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Effects of Burning and Mowing on Prairie Grouse Habitat
Llewellyn L. Manske PhD
Associate Range Scientist
North Dakota State University
Dickinson Research Extension Center
Prescribed burning and mowing are essential defoliation management tools needed to assist in proper ecological management of the Sheyenne National Grasslands. Livestock grazing can not be the only defoliation tool used to manage grassland plant communities. Cattle generally graze very little on the sedge meadow and switchgrass areas during the mid and late portions of the grazing season because the plants tend to mature early. This in effect causes the grazing pressure to be shifted to other plant communities. Grazing pressure use on the forage plants of unmanipulated sedge meadow areas was generally 10% or less. If portions of the sedge meadow are manipulated by burning and mowing before cattle enter the pasture, cattle can be attracted to graze the regrowth tillers on the sedge meadow areas and reduce the grazing pressure on the other plant communities. Burning and mowing can also be used to reduce undesirable shrub encroachment onto these areas.
Prairie grouse use the switchgrass areas for nesting, roosting, escape, and concealment cover which make this a very important habitat for the grouse. The effects of mowing and burning on this prairie grouse concealment cover habitat were not previously evaluated quantitatively. A summer mow trial and a spring burn trial were conducted separately. The summer mowing trial was conducted on switchgrass areas that had been mowed one time on known years during the period of 1974 to 1979 between early July and mid August. Areas that had been excluded from grazing and mowing during the spring of 1975 were used as control plots. Height-density pole readings were taken according to the method developed by Robel et al. (1970) and modified by Kirsch (1974).
Generally, with the increase in time after the mowing treatment, the mean 100% visual obstruction measurements (VOM) increased progressively until the 4th spring after treatment then the measurements decreased to a height-density that can be considered to be at an equilibrium level with the climatic conditions (Table 1). The mean height-densities of the 100% VOM collected during the first spring after a summer mowing treatment did not meet the minimum for good concealment cover of 1.5 decimeters. No nesting or night roosting would be expected to occur in these and similar areas. If areas with dense cover of greater than 1.5 decimeters were adjacent, prairie grouse would have used these first spring mowed areas for courtship display grounds, morning and evening feeding sites, and a small amount of day loafing. During the second spring after mowing, the sites had a mean height-density for the 100% VOM of 1.5 decimeters. This was considered the minimum for nesting and night roosting cover. Some roosting and possibly some nesting could be expected to occur in these second spring after mowing areas. These areas would have been used more for day roosts, some summer brood rearing, and day loafing sites on days that were not too hot. The mean height-densities for the 100% VOM for the third and fourth spring after mowing treatments were 2.3 decimeters and 2.7 decimeters, respectively. These levels provided excellent nesting, night roosting, escape, and concealment cover for the prairie grouse. The mean height-densities for the 100% VOM for the fifth and sixth spring after mowing treatments were 1.8 and 1.7 decimeters, respectively. These had greatly decreased from the third and fourth spring after mowing levels. The fifth and sixth spring after mowing treatments were still above the minimum level of 1.5 decimeters and would provide some concealment cover. The control plots, which had been unmowed and ungrazed for four and five springs, followed the same pattern as the mowed and grazed areas. The mean height-density for the 100% VOM was excellent at 2.6 decimeters for the fourth spring of no mowing or grazing and decreased to 1.8 decimeters in the fifth spring after exclusion from defoliation. The areas that were unmanipulated appeared to naturally maintain a level between 1.6 and 1.9 decimeters for the 100% VOM for both grazed and ungrazed treatments under the climatic conditions experienced during this study. This natural level was reached during the fifth spring after the summer mowing treatments and during the fifth spring after exclusion from defoliation. Grazing appeared to have very little effect on the switchgrass areas. The cattle naturally tended to not graze the switchgrass plants very much because they became course very early. The switchgrass herbage had a very high percentage of flower stalks soon after vegetative growth began. The switchgrass areas can be enhanced as concealment habitat for prairie grouse by summer mowing if it is conducted on a four or five year cycle. Without manipulation these fringe areas of switchgrass on the foot slopes would remain near the minimum of 1.5 decimeters level for concealment cover.
