Benefits derived from controlling Gambel oak in southwestern Colorado

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BENEFITS DERIVED FROM

CONTROLLING GAMBEL OAK

IN SOUTHWESTERN COLORADO

R. W. Ma r qui s s, Gary Davis, and

Lawrence Bartel'

The improvement of Gambel oak rangelands for better livestock management and meat production has been a goal of range science studies in the San Juan Basin. Gambel oak can be controlled by herbicides, as well as other methods, but good follow-up treatment is necessary to assure a high percentage of control. A high percentage of control is necessary to attain the benefits of increased meat production from Gambel oak rangelands.

Soil Moisture Studies

Soil moisture samples from the oak-grass type ,included open areas between oak clumps, undisturbed oak clumps, oak sprout areas where 80-90 percent of crown had pre-viously been controlled, and 100 percent controlled oak with no sprouts. Sampling dates were at two-week intervals during the summer months of four consecutive years.

A significant increase in soil moisture was observed where the oak was totally controlled. The largest differ-ences in soil moisture between treatments occurred during mid-summer months (Figure 1).

The soil moisture differences were greatest from the three- to five-foot depths. Small differences of soil moisture occurred from the surface to a depth of two feet in all treatment plots. Below the two-foot depth, increases in soil moisture were notably higher for the effectively controlled oak.

Forage Production and Grazing Studies

Two pastures, each approximately twenty-five acres in size, were used as a paired plot grazing study. The vegeta-tion types in each pasture were similar in percent of acreage of open grassland, sagebrush-grass, and oak-grass. One pasture was left untreated; the other was treated with herbicides to control the dominant brush species. Both pastures have been grazed moderately (approximately 50 percent) since 1963.

FORAGE PRODUCTION: Forage production was deter-mined by clipping the forage from caged plots within each vegetation type. Utilization was determined by clipping of grazed and ungrazed plots.

Forage production at the end of each growing season (1966-1970) was substantially increased as a result of brush 1 Assistant Range Scientist and Research Technicians, respectively, San Juan Basin Branch Station, Hesperus, Colorado.

PR71-10

June1971

control. This relationship of increased forage production held true for each vegetation site, but was most evident within the oak thickets (Table 1). Plant composition and forage production was improved in both pastures during the past five years.

Forage production in the open grassland type was increased 64 percent as a result of plant composition changes due to herbicide applications. Forage production in the sagebrush-grass type was increased 81 percent. Herbi-cide treatment of oak increased the understory forage production 7 4 percent one year following the 1969 treatment. 15 10 0-1 F'oot depth

1

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f

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I 20 3 17 25 15 30 12 23 9 20

l!ay Ju.."1.e July Aurr Sept.

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Figure 1. Percentage soil moisture taken at five depths, four sites, and four summer seaso·ns on Gambel oak rangeland in southwestern Colorado.

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GRAZING STUDIES: Animal response was determined by grazing 550- to 600-pound yearling steers during the mid-summer months. Livestock gains were based on average daily gain and total gain per acre during the grazing season for each pasture.

Five years of grazing results indicate an increase in beef production on the treated pasture. Stocking rate, total gains, and gains per acre increased as a result of increased forage production, reflecting the benefits of brush control practices (Table 2).

Livestock gains were increased by an average of 18 pounds per acre over a five-year period as a result of brush control practices. Increased livestock gains in both pastures

may be attributed to improved range condition as a result

of moderate utilization during the past five years of the study.

Summary

Controlling Gambel oak and other brushy species with herbicides can produce increased forage production.

In-creased forage and beef production are products of a good

brush control practice. A high percentage of oak control is

necessary to offset regrowth by sprouting. Soil moisture was significantly increased in the top five feet of soil during

the summer months by controlling the oak. Forage

produc-tion was doubled within a five-year period and animal

weight gains per acre nearly doubled as a result of brush control practices.

Table 1. Percent utilization and pounds of dry forage produced from treated and non-treated oakbrush pastures from

1966 through 1970.

No _Brush Control Brush Controll

OPEN GRASSLAND 1966 1967 1968 1969 1970 1966 1967 1968 1969 1970

Utilization (%) 54 64 48 60 64 63 69 61 56 67

Forage Production (lbs.) 410 683 1146 1088 815 655 851 1370 1331 1335

Production increase attributed 245 168 224 243 520

to brush control (lbs.)

to brush control(%) SAGEBRUSH-GRASS

Utilization (%) 48 50 44 33 50 50 52 55 49 65

Forage produced per acre (lbs.) 440 567 884 752 626 562 904 1363 1031 1136

to brush control(%)

OAKBRUSH (BENEATH THE CANOPY)

Utilization (%) 50 50 51 26 61 51 44 65 47 62

Forage produced per acre (lbs.) 475 424 630 633 762 592 994 1292 1101 1324

to brush control (%)

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Table 2. Four-year grazing information and weight gain on a non-treated pasture and a brush control treated pasture.! Animal

Steer Total gain Gain

Grazing dated days Utilization gain per day per acre

(percent) (pounds) (pounds) (pounds)

NON-TREATED PASTURE 1966 ( July 23-Sept. 25) 435 49 518 1.19 20.72 1967 (Aug. 22-Sept. 27) 324 58 662 2.04 26.48 1968 (Aug. 5-Sept. 2) 392 49 916 2.34 36.64 1969 (July 29-Sept. 9) 420 37 986 2.35 39.48 1970 (July 5-Sept. 4) 510 58 663 1.30 26.52 Average 416 50 749 1.84 29.97 TREATED PASTURE 1966 (July 23-Sept. 9) 521 51 838 1.63 31.04 1967 (Aug. 22-Sept. 27) 468 53 930 1.99 34.44 1968 (Aug. 5-Sept. 2) 728 60 1692 2.32 62.67 1969 (July 29-Sept. 9) 840 50 1883 2.24 69.74 1970 (,July 15-Sept. 4) 1020 64 1125 1.10 41.63 Average 715 56 1294 1.86 47.91

lThe sagebrush was treated in May 1965, the oakbrush treated in June 1966 and July 1969 on the brush control pasture.