The last time I told you about my experience of the California’s deserts. There’s still a few communities and several ecological topics I would like to discuss in the context of the Golden State before finally wrapping up the series. Let’s start with chaparral. Given the uncharacteristically early start of the fire season in Southern California this seems like an appropriate topic to discuss now.
While California is a huge and incredibly diverse state harbouring tens of different ecological regions, one type of plant community, chaparral, is specifically associated with California. In short, chaparral is the archetypal Mediterranean type vegetation, shaped by climate (wet, mild winters and dry, hot summers) and distinctive fire regime. It’s known by different names in other regions with Mediterranean climate, for example, maquis in France, macchia in Italy, fynbos in South Africa and kwongan in Australia.
Typically, chaparral is dominated by single-layer shrubby vegetation. Depending on the location within the state, chaparral is usually found between 150 – 1500 m elevation (higher in the south and lower on the hills in the north). Shrubs are evergreen and usually have small sclerophyllous leaves with thick cuticles and heavy armour: most have spines or toxins, such as tannins, to deter herbivores and protect precious leaves. Shrub growth is very dense, and can be up to 2 – 4 m in height; there is little to no understory vegetation. The most common chaparral type in California is Chamise (Adenostoma fasciculatum) chaparral. Chamise tend to form monostands, with only few other species found. Other typical chaparral plants, which sometimes come to dominate, include various Manzanita Arctostaphyllos spp., Ceanothus Ceanothus spp., and Scrub oaks, e.g. Quercus dumosa and Q. durata (first grows on non-serpentine soils, while the latter is serpentine species). Yerba buena, Coffeeberry and Toyon are some other important species found in chaparral. I’m familiar with the latter one the best by its Latin name Heteromeles arbutifolia. During the fieldtrip to Stebbins Cold Canyon Reserve in October, 2011 with my Plant Ecology class I was in a group that measured leaf characteristics of H. arbutifolia growing under different light conditions. Classic Sun and Shade leaves plasticity exercise! I saw Heteromeles again only around Christmas time in the hills around Santa Barbara, CA – they were all red with beautiful berries. Appropriately, the plant is also known as Christmas berry :-)
As mentioned above, fire is key in forming and maintaining chaparral. The historical frequency, or Fire Return Interval (FRI), is estimated to be somewhere between 30 to 50 years. Fires are high intensity and stand-replacing, meaning that vegetation is burned completely to the ground. While shoots have no adaptations to resist fire (in contrast to redwoods and sequoias), vegetative recovery is very rapid from extensive dormant seed banks and root sprouting. Depending on their regeneration strategy, chaparral species are often classified as seeders or sprouters. Chamise, for instance, is facultative seeder, meaning that if necessary it can resprout from roots too. Ceanothus species are mostly obligate seeders, while toyon, scrub oaks and coffeeberry are all sprouters. There is a lot of interesting research being done examining the possible regeneration triggers: smoke, charred-wood leachate and for some species the heat from the fire can all induce germination.
After the fire the growth of various herbs, shrub seedlings and shrub crown-sprouts accelerates following the first winter rains. Majority of the herbs are annuals and their seeds germinate either triggered by fire or chemicals released from burning chaparral wood. For one season immediately following the fire chaparral is flushed with wildflowers. However, shrub suckers and seedlings continue to grow bigger, while remaining herbs are rapidly replaced by grasses as grazing by small mammals increases. Shrub canopy reaches maximum height normally within six years after the fire thus completing the succession. Herb layer is almost non-existent in mature chaparral due to most of the herbs being fire-dependent for regeneration, also intolerant to intensive shading and grazing.
So what are the major threats that California’s chaparral faces? While most forests in the state are threatened by the lack of fire and intensive fire suppression, heavily fire-dependent chaparral is somewhat ironically being lost due to too frequent fires and lack of suppression. As a result of more common fires, seeders which are slower to respond to triggers cannot reach reproductive size before the next fire. If fires get even more frequent, sprouters will also be hit as their underground reserves become exhausted and thus plants cannot regenerate anymore. Chaparral is then rapidly replaced by grassland, which prefer higher fire frequency (i.e. typically less than 5 years between fires). Most fires today are caused by human recklessness, and due to chaparral characteristics fires are usually of such high intensity that they can easily get out of control. Due to climate change, fires are projected to be larger, more frequent and of greater intensity. California is already getting taste of this fire future. While the primary concern is human lives and property, the protection of valuable chaparral communities should not be ignored as well.
I returned to Stebbins Cold Canyon Reserve again with another class in May, 2012 after the long and relatively dry winter. It hadn’t rained since the beginning of April, but the place still looked very different from what I saw in the Fall before the start of the winter rains. It was now green and vibrant, and there were still flowers here and there and different colours of leaves and bark. And the smell! It was hot and sticky, we were tired from counting water striders in the pools (our exercise for the day), climbing up the hill, jumping over the rocks and looking out for poison oak, but what I remember the best from that beautiful May afternoon is the intoxicating and enchanting smell of chaparral.
These first two are very interesting and easy reads:
- The changing chaparral. Difference engine: circle of life (economist.com) More on the succession and triggers
- Living with fire: Survival and stubbornness in California wildfire country (grist.org) Personal story of living in fire country
More scientific articles:
- Sensitivity of Fire Regime in Chaparral Ecosystems to Climate Change (Davis and Michaelsen 1995)
Effects of Climate and Extreme Events on Wildfire Regime and Their Ecological Impacts (Duguy et al. 2013) *behind paywall
- The effects of elevated CO2, climate variability, and fire on the functioning of the chaparral of Southern California (Oechel et al. 2011)