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Fig. 4-1. Zone of adaptation and use