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Fall Grazing Affects Grass-Leaf Height

Llewellyn L. Manske PhD

Range Scientist
North Dakota State University
Dickinson Research Extension Center

Introduction

Most livestock producers in the Northern Great Plains are familiar with the axiom "after a frost in the fall, grazing does not hurt perennial grasses". Grazing beef cattle on native range during the fall season is an optional management practice used in the Northern Great Plains. This late-season management practice is frequently incorrectly referred to as "winter grazing". Fall occurs between the autumnal equinox (22 September) and the winter solstice (21 December) and includes October, November, and December. A search of the pertinent scientific literature does not produce data to support the belief that native grasses are unaffected by late-season grazing. In fact, results of a study conducted from 1958 to 1962 at the Dickinson Research Extension Center indicated that fall grazing is detrimental to perennial grasses, greatly reducing leaf height of graminoid plants the following growing season.

Methods

Beef and range research were halted at the Dickinson Experiment Station for the duration of World War II. Following the war, the beef herd was built up and managed with a contemporary repeat spring, summer, and fall pasture grazing schedule. During the growing season, the 40-acre fall pasture was used as a native-grass study area on which basic plant growth data were collected for numerous range-related investigations. An exclosure (A) was constructed on the fall pasture during the spring of 1958, and a second exclosure (B) was constructed during late summer of 1961. From 1958 to 1962, Dr. Warren C. Whitman and Dr. Harold Goetz conducted a five-year study designed to evaluate the effects fall grazing had on the height of grass leaves during the following growing season.

Plant heights were determined by measuring leaves of an average of ten ungrazed lead tillers of each species to the nearest 1 cm. Measurements were collected at approximately 7- to 10-day intervals from early April to mid September. For plants with basal leaves, leaf heights were measured from the ground to the tips of extended leaves. For single-stalked species, in which the leaves are attached to a culm, height measurements were made by extending the leaves upward and measuring from the ground to the apex of the uppermost leaf. Initial leaf-height measurements were collected in 1958. During the growing seasons of 1959 to 1962, leaf-height measurements for needleleaf sedge (Carex eleocharis), needle and thread (Stipa comata), western wheatgrass (Agropyron smithii), and blue grama (Bouteloua gracilis) were made on the fall-grazed pasture and exclosure A. Additional measurements were collected from exclosure B in 1962. The annual maximum leaf heights for the four graminoids from the study were reported by Goetz (1963), and measurements on the three treatments--fall grazed, exclosure A, and exclosure B--were compared. A summary of these data and their interpretation is the primary subject of this report.

Growing-season conditions affect range plant growth (Manske 1998) and should be included as a factor in the assessment of grass and sedge growth. The average monthly temperature and monthly precipitation data for 1958 to 1962 from the Dickinson Research Extension Center (Manske 2000) were evaluated through use of an ombrothermic graph technique reported by Emberger et al. (1963). These data were used to identify water-deficiency months and to characterize growing-season conditions. Maximum leaf heights reported by Goetz (1963) and collected during normal, drought, and wet growing-season conditions are compared in this report.

Results

The ombrothermic diagram (fig. 1) for 1958 to 1962 identifies monthly periods with water-deficiency conditions. Water-deficiency periods are indicated when the monthly precipitation data bar drops below the mean monthly temperature data curve. During water-deficiency periods perennial plants experience water stress that results when plants are unable to absorb adequate water to match the transpiration rate. Water-deficiency periods lasting for a month place plants under water stress severe enough to reduce herbage biomass production. During fall, average monthly temperatures are near or below freezing (32 F, 0 C), and most grass leaves are senescent and contain only a small amount of green tissue; however, plant growth continues at low levels. A summary of the weather conditions from 1958 to 1962 is in table 1. The conditions of the growing seasons of 1959 and 1961 were normal, the growing seasons of 1958 and 1960 had drought conditions, and the growing-season condition of 1962 was wet.

