Grazing Systems, Exclosures, Increasers, and Decreasers

Article: The Vegetative Response under Various Grazing Management Systems in the Edwards Plateau of Texas

Authors: Reardon, Patrick O.; Merrill, Leo B.

Published:  Journal of Range Management (1976), Volume 29 (3)

This article describes a twenty year study conducted in the Edwards Plateau of Texas.  The study compared the vegetative response of five different grazing management schemes.  The five schemes were as follows:

(1)   Pasture that was ungrazed by livestock or white-tailed deer (exclosure)

(2)   Pasture grazed by deer only

(3)   Pasture lightly grazed at 16 AU/Section

(4)   Pasture heavily grazed at 48 AU/Section

(5)   4 deferred rotation pastures at 32 or 43 AU/Section

The research was determined by weighing clippings from each section in grams.  The plant material was divided into four groups: decreasers—plants that decrease under excessive grazing pressures; increasers—plants that increase when decreasers decrease because of excessive grazing; Weeds were not classified as desirable or undesirable; and dry organic matter to include all dead grass, weeds, tree leaves, and manure.

After the twenty year study, several conclusions were reached.  First, they take a look at the decreaser plants.  The enclosures both had a lower yield of decreaser plants than the deferred pasture.  This tells us that these plants need some grazing in order to flourish.   Also, the heavily grazed pasture had significantly less decreaser plants.

The increaser plants were highest in the lightly grazed pasture.  The lightly grazed pasture, the deferred pasture and the livestock exclosure were all pretty high and significantly higher than the other two pastures, which showed little difference between the two of them.

The weeds and forbs varied very little among all five pastures.  However the weeds found on the heavily grazed section were the lowest number and also were very low quality weeds.  They were about 90% bitterweed (a poisonous plant).  The rotation pasture was found to have the highest quality weeds.  The conclusion was made that the reason for this is because there were no deer on the heavily grazed pasture and at least 10 AU/Section of deer on the rotation pasture.  This indicates the rotation pastures were actually grazed at a higher rate than the heavily grazed pasture while still producing higher yields of plants and of much higher quality which means a higher net profit per acre.

Finally, dry organic matter was highest on the rotation pastures.  The deer-livestock enclosure had only a little more litter than the heavy grazed pasture.  They noted this could be from a lack of stimulation in the land.  There was nearly twice as much litter in the rotation pasture compared to the total enclosure and the heavily grazed pasture; the other pastures did not show many differences.

Total organic matter—all four plant types combined were also shown here.  The rotation system had more than the others, and the heavily grazed system was the lowest.  Also noted is the heavy grazed pasture and the deer-livestock enclosure are nearly the same.

The authors draw two conclusions from this twenty year study.  First, is that the ungrazed area needs to be considered before using it to compare for research.  Vegetation may actually deteriorate and decrease after an extended period of deferment (i.e. total rest).  The second conclusion they draw is that the use of a grazing management system in this area, allows the development of a highly productive vegetation complex and also the maintenance and improvement of the livestock and wildlife habitat.

Interesting about this article is that it shows clear evidence that some sort of deferred grazing (rest-rotation) is much more effective than heavy grazing and more effective than light grazing also.  However the light grazing was done at 16 AU/Section and the deferred grazing at up to 43 AU/Section (excluding wildlife in both).  According to the data, more profit could be made and higher density of vegetation using a deferred grazing method.   Much of the information in this study corroborates lessons learned in Holistic Management over the past 25 years.

I included the table below which shows the results.  Numbers in a row followed by the same letter are not significantly different at the 5% level as determined by a Duncan’s multiple range test.