Range science research
We examine ten range science experiments conducted across East Africa from 1948 to the 1960s (Table 5.2). The aims under general range science research were: first, to determine the relationship between rainfall variabih ity and grazing capacities and carrying capacities; second, to determine whether grazing systems influence rangeland productivity; third, to determine if (according to expectations) indigenous continuous rangeland grazing practices perform poorly compared to the alternative rotational and rest grazing system; fourth, to determine if rehabilitation of degraded rangelands—through bush clearing and reseeding—promotes grass production; fifth, to deter- mine if the range conditions and trends are declining (according to the environmental crisis hypothesis). Finally, our aim was to determine if the responses in both agronomic and range science reflect equilibrium (again inferring an environmental crisis) or the alternative hypothesis. We discuss individual experiments in turn.
Rainfall variability and grazing capacity
In the Machakos grazing experiments that related rainfall and grazing capacity, and measured rangeland carrying capacity,44 the results show that grazing capacity forms mirror images of rainfall patterns (Figure 5.6A). By contrast, the carrying capacity (animals/unit area/unit time) varied over time (Figure 5.6B). During the last year of data collection (1957), the
Figure 5.6 (A) Data showing relationships between rainfall and grazing capacity (GC) and (B) carrying capacity and time.
Source: H.C. Pereira, “Lessons gained from grazing trials at Makavete, Kenya,” Bast African Agricultural Journal XXV.1 (1959): 59—62.
carrying capacity declined slightly when both rainfall and grazing capacity remained high. From the data alone, we are unable to explain the inverse response of carrying capacity to the variable rainfall. There are two pos- sible reasons why carrying capacity did not respond to rainfall. First, the experiment would have excluded any biological data, for example, if the rangelands had been attacked by pests such as locusts (see Chapter 9). Second, there was possibility of inaccuracies in the calculations of carrying capacity. Both theoretical and practical knowledge of rangeland research in East Africa show that rainfall variability is the main driver of carrying capacity.4’ Nonetheless, the view of colonial officials was that livestock grazing diminished rangeland productivity. Accordingly, the rainfall factor was downplayed when colonial officials and researchers promoted the use of rotational grazing as opposed to indigenous grazing practices.
Rotational grazing
Rotational grazing (i.e., moving livestock between different pastures at fixed periods) is compared with the indigenous method of continuous grazing in terms of changes in plant production and animal weights. The purpose of rotational grazing is to rest some pastures while grazing other pastures, compared to the indigenous practice of continuous grazing over all pastures. The environmental crisis hypothesis perspective is that rangeland productivity would be improved under rotational as opposed to continuous grazing.46 The assumption is livestock grazing is the dominant influence on changes in vegetation. Considering that the grazing locations and timing are fixed, the folly of the rotational grazing plan becomes apparent when rainfall fails in pastures scheduled for grazing but falls in distant areas. Researchers4, found either ‘no significant difference,’ or that the continuously grazed pastures demonstrated superior grass production compared to rotational grazing, contrary to the environmental crisis hypothesis. In the indigenous system, the grazing was uniform across pastures and the grass swards had remained palatable to cattle. The differences were also reflected in changes in cattle weights (see below).
Other researchers were more forthright,48 concluding that resting the pastures frequently was undesirable as it failed to promote pasture production compared to continuously grazed pastures. This finding demonstrates that the African rangelands—having co-evolved with herbivores—produce more forage when closely grazed than when grazing is deferred.49 This is clearly contrary to the claims of the environmental crisis hypothesis.
