Introduction to Fire Ecology

Fire is Natural in our  Climate

We  live in what is called a ''Mediterranean'' climate. This means that the summers are warm and dry, while winters are cool and wet. As a result of this, the end of summer and beginning of fall is a natural fire season. This is true in all locations that have this type of climate, including California. There are 5 places worldwide with our type of climate: California and Northern Baja California, Central Chile, the Mediterranean Basin, Western Cape in South Africa, and Southwest and South Australia.

Ecosystems of California 

 While fire is a natural part of California's ecosystems, each of them will have different patterns. Specifically, each ecosystem has a different

• • • Fire frequency/return interval: Some ecosystems burn every 20 years, others every couple hundred years. 
    • Fire intensity: the fire might burn everything to the ground (Stand Replacement)  or it might only burn some of the plants (Understory would be just the plants on the ground and Mixed Severity means it depends on weather conditions) 

Here is a map showing different fire return intervals and fire intensity. 

Understory fire.	Stand Replacement Fire

Adaptations to Fire

Since fire is a natural part of California's ecosystems, the plants and animals of California are adapted to deal with fire.

Fire Adaptations: Thick Bark

The outer bark of a tree is non-living tissue that protects living tissue within.  Thick bark can insulate the tissues beneath when there is a fire, minimizing damage caused to these tissues by increase temperatures.  In contrast, fire-sensitive trees have relatively thin outer bark that burns through quickly, allowing damage to the living tissues underneath.

Many local trees have thick bark that allow them to survive fires.  Below are some pictures of species with this adaptation and the ecosystems in which they are found.

Fire Adaptations: Resprouting

Many fire-adapted trees and shrubs are able to grow new shoots after fire. These plants resprout from buds belowground that are protected from fire damage.  Below are some picture of local species that can resprout, and the ecosystems in which they occur.

Image Description: The trees featured are a Leather Oak in a Chaparral region, a California Bay in Northcoast Forest with an Oak Woodland in a mixed Evergreen Forest, and a Toyon in a Chaparral region.

Fire Adaptations:  Sealed Cones

Some conifers have cones that say closed on a tree after the seeds inside mature, because the cones are sealed with resin.  These cones are called serotinous.  Serotinous cones can remain on a tree for decades until the heat of a fire melts the resin, opening the cone and releasing the seeds.  The adult trees are often killed, but the seeds released from the parent generation will germinate and grow together as a new cohort of trees.  

Watch the short video below of a cone opening in a toaster oven.

We have local conifers that produce serotinous cones, and they often occur in a unique forest type called "closed cone forests."

Image Description: Featured are the small, circular cones of a Sargent Cypress, the larger, brown, more pointy cones of a Bishop Pine, and the large, greener, and less pointy cones of Knobcone Pine.

Fire Adaptations: Seed Germination Triggered By Fire

The seeds of some plants can remain dormant in the soil for long periods of time until they receive an environmental cue to germinate.  For some plants, fire is this cue.  In some species, the heat of a fire can damage the tough seed coat, allowing germination to occur.  In other species, chemicals in smoke can trigger germination.  

Seed germination as a fire adaptation can occur in trees or shrubs that exhibit some of the adaptations discussed above.  For example, a shrub called chamise, found in chaparral, can survive and resprout, but also has seeds that germinate after a fire.  Other shrubs, like some manzanitas and California lilacs (in the genus Ceanothus)  also found in chaparral are killed by fire, but their seeds will germinate, reviving the population.  

Some annual plants are triggered to germinate after a fire.  The seeds will remain dormant in the soil until the fires triggers germination.  They will then grow, often in large numbers, for only the first spring following the fire.  Once they flower and produce seed, the adults die, and they population will hide out of site in the soil until the next fire.  These annual plants are often referred to as "fire followers" because they are ony seen following a fire.

A common fire follower seen in Sonoma County after the 2017 fires is Whispering Bells, shown below.

Watch the short video below about fire followers in montane forests.