Green Planet: How Plants Keep the Earth Alive by Stanley A. Rice

Author:Stanley A. Rice [Stanley A. Rice]
Language: eng
Format: epub
Tags: AvE4EvA
ISBN: 9780813544533
Publisher: Rutgers University Press
Published: 2009-05-04T20:00:00+00:00

Edaphic Conditions

Edaphic conditions refer to the material in which a plant grows, usually but not always soil. It can also refer to rocks on which plants grow or the floating mat of moss that covers a bog. Normal, rich soil is a complex structure of many components, a world in itself (chapter 7). Edaphic conditions, such as rocks or unusual soils, can cause an almost entirely different plant community to dominate over a small area, as shown in the following examples.

Consider what happens with rocky, sandy, or shallow soils. Such soils are both drier and poorer in nutrients than normal soils. In Michigan, areas of rich loam soil alternate with poor sandy soils left by glaciers when they melted. Beech-maple forests dominate the rich soils, while jack pines dominate the sandy soils. Jack pines are more commonly found in the poorer soils of the boreal forest. Hemlocks (Tsuga canadensis)

[165]

are often found on poor, rocky soils in the eastern deciduous forest.6 In parts of Illinois, normal soils also alternate with sand deposits. Black oaks dominate the normal soils, but the sand deposits are so nutrient-poor and dry that no trees at all grow on them. Instead, grasses that are more typical of the western prairies, and even beavertail cacti, grow there. Sand dunes along beaches have different plant species than surrounding habitats. Small cacti grow on granite outcrops in regions of Oklahoma where oaks are the dominant plants.These edaphic conditions, by creating dry microclimates, compress several hundred miles’ worth of climatic change into a few yards.

Along the coast of northern California, tall conifers such as redwoods dominate the normal soils. In some small areas, the soils are very shallow and acidic. In these places, rather than tall redwoods, you see a “pygmy forest” of short bishop pines, tiny cypresses, and plants such as rhododendron bushes that are typical of acidic soils. The trees resemble bonsai trees because, just as bonsai trees do, they grow in very poor soils.

Some soils contain toxic minerals that inhibit the growth of most plants. For example, soils derived from serpentine rock contain high levels of chromium and nickel. These rocks resemble those of the earth’s mantle rather than the continental crust, and they have been lifted up by the movement of the continental plates. Therefore, serpentine deposits are most common near California’s San Andreas Fault. Some species of plants, or varieties of plants within species, are able to grow in these toxic soils. There is a cost to this adaptation, however. These plants grow more slowly in normal soils than do the normal plants. This is what restricts such plants to the patches of toxic soil.

Another unusual soil is diatomaceous earth, an almost perfectly white, powdery soil formed from rock that is made of the shells of billions of diatoms (single-celled plantlike organisms) that accumulated on the bottoms of ancient oceans. I undertook my earliest botanical research project on Harris Grade in the Purísima Hills north of Lompoc, California, where large deposits of this white dirt support a forest of bishop pines (Pinus muricata).

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.