Brian Walker’0 conducted grazing trials involving rotational (R), continuous grazing (CG), and grazing and rotational (GR) systems (Table 5.2). These trials showed that—contrary to the expectation that rotational grazing would yield superior forage production than continuous
|
Year |
Country |
Problem |
Experiments |
|
1948-1954 |
Tanganyika: Iringa |
Rangeland overgrazing |
Controlled grazing, bush clearing and application of fire.” |
|
1950s |
Kenya: Machakos |
Land degradation |
Restoration experiment using three treatments: bush clearing, reseeding and ploughing. The objective was to provide information on the productivity of the eroded landscapes over a seven-year period. The paddocks were stocked at 15 bulls per pasture. Rainfall during the period was above average.” |
|
1951-1959 |
Uganda: Karamojong |
Bush clearing |
Controlled grazing experiments, aimed at rehabilitating grass production.” |
|
1953-1955 |
Kenya: Kitui |
Land rehabilitation |
Tested the cost and efficiency of bush clearing using arboricides to kill bushy vegetation. The cleared areas were subdivided into paddocks of 150 acres each for trials with rotational grazing. Cattle in the grazing experiments were regularly weighed since weight was used as an indicator of growth performance.’8 |
|
1954 |
Kenya: Baringo |
Bush clearing |
Investigated loss of grass cover, bush encroachment and high stocking densities. Modified season of grazing and reduced stocking density.’9 Bush clearing using mechanical means. The experiments involved the use of ‘Holt rollers’ pulled by a tractor to crush bushy plants. This was followed by burning the woody residue and then reseeding to regenerate grass. The area was rested for some time before being grazed/'' |
|
1950s |
Kenya: Kitui |
Land rehabilitation |
Two grazing treatments were attempted. The first involved subdivision of the land in accordance with individual farms that were fenced to protect them from livestock grazing in order to allow recovery. In the second experiment, all bushy plants were cleared and the areas ploughed and sown with perennial grasses before arrival of the rains. The treatments comprised sowing seed on bare ground and ploughed up ground and sowing seeds. The controls were areas which had been cleared of bushes and left unseeded.58 |
continued
|
Year |
Country |
Problem |
Experiments |
|
1957-1961 |
Kenya: Baringo |
Land rehabilitation |
The Njems plains had been grazed by 36,000 stock in 1957 and were reported as being completely bare of any herbaceous cover. Three of the experimental sites were fenced to exclude livestock entry. Treatments included reseeding, and ploughing followed by reseeding. The growth performance of the reseeded plots was evaluated at the end of every growing season.'4 |
|
1957-1961 |
Kenya: Kitale |
Rotational/ traditional grazing |
The grazing experiment involved a scheme of 29,780 acres stocked with 3,000 head of cattle. The area was subdivided into four blocks designed for cattle to spend about four months in each paddock before moving to the next paddock. The blocks were rested for at least 12 months. All the blocks, including the control ones that were open to continuous grazing, had their soil surfaces ploughed using tractors to embed the seeds. All the grazing blocks were protected from illegal grazing by being fenced and patrolled by armed guards. The experiments were abandoned in I960.60 |
|
1960s |
Tanzania: Sukumaland |
Rotational grazing |
Five-year grazing/rest treatments in grazing trials involving rotational and continuous traditional systems. Rotational grazing plots in four replications, each grazed for eight weeks: two weeks of grazing and six weeks of rest. During the same period, three paddocks were rested for one-third of the time in a three-year grazing cycle. The paddocks were rested during the early growing seasons to allow them to recover from previous grazing seasons. The treatments were then compared with continuous grazing. The effects of grazing and resting of the pastures were measured in terms of sward production and changes in livestock body weights on the different grazing systems.62 |
|
1967 |
Kenya: Kedong |
Rotational grazing |
Conducted grazing trials involving rotational (R), grazing and rotational (GR) and continuous grazing (CG) at Ukiriguru. The different grazing treatments were compared for changes in botanic composition and productivities of the natural pastures.55 The grazing experiments were completed by EAAFRO in 1967. The design included two-four acres per steer rotational and continuous grazing, seven acres per steer rotational grazing, and seven acres per steer continuous grazing, compared to 13 acres per steer rotational and continuous grazing. Each replicate was stocked at six Borana breed steers, grazed for six months and rested for 12 months. The rotational grazing pastures were burned in year 3. The continuously grazed pastures were not burned.” |
grazing—the former grazing system performed poorly, leading Walker to conclude:
The botanic composition of the three treatments ... remained very much the same over the period of experiment— Except for the increase in stocking rate, the continuous grazing treatment remained
the same as in the two [other] treatments____What would this mean ...
is that at low grazing pressures continuous grazing is favoured over rotational grazing, because the pasture on that treatment is ... kept at a more nutritive stage than the pasture on the rotational [grazing system where grass was of a poor quality].
The conclusion would be a surprise to the colonial officials who advo- cated for rest and rotational grazing as opposed to the traditional con- tinuous grazing system. Grazing seasons added another dimension to the outcomes of the experiments—that is, whether grazing takes place during periods of plant dormancy or during a growth season. Heavy stocking during dormancy would have little or no long-term effects on forage plants.
In another experiment, Walker and Scott"'1 reported that continuous grazing at low stocking densities on the hard pan soils of Sukumaland tended to redistribute grazing pressure over the pasture. They recommended continuous grazing over rotational grazing for beef cattle production at low stocking rates.
In 1969, the steers in each treatment plot were slaughtered and the total carcass weights were measured (Table 5.2). Rotational grazing at 4 acres per steer and 7 acres per steer (i.e., high stocking density) showed lower weight gains than their continuous grazing counterparts (Figure 5.7). At the stocking rate of 13 acres per steer (i.e., low stocking density), the rotational and continuous treatments showed comparable results. The carcass grades under the rotational treatments had lower weights compared to those under continuous grazing.12 Bearing these results in mind, we now compare the findings of experiments on range restoration.
