PDC Test - Fundamentals of Fire
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Fundamentals of Fire
by Renée Cohen
American idioms abound with references to fire. You can get fired, get fired up, burn your bridges and on and on. We tend to find peace and joy in candlelight, campfires and fireplaces. Yet we panic madly about natural wildfires and children with matches. Fire has brought us out of the wilderness, as it has aided tremendously in human advancements. Yet it retains the power to swiftly put us right back in the vast harshness of the natural elements. It has the ability to destroy our homes and livelihoods to a frightening extent. In general, we adore fire as a provider of warmth, light, comfort and power; and yet we are terrified whenever fire is not under our strict control. It is no wonder that humans have placed fire central to myth and culture throughout time. While we have tamed wild beasts, learned to fly, successfully crossed the oceans and learned to predict the patterns of the heavens, fire remains one of the last earthly powers to repeatedly humble us.
One fascinating aspect of fire is that it shares its fundamental elements with human life. Both fire and humans consume oxygen from our oxygen-rich atmosphere, and both also rely on carbon, which is the base of life on planet Earth. Humans have evolved employing fire to communicate, to worship deities and perform religious rituals, to clear lands for agriculture, to prepare foods, and to change the chemistry of all kinds of substances for medicine, industry and the arts. Although we rely on fire every day, we rarely pause to consider fire's enormous influence, values and uses in society and in natural systems.
While it is clear that fire and human life go hand in hand, you might not realize how fire and many plant ecosystems are dependent upon each other. Many plants, for example, are encouraged by or even directly dependent on fire.
Eucalyptus, for example, is an Australian plant genus that consists of fire- tolerant plants. In fact, Eucalyptus species show signs of having evolved specifically to take advantage of fires. By burning up dead wood and other debris, fires release copious amounts of nutrients into the environment in the form of ash and smoke. This makes these nutrients readily available to any plant that survives the fire. Its hard, chemically defended leaves, typical of scleromorphs, often fuel the fire, but plants from the Eucalyptus genus are equipped to survive fires by shedding their many layers of tough, thick bark as they get burned. If branches are seared off by fire, Eucalyptus can sprout new ones from epicormic buds, which are growth sites under the trees' bark. Even if the body of a tree were to burn down, the Eucalyptus is equipped to grow the trunk back relatively quickly. Beyond surviving the fire, Eucalyptus plants can take advantage of other plants' deaths because they are able to seize and store large amounts of nutrients which can be used when nutrients in the environment become scarce. This means that while fires are capable of destroying many plants, fires actually assist Eucalyptus plants in succeeding in their environments.
The example of the Eucalyptus as a plant that thrives in the face of fire might seem like a very uncommon one, but there are many plants, and even entire ecosystems, throughout the world that rely on periodic burning in order to maintain some stability. Natural fires, which used to occur every 10-40 years on average in the Californian coastal scrub, were responsible for nutrient cycling and the germination of many plants' seeds. Just like the Australian Eucalyptus forests, many of the plants in the Californian chaparral, like chamise (Adenostoma fasciculatum) and manzanita (Arctospaphylos gladulosa), tolerate regular fires by resprouting branches and green leaves from their subterranean woody stumps called basal burls or lignotubers. A lignotuber can actually be burnt down to ground level then exposed to several seasons of weathering and then resprout after a few rains. Most plants would be long dead, but tough, persistent pyrophytes rehabilitate themselves after fires.
Many lotus species and other wildflowers native to California also require fire's smoke, intense heat or physical burning of the seed coat in order to begin germination. While this may seem odd, it is actually quite a logical strategy for a plant in a harsh, nutrient-poor ecosystem. As previously mentioned, fire frees up nutrients as it burns through an area. Thus, a seed which germinates only after a recent fire can almost be sure to have plenty of essential nutrients readily available to develop fully. For this reason, many colorful wildflowers have waterproof seed coats which preserve the seeds by the millions until they have been charred by fire. After a fire, an entire hillside of colorful blooms might appear due to this adaptation.
Similarly, many pine species drop their seeds only after a fire triggers them to. Knobcone pines, which are shade intolerant, may not open their cones for 80-100 years if there is no fire. Once a fire passes through, though, the cones drop millions of seeds to the ash-covered ground. Such cones are called serotinous cones. This strategy works for the knobcone because the germinating seeds get to take advantage of both the nutrient-rich ash and the direct sunlight that can only reach the ground after a fire has cleared the other plants away. Fires also help serotinous conifers reproduce because they destroy many soil fungi which attack and kill new seedlings. Worldwide there are many examples of serotinous plant seeds which require fire for germination.
Overall, it is difficult to generalize about fire's effects and benefits because fire ecology has so many complicated factors. Some species rely on regular fires while others are destroyed by it.
What is important is to realize that by panicking about fires and religiously preventing them, humans oftentimes end up allowing fire-dependent ecosystems to build up fuel in the form of downed wood and dry leaf litter. When a fire does manage to catch in such an area, the effects can be far more dramatic and traumatizing than if regular, managed fires had been allowed or encouraged. So while this type of burning, known as prescribed burning, might force us to re-examine our fear of large fires in natural areas, it might also help us more deeply understand yet another of fire's profoundly valuable uses.
About the Author
Renee Cohen is a JCR Contributing Editor.
1. While fire was central to the development of prehistoric cultures, it is not very important in modern times.
2. Fire relies on:
a) nitrogen from the atmosphere and coal from the earth
b) oxygen from the atmosphere, coal from the earth
c) nitrogen from the atmosphere, carbon from the earth
d) oxygen from the atmosphere, carbon from the earth
3. Humans have employed fire to communicate, maintain agricultural systems and create medicines.
4. Fire generally does harm to the ecosystem.
5. Fire-tolerant plants are called:
6. Eucalyptus is an allelopathic plant originally from Australia.
7. As a fire passes through an area, it harms many plants, releases nutrients that had been trapped in fuel and provides growth opportunities for scleromorphs.
8. Eucalyptus is considered fire-loving because:
a) it requires heat before it will drop its seeds
b) its leaves are easily shed when fires pass through
c) it can store excess nutrients to use in times of scarcity
d) the trees only grow during fires
9. Epicormic buds:
a) sprout leaves
b) are found under the bark
c) are only found in the Eucalyptus genus
d) are in the cell nuclei
10. Which of the following are scleromorphs?
11. Lignotubers are:
b) fireproof seeds
c) sub-bark branch origins
d) flower roots
12. Smoke, heat and burning is required by some seeds in order to germinate.
13. It is advantageous for a shade-intolerant plant to be a scleromorph.
14. Before they drop their seeds, some pines must be triggered by fire.
15. A serotinous cone opens yearly.
16. Serotinous cones are aided by fire's ability to kill soil fungi.
17. Generally, an ecosystem affected by fire is:
c) depleted of resources
18. Prescribed burning is:
a) unnecessary and harmful to animals
b) often appropriate in chaparral ecosystems
c) a healthy part of rainforest management
d) an aquatic phenomenon
19. According to historians, natural fires in the coastal scrub ecosystem of California used to occur how often?
a) every summer
b) every decade
c) every few decades
d) every century
20. Smoke from burning vegetation leads to decreased rainfall.