Goetz (1963) reported maximum leaf heights (table 2) of ungrazed lead tillers of needleleaf sedge, needle and thread, western wheatgrass, and blue grama measured from 1958 though 1962. Sample dates on which maximum leaf heights were attained for each of the four graminoid species (Goetz 1963) are in table 3. Leaf-height measurements were collected in the fall pasture during the growing seasons following treatments of fall grazing and in exclosure A, which was not grazed in the fall. Goetz also reported leaf-height measurements collected in exclosure B during 1962 (table 2). Goetz (1963) stated that these data show that leaf heights for the four species of grasses and sedge were greater inside the exclosures than outside on the fall-grazed rangeland, irrespective of moisture conditions. Goetz (1963) concluded that the results of the study indicate a great reduction in maximum leaf height because of the decreased vigor of the plants on rangeland subjected to fall grazing. On rangeland grazed during the fall, maximum leaf heights were reduced 23.0%, 17.3%, 30.4%, and 43.0% for needleleaf sedge, needle and thread, western wheatgrass, and blue grama, respectively, compared to the maximum leaf heights attained on treatments not fall grazed (table 4). Fall grazing reduced the maximum leaf height of major graminoids by an average of 28.4% during the succeeding growing season.

Maximum leaf-height differences between treatments that were fall grazed and treatments that were not fall grazed were greater under growing-season conditions of some years than under growing-season conditions of other years. In 1962, a wet year, leaf heights (table 5) of all the species on the treatments not grazed in the fall were considerably greater than leaf heights of the plants grazed the previous fall. In 1962, leaf heights of blue grama on exclosure A were more than twice the leaf heights of the fall-grazed plants (table 5). In 1958 and 1960, when the growing seasons were characterized by drought conditions, leaf heights (table 5) of the major species on the treatments not grazed in the fall were not much greater than leaf heights of the plants grazed the previous fall. In 1958 and 1960, leaf heights of needleleaf sedge and needle and thread on treatments not grazed in the fall were not different from leaf heights attained on the fall-grazed treatments (table 5).

Maximum leaf heights attained under wet growing-season conditions were greater than maximum leaf heights attained under normal growing-season conditions (table 6). During growing seasons with wet conditions, maximum leaf heights were 22.5%, 46.6%, 69.7%, and 65.4% greater for needleleaf sedge, needle and thread, western wheatgrass, and blue grama, respectively, than maximum leaf heights attained during growing seasons with normal conditions.

Maximum leaf heights attained under drought growing-season conditions were below maximum leaf heights attained under normal growing-season conditions (table 6). During growing seasons with drought conditions, maximum leaf heights decreased 25.8%, 14.0%, and 11.8% for needleleaf sedge, needle and thread, and blue grama, respectively, from maximum leaf heights attained during growing seasons with normal conditions. During the study conducted by Whitman and Goetz, maximum leaf heights of western wheatgrass were 8.0% greater during growing seasons with drought conditions than during growing seasons with normal conditions (table 6). This inconsistency can be explained by the precipitation patterns of the drought and normal growing seasons of 1958 to 1961 (table 1). Western wheatgrass completes most of its growth during May and June. During the two years with drought-condition growing seasons, 1958 and 1960, precipitation levels were greater than three inches during June of both years. During the two years in which growing-season conditions were normal, 1959 and 1961, precipitation levels were greater than three inches during June only in 1959. The differences between the precipitation patterns of the drought and normal growing seasons can cause the observed differences in leaf heights of western wheatgrass.

Discussion

Growth in height of the major graminoid species of the mixed prairie in the Northern Great Plains was affected both by precipitation patterns and moisture conditions during the growing season, and by grazing during the previous fall. Upland sedges attained an average maximum leaf height of 12.0 cm (4.7 in) in early to mid June during growing seasons with normal conditions. Leaf height of upland sedges was reduced 26% under drought conditions and increased 23% under wet conditions. Fall grazing reduced leaf height of upland sedges 23%. Needle and thread attained an average maximum leaf height of 19.3 cm (7.6 in) in late June to early July during growing seasons with normal conditions. Drought conditions reduced leaf heights 14% from leaf heights attained under normal conditions, and wet conditions increased leaf heights 47% over leaf heights attained under normal conditions. Fall grazing reduced leaf height of needle and thread 17%. Western wheatgrass attained an average maximum leaf height of 23.8 cm (9.4 in) by mid July during growing seasons with normal conditions. Wet conditions increased leaf height 70%. In growing seasons with drought conditions but with greater than three inches of precipitation in June, leaf height for western wheatgrass was not reduced. Drought conditions with below-normal precipitation in June would cause a reduction in maximum leaf height for western wheatgrass. Fall grazing reduced leaf height of western wheatgrass 30%. Blue grama attained an average maximum leaf height of 12.7 cm (5.0 in) in early to mid July during growing seasons with normal conditions. Under drought conditions, leaf height decreased 12%, and under wet conditions leaf height increased 65%. Fall grazing reduced leaf height of blue grama 43%.

