Abstract

Cattle grazing can cause substantial damage to stream and riparian ecosystems.  Grazing negatively affects riparian vegetation, stream bank structure, channel morphology, and water quality.  Installing fencing around riparian areas to keep cattle out can greatly improve the environmental conditions associated with streams.  The United States Fish and Wildlife Service Green Bay Fishery Resources Office, Marinette County Land and Water Conservation Department, and Wisconsin Department of Natural Resources participated in a restoration project on a trout stream located in Marinette County, Wisconsin.  The objective of the project was to restore a stretch of stream that had been degraded by cattle grazing by installing an exclosure.  Index of biotic integrity scores, brook trout catch per unit efforts, and water temperatures were used to compare pre and post restoration conditions.  Index of biotic integrity scores and brook trout abundances both improved following installation of the exclosure.  Temperatures remained fairly constant thought the study, suggesting that climatic conditions were more important in determining water temperatures.  This study demonstrates the negative impacts grazing can have on riparian ecosystems and the improvements that can be made by removing the grazers.     

Introduction

Many human influences degrade riparian habitats despite their importance to fish and wildlife (Rinne 1998).  Approximately 70-80 percent of America’s native riparian resources have been lost and much of the remaining resources have been severely damaged (Young and Giese 2003).  Livestock grazing and road construction are among the principal causes of riparian degradation (Young and Giese 2003).  Grazing negatively affects streamside vegetation, stream channel structure, and water quality (Knapp and Matthews 1996).  The fish community of a stream, especially of salmonids, can be altered by the changes induced by grazing (Knapp and Matthews 1996). 

Understanding the population structure of a coldwater stream helps to explain why changes in habitat and fish population structure are correlated.  High quality coldwater streams typically contain a fish population composed solely of one or more salmonid species like the brook trout Salvelinus fontinalis and one or more native stenothermal coldwater or coolwater species like the mottled sculpin Cottus bairdi (Lyons et al. 1996).  Brook trout and mottled sculpin are defined as being intolerant because they are unable to tolerate environmental degradation and harsh environmental conditions (Lyons et al. 1996).  Other species may easily colonize a coldwater stream following degradation because they have the ability to tolerate environmentally degraded conditions (Lyons et al. 1996). 

For many years, riparian buffer zones along streams have been suggested as a way to protect the biological integrity of ecosystems (Wenger 1999 in Blann et al. 2002).  Many studies have confirmed that limiting grazing pressure with fencing can cause a quick reestablishment of riparian vegetation (Opperman and Merenlender 2004).  Fencing allows a passive restoration of aquatic ecosystems by removing the source of environmental stress (Opperman and Merenlender 2004).    

We examined the benefits of eliminating unlimited access of cattle to a stream and riparian ecosystem.  Our objectives were to (1) restore a stretch of stream that had been degraded by cattle grazing, (2) determine if index of biotic integrity scores improved following restoration, and (3) determine if temperature regimes decreased following restoration.  This information will be used to demonstrate the negative impacts grazing can have on riparian ecosystems and to promote the Partners for Fish and Wildlife program.   

Methods

Field studies were conducted on a stretch of the South Branch Beaver Creek located on private property in Marinette County, Wisconsin.  Prior to the summer of 2002, the landowner grazed cattle in a pasture which the stream flows through.  This practice caused noticeable degreases in streamside vegetation and increased erosion.  Fencing was installed in 2002 to protect and provided buffer area for the stream.  Approximately 400 meters of stream and eight acres of riparian land were excluded from the pasture.

A cattle crossing was installed to give cattle access to both sides of the fenced pasture and continued use of the steam as a water source.  The cattle crossing was constructed by installing a base of Geotextile fabric and layering it with 18 inches of quarry run rock, Teracell surfacing material, and 1.5 inches of washed stone.  An excavator dug out the area for the crossing prior to installation so the finished surface would be level with the normal creek bottom.  The crossing extends 20 feet up each bank and is about 20 feet wide.  Fencing runs along both edges of the crossing, perpendicular to the stream.   

