RELATIONSHIP BETWEEN METEOROLOGICAL MEASUREMENTS AND FLOWERING OF INDEX SPECIES TO FLOWERING OF 53 PLANT-SPECIES

Agriculturists and range managers need advanced knowledge of when a plant will reach a specific developmental stage to plan when to apply herbicides, to begin grazing season, to change pastures in a grazing system, and to harvest forage. Relationship between flowering dates of 53 plant species and accumulation of temperature, temperature plus solar radiation, and the flowering of index species was studied for four years near Sidney, Montana. Accumulation of thermal days (a nonlinear heat unit system which discounts mean temperatures over an optimum) was the most accurate of eleven methods tested in accounting for variation among flowering dates. It accounted for 49% of the variation for early-flowering species but only accounted for 34% of the variation for late-flowering species. However, the degree days (remainder) was simpler to calculate and resulted in only 0.3-day standard deviation (SD) loss of accuracy. The degree days (remainder) was equal with the degree hours (duration-summation) in accuracy and both were a day more accurate than the NOAA-degree days. The 20-day moving average of maximum air temperatures was the least accurate of the eleven methods in accounting for variation of flowering dates. The addition of solar-radiation with temperature did not account for any more of the variation among flowering dates. The date that a selected index species flowered was the simplest and probably the most practical method of estimating flowering dates if a 1.0 day (SD) loss of accuracy was acceptable. Knowing the time that a selected index species flowered made possible estimating within five days (SD) the flowering dates of 40 species one to three months earlier. © 1979.