Data collected by Whitman and Goetz during their study clearly show that fall grazing on native rangeland hurts range plants and reduces leaf height by diminishing the vigor of the plants. Pastures grazed during the fall season cannot carry the same stocking rate as pastures grazed during the summer season. Fall-grazed pastures should have the stocking rate reduced initially to about 50% of the stocking rate that that pasture could carry during the summer season.

The range condition of pastures that have a history of being grazed during the fall season can be improved if the fall grazing management is changed from the native range pasture to an alternative forage type, like a variety of perennial wildrye (Altai, Russian, Basin) or a spring-seeded winter rye pasture. The data from Goetz (1963) can be used to help predict the levels of improvement in the major species after the fall grazing practice has been changed. The average maximum leaf height of the major native range graminoids could be expected to increase 17.2% during the first year if the growing season had normal conditions, and an increase in leaf height of 33.3% could be expected during the first year if the growing season had wet conditions. An increase in leaf height of 42.5% could be expected within four years of changing from a fall grazing management practice.

Summary

The scientific results from the five-year research project Dr. Whitman and Dr. Goetz conducted at the Dickinson Research Extension Center to evaluate the effects fall grazing has on grass leaf height contradict the popular opinion that fall grazing native rangeland is a benign practice and provide evidence that fall grazing of native range causes biological damage to the major range species. Leaf heights of the major graminoids of the mixed grass prairie are affected by the grazing management practices used during the previous fall season, and by the precipitation pattern and moisture conditions of the growing season. In growing seasons with wet conditions, leaf height increases about 51%. In growing seasons with drought conditions, leaf height is reduced about 11%. Precipitation occurring during important growth periods can greatly benefit single grass species even during growing seasons with generally stressful conditions. Fall grazing of rangelands causes a decrease in plant vigor and a great reduction in leaf height (28%) of the major graminoids during the succeeding growing season, regardless of the growing-season moisture conditions. Fall grazing does hurt perennial grasses.

Acknowledgment

I am grateful to Amy M. Kraus for assistance in preparation of this manuscript. I am grateful to Sheri Schneider for assistance in production of this manuscript and for development of the figure and tables.

Table 1. Summary of weather conditions during fall grazing effects on leaf height study (1958-1962).

Year

 

1958

1959

1960

1961

1962

Growing season precipitation

(in)

9.42

11.56

8.54

12.65

16.41

 

Percent of long-term mean

(%)

69.44

85.21

62.95

93.25

120.96

Months with water stress

 

May, Aug, Sep

Apr, Jul, Aug

Apr, Jul, Sep, Oct

Jul, Aug, Oct

Sep, Oct

Percent growing season months with water stress

(%)

50

42

50

42

25

Months with > 3" precip.

 

Jun, Jul

Jun, Sep

Jun

Sep

May, Jul

Spring conditions

 

Dry

Dry

Dry

Normal

Wet

Fall conditions

 

Dry

Wet

Dry

Normal

Dry

Growing season conditions

 

Drought

Normal

Drought

Normal

Wet

Data from Manske 2000

 

Table 2. Maximum leaf height [centimeters (cm) and inches (in)] of ungrazed lead tillers measured during growing seasons following treatments fall grazed or not fall grazed (1958-1962), data from Goetz (1963).

Year

 

1958

1959

1960

1961

1962

Treatment

 

Initial

Exclosure A, 1 yr

Fall grazed

Exclosure A, 2 yr

Fall grazed

Exclosure A, 3 yr

Fall grazed

Exclosure A, 4 yr

Exclosure B, 1 yr

Fall grazed

Upland sedge

(cm)

9.0

10.7

9.0

8.7

9.0

13.3

9.0

16.3

13.0

11.0

(in)

3.5

4.2

3.5

3.4

3.5

5.2

3.5

6.4

5.1

4.3

Needle and thread

(cm)

16.7

20.0

19.0

16.5

17.0

18.6

16.0

29.5

27.0

23.0

(in)

6.6

7.9

7.5

6.5

6.7

7.3

6.3

11.6

10.6

9.1

Western wheatgrass

(cm)

23.0

22.3

20.0

28.3

19.0

25.3

22.0

41.7

39.0

26.0

(in)

9.1

8.8

7.9

11.1

7.5

10.0

8.7

16.4

15.4

10.2

Blue grama

(cm)

9.7

12.0

9.0

12.7

8.0

13.3

7.0

25.0

17.0

11.5

(in)

3.8

4.7

3.5

5.0

3.1

5.2

2.8

9.8

6.7

4.5

Table 3. Date maximum leaf height attained (1958-1962), data from Goetz (1963).

