To create highly detailed and accurate suitability maps for tall fescue (or any other species), it is necessary to change from the traditional qualitative description of plant characteristics to an approach that defines tolerances quantitatively. Estimates of climatic and soil factor tolerances for tall fescue have been developed based on summary publications (e.g., Moser et al., 1996; USDA-NRCS, 2006b), specific research publications, and current expert knowledge of forage scientists.

The type of tall fescue mapped here represents the continental (temperate), summer-active types that already are grown widely in the United States and usually presumed to be infested by the wild type of Neotyphodium coenophialum fungal endophyte (see Chapter 1). In this context, summer-active refers to the ability of a population to grow in summer if precipitation is adequate and temperatures are sublethal, as is exhibited typically by the long-established cultivars Kentucky-31 and Alta (see the Summer Survival section of this chapter).

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