Biodiversity, Geography, and Ecology of Southern California: Southern California

Geographical Overview and Biodiversity of Southern California

• Southern California is recognized as one of the world’s biodiversity hot spots.

• The high level of biodiversity in this region mirrors its extensive ecological diversity.

• This ecological diversity is primarily due to the region's geographical complexity.

• Southern California is categorized into three primary geographical regions: * *     

  • Cismontane: Defined as the coastal regions located west of the mountains.   -  

  •        Montane: Defined as the mountain regions.   

  • Transmontane: Defined as the desert regions located east of the mountains.

• The geography is exceptionally complex, consisting of various landforms including beaches, coastal bluffs, mesas, inland valleys, foothills, mountains, and open deserts.

Tectonic Evolution and Physiography

• The biodiversity of southern California is ultimately tied to the dynamics of plate tectonics.

• A major geological event was the subduction of the Pacific plate along the western edge of the North American plate, which began the uplift of the granitic Peninsular Ranges approximately $95\,mya$ (this formed the montane region). pacific plate shifted against north american plate, this created the montane region.

• This mountain range divides southern California into western (cismontane) and eastern (transmontane) sections.

• Characteristics of the Western side: -

  • It is subject to higher rates of erosion and sedimentation originating from the montane region. More moisture from the coast.

• Role of Mountains in Climate:  The mountains trap easterly moving storms, forcing them to release moisture, a process known as a rain shadow. This was mentioned in another lecture   

• Eastern slopes are notably steep and are bordered by the Salton Trough, which sits at the northern end of the Gulf of California.

• Plate Boundary Action: Strike-slip motion occurs along plate boundaries, specifically the San Andreas Fault.   - The Pacific plate is moving north relative to the North American plate.

• History of Baja California:   - Approximately$4.5\,mya$, Baja California was sutured to mainland Mexico.   - Baja is situated on the Pacific Plate, while Mexico is on the North American Plate.   - Baja eventually broke away and drifted northwest along the San Andreas Fault; this drift continues today.   - Prediction: In $4.5\,my$ more, Los Angeles will be located next to San Francisco.

• Physiography (Shape of the Land):   - The tectonic movement shaped the physiography of southern California.  (plate movement shaped southern california)

•  - Uplift of the Peninsular Ranges in the montane regions began approximately$3.5\,mya$.   

• - Mountains were uplifted by approximately$2\,km$.   - This uplift created a marked distinction in geography and climate between cismontane and transmontane regions and created the distinct upland (montane) region.   

• - This activity is responsible for the disjunct series of mountains, including Laguna Mnts, Palomar Mnt, Hot Springs Mnt, Santa Rosa Mnt, and San Jacinto Mnt. Mountains being uplifted, created distinction between geography and climate in cis and trans regions as well as gave rise to upland regions.

Glacial Cycles and Climatic Evolution

• During and subsequent to mountain uplift, North America became hotter and drier as glaciers receded to their current positions.

• The region is currently in a period of glacial minimum.

• Sea levels and temperatures have fluctuated cyclically for $4\,my$:

•   - When glaciers melt: Sea levels and air temperatures rise; montane forests retreat upslope.  

•  - When glaciers form/expand: Sea levels and air temperatures drop; montane forests migrate downslope.   - These cycles occurred approximately times within the last$2.5\,my$.

• The Last Glacial Maximum (LGM):   - Occurred between $33,000 - 14,000\,ybp$.   - This was the most recent time during the last glacial cycle where ice sheets covered much of North America, Europe, and Asia.   - Effects included drought, desertification, low sea levels, and lower temperatures (approximately lower than today).   - During the LGM, montane forests spread downslope, covering much of the lowland areas.

• Transition to the Holocene:   - The LGM ended between$14k–8k\,ybp$, marking the start of the Holocene.   - Temperatures rose and precipitation dropped, causing montane forests to retreat upslope.   - Transmontane areas expanded (east of mountains, desert regions)

• The Creosote Bush: This is the dominant plant of southwestern deserts. (example of transmontane regions expanding)

•   - Verbatim data: The plant did not exist in California until $6\,ybp$ (as per transcript slide$17$; note map indicates $6k$).

• The mountains maintain rain shadows that still prevent precipitation and cool air from reaching the deserts today.

Cismontane Southern California Habitats

• The weather is relatively cool and moist, supporting varied habitats.

• Environmental Gradients:   - From coast to western foothills: Elevation, temperatures, and rainfall generally increase.   - From western foothills to mountains: Elevation and rainfall increase, while temperatures decrease.   - From mountains to desert: Elevation and rainfall decrease, while temperatures increase. (draw out gradient)

• Estuaries:   - These are wetlands along coastal waters where rivers (such as the San Diego River) empty into the Pacific Ocean.   -

  • Characterized by brackish water, defined as partially saline with a salinity gradient from fresh to sea water.   -

  • Plants are adapted to saline conditions and low oxygen content.   -

  • Serves as a breeding ground for many birds and stop-over feeding points for migrating birds.   

