Cypress-gum swamp

Figure 9. Both cypress and gum trees have adapted to life in a wetland by spreading their roots wider for stability. (Photograph by the author. More about the photograph)

As we cruise downstream along our virtual river, we will find places where the river bank is inundated almost all of the time. These habitats support swamp forests dominated by trees adapted to living in flooded soil. The most common type of these forests on the southeastern U.S. coastal plan is the cypress-gum swamp shown in Figure 9.

Interestingly, the seeds of trees characteristic of this habitat cannot germinate underwater, so the presence of mature trees tells us that the area in which they grow was once dry. One of the major adaptations of these species is obvious from a distance — the swollen lower trunks of both species. These features help spread the roots over a wider area than would otherwise be possible. A series of ads for Pontiacs used to say “Wider is Better,” — and it is, if resistance to horizontal forces is your goal. In automobiles the horizontal forces are associated with cornering; in trees they are associated with wind. A wide root base helps keep a tree anchored, especially in a swamp. Waterlogged soils provide much less resistance to root mass movement than do dry soils — a fact shown dramatically all across the southeast when the winds of hurricanes cause huge tree losses when they follow heavy rains. Thus there is an evolutionary advantage for swamp trees to start their root growth from as wide as base as possible.

next