Plant species use different strategies to compete for limited resources. A plant species may “muscle out” its competition by using relatively constant (though possibly scarce) supplies of a resource more efficiently or aggressively than its neighbors. This is often seen in relatively moist environments where deeper rooted species use water and soil nutrients more effectively than their shallower rooted competitors. An analogy from the business world is the large corporation that can produce a product cheaper than its smaller competitors because of vertical integration and economies of scale. It can, therefore, control the supply of raw materials and obtain them at less expense.
Plants may also compete by using less of a chronically limited resource than their neighbors. One example of this “strategy” is cactus, which requires very little water to survive. Another example is a plant species adapted to the dense shade of heavy forest canopies that can carry on photosynthesis at high rates in limited light. An analogy in the business world is the enterprise that specializes in low input, low cost production. Though total productivity may be relatively low, they can sell their product cheaper, or survive longer during unfavorable conditions until the market improves.
Another adaptive strategy is to use a particular resource at a different place, the way some shrub species use water from deeper in the soil profile than shallow rooted herbaceous plants. They may be the only species with a significant quantity of roots in that part of the profile, and so can exploit that source without competition. In an economic system, these types of businesses are those that utilize small, localized sources of material to produce an item.
Another way plants sometimes compete is to opportunistically utilize resources by “hogging” them during times of abundance, and then die or go dormant when resources become scarce until they are again available. This strategy is used by annual species and some perennials that go dormant during periods of scarcity. In the business world, these people are called speculators, who only invest their money when they see what appears to be a short term opportunity to make a big profit.
Tolerance mechanisms are commonly found in plants that evolved with a history of grazing by large herbivores. These plants are often palatable and grazed by animals when they are present. Tolerance mechanisms that allow plants to be grazed without long-term harmful effects include the ability to change shape, structure, stature, or leaf arrangement and the use of alternate forms of reproduction. When some plants are repeatedly defoliated, they change their stature or the structure of the leaves or stems in an attempt to maintain enough leaf area and protect their growing points. Examples include the lower, denser vegetation of a well-tended lawn compared to an unmown lawn. The “hedged” appearance of some shrubs, where the leaves grow among a dense growth of twigs and are less likely to be browsed, is another example. Alternate forms of reproduction include rhizomes, stolons, and recruitment of additional stems from secondary buds.
Mechanisms include a low stature that makes it more difficult for grazing animals to remove excessive leaf material or the growing points of the plants. This avoidance mechanism is commonly seen in short grasses and some annual plants. Another avoidance mechanism is the adaptation of specialized structures such as thorns, spines, prickles, hairs, or waxy coatings which make the plant either mechanically undesirable or unpalatable.
The other avoidance mechanism often seen in plants as a defense against grazing is production of secondary compounds. All plants do this to an extent by increasing structural compounds like cellulose and lignin as they mature. However, in this context we refer more to compounds that affect palatability, nutrient availability or to toxic compounds. Often, these secondary compounds vary in concentration over time. Also, some secondary compounds offset the effects of other secondary compounds, at least partially, if both are consumed at the same time. By timing grazing events to either allow mixing of different compounds, or using plants in an area when secondary compounds are particularly high or low compared to other plants in the area, we can sometimes affect which plants are chosen by grazing animals, and in what proportions. By doing so, we can often make it easier to achieve animal and plant community goals.