Climatic conditions have an obvious effect on plant growth, especially influencing the biomass of annual and perennial herbaceous species. A strong relationship between rainfall and herbaceous biomass has been developed for many rangeland types, including the semi-arid grasslands of southern Arizona, annual grasslands of California, the cold-deserts of the Great Basin, and the prairies of the Great Plains. In areas with distinctive seasonal rainfall patterns, precipitation during the growing season provides a better relationship than does annual rainfall. For example, more than 91% of the year-to-year variation in the ungrazed standing crop in the grasslands around Tucson, Arizona, is accounted for by rain falling in the June-September growing season. In other environments, the inclusion of additional attributes such as temperature or plant residue levels may improve the prediction of biomass.
The main drawback of this approach is that rainfall and biomass data must be concurrently gathered for a number of years before the relationship can be developed. The relationship is also specific to the population where the data is collected, and should not be extrapolated to other sites with different soils, topography, temperature, or rainfall patterns. On the otherhand, once the relationship is validated, little additional field work is required. Furthermore, the model can be a useful management tool, whereby future stocking rate decisions may be evaluated by considering possible biomass levels in response to various rainfall scenarios.
References and Further Reading
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Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. p 212.
Cable, D.R. 1975. Influence of precipitation on perennial grass production in the semi-desert southwest. Ecology 56:981-986.
Currie, P.O., and G. Peterson. 1966. Using growing season precipitation to predict crested wheatgrass yields. Journal of Range Management 19:284-288. (pdf)
Duncan, D.A., and R.G. Woodmansee. 1975. Forecasting forage yield from precipitation in California's annual rangelands. Journal of Range Management 28:327-329. (pdf)
George, M.R., Raguse, C.A., Clawson, W.J., Wilson, C.B., Willoughby, R.L., McDougald, N.K., Duncan, D.A., and A.H. Murphy. 1988. Correlation of degree-days with annual herbage yields and livestock gains. Journal of Range Management 41:193-197. (pdf)
Pieper, R.D. 1988. Rangeland vegetation productivity and biomass. In: P.T. Tueller. (ed). Vegetation science applications for rangeland analysis and management. Handbook of Vegetation Science, Volume 14. Kluwer Academic Publishers, Dordrecht. pp 455-456.
Sneva, F., and D.N. Hyder. 1962. Estimating herbage production on semi-arid ranges in the Intermountain Region. Journal of Range Management 15:88-93. (pdf)
Wight, J.R., Hansen, C.L., and D. Whitmer. 1984. Using weather records with a forage production model to forecast range forage production. Journal of Range Management 37:3-6. (pdf)
Wisiol, K. 1984. Estimating grazingland yield from commonly available data. Journal of Range Management 37:471-475. (pdf)