Why Are Native Plants Important?

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Table of Contents

The Importance Of Native Plants To Wildlife And The Ecology Of An Area
The Importance Of Native Plants To Humans
Plant Communities
Plant Adaptabilities, Especially Due To Climate Change, And The Effect Of Habitat Fragmentation
Sources and Further Reading


The Importance Of Native Plants To Wildlife And The Ecology Of An Area

Plants are the basis of the entire food chain and oxygen in the atmosphere. When the Earth formed 4.6 million years ago, the primitive atmosphere was a witch's brew of toxic chemicals such as ammonia, hydrogen and methane, without any oxygen. The composition of the atmosphere gradually changed to nitrogen, water and carbon dioxide from 4.0 to 3.3 billion years ago. Somewhere around 3.6 billion years ago, a primitive plant appeared that could convert carbon dioxide, water and sunlight into glucose and oxygen through what is called photosynthesis:

     6 CO2   +   6 H2O   -------->   C6H12O6   +   6 O2 
                                   (glucose)

Photosynthesis is actually a chain of reactions, which essentially first splits water into hydrogen and oxygen, and then adds that hydrogen onto carbon dioxide to make glucose. Glucose is therefore a solid made essentially from a gas, 93% by weight from carbon dioxide plus 7% by weight from the hydrogen from water.

As a result of photosynthesis, levels of oxygen gradually rose, and life changed from anaerobic bacteria to aerobic bacteria. By ~500 million years ago (mya), oxygen levels were high enough to form the ozone layer and screen out harmful ultraviolet light from the sun, enabling higher organisms to evolve and for life to be possible on land. Land plants first appeared ~440 mya, and flowering plants ~140 mya.

Glucose is not only a direct energy source, but also makes up the cells of plants. Cell walls are made of cellulose, which is simply thousands of glucose molecules linked together into a polymer. Since wood itself is made of bound up or polymerized glucose and cellulose, the mightiest tree trunk has been created out of thin air by plants!

Oxygen is the basis of nearly all life on Earth at present, required for both plants and animals to burn (oxidize) the sugars created by plants to produce the energy needed by life.

If plants were suddenly wiped out, all the oxygen accumulated over billions of years would be used up in several thousand years! Six billion humans alone would have reduced the oxygen level to the point where movement was impossible in only 150,000 years. (That point is reached at an oxygen concentration by volume of 16%, compared to the current concentration of 21%. Humans require about 1 kg of oxygen per day, and there is about 1018 kg of oxygen in the entire atmosphere.)

Plants and animals have evolved together to best match the environment.

Plants and animals have an ongoing war that has created intimate associations. In particular, animals want to eat plants, and plants don't want to be eaten. As a result, plants have evolved physical and chemical defenses.

Examples of physical defenses are spines, prickles and thorns; unpleasant odors; gummy secretions; and thick, tough leaves.

There are many different types of chemical defenses. A passion vine has at least two different types. First, it produces nicotine sulfate, a toxic alkaloid which is a potent pesticide. Second, it has the neat trick of putting cyanogenic glycosides in an intracellular compartment, and a glycosidase enzyme in a separate compartment. When a herbivore munches on green tissues of a passion vine, the enzyme is brought into contact with the glycoside and cyanide is released.

There is literally thousands of different toxic chemicals produced by plants in their ongoing struggle to avoid being eaten. There are two major strategies that animals have evolved to counteract them. First, an animal could evolve a specific detoxifying mechanism for the particular toxins produced by a single species. Second, since many of these toxins are produced by "variations on a theme", an animal could evolve a special organ that could use some general themes to detoxify a wide variety of substances.

Many insects have taken the specific route. You can imagine that this is the least costly mechanism to an insect, but it comes at a cost: the insect is forever tied to that particular species.

This approach is taken by essentially every butterfly species. Their caterpillars feed on only a very limited range of host plants. The most famous example is the Monarch butterfly, which has carried detoxification to a fine art - it has developed enzymes to take the toxin intact from milkweeds and incorporate it into its body, so the caterpillar and butterfly itself becomes toxic to their would-be predators.

No one knows the number very well, but probably the majority of insects eat only a small number of plant species. Think of the corn plant, which is eaten by the corn borer, the corn earworm, and the corn rootworm. Plant galls are a very visible example of this relationship, where an insect lays its eggs on only one species of plant, which then is stimulated to form an unusual plant growth solely for the benefit of the insect larvae. The larvae eats the plant, and lives within the gall its entire life until it is ready to repeat the process over again.

Even some mammals are specialists - koala bears, panda bears, and sloths all have quite restricted diets.

The other approach is taken by most mammals like ourselves. We have evolved a liver whose task is to detoxify the vast array of poisons plants throw at us.

From an article by Bruce Ames, the developer of the Ames test for the cancer-causing potential of a substance:

On average, Americans ingest roughly 5,000 to 10,000 different natural pesticides and their breakdown products. Americans eat about 1,500 mg of natural pesticides per person per day, which is about 10,000 times more than the 0.09 mg they consume of synthetic pesticide residues.

You'll recognize the names of some toxic alkaloids: strychnine, caffeine, nicotine, cocaine, and morphine are all alkaloids which we extract from plants for pharmaceutical, recreational and agricultural uses. It is relatively safe for us to consume these toxins because we have a liver which was designed to detoxify such things.

However, there are always exceptions to general rules, and alkaloids are no different. Poison hemlock has about 1% alkaloid concentration in all plant parts, and is extremely toxic to humans. The Greeks used to kill criminals by forcing them to eat poison hemlock (Socrates was perhaps the most famous example).

