October 3, 2023
Dickinson Research Extension Center Updates

Problems of Repeated Heavy Grazing




Llewellyn L. Manske PhD
Scientist of Rangeland Research
Dickinson Research Extension Center
701-456-1118
Severe defoliation that removes greater than 50% of the leaf material and repeated defoliation with rapid frequency results in insufficient leaf area retained on the tiller for even partial foliage recovery using current photosynthetic assimilates. Tillers with more than 50% of the aboveground leaf material removed reduce root growth, root respiration, and root nutrient absorption. 
 
Root mortality and decomposition begin within 2 days of severe leaf defoliation. Severely defoliated tillers only have very small quantities of stored carbohydrates upon which they must depend for partial replacement of leaf and root growth. 
 
There is a high biological cost to the tiller when the photosynthetic system needs to be replaced from low quantities of stored carbohydrates. This implied reduction in efficiency results in reduced total root growth, decreased tiller development, and very low growth rates causing decreased tiller numbers, reduced total basal area, and reduced quantities of herbage biomass produced. 
 
Continuation of severe defoliation inhibits herbage production further as a result of additional restrictions caused by low levels of stored carbohydrates.
 
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