Defoliation - Grazing Response

Grazing Response:
Tim Griffin is the Rangeland Management Specialist at the Nebraska National Forest, Bessey Range District, Halsey, NE. He is in charge of managing the Forest’s grasslands that are leased to local ranchers for cattle grazing. Based on lease agreements, each rancher is allocated a portion of the Forest’s grasslands for grazing. Tim sets the stocking rates, monitors the use and condition of the grasslands through the grazing season, and works with the ranchers in developing management and improvement plans. Tim is concerned about managing the Forest’s grasslands so that they provide ranchers’ cattle with excellent grazing while maintaining a healthy grassland ecosystem that can have other uses, including wildlife habitat, recreation, and ecotourism.

Figures 1 & 2. Tim Griffin, Rangeland Management Specialist, evaluating rangeland condition of grazingland on the Nebraska National Forest. (Walter Schacht, 2005)

In late summer, Tim went out to assess the condition of the grasslands and the plant health of desirable grass species. Grass species of particular interest are prairie sandreed and sand bluestem. His attention was drawn to two pastures in a particular allotment that were looking unhealthy: there were few desirable warm-season, mid- and tall grasses, and those remaining were in low vigor. There were eight pastures in this allotment and two herds of cows moved through a fixed sequence of four pastures each. The cattle were moved from one pasture to next every 25 to 40 days. Tim decides to review the grazing schedule records for the past several years to determine why the two pastures are in low condition. Help Tim figure out what’s going wrong and how to fix it by answering these questions.

Figure 3. Cattle grazing pastures when prairie sandreed and sand bluestem are at the elongation stage in late June and July. (Walter Schacht, 2005)

Question : What factors should be of concern to Tim? Date of grazing Frequency of gracing Intensity of grazing All of the above

To review this concept click on the link Defoliation of Grasses and Broadleaves.

Question : A review of grazing records indicates that the pastures in the allotment have been grazed in same sequence for nearly a decade and that the pastures of concern have been grazed heavily in late June to late July of each year. The warm-season grasses are in what stage of growth at this time? Vegetative Elongation Reproductive Dormancy

To review this concept click on the link How Perennial Plants Grow.

Question : With this background information on timing and intensity of grazing and stage of growth of the warm-season grasses, Tim needs to work through a series of questions to develop grazing options that will allow him to achieve his goal of improving rangeland condition. At what stage of growth is removal of the apical meristem (growing point) by grazing most likely to occur? Early vegetative Late vegetative Early elongation Late elongation

To review this concept click on the link Defoliation of Grasses and Broadleaves.

Question : What is the location of new growth for tillers that have their apical meristems removed? Intercalary meristem at the base of intact mature leaves Tiller buds at the base of defoliated tiller The tiller just continues to grow There is no mechanism to initiate new growth

To review this concept click on the link Defoliation of Grasses and Broadleaves.

Question : What are sources of energy (carbohydrate) to fuel new tiller growth? Carbohydrate reserves Remaining leaf area Nitrogen stored in the roots a and b

To review this concept click on the link Carbohydrates and Defoliation.

Question : For what purposes are carbohydrate reserves used? Respiration Energy for growth following dormancy Energy for growth following severe defoliation All of the above

To review this concept click on the link Carbohydrates and Defoliation.

Question : When does a perennial grass plant store carbohydrates? Throughout the year During the dormant season when there is not demand for aboveground growth When carbohydrate supply is greater than demand When leaf area is rapidly expanding at the beginning of the growing season b and d

To review this concept click on the link Carbohydrates and Defoliation.

Question : What will the carbohydrate reserve level be for most perennial grasses at the late elongation stage? Near its lowest point for the growing season Near its highest point for the growing season Level of carbohydrate reserves doesn’t change over time All of the above

To review this concept click on the link Carbohydrates and Defoliation.