The prescribed burning trial was conducted in two allotments. Burns were conducted in early May as a cooperative project between the Sheyenne Valley Grazing Association, U.S. Forest Service, and NDSU range research team. Areas of similar habitat outside the area to be burned were sampled as control, no burn, treatments. Height-density measurements were taken according to the method developed by Robel et al. (1970) and modified by Kirsch (1974) and were collected along permanent transects in switchgrass areas: preburn (May), postburn; 1st Spring (May), 1st Fall (October), 2nd Spring (May), and 2nd Fall (October) (Table 2).
The burn treatments were very similar on each treatment pasture of the two allotments. The grazing treatments following the burns were very different. One treatment was not grazed after the May burn until October and November of that year. The vegetation from the regrowth following the burn had matured by the time the cattle entered the pasture. The cattle received very little nutritional benefit from the spring burn and as a result spent very little time on the burn treatment area. Because of the long deferment period between the burn and grazing period the natural grazing pattern was not changed and grazing pressure was concentrated on the other plant communities of this pasture the same as if the burn treatment had not been applied. The height-density measurements were 1.5 decimeters in May and 1.6 decimeter in October the second year after treatment. This was considered the minimum height-density for nesting, roosting, and concealment cover. These areas could be expected to have some use by grouse. These second spring values on this burn treatment were not much different from the height-density values collected during the second year after the summer mowing treatment. It was suspected that the height-density pattern following burning would have been very similar to the six year pattern following mowing. The grazing treatment of a pasture following a burn treatment should not be deferred. Grazing should occur two to four weeks postburn treatment.
The second burn treatment was grazed soon after the burn. The number of days the cattle were in the burn treatment pasture was increased by 31% over previous years. The cattle were attracted to the burn areas, and selectively grazed these areas while on pasture which was the desired goal of the burn treatment. The grazing pressure on the other plant communities was not reduced because of the increase in number of days grazed on the treatment pasture. By the second fall the height-density measurements were above 1.5 decimeters and were expected to receive some grouse use. The height-density measurements for the third and fourth year post burning treatment would be expected to follow a similar six year pattern as the height-density values following the summer mow treatments. Grazing pressure should not be increased disproportionately on the burn treatment pastures of an allotment. No prairie grouse nesting would be expected to occur in the burn treatment areas of either trial for the first spring after treatment. Only very little nesting or night roosting would be expected on either burn treatment during the second spring after treatment, because the mean height-densities were near the minimum level of 1.5 decimeters in the second spring sampling period.
The intended purpose of the burn treatment was to remove the old growth and to stimulate young and nutritious growth of the vegetation. Livestock were attracted to the burn areas for at least 2 years after the treatment. Drawing cattle to the sedge meadow increases grazing pressure on an area that naturally has very little use and it decreases the grazing pressure on the upland and midland plant communities which customarily have relatively greater use.
|Table 1. Mean height-density measurements (100% VOM) from switchgrass plant community after summer mowing treatments of known age (1974-1979) and control of no treatment since 1975.|
Post Mow Treatment
Grazed Each Year
Table 2. Mean height-density measurements (100% VOM) from switchgrass plant community after spring (May) prescribed burn followed by two grazing treatments.
|Spring Burn &
|Spring Burn & 31%
Increase in # of Days Grazed
Kirsch, Leo M. 1974. Instructions for use [of] a height-density pole for obtaining vegetative measurements on upland habitats. Unpublished. 3 p.
Robel, R.J., J.N. Briggs, A.D. Dayton, and L.C. Hulbert. 1970. Relationship between visual obstruction measurements and weight of grassland vegetation. Journal of Range Management 23 (4):295-297.