Biology Reference
In-Depth Information
These are among the remarkably useful methods that augment the two tra-
ditional approaches to the study of fossil plants—paleobotany dealing with
plant macrofossils such as leaves, fruits, seeds, fl owers, wood (dendrochro-
nology), and rodent middens, and palynology dealing with spores and pol-
len, phytoliths (plant crystals), starch grains adhering to tools and utensils,
and other plant microfossils preserved in the rocks of the Earth.
It is exciting to contemplate that after some fi ve hundred years of ob-
servation and study, we are at a time when information from biology, ge-
ology, and climatology, past and present, can be integrated into a better
understanding of the Earth's ecosystems. The early founders of geology, tax-
onomy, evolutionary biology, and biogeography—Lyell, Linnaeus, Darwin,
Wallace, and Humboldt—would be amazed and undoubtedly immensely
pleased.
THE GOAL: THE MODERN PLANT COMMUNITIES OF THE NEW WORLD
Having set 100 Ma as a convenient time for the start of our survey, it is
worthwhile to defi ne the endpoint. The goal is to trace the origin and devel-
opment of the existing plant communities of the New World, and to iden-
tify the various events that have guided the process. To do this, a system of
vegetation classifi cation must be developed that is suitable for the purpose.
It is a work in progress because the biota is diverse; in places no natural
vegetation or only remnants remain (fi g. 1.1), and in the vast extent of the
tropics many groups and regions are poorly known. Only two countries in
South America, Peru and Ecuador, have relatively complete lists of native
plants and, as inventories are completed, unexpected results are emerg-
ing. About 27 percent of the plant species of the world are threatened, and
among these, endemics are especially vulnerable because of their limited
distribution. In an analysis of catalogs for Ecuador, an astonishing 83 per-
cent of the endemic plants qualifi ed as threatened (Pitman and Jørgensen
2002).
The hierarchy of categories used to classify vegetation are the plant forma-
tions (e.g., the deciduous forest), associations (beech-maple or oak-hickory
woods within the deciduous forest), and stages (a fern glade or a tempo-
rary open weed community within a beech-maple wood). Several criteria
were used to develop a system suitable for an introduction to New World
vegetation and applicable specifi cally to a discussion of ecosystem history.
First, the categories should be consistent across geographic, political, and
linguistic boundaries. A vegetation type in Mexico called the bosque tropi-
