The ecosystems on The Irvine Ranch and adjacent wildlands are part of the California coastal sage and chaparral ecoregion; a bio-geographic unit within the California Mediterranean-climate province. Mediterranean-type ecosystems, wherever they occur, represent a global conservation priority. They are home to an extraordinary concentration of unique plant and animal species - and they are under great threat wherever they occur. In most areas, habitat conversion has been extensive and exceeds habitat protection by 8:1, making it one of the most endangered biomes on the planet and a hot spot for species extinction. Fortunately, more than 50,000 acres of this precious ecosystem have been set aside on The Irvine Ranch and adjacent areas. The mission of the Irvine Ranch Conservancy is to ensure that these special lands are cared for as a representative sample of this unique biodiversity.
Mediterranean-climate ecosystems are characterized by warm, dry summers and cool, relatively wet winters. Although the five Mediterranean-climate areas occupy less than five percent of the Earth's surface, they support roughly 48,000 catalogued vascular plant species - almost 20 percent of the known plants in the world. Mediterranean floras are notable for very high levels of endemism (species found only in one place), including a large number of restricted-range species (species with very small distributions) (Cowling et al. 1996, Myers et al. 2000).
The Santa Ana Mountains and associated coastal ranges are one of the very last places where relatively large blocks of intact lowland habitats characteristic of Southern California occur. Throughout California, the vast majority of the coastal sage scrub (less than 10 percent remains and few, larger blocks persist), native grasslands (less than one percent remains intact), and other lowland habitats have been converted for development and agriculture. Less than 10 percent of coastal sage scrub and around one percent of native grasslands remain today – some of which is protected on The Irvine Ranch. The loss of these habitats has endangered a suite of highly adapted species such as the tiny California gnatcatcher (Polioptila californica californica) a bird that nests only in coastal sage scrub. Other declining species include the coastal cactus wren (Campylorhynchus brunneicapillus sandiegensis), pacific pocket mouse (Perognathus longimembris pacificus), and thread-leaved brodiaea (Brodiaea filifolia). For these reasons, the protected wildlands on The Irvine Ranch and adjacent areas are a globally important conservation priority.
The wildlands of the North Ranch are connected to the Cleveland National Forest and are one of the few places where natural habitat ranges relatively unbroken from lowland scrub, grassland and oak woodlands up to higher altitude montane chaparral and conifers. The Venturan and Diegan associations of coastal sage scrub and native grasslands of Southern California are all critically endangered and The Irvine Ranch and adjacent wildlands offer one of the last, best places to protect these ecosystems and many of the species associated with them.
This area is also sufficiently large and continguous to support native ecosystems that still benefit from the presence of large predators, such as mountain lion, coyote, golden eagle and bobcat. Their ecological role as top carnivores helps maintain a healthy and resilient ecosystem. The wildlands are some of the last and most extensive lower elevation habitat for these important predators. For all of these reasons, The Irvine Ranch wildlands and parks has been identified by The Nature Conservancy as one of the top 50 priority conservation landscapes in California.
Not only are these natural areas a globally important conservation priority, they are remarkably close to one of the world's largest urban regions. This offers an unparalleled opportunity for people to experience and enjoy these extraordinary native ecosystems in their own backyard, while enhancing understanding and support for their protection and stewardship.