Figure 1. Map showing location of Fort Collins in

relation to FRIRP study area and demonstration area.

Woody Riparian Communities

Riparian Restoration

 Riparian (streamside) vegetation

communities are of interest in the context of the Front Range Infrastructure 

Resources Project (FRIRP) because they

are often a focal point for conflicting

societal demands. The cottonwoods and

willows comprising these communities

are structurally complex compared to the

surrounding landscape and support diverse assemblages of mammals, birds,

reptiles, and amphibians. However,

riparian areas are also primary sites for

water development, agriculture, grazing,

sand and gravel mining, and recreation,

each of which may limit other uses. 

Direct and indirect impacts of these

activities have led to exploration of new

opportunities and techniques for restoring

disturbed riparian habitats and to greater

concern for some of the scarce species that

inhabit them.

 Cottonwoods and willows produce

abundant wind-borne seeds adapted to

germinate on disturbed patches of bare,

moist soil in full sunlight. Cottonwoods

in particular are intolerant of shade and

germinate poorly in plant litter; they

rarely become established under an

existing stand of trees. Successful

recruitment of these species also requires

that germination sites be safe from

subsequent floods and ice scour, at least

for a few years, and that roots be able

to make contact with the subsurface

water table during the first year of

growth to prevent drought mortality.

In the past, spring and early summer 

flood flows created these disturbance

patches along Front Range rivers. In

cooperation with the city of Fort Collins

and Western Mobile, Inc., U.S. Geological

Survey (USGS) scientists are examining

an approach to reclamation of sand and

gravel pits that uses hydrologic manipulation to mimic the effects of flooding to

produce appropriate germination sites.

 The 17-ha WREN pit (named for a

broadcasting company that once owned

the property) is located adjacent to the

Cache la Poudre River in east-central

Fort Collins (fig. 1). Water seeps into

the pit from the river, and a drain culvert and screw gate on the opposite side

allow control of water levels. Western

Mobile prepared the site according to a

plan provided by the city of Fort Collins.

Side-slopes were reduced from their

after-mining condition, the floor was

sloped gradually toward the drain, and

two small islands were constructed near

the middle of the pit. Nearly all existing

vegetation was removed or covered by

these operations.

 We simulated a natural hydrograph by

filling the pit with water and conducting

a series of annual drawdowns during

natural seedfall (fig. 2). We gradually

lowered the water level (about 1 cm/day)

to provide a fringe of moist soil suitable

for germination of cottonwood and

willow seeds. We repeated this process

at successively lower elevations for 3

years, in each case raising the spring

water level back to approximately the

lowest elevation at which establishment

occurred in the previous year before

initiating the drawdown. While judgments about the ultimate success of this

project in producing mature trees will

not be possible for several years, woody

vegetation is developing well. The

city of Fort Collins has now purchased

the WREN pit as part of its natural areas

program.

Printed on recycled paper U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–117–98

October 1998

FRONT RANGE INFRASTRUCTURE RESOURCES PROJECT

Biological Resources

Demonstration Area

Cheyenne

Fort Collins

Greeley

Boulder

Denver

Colorado

Springs

Pueblo
Figure 4. Preble's meadow jumping mouse. 

Figure 2. The WREN pit, filled and ready for drawdown.

Figure 3. Flooding mortality of cottonwood and saltcedar seedlings is being studied in a controlled

experiment.

 Concurrent establishment of saltcedar,

an undesirable non-native species, was a

problem during our work at the WREN

pit. In Colorado, saltcedar disperses seed

somewhat later, but for a longer period of 

time, than does cottonwood. This difference in dispersal, coupled with the fact

that saltcedar seeds are very small and

therefore contain few energy reserves,

means that saltcedar seedlings usually 

remain smaller than cottonwood seedlings

through the first growing season. During

our first year of work, we reflooded the

pit to try to eradicate a severe infestation

of saltcedar seedlings, attempting to

control water levels such that most of the 

 One species that is found almost exclusively in heavily vegetated riparian

areas is the Preble's meadow jumping

saltcedar seedlings were completely

inundated but the larger cottonwood

seedlings were not. This control

effort appeared to be successful; most

saltcedar seedlings were killed, and

many cottonwood seedlings survived.

We subsequently began a controlled

experiment, using pot-grown cottonwood and saltcedar seedlings, to

examine further the effects of both fall

and spring flooding (fig. 3).

mouse (Zapus hudsonius preblei), a

subspecies recently listed as threatened

by the U.S. Fish and Wildlife Service

(fig. 4). It is presently known to occur

in seven counties along the Front Range

of Colorado and in two counties in

Wyoming. Historical records indicate

that it was formerly present in a few

additional counties in both States. Habitat

loss and degradation caused by agricultural, residential, commercial, and

industrial development are believed to

imperil its continued existence.

 Much of the remaining habitat for the

mouse occurs in areas with known or 

potential sand and gravel resources,

which are being mapped as part of the

Front Range Infrastructure Resources

Project. We are also cooperating with

the Colorado Division of Wildlife to

develop detailed maps of riparian

vegetation in parts of the Front Range

and with the Colorado Natural Heritage

Program to compile data on locations

where the mouse has been trapped. We

will combine this information in a

geographic information system to analyze

the relationship between mouse locations,

riparian vegetation, and sand and gravel

resources. We will work closely with

other scientists who are studying the

mouse to determine how best to use these

data to identify areas of potential mouse

habitat. Data on specific habitat requirements of the mouse may also be useful in

developing guidelines for reclaiming 

sand and gravel pits to benefit this

threatened species.

For additional information, contact:

James E. Roelle

Midcontinent Ecological Science Center

4512 McMurry Avenue

Fort Collins, CO 80525

970-226-9435

butch_roelle@usgs.gov

Saltcedar Control

Preble's Meadow Jumping

Mouse

FRONT RANGE INFRASTRUCTURE RESOURCES PROJECT

Biological Resources