    • wiping out species

      • species could die and go extinct if we take out a whole habitat.

  • Resident endemic birds currently endangered in these habitats include the Ridgeway Rail and Clapper Rail.

• Coastal Sage Scrub:  

  •  - Dominated by low-growing, drought-deciduous plants adapted to a Mediterranean climate.   

    • - Only $15\%$ of this habitat remains in southern California due to urbanization.   

    • - Harbors endangered species restricted to this habitat, such as the Black-tailed Gnatcatcher and the Orange-throated whiptail lizard.

      • bird wont cross road :(

• Chaparral:

  •   - Characterized by plants with sclerophyllous leaves, defined as thick and leathery, adapted to a semi-arid climate.  (waxy coating that help resist evapotranspiration; retain water in leaves instead of releasing it to atmosphere)

  •  - Adaptations to reduce evaporation include waxy coatings, thicker cell layers, recessed stomata, and oblique orientation to the sun.

  •   - Plants often contain flammable oils.  

  •  - Chaparral communities are primarily endemic to California, with the largest pristine stands occurring between $500$ to feet in elevation.   

  • - Chaparral Communities types:   

    •   - Red shank chaparral: Found in inland and foothill areas; dominated by Red Shank (which can live for over years).    

    •  - Lilac chaparral: Found in coastal and arid inland areas adjacent to coastal sage scrub; dominated by Lilac.     

    • - Chamise chaparral: Found primarily in inland areas; dominated by chamise.     

    • - Mixed chaparral: Contains small and large plants and a wide variety of shrub species.

    •  - Fire Adaptation: Chaparral is fire-adapted; fire is a part of its ecology.     - Some seeds require fire to germinate.    

    •  - Plants feature a thick woody "basal bural" (sic) system below ground unaffected by fire, allowing plants to re-sprout from the base.    

    •  - Some believe these communities never reach a climax state.   - Vertebrates: Includes the California Quail and Ring-neck Snake.

Montane Region Habitats and Endemics

• The climate is cool and moist with winter freezes, which limits the number of different habitats.

• Coniferous Forests:   - Species are evergreen with needle-like leaves to reduce water loss and snow retention.  

  •  - Needles have a waxy coating to reduce water loss and a dark color to absorb heat.   

  • - Drooping branches in some species help shed excess snow.

• Meadows and Lakes:   

  • - Formed in large, flat, open areas that serve as places of drainage.   

  • - These features increase the total biodiversity of the region.

• Montane Endemics:   - Large-blotch Salamander.   - Mountain Kingsnake.   - Grey Tree Squirrel.   - Mountain Quail.

• cool and moist weather limits number of different habitats

Transmontane Region Habitats and Adaptations

• The climate is hot and dry.

• Plant Adaptations to Extreme Heat and Low Precipitation:  

•  - Allelopathy: Defined as the chemical inhibition of one plant by another to prohibit germination and growth.

•   1. Root-mediated allelopathy in Creosote bushes prohibits the germination of the plant's own seeds during stress to reduce competition.   

• 2. Reduced leaves: Prevents water loss via evapotranspiration (e.g., Cacti leaves converted to spines).   

• 3. Ocotillo adaptation: Small leaves appear only after rain events.

•   4. Water storage in trunks to prevent loss during evapotranspiration.

•    5. photosynthesis: Performed in trunks and small leaves to reduce water loss from large leaf surfaces.

• Transmontane Habitats:   

• Rocky Foothills: Located on eastern slopes of Peninsular Ranges extending to the desert floor. Species include the Collard Lizard (sic), Cactus Wren, and Speckled Rattlesnake.

•   - Desert Flats: Low-lying regions of the desert floor containing multiple microhabitats.     -

• Sand Dunes: Home to the Flat-tailed Horned Lizard, Fringe-toed Sand Lizard, and Sidewinder Rattlesnake.     

• Yucca/Agave Forests: Home to Yucca, Agave, and the Night Lizard. Lizards live in dead yuccas 

• - Sandstone: A very unique microhabitat with a limited number of species, including the Sandstone Night Lizard.

Riparian Habitats

• These habitats occur in all regions of southern California (Cismontane, Montane, and Transmontane).

• Defined as plant communities supporting woody vegetation along rivers, creeks, and streams. The river runs through all these communities. Transition zone between the water and land.

• Structure ranges from dense thickets of shrubs and closed canopies to completely open areas.

• Ecological Functions:   

  • - Supply food, cover, and water for many species.  

  •  - Serve as migration routes and stopping points between different habitats.   

  • Stabilize streambanks against the flow of floodwaters. (provide support when there are flood waters)

•       - Provide essential nesting habitat and migration corridors.

• These habitats significantly increase the biodiversity of all regions.

• Associated Species: Mountain Yellow-legged Frog.   - Two-striped Garter Snake.   - California Canyon Tree Frog.   - Mention of La Sierra University within the context of regional geography.