Data on the presence and abundance of fishes were collected by conducting electrofishing surveys on two stretches of stream within the protected area.  The stretches of stream to be surveyed were determined to be 127 and 143 meters (Lyons 1992).  A representative sample of the fish community was collected from each site by performing a single upstream pass with a backpack electrofishing unit (Lyons 1992).  Species and numbers of individuals caught were recorded for each site.  Electrofishing surveys were conducted prior to installing the fence in 2002 and again in 2003, 2004, and 2005 to determine if any changes occurred in the fish community. 

Fishery data from each stream site were combined and analyzed using the index of biotic integrity (IBI) for coldwater streams in Wisconsin (Lyons et al 1996) and catch per unit efforts (total catch divided by minute’s electrofished) for brook trout.  The IBI uses a scoring system to determine the environmental quality of an aquatic ecosystem by analyzing its species composition, diversity and functional organization.  Five metrics (total intolerant species caught, percent tolerant species caught, percent top carnivore species caught, percent stenothermal cool and coldwater species caught, percent of salmonid individuals that are brook trout) are calculated.  Each calculation is assigned a score; the scores are compiled; and an overall IBI score is obtained.  A score of 0 indicates substantial human disturbance, environmental degradation, and diminished natural coldwater fish populations.  A score of 100 indicates minimal human disturbance and abundant natural coldwater fish populations.  Catch per unit efforts were used to measure changes in brook trout abundance.  IBI scores and brook trout catch per unit efforts were calculated for each year and compared to see if stream conditions and brook abundances improved following installation of the exclosure.            

Temperature loggers were placed upstream and downstream of the project area to determine if temperature regimes were affected by the exclosure.  Temperatures were collected hourly.  Average daily temperatures were calculated for both temperature locations using data from 20 July to 4 September.  Temperatures from each year were compared to see if the exclosure was encouraging positive thermal impacts, causing downstream temperatures to shift closer to upstream temperatures.     

Results

The fish population structure changed following installation of the exclosure.  Catches of intolerant coldwater species demonstrated overall increases and the total number of species caught decreased (Table 1).  Catch per unit efforts for brook trout were higher following installation of the exclosure.  Brook trout catch per unit efforts for 2002, 2003, 2004, and 2005 were 2.14, 4.19, 4.32, and 2.64, respectively.

Index of biotic integrity scores were higher following installation of the exclosure.  Index of biotic integrity scores for 2002, 2003, 2004, and 2005 were 60, 90, 90, and 80, respectively.  Four of the five IBI metric calculations used to determine IBI scores demonstrated improvements while one, percent of salmonid individuals that are brook trout, remained fairly constant (Table 2).

Downstream mean water temperatures did not shift closer to that of upstream mean water temperatures following installation of the exclosure (Table 2).  Temperatures remained fairly constant throughout the monitoring period.

Discussion

Improved conditions on the South Branch Beaver Creek following installation of the exclosure are evident.  IBI’s and brook trout abundances both improved.  These improvements can be explained by the destruction of riparian habitat caused by grazing.  Many past studies have documented the destruction of riparian vegetation, stream bank structure, channel morphology, and water quality because of livestock grazing (Platts 1997, 1982, 1989, 1991; Rinne 1988; Myers and Swanson 1995; in Blann et al. 2002).

Streamside vegetation, and the many benefits associated with it, can be negatively impacted by grazing.  Riparian vegetation supplies bank stabilization, contributions of large woody debris, and shade (Opperman and Merenlender 2004).  Aquatic vegetation also increases the abundance of aquatic macroinvertebrates (Egglishaw and Shackley 1997; in McRare and Diana 2005), which provide food for trout (Jowett 1992; in McRare and Diana 2005).  Vegetation loss caused by grazing thus increases erosion, eliminates habitat, causes summer water temperatures to increase, and reduces terrestrial food inputs (Clarkson and Wilson 1995).       

Opperman and Merenlender (2004) found that riparian restoration can result in rapid increases of large woody debris (LWD).  Increases in LWD following riparian restoration initially results because young riparian trees trap wood as it floats downstream (Opperman and Merenlender.  2004).  LWD is deposited directly to restored stretches of stream as trees within an exclosure grow (Opperman and Merenlender 2004).  LWD ultimately improves fish habitat.      

