4.4: Native and Unique Flora

California native plants are plants that existed in California prior to the arrival of European explorers and colonists in the late 18th century. California includes parts of at least three phytochoria. The largest is the California Floristic Province, a geographical area that covers most of California, portions of neighboring Oregon, Nevada, and Baja California, and is regarded as a "world hotspot" of biodiversity.

The California Floristic Province (CFP)

The California Floristic Province (CFP) stretches along the Pacific Coast, encompassing most of California and spilling into parts of Oregon, Nevada, and Baja California (see figure 4.8). This region boasts a distinctive plant life like areas with Mediterranean climates, characterized by wet winters and dry summers.

In 1996, the CFP earned recognition as a global biodiversity hotspot due to its exceptional concentration of unique plant species. Conservation International estimates the CFP to be home to over 8,000 plant species, with a staggering 60% found nowhere else on Earth (endemic). Despite its incredible biodiversity, the CFP faces a significant challenge: habitat loss. Sadly, over 70% of its original vegetation has disappeared. This loss is primarily driven by human activities like large-scale agriculture and urban expansion.

Recognizing the urgency, Conservation International proposed a strategy in 1998 to prioritize areas within the CFP most affected by human impact. The goal is to minimize threats to this vital ecosystem. Several factors contribute to the CFP's vulnerability, including population growth, habitat destruction, unsustainable resource use, and invasive species.

By understanding these threats, conservation efforts can be targeted more effectively to protect this irreplaceable treasure trove of plant life.

The California Floristic Province is a floristic province with a Mediterranean-type climate located on the Pacific Coast of California with a distinctive flora like other regions with a winter rainfall and summer drought climate like the Mediterranean Basin (figure 4.8). In 1996, the province was designated as a biodiversity hotspot allowing it to join ranks among 33 other areas in the world with many endemic species, as it is known for being the home of the Sierran giant sequoia tree and its close relative the coast redwood. The CFP is home to over 3,000 species of vascular plants, 60% of which are endemic to the province.

Figure 4.8: Map of California’s Floristic Province. Image by California Department of Forest and Fire Protection is in the public domain.

Climate & Topography

The California Floristic Province is one of the five biodiversity hotspots with Mediterranean climates, and it is characterized by hot, dry summers and cool, wet winters. Many parts of the coastal areas of this hotspot, being moderated by the ocean, experience cool summers due to the regular occurrence of ocean fog, which sustains redwood forests amongst other communities.

In California, the province includes most of the state excluding the Modoc Plateau, Great Basin, and deserts in the southeastern part of the state. In Oregon, the province includes the coastal mountains south of Cape Blanco and most of the Rogue River watershed.

In Baja California, the province includes the forest and chaparral belts of the Sierra Juarez and the Sierra San Pedro Mártir (but excluding their desert slopes to the east), coastal areas south to about El Rosario, and Guadalupe Island.

Parts of the following mountain ranges are included in the province:

• The Klamath Mountains
• The Cascade Range
• The Coast Ranges
• The Sierra Nevada
• The Transverse Ranges
• The Peninsular ranges south into Baja California
• The Great Central Valley

Case Study - The Ancient Bristlecone Pine

The term ‘bristlecone pine’ covers three species of pine tree (family Pinaceae, genus Pinus, subsection Balfourianae). All three species are long-lived and highly resilient to harsh weather and traditionally poor soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species.

Bristlecone pines grow in isolated groves just below the tree line, between 5,600 and 11,200 ft (1,700 and 3,400 m) elevation on dolomitic soils. The trees grow in soils that are shallow lithosols, usually derived from dolomite and sometimes limestone, and occasionally sandstone or quartzite soils. Dolomitic soils are alkaline, high in calcium and magnesium, and low in phosphorus. Those factors tend to exclude other plant species, allowing bristlecones to thrive. Because of cold temperatures, dry soils, high winds, and short growing seasons, the trees grow very slowly.

The bristlecone pines root system is mostly composed of highly branched, shallow roots, while a few large, branching roots provide structural support. The bristlecone pine is extremely drought tolerant due to its branched shallow root system. The tree's waxy needles, and thick needle cuticles also aid in water retention.

The pine needles, which grow in bunches of five and can remain on the tree for forty years, give the twisted branches a bottle-brush appearance. The needles of the tree surround the branch to an extent of about one foot near the tip of the limb. The name bristlecone pine refers to the dark purple female cones that bear incurved prickles on their surface. The dark color of these cones helps to absorb heat. After maturity, which takes about two years, the cones will become brown in color. These ancient trees have a gnarled and stunted appearance, especially those found at high elevations, and have reddish-brown bark with deep fissures. As the tree ages, much of its vascular cambium layer may die. In very old specimens, often only a narrow strip of living tissue connects the roots to a handful of live branches. Even though the trees' needles may age, they remain functional in regulating water and by their ability to photosynthesize.

The wood is very dense and resinous, and thus resistant to invasion by insects, fungi, and other potential pests. The tree's longevity is due in part to the wood's extreme durability. While other species of trees that grow nearby suffer rot, bare bristlecone pines can endure, even after death, often still standing on their roots, for many centuries. Exposed wood on living and dead trees does not rot, but rather erodes like stone due to wind, rain, and freezing, which creates unusual forms and shapes.

The bristlecone pine has an intrinsically low rate of reproduction and regeneration, and many believe under present climatic and environmental conditions the rate of regeneration may be insufficient to sustain its population.

Field Trip: The Bristlecone Pine

Let’s head on field trip to visit some of the oldest trees on Earth! Either scan the QR code or visit this link to see Professor Patrich explore The Ancient Bristlecone Pines, in the White Mountains, California. (Video length: 9 min).