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In the past, more than
200 miles of the Platte—from west of North Platte all the way to
Chapman—provided this type of habitat for sandhill cranes, whooping cranes,
least terns, piping plovers, and grassland nesting birds. Over the last
century, however, the Platte River valley has undergone a dramatic
transformation. Numerous dams and water diversions in Wyoming, Colorado and western Nebraska have reduced the river’s flow and sediment supply
substantially (peak discharge, for example, has declined by nearly 70%).
After such changes in flow, the floods that scoured the river of seedlings
and maintained braided channels do not occur anymore, and forests of
cottonwood and willow have become permanently established on sandbars and
islands. This has caused the river channel to narrow-by more than 80% in
some areas—and has eliminated roost sites for cranes and important habitats
for other native birds. (Sandhill cranes will roost in channels as narrow
as 50 feet, but they prefer channels that are 500 feet or more wide, and
whooping cranes select channels that are 1000 feet wide.) Less than half of
the Platte’s open, braided river channel
habitat remains, and now cranes roost primarily in the 40-mile reach of the
river between Kearney and Grand Island and in two smaller areas
upstream. The cranes have abandoned completely more than 100 miles of the Platte river, crowding in
ever—increasing densities into the few remaining open areas.
As river flows have dropped, so have groundwater
levels beneath the riparian wet meadows, and now approximately 75% of the
native wet meadows associated with the Platte have been converted to cropland and other uses. These grasslands
are so necessary a component of the habitat that, for cranes in particular,
the birds’ distribution in the Platte valley is strongly correlated with the locations of the remaining
meadows.
Although much of the
native Platte has changed dramatically, the
open channel areas and riparian grasslands that remain provide essential
habitat for cranes and other migratory birds. Therefore, conserving these
remnant areas of wide, open channels and reclaiming additional degraded
areas are high priorities for the Trust’s habitat protection program.
Conserving and restoring Platte River meadows also are high
priorities in the Trust’s land management program.
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Ultimately, the Trust’s
habitat protection goal is to develop eleven habitat complexes, one in each
bridge segment of the Platte River between Overton and Chapman.
Each complex is a small pocket of the native Platte River ecosystem and is designed to
fulfill numerous habitat requirements of migratory birds. Each habitat
complex consists of:
- 2
miles of water-filled Platte
River channel that is 1000 feet
wide
- 640
acres of wetland habitat that is adjacent to the river channel
- 1,760
acres of native grassland and wet meadow (in addition to the wetland
area) that is within 3-1/2 miles of the river channel
- a
buffer zone around the grassland, half a mile wide, in which human
disturbance is minimized (often, this is agricultural land).
To meet
the ultimate objective, about 29,000 acres of habitat will need to be
protected.
To date, the Trust has
protected 10,000 acres of habitat in the Platte River valley, in eight of the eleven
river sections, by purchasing land and conservation easements from willing
sellers. (The Trust also pays property taxes on all its land, in part so
that our conservation activities do not increase the tax burden on other local
property owners.) The largest component of the Trust’s habitat is native
and reseeded wet meadow (6,400 acres), which is an important habitat for
whooping cranes, sandhill cranes, and other native migratory birds. The
river channel—another important component—provides roosting, nesting, and
feeding habitat for numerous migratory birds, including cranes, least
terns, piping plovers, geese and ducks, and shorebirds (about 20 miles of
channel have been protected). The remainder of the Trust’s habitat is woodland
and crop land (about 2,300 acres).
The Trust’s
conservation partners—the National Audubon Society and The Nature
Conservancy—have protected another 4,000 acres of habitat along the Platte. These areas, together with the
Trust’s land, fulfill about 40% of the habitat goal for the Big Bend reach of the Platte.
Currently, the Trust’s
goal is to protect, on average, 220 acres of habitat per year over the next
25 years. Open river channel and native wet meadow habitats continue to be
the highest priorities for protection.
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HABITAT MANAGEMENT
& RESTORATION
River
channel—Since
1982, the Trust has been reclaiming river habitat to enhance and maintain
roost areas. Vegetation is removed mechanically from river islands, to
eliminate obstructions in the channel, prevent tree establishment, and
encourage erosion. When they occur, high spring flows then churns and
distributes the sediment to form the sandbars that provide roosting and
nesting habitat. It would be impossible to restore the river completely to
its historic state, so our goal is to combine natural and managed areas
into smaller pockets of habitat that maintain their ecosystem function and
meet the roosting needs of sandhill cranes and whooping cranes. Since
beginning river reclamation activities, the Trust has cleared and
maintained more than 28 miles of open river channel on its property and on
areas owned by the National Audubon Society, The Nature Conservancy, and
numerous individual landowners.