Brook trout cover, provided by shade, depth, and surface turbulence (Gibson 1978), can be negatively impacted by grazing.  Hoof-induced activity widens the stream channel and destroys undercut banks (Clarkson and Wilson 1995).  Shallower, wider streams have less shoreline relative to surface area and a reduced diversity of habitat compared to smaller, narrower streams (Stoneman and Jones 2000).  Additionally, increased sedimentation caused by bank erosion can be harmful to spawning habitat (Blann et al. 2002).  Brook trout favor spawning in gravel substrate (Brasch et al. 1973; Brynildson et al. 1973; in McRare and Diana 2005).  Increased sedimentation can suffocate eggs and fry (Clarkson and Wilson 1995) and alter the composition of spawning substrate. 

Many of the factors associated with buffers, including thick vegetative cover, stable banks, and deep, narrow channels (Zimmerman et al. 1967; Murgatroyd and Ternan 1983; Beschta and Platts 1986; Peterson 1993; Sweeney 1993; Trimble 1993, 1997, 1999; Sovell et al. 2000; Nerbonne and Vondracek 2001; in Blann et al. 2002), can influence fish survival indirectly by affecting water temperature.  Cold water must be accessible for trout species to thrive (Stoneman and Jones 2000).  McCormick et al. (1972; in McRare and Diana 2005) found that the ideal temperature range for growth and survival of juvenile brook trout is 12-15°C and that the maximum tolerance level is 18°C.  Hunt (1979; in Blann et al. 2002) found that brook trout flourish in temperatures between 13°C and 18°C.  Cherry et al. (1997; in Blann et al. 2002) found that brook trout prefer 19°C but can tolerate 24°C. 

Many past studies document the importance of temperature to the survival of fishes. 

Opperman and Merenlender (2004) found that water temperatures within exclosures were able to maintain temperatures significantly lower then upstream controls that were not excluded from grazing.  Temperatures outside exclosures reached levels that can cause oxygen deprivation (21°C) (McEwan and Jackson 1996; in Opperman and Merenlender 2004) or death (23°C) (Moyle 2002; in Opperman and Merenlender 2004) for steelhead, whereas temperatures inside exclosures maintained optimal to just above optimal temperatures (15-18°) (Moyle 2002 in Opperman and Merenlender 2004) for steelhead growth.  McRare and Diana (2005) determined that water temperature was the key variable associated with age-0 brook trout density when mean water temperatures were close to their maximum tolerance.  MacCrimmon and Campbell (1969; in McRare and Diana 2005) found that maximum summer water temperature was the principal factor restricting brook trout distribution.

Cooler water temperatures within exclosures may be a result of increased shading, channel form, and improved infiltration of groundwater feeding in deeper pools (Poole and Berman 2001; in Opperman and Merenlender 2004).  Blann et al. (2002) found that, on a stream with a width of 4.9 m, a grazed buffer provided 6% shade and had a water temperature 1°C warmer then a successional buffer which provided 38% shade.  A wider and shallower channel increases the air-water interface, which can also increase temperature (Blann et al. 2002).

Ecosystems are undoubtedly affected by countless factors.  Typically, water temperature is influenced greatest by air temperature, followed by relative humidity, streamflow, percent shade, inflow temperature, stream width, solar radiation, and wind speed (Bartholow 1989; in Blann et al. 2002).  The slight changes in temperature observed on the South Branch Beaver Creek can most likely be explained by fluctuations in climatic conditions.  Additionally, substantial short-term variations in stream fish populations can also be caused by changes in climatic conditions (Clarkson and Wilson 1995).                  

The purpose of our study was to restore a stretch of stream that had been degraded by cattle grazing.  Improvements in IBI scores and brook trout abundances following completion of the cattle exclosure provide evidence supporting the success of the project.  This study provides an example of the negative impacts grazing can have on the environment.  It also demonstrates the improvements that will occur if grazers are eliminated.  

