Article: The Charter Estate Grazing Trial Results of the Botanical Analysis
Author: Clatworthy, J.N.
Published: Zimbabwe Journal of Agricultural Research (1984), Vol. 81 (2)
In implementing the Charter Grazing Trials, changes in vegetation were carefully monitored to detect changes in range as a result of short duration grazing. Five .3 ha plots were established in each of the four experimental blocks (S1, S2, C1, C2). These plots were located in an attempt to represent the variety of land features and soil types within the study area.
Grass species composition and basal cover were monitored during each year of the study. The methods for doing so are described by the author as follows:
Composition was expressed as the percentage frequency with which each species occurred in 240 quadrats each 40 x 20 cm arranged in a grid pattern within the plot. Basal cover was the percentage interception at ground level along 48 lines each 5 m long and again arranged on a grid basis.
The research team expected to see improvements in what is described as a degraded range: “Except for the C2 plot…these plots were on degraded veld, in which it was expected that changes would be most rapid.” The presence of indicator grass species like Pogonarthria squarrosa, which is known to occur on disturbed and degraded habitat, supports this description.
Annual summaries by treatment are included in the published paper as tables. To better visualize and compare this data, it has been adapted and placed into a graphic format.
Fluctuations in basal cover from one year to the next are mirrored in each of the four treatments. The pattern above is strikingly similar to the pattern observed in annual precipitation, the visual representation of which has also been adapted from tabular data. While the peaks and valleys don’t correspond perfectly to the vegetation data, this is most likely a result of the nature of the data itself. Precipitation was recorded by season, including two seasonal years as a single data point, while vegetation was recorded as a single point for each year.
Analysis and interpretation of this data is best summarized by the author:
…if marked changes in the vegetation had occurred as a result of the different systems of management, they should certainly have been detected by our analyses. These marked differential changes did not occur…This lack of spectacular changes in the grass cover on any of the plots can be regarded as negative in that rapid rotational grazing thus failed to produce the marked improvements in the grass cover so often claimed to result from its application. However, on the credit side the numbers of cattle carried were greatly increased on the rotationally-grazed farms without any evidence of harmful effects on the grass cover.
As noted in a previous post, dramatic increases in the stocking rate allowed for greater per hectare production. The fact that these increases in stocking rate were not accompanied by deterioration in range quality should certainly be viewed favorably, and this points the way towards a management intensive approach to increases in ranch productivity.
It is possible that improvements in soil biology or soil organic matter were considerable under the rotationally grazed treatments, and subsequent improvements in vegetation lagged behind improvements at and below the soil surface. Because no monitoring of soil characteristics was included in the research design, these statements are purely speculative.
Nevertheless, in my opinion it is becoming increasingly clear that the utility of high density grazing has been misunderstood. High density grazing is an ecological tool that can have certain effects under certain circumstances. This does not necessarily mean that it will always have the effect that we expect it to, nor will it always improve degraded range regardless of conditions on the ground. The role of research and monitoring is to help us sharpen our understanding of the effects of management decisions on ecosystem processes, and to answer critical questions like those raised by the Charter Trials and other studies. One pressing question is this: under what circumstances is high density grazing effective?
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