Geoscience Reference
In-Depth Information
Figure 2.7 Little vegetation grows on the forest floor of Madidi National Park, Bolivia.
(Photo by author.)
and oxygen exchange, as well as channeling stem flow and dissolved nutrients to
the roots. Buttresses can increase the surface area of a tree so that it can ''breathe
in'' more carbon dioxide and ''breathe out'' more oxygen. Buttresses can be 15-32
ft (5-10 m) high where they join into the trunk. (see Figure 2.8).
Large Leaves and Drip Tips.
Large leaves are common among trees of the C and
shrub layers. Young trees destined for the A and B layers may have large leaves.
The large leaf surface helps intercept light in the sun-dappled lower strata of the for-
est. If these trees reach the higher canopy layers, their newer leaves will be smaller.
Leaves of tropical rainforest plants often come to a point at the top or end of the
leaf. These are called drip tips, and they ease the drainage of rainfall off the leaf
and promote transpiration (see Figure 2.9). They occur in the lower layers and
among the saplings of species of the emergent layer (A layer).
Thin Bark.
Another characteristic that distinguishes tropical species of trees from
those of temperate forests is exceptionally thin bark, often only 0.02-0.07 in (1-2
mm) thick. In temperate forests, trees need thick bark to limit water loss through
evaporation. Since moisture is not a limiting factor within the rainforest, thick bark
is not necessary. The bark is usually smooth, making it difficult for other plants to
grow on its surface. A few tropical trees are armed with spines or thorns to detract
herbivores (see Figure 2.10).
