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Review the indicators
at a glance
- What fraction of grasslands and shrublands is found in patches
of various sizes? Grasslands and shrublands are commonly found
intermingled with each other and with forests and woodlands. Changes
in the mix of patch sizes and types can affect the value of habitat
for different species, may encourage the spread of non-native
species, and can change fire frequency and intensity. Data are
not adequate to report nationally on this indicator.
Chemical and Physical Conditons
Four indicators describe the chemical and physical condition of
grasslands and shrublands. Two are quite similar to two forest indicators:
nitrate in water and carbon storage. We track nitrate in groundwater
because elevated concentrations of this nutrient can be a sign that
inputs from human sources have increased or that plants are under
stress. We track carbon storage because carbon is the major building
block of grasslands and shrublands and because increased carbon
storage can play a role in offsetting emissions of carbon dioxide
from burning fossil fuels.
Water—or the lack of it—is important in many grassland
and shrubland regions. Two indicators focus on the availability
of water in these low-rainfall regions: we track how often streams
go dry and, when they do, for how long; and we report depth to groundwater.
- How much nitrate is there in groundwater in grasslands and
shrublands? Increasing levels of nitrate (a common form of
the essential plant nutrient, nitrogen) in groundwater is a signal
that plants in the ecosystem are under stress or that the amount
of nitrogen entering the system is increasing. Such increases
can come from fertilizer use and disposal of animal waste and
from rain and snowfall (acid rain), or from changes in vegetation.
Data are not adequate for national reporting on this indicator.
- How much carbon is stored in grasslands and shrublands?
Soil organic matter (decaying plants and animals) consists primarily
of carbon. Organic matter helps soils hold water and can be a
source of plant nutrients and a deterrent to erosion. Increased
carbon storage by ecosystems can offset emissions of carbon dioxide,
of concern because of climate change. Data are not adequate for
national reporting on this indicator.
- How many streams have zero flow for at least one day a year?
For these streams, are the dry periods getting longer or shorter?
Flowing water in streams and rivers is important for human needs
such as drinking water and irrigation; it also sustains plants
and animals, both in the stream and nearby. When this flow stops—even
for short periods—both human uses and ecological functioning
can be disrupted. In the 1970s, 1980s, and 1990s, the percentage
of streams experiencing periods of zero flow was noticeably lower
than in 1950s and 1960s. Fewer streams and rivers had longer than
average zero-flow periods in the 1970s, 1980s, and 1990s, compared
with the 1950s and 1960s.
- What is the depth to shallow groundwater in various parts
of the country? Shallow aquifers provide water for streamflow
and maintain water levels in lakes, are used for a variety of
human uses, and can be used directly by some plants. Increased
groundwater pumping and reduced percolation of water through soils
due to development or soil compaction can lead to lower groundwater
availability. Data are not adequate for national reporting on
this indicator.
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