Question : What will happen to the carbohydrate reserve level immediately after defoliation of the plant, including removal of the apical meristem? Increase Decrease No change

To review this concept click on the link Defoliation of Grasses and Broadleaves.

Question : By the end of the growing season, what will the level of carbohydrate reserves be for this defoliated grass plant compared to a non-defoliated plant? Higher Same Lower

To review this concept click on the link Defoliation of Grasses and Broadleaves.

Question : Which of these photographs represent a plant community that has been grazed annually at the late-elongation stage? Figure 1 (Walter Schacht, 2005) Figure 2 (Walter Schacht, 2005) Figure 3 (Walter Schacht, 2005) Figure 4 (Walter Schacht, 2005)

Figure 1 Figure 2 Figure 3 Figure 4

To review this concept click on the link How Perennial Plants Grow

Question : Which of the above sketches best illustrates the below and above-ground relations in a pasture grazed annually at the late-elongation stage? left sketch right sketch

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Question : Tim decides that the timing of grazing needs to be change. He recommends changing the timing of grazing to either the vegetative stage or the dormant season. Why would a change to grazing at the vegetative stage most likely result in an increase in the desired warm-season grasses (i.e., prairie sandreed and sand bluestem) and rangeland condition? The apical meristem of the desired grasses would not be removed at this stage. There would be plenty of time left in the growing season for them to grow. Their leaf area would be replenished quickly. All of the above

To review this concept click on the link How Perennial Plants Grow.

Question : Why would the practice of grazing during dormancy likely not negatively impact the desired warm-season grasses and improve rangeland condition? At this stage, the grasses are producing far more carbohydrates than the plant is demanding for growth. Above-ground plant material is dead, removing it has no impact on grass growth and carbohydrate reserve levels. Root growth has stopped and all carbohydrates can be used for new growth of above-ground plant material. All of the above

To review this concept click on the link How Perennial Plants Grow.

Clayton Gibbs is the rancher who has the lease on the allotment of concern. Clayton would like work with Tim on improving the range condition of his Forest pastures and accepts the fact that he needs to change the sequence of grazing of the pastures in his allotment. The grazing season on Forest Service leases are from May 20 to October 20 of each year; in other words, ranchers can move cattle onto their lease as early as May 20 and must have the cattle off the leased pastures by October 20. Clayton and Tim agree that the first pastures grazed in the upcoming year will be those that have been grazed historically in late June to late July. Clayton reminds Tim that he usually grazes his first pastures for about 25 days before moving onto the next set of pastures, and then moves back to the first pastures towards the end of the grazing season (around September 30) after the first killing frost. He does this because the first pastures in the sequence recover from the early-season grazing and have much available forage by the end of the season. He likes to take advantage of this forage and have his cattle graze it before removing them from the allotment on October 20.

Question : Tim decides to allow Clayton to graze the pastures of concern twice during a grazing season, once in May and early June and a second time in October. Based on what you know about grass morphology and physiology, why does Tim’s decision seem reasonable? The pastures are already in poor condition, why be concerned about further abusive grazing. The rancher should be allowed to use all available forage, regardless of consequences. The desired grasses have most of the growing season to recover and are not grazed a second time until dormancy. The leaf area normally produced early in growing season is of little consequence for carbohydrate storage

Question : Tim expects the two pastures of concern to recover and be in good to excellent condition within 5 years. Once they have recovered, what would you recommend? Maintain the same sequence of grazing where they are the first pastures grazed each year. Change back to the sequence of grazing where the two pastures are grazed in late June to late July annually. Develop a grazing plan where the sequence of grazing of the pastures changes annually. Change to continuous grazing.

Development of this lesson was supported in part by the Cooperative State Research, Education, & Extension Service, U.S. Dept of Agriculture under Agreement Number PX2003-06237 administered by Cornell University, Virginia Tech and the American Distance Education Consortium (ADEC) and in part by the New Mexico and Nebraska Agricultural Experiment Stations. Any opinions,findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.