Grasslands—The Trust has used a variety of
management techniques to maintain and enhance grassland habitats for
whooping cranes, sandhill cranes, and grassland birds. In general, our
goals are to enhance plant species diversity and provide the vegetative
structural diversity required by cranes and other birds. Enhancing native
plant species diversity is important because high plant diversity
corresponds to high invertebrate abundance and diversity in grasslands, and
invertebrates comprise the critical food sources for cranes and grassland
birds. In addition, we strive to maintain a mosaic of grassland patches
with varying vegetation heights. Short stature vegetation, which is
preferred by whooping cranes and sandhill cranes, is combined with areas of
the moderate and tall stature vegetation required by many grassland bird
species.
[ PHOTO:
PRESCRIBED BURNING HELPS RESTORE PLATTE RIVER HABITAT. ]
The Trust manages its
grasslands using prescribed burning, grazing, and haying. Each management
unit is burned once every 3-4 years, and approximately 1,500 acres are
burned in a single year. The goals of the prescribed burning program are to
reduce vegetation structure, eliminate woody vegetation from encroaching
into wet meadows, suppress exotic plant species, and promote the growth of
native vegetation. Approximately 4,000 acres of grassland are in grazing
rotations and other management, and haying rotations are used on 1,000
additional acres. Grazing and haying are accomplished through leases to
approximately 15 local farmers and ranchers. Haying is restricted to drier
meadows with relatively flat topography, and areas that are wet or rough are
grazed. The primary goal of both grazing and haying is to reduce the
stature of the vegetation to levels preferred by cranes. In the rotation
systems, a few areas are left unharvested each year. The tall vegetation in
these areas provides the type of habitat required by grassland bird
species, and it provides protected areas where cranes can find shelter
during stormy and windy weather.
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Cropland—The Trust’s crop land
(approximately 1,500 acres) also is leased to local farmers, on a
cost-share basis. This land is farmed conventionally, using crop rotations
to reduce pesticide use and hopefully to improve soil conditions. The
majority of the cropland is irrigated by center pivots and gravity systems,
and a variety of crops is grown, including corn, soybeans and alfalfa.
Besides generating income for the Trust, the cropland provides feeding
habitat for cranes and waterfowl—the birds feed primarily on waste
corn—and, in some areas, secondary roost sites where cranes gather in the
evenings before flying to their river roosts.
Prairie restoration—In some areas of the river,
there are not enough native wet meadows remaining to provide sufficient
habitat for cranes and other migratory birds. Therefore, to meet its
habitat protection goals, each year the Trust restores wet meadows that
have been drained and converted to crop land. Fields near the river that
are marginally productive as crop land—due to high water table, low
fertility, and/or high soil pH—are good candidates for wet meadow
restoration. The Trust has experimented with several restoration techniques
and has evaluated the most effective methods for developing reclaimed,
functioning grasslands that resemble native wet meadows. Currently, our
restoration methods incorporate land surface recontouring to restore the
ridge and slough topography that is typical of native meadows, followed by
high diversity plantings of 200+ native prairie species (including grasses,
forbs, and aquatic plants). To date, the Trust has completed 20 wet meadow
restorations totaling 1,200 acres in area. The goal, for at least the next
ten years, is to restore an average of at least 50 acres of wet meadow per
year.
[ PHOTO:
THE TRUST IS RESTORING HABITAT THROUGH CLEARING AND REPLANTING.]
Wetland restoration—Numerous birds depend on
aquatic habitats during their stay on the Platte. This is most dramatically obvious for species like the
whooping crane, least tern and piping plover. For this reason, the Trust
has incorporated wetland construction into its recent grassland
restorations. We have experimented with several construction methods and
still are learning about which give the best results. Our current approach,
when a prairie restoration is initiated, is to structure the land surface
recontouring so it creates the maximum possible linear length of slough
with topography similar to native sloughs. To do this, we excavate a slough
to a depth that is below the water table in some places and just above the
water table in others. The goal is to create a few areas of permanent
aquatic habitat and more extensive areas of seasonally inundated wetland.
These areas provide habitat for a variety of aquatic and wetland plants and
animals that, in turn, provide food for migratory birds. Plans call for wetland
areas to be constructed in almost all of our future grassland restorations.
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