Tall fescue can survive episodes of temperatures above and below those extremes with proper hardening. Ability of tall fescue to survive temperature extremes interacts with the occurrence of snow cover at the low extreme and the severity of water deficit at the upper extreme. Snow cover as it relates to tolerance of low temperature extreme is not accounted for in this process since the purpose is to map suitability during a defined growing season; however, water deficit is calculated in the water-balance function.
January mean minimum temperatures of -12, -15, and -18°C and July mean maximum temperatures of 31, 33, and 35°C were the input values to set the boundaries for well-suited, moderately suited, and marginally suited categories, respectively (Table 3-1, Figures 3-3e and f). These temperature values were chosen based on northern limits of cold survivability, and iteration of values and resultant maps consistent with local experts' observations.
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Table 3-1. Limit input values in the PRISM Species Suitability Model for setting tall fescue suitability categories. Grid locations for which values fall outside the threshold extremes are mapped as unsuited for tall fescue.
|Fig. 3-3e. Tall fescue suitability map for the conterminous US based on a combination of Jan mean minimum temperatures (-12, -15, and -18 C) and July low (13, 9, and 6 C) and high (on 31, 33, and 35 C) mean maximum temperature tolerance values.||Fig. 3-3f. Tall fescue suitability map for the PRC based on a combination of Jan mean minimum temperatures (-12, -15, and -18 C) and July low (13, 9, and 6 C) and high (on 31, 33, and 35 C) mean maximum temperature tolerance values.|