"Nature Guide Journal"

"Why is that plant growing there?" Successful gardeners are adept at matching the plants to the micro-environments of their plot. Deducing the micro-environment from plant communities in nature is a delightful exercise.

Clearly, individual species of land plants have somewhat different requirements for the basics: sun, water, nutrients. And, plants that have similar requirements tend to live together. Plant communities are a basic tool for viewing and understanding nature; for seeing patterns in a larger whole.

Sun or shade may seem clear-cut, until you consider different depths of shade and shade at different times of the day. Or shade at different times of the year. For example: Douglas fir casts heavy shade year-long; red alder casts light shade through the summer, but allows plenty of light to the ground in early spring before the tree's leaves fully emerge.

The amount of available water can profoundly affect the plants in a given site. As with the sunlight, the timing can be as important as the amount. In winter, there may actually be more water standing in the deflation plain between sandy dunes than you'd find in a marsh. But the marsh's ability to retain water through the dry summer–and the inability of the sand to hold it–is the critical element that makes the two plant communities very different.

Several aspects of soil influence plants, particularly the specific minerals and nutrients and the amount of water-retaining materials. A downed log often provides an enriched micro-environment that produces a line of trees and shrubs over a more-barren forest floor. Besides wood-decaying mushrooms, there are a few seed plants, like fool's huckleberry, that require substantial woody material.

Certainly, it's not quite that simple. Where specific plants grow is also influenced by each species' tolerance for less-than-perfect conditions, by its ability to withstand catastrophic events, and many other factors. The available seed plants also play a role in determining the plants in a given community, as do the animals that fertilize flowers, spread seed, eat select plants, or help decompose dead ones.

Sun, water, and nutrients affect each other, as well. An increase of water would likely lead to an increase of plants, which would augment the nutrients in the soil as they die. More organic material helps the soil retain water.

Further, the plants living in a given place influence each other. Taller plants shade shorter ones, dense plants give shelter from the wind, and all plants draw water from the soil in life and add nutrients in death. Less obvious are the influences of non-related plants to others in the community, such as the parasitic plants that weaken others or the symbiotic plants (like some fungi) that help other plants obtain nutrients.

Pondering the changing plant communities gives a Sherlock Holmes flavor to a walk in the woods. Finding the shade-loving wild lily of the valley in a bright sun spot can lead you to discover the fallen tree that opened up the forest's canopy. Further investigation might even reveal evidence of the beaver that felled the tree. The whole investigation will deepen your understanding of that natural community.