In North American subalpine and alpine pastures, forbs may supply much spring-summer forage for deer (e.g. elk Cervus elaphus), sheep and cattle. This study on the Wasatch Plateau (Utah) was designed to provide guidelines for best grazing utilization of three important perennial forage forbs by determining the effect of different degrees of clipping (mimicking natural grazing intensities) on herbage and flower stalk production over 10 years.
The study plants were: Richardson geranium Geranium richardsoni, Porter’s ligusticum Ligusticum porteri and edible valerian Valeriana edulis (between about 2,575-3,000 m altitude).
Twelve plants of each species were chosen in each of two adjacent blocks, protected from grazing and randomly assigned one of four treatments: control (unclipped), or clipped 50, 75 or 90% (by above-ground weight) once each year from 1951-1960.
Plants were clipped at flowering near maximum growth (usually mid-July for geranium and during the first 10 days of August for ligusticum and valerian). Herbage production (dry weight) was estimated and flower stalks counted. Plants were checked in autumn 1965 to determine mortality and to estimate vigour.
Herbage production of plants clipped at 75 and 90% decreased rapidly over the years and production by 1960 (as a percentage of unclipped plants) was:
Ligusticum: 50% clipped - 60%, 75% clipped - 28%, 90% clipped - 14%;
Valerian: 50% clipped - 55%, 75% clipped - 20%, 90% clipped - 13%;
Geranium: 50% clipped - 35%, 75% clipped - 7%, 90% clipped - 1%.
Compared to the controls, flower stalk production also declined (flower stalk production/plant; 10 year average):
Ligusticum: control - 4.1, 50% clipped - 3.1, 75% clipped - 2.0, 90% clipped - 1.4;
Valerian: control - 1.7, 50% clipped - 1.0, 75% clipped - 0.7, 90% clipped - 0.6;
Geranium: control - 6.8, 50% clipped - 4.3, 75% clipped - 2.8, 90% clipped - 2.1.
Under the two higher clipping intensities, few mature seeds were produced after 3-4 years of treatment and in the last three years (1958-60) no geranium flowered.
In 1965, all unclipped plants were alive and ‘vigerous’. All clipped Ligusticum were doing well, except one weak 90% clipped plant. Valerians clipped 50% were recovering well and those clipped 75% generally recovering less well. One clipped 90% was dead, and two were weak. Geraniums clipped 50% were all alive, two clipped 75% were dead, all clipped 90% were dead.
Overall, ligusticum was most tolerant to clipping. Geranium was least tolerant indicating that grazing intensity should accordingly be lower in order to ensure its perpetuation.
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