Acknowledgements

The author thanks Stewart Cogswell of the United States Fish and Wildlife Service, Greg Cleereman and Paul Klose of the Marinette County Land and Water Conservation Department, Justine Hasz of the Wisconsin Department of Natural Resources, and Melvin Brault, landowner.  Funding for this project was provided through the United States Fish and Wildlife Service Partners for Fish and Wildlife Program, the Marinette County Land and Water Conservation Department, and Melvin Brault.  For more information of the Partners for Fish and Wildlife Program visit www.fws.gov/partners/.

References

Blann, K., J. F. Nerbonne, and Vondracek, B.  2002.  Relationship of riparian buffer type to water temperature in the driftless area ecoregion of Minnesota.  North American Journal of Fisheries Management 22:441-451.

Clarkson, R. W., and J.R. Wilson.  1995.  Trout biomass and stream habitat relationships in the White Mountains area, East-Central Arizona.  Transactions of the American Fisheries Society 124:599-612.

Gibson, R. J.  1978.  The behavior of juvenile atlantic salman (Salmo salar) and brook trout (Salvelinus fontinalis) with regard to temperature and to water velocity.  Transactions of the American Fisheries Society 107(5):703-712.

Knapp, R. A., and K. R. Matthews.  1996.  Livestock grazing, golden trout, and streams in the Golden Trout Wilderness, California: impacts and management implications.  North American Journal of Fisheries Management 16:805-820. 

Lyons, J.  1992.  Using the index of biotic integrity to measure environmental quality in warmwater streams of Wisconsin.  United States Department of Agriculture, Forest Service, North Central Forest Experiment Station, General Technical Report NC-149, St. Paul, MN.   

Lyons, J., L. Wang, and T. D. Simonson.  1996.  Development and validation of an index of biotic integrity for coldwater streams in Wisconsin.  North American Journal of Fisheries Management 16:241-256.

McRare, B.J., and J.S. Diana.  2005.  Factors influencing density of age-0 brown trout and brook trout in the Au Sable River, Michigan.  Transactions of the American Fisheries Society 134:132-140.

Meisner, J. D. 1990.  Potential loss of thermal habitat for brook trout, due to climatic warming, in two southern Ontario Streams.  Transactions of the American Fisheries Society 119:282-291.

Opperman, J. J., and A. M. Merenlender.  2004.  The effectiveness of riparian restoration for improving instream fish habitat in four hardwood-dominated California streams.  North American Journal of Fisheries Management 24:822-834.

Rinne, J. N.  1998.  Grazing effects on stream habitat and fishes: research design considerations. North American Journal of Fisheries Management 8:240-247. 

Stoneman C. L., and M. L. Jones.  2000.  The influence of habitat features on the biomass and distribution of three species of southern Ontario stream Salmonines.  Transactions of the American Fisheries Society 129:639-657. 

Young, R. A., and R. L. Giese.  2003.  Introduction to forest ecosystem science and management, 3^rd edition.  John Wiley & Sons, Inc. 

Tables

TABLE 1. – Classification of fish species into tolerance, feeding, and temperature preference groups (Lyons et al. 1992, 1996) and total numbers caught by species (Lyons et al. 1992, 1996) per year.  For tolerance, I = intolerant; O = other (tolerance levels between intolerant and tolerant); T = tolerant.  For feeding, TC = top carnivore; - = not a top carnivore.  For temperature, ECD = exotic stenothermal coldwater; NCD = native stenothermal coldwater; NCL = native stenothermal coolwater; NEU = native eurythermal.

TABLE 2.—Index of Biotic Integrity (Lyons et al. 1996) calculations and mean daily water temperatures for data collected during four consecutive years on the South Branch Beaver Creek.  For Metric, I = number of intolerant species; T = percent of all individuals that are tolerant species; TC = percent of all individuals that are top carnivore species; SCC = percent of all individuals that are stenothermal coolwater and coldwater species (native and exotic); BKT = percent of salmonid individuals that are brook trout.  For temperature, Up = upstream temperature location; Down = downstream temperature location. 

Return to Table of Contents.