Year

1958

1959

1960

1961

1962

Upland sedge

15 May

8 Jun

15 Jun

8 Jun

22 Jun

Needle and thread

15 Jul

8 Jul

22 Jun

22 Jun

22 Jun

Western wheatgrass

22 Jun

15 Jul

1 Jul

22 Jul

22 Jul

Blue grama

15 Jul

29 Jun

1 Jul

8 Jul

15 Jul

Table 4. Average maximum leaf height [centimeters (cm) and inches (in)] of ungrazed lead tillers measured during growing seasons following treatments fall grazed or not fall grazed (mean of 1958-1962), summary of data from Goetz (1963).

Treatments

 

Exclosure

Fall grazed

Percent difference from
treatments not fall grazed
(%)

Upland sedge

(cm)

12.6

9.7

-23.0

(in)

5.0

3.8

 

Needle and thread

(cm)

23.1

19.1

-17.3

(in)

9.1

7.5

 

Western wheatgrass

(cm)

32.6

22.7

-30.4

(in)

12.8

8.9

 

Blue grama

(cm)

16.5

9.4

-43.0

(in)

6.5

3.7

 

Table 5. Maximum leaf height [centimeters (cm) and inches (in)] of ungrazed lead tillers measured during three growing-season conditions following treatments fall grazed or not fall grazed (1958-1962), summary of data from Goetz (1963).

Growing season conditions

 

 

Normal

 

Drought

 

Wet

Years

 

1959 & 1961

1958 & 1960

1962

Treatments

 

Exclosure
A

Fall grazed

Exclosure
A

Fall grazed

Exclosure
A

Exclosure
B

Fall
Grazed

Upland sedge

(cm)

12.0

9.0

8.9

9.0

16.3

13.0

11.0

(in)

4.7

3.5

3.5

3.5

6.4

5.1

4.3

Needle and thread

(cm)

19.3

17.5

16.6

16.8

29.5

27.0

23.0

(in)

7.6

6.9

6.5

6.6

11.6

10.6

9.1

Western wheatgrass

(cm)

23.8

21.0

25.7

21.0

41.7

39.0

26.0

(in)

9.4

8.3

10.1

8.3

16.4

15.4

10.2

Blue grama

(cm)

12.7

8.0

11.2

8.8

25.0

17.0

11.5

(in)

5.0

3.1

4.4

3.5

9.8

6.7

4.5

Table 6. Average maximum leaf height [centimeters (cm) and inches (in)] of ungrazed lead tillers measured during three growing-season conditions on treatments not fall grazed (1958-1962), summary of data from Goetz (1963).

Growing season conditions

 

Normal

Drought

Wet

Treatments

 

Exclosure

Exclosure

% Difference
from Normal
(%)

Exclosure

% Difference
from Normal
(%)

Upland sedge

(cm)

12.0

8.9

-25.8

14.7

+22.5

(in)

4.7

3.5

 

5.8

 

Needle and thread

(cm)

19.3

16.6

-14.0

28.3

+46.6

(in)

7.6

6.5

 

11.1

 

Western wheatgrass

(cm)

23.8

25.7

+8.0

40.4

+69.7

(in)

9.4

10.1

 

15.9

 

Blue grama

(cm)

12.7

11.2

-11.8

21.0

+65.4

(in)

5.0

4.4

 

8.3

 

 

Literature Cited

Emberger, C., H. Gaussen, M. Kassas, and A. dePhilippis. 1963. Bioclimatic map of the Mediterranean Zone, explanatory notes. UNESCO-FAO. Paris. 58p.

Goetz, H. 1963. Growth and development of native range plants in the mixed prairie of western North Dakota. M.S. Thesis, North Dakota State University, Fargo, ND. 165p.

Manske, L.L. 1998. Environmental factors' effect on range plants. NDSU Dickinson Research Extension Center. Summary Range Research Report DREC 98-3006. Dickinson, ND. 3p.

Manske, L.L. 2000. Environmental factors to consider during planning of management for range plants in the Dickinson, North Dakota, region 1892-1999. NDSU Dickinson Research Extension Center. Range Research Report DREC 00-1018c. Dickinson, ND. 36p.