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What is this Indicator and Why Is It Important?
This indicator presents the area of the four major land-based
ecosystem types covered in this report (forests, farmlands,
grasslands and shrublands, and urban and suburban areas)
as a percentage of the total U.S. land area, for the
most recent 50-year period and compared to presettlement
estimates. It also reports on a key component of freshwater
ecosystems (freshwater wetlands) and will report on
the area of brackish water, a key component of coastal
and ocean ecosystems when data become available. The
change in area since 1955 is also shown for each ecosystem
type.
The area occupied by an ecosystem is one of the most
basic elements of its condition. The area devoted to
different ecosystem types directly influences the character
of the American landscape and largely determines the
ecosystem goods and services that are derived from it.
Conversion from one ecosystem to another means that
the ecosystem goods and services that can be derived
from the original ecosystem are no longer available,
replaced by the goods and services provided by the new
system.
Even though ecosystem area is a basic ecosystem characteristic,
reporting on it is not simple. The area of different
ecosystem types is tallied by different agencies, using
different methods and definitions of the ecosystems.
These estimates provide important trend data and are
generally well regarded. However, because they use different
methods and definitions, data from these different sources
cannot be compared or pieced together for a full national
picture. Satellite remote sensing can provide such an
overall, integrated view (see Map
4.2). However, it is only available at the appropriate
scale for one time period (1992) and thus cannot provide
information on changes in ecosystem area. In this report,
we have generally used the estimates provided by the
various agencies as the basis for reporting on ecosystem
extent. We present the satellite data for comparison
purposes and because, if repeated, it can provide frequent,
consistent, and non-overlapping estimates of changes
in ecosystem extent.
What Do the Data Show? Before European settlement,
the land that was to become the United States was dominated
by forests and grasslands and shrublands. Researchers have
estimated that, before European settlement, there were about
920 million acres of forests
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