Interestingly, plants have evolved to take advantage of their "enemies". Trade nectar (or even seeds) for pollination Trade food (berries) for seed dispersal some plants are pollinated only by a specific insect. (yucca moth) if one dies, so does the other. hence the loss of a single plant may have unknown much larger repercussions (homeostasis vs. catastrophic change) example: decline of sea otters in aleutian islands, from 50-100,000 down to 6,000 in 2000. A handful of killer whales began eating sea otters, perhaps due to a decline in ground fisheries and a change in ocean currents that resulted in their usual prey (Steller sea lions and harbor seals) becoming less abundant. Because sea otters eat sea urchins, their smaller numbers have caused an increase in urchins and a loss of kelp, which urchins graze on. As a result, kelp forests may decline, affecting other species such as seabirds. a single killer whale could consume about 1,800 otters in a year. LAT 10/28/00; sdut 11/11/00. alternatively, when a non-native plant is introduced, there can be a number of deleterious effects: uncontrolled weeds that provide no food for native fauna, and displacement of natives. This is not "survival of the fittest" - this is "unfair competition". (;-)

The Importance Of Native Plants To Humans

2. the importance of native plants to humans; 1. ecology (preserve a balance of nature). What happens when we run out of water during an extended drought? What kind of world would it be if we had only the relatively few plants sold by nurseries, along with only insects that live off humans and their pets (mosquitoes, ticks, fleas, biting flies, cockroaches)? 2. drugs. The vast array of natural chemicals is already the basis for ~25% of all U.S. prescriptions, ranging from aspirin (bark of willow tree) to taxol (bark of pacific yew tree) 3. aesthetic. These plants are in perfect harmony with their environment, have amazing adaptations to survive, and are beautiful and interesting. Imagine how boring it would be to hike only through avocado groves!

Plant Communities

3. plant communities; it is easy to recognize the fundamental types of plant communities (forests, grasslands, riparian and chaparral). Finer divisions are the subject of much debate. except for some generalists, plants like specific environments. Riparian - abundant water supplies, but have to deal with flooding and erratic flows. Short-lived plants with big leaves, and a dynamic community. Riparian habitats have undergone the most degradation of almost any community, due to damming of rivers, channelization, or grading them out of existence. As a result, many endangered species are (not) found there. Plant list: willow, mule fat, cottonwood, coast live oak, poison oak, western sycamore. Chaparral - one of the most characteristic plant communities of california. Chaparral is found only in areas with wet, mild winters and hot, dry summers. Chaparral is from the Spanish, "a place of scrub oak". Because it contains many plants with hard leaves, and is often impenetrable, "chaps" were invented to protect the legs of people on horseback. Chaparral is a very underappreciated community of plants, with a number of amazing and unique features: - Chaparral plants are perfectly adapted to the climate regimen. They produce new leaves during the wet season, and often drop their old leaves only after the new growth is established and the plants go dormant. In this way, they are ready to go as soon as the rains return. - Chaparral is adapted to regular fires. Many species resprout from the base after a fire, others require a fire for their seeds to germinate. - Surprisingly, one of the main plants of chaparral, ceanothus species, produces more biomass in 20 years than do the Douglas fir forests of Washington or the deciduous forest in the eastern U.S., despite being a much shorter plant. - Chaparral is incredibly diverse and contains one of the largest number of species of any community. that's why it contains a lot of endangered species. It contains ~900 plant species, about 1/3 woody plants, 1/3 annual herbs and 1/3 perennial herbs. Plant list: laurel sumac, chamise, hoaryleaf ceanothus, scrub oak, mission manzanita, manzanita. Coastal Sage Scrub - these are coastally-influenced lower elevation (below about 3000') "scrubby" plants that are 1-6' high. The name comes from the presence of white sage or black sage. Other typical species are California sagebrush, California buckwheat, and Poison Oak. (all on plant list)

Plant Adaptabilities, Especially Due To Climate Change, And The Effect Of Habitat Fragmentation

4. plant adaptabilities, especially due to climate change, and the effect of habitat fragmentation climate changes: 1.6 million years ago, the area here was covered with pines and oaks. redwoods grew in santa barbara, and the current sierra nevada pine forest grew in the mtns here. currently, redwoods are almost extinct, confined to a couple of small areas. 10,000 years ago, at the height of the ice age, chaparral was restricted to the more deserty areas. it moved to its current location as the climate warmed. timescale for new species: ~1 million years. (it took ~3 million years to recover from the terminal K-T extinction.) timescale to migrate: ~100 years(?) (1 km / year, 100 km for 1 degree warming) ===> plants need connected habitat in order to migrate, cause they ain't gonna evolve new species fast enough, and we need to minimize extinction of species. also, habitat loss nearly always results in the loss of some species. (consequence of n(species) ~ Area^x ==> one place is never exactly like another) 5. how to identify plants 4 methods: 1. flip through picture books (hard!) 2. flip through picture books starting from a plant list (medium) 3. learn with a guide (easiest) 4. learn plant terminology and characteristics, and use jepson et al. (hard to learn! but much easier in the end) (6. i assume giessow will already have made the points about non-native plants. 1/8 of the flora of california are non-native plants now.) we'll have only ~10 minutes per topic inside, so will need to hit some of these points more on the outside. "plant communities" is probably the best one for the outside, as well as how to id plants (if we run out of time inside, this can be solely an outside topic). in addition, you do a great job talking about the indian uses for plants, so that is a good topic for outside when we see specific plants. finally, we'll need to hit hard 3 species for them to really learn on the walk - perhaps chamise, california buckwheat, and white sage or black sage?

Sources and Further Reading

Earth, F. Press and R. Siever, 1978, Freeman. (early atmosphere of Earth, evolution of life and oxygen)


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