Chaparral
It is shaped by a Mediterranean climate (mild wet winters and hot dry summers) and infrequent, high-intensity crown fires.
Some chaparral species are adapted to nutrient-poor soils developed over serpentine and other ultramafic rock, with a high ratio of magnesium and iron to calcium and potassium, that are also generally low in essential nutrients such as nitrogen.
Additionally, Native Americans burned chaparral near villages on the coastal plain to promote plant species for textiles and food.
Some chaparral plant communities may grow so dense and tall that it becomes difficult for large animals and humans to penetrate, but may be teeming with smaller fauna in the understory.
The seeds of many chaparral plant species are stimulated to germinate by some fire cue (heat or the chemicals from smoke or charred wood).
[14] Because of the hot, dry conditions that exist in the California summer and fall, chaparral is one of the most fire-prone plant communities in North America.
Nearly all of the very large wildfires are caused by human activity during periods of hot, dry easterly Santa Ana winds.
A high frequency of fire (less than 10-15 years apart) will result in the loss of obligate seeding shrub species such as Manzanita spp.
If high frequency fires continue over time, obligate resprouting shrub species can also be eliminated by exhausting their energy reserves below-ground.
Today, frequent accidental ignitions can convert chaparral from a native shrubland to non-native annual grassland and drastically reduce species diversity, especially under drought brought about by climate change.
[15][16] There are two older hypotheses relating to California chaparral fire regimes that caused considerable debate in the past within the fields of wildfire ecology and land management.
[19] However, according to recent studies, California chaparral is extraordinarily resilient to very long periods without fire[20] and continues to maintain productive growth throughout pre-fire conditions.
[21][22] Seeds of many chaparral plants actually require 30 years or more worth of accumulated leaf litter before they will successfully germinate (e.g., scrub oak, Quercus berberidifolia; toyon, Heteromeles arbutifolia; and holly-leafed cherry, Prunus ilicifolia).
When intervals between fires drop below 10 to 15 years, many chaparral species are eliminated and the system is typically replaced by non-native, invasive, weedy grassland.
[27] However, chaparral has a high-intensity crown-fire regime, meaning that fires consume nearly all the above ground growth whenever they burn, with a historical frequency of 30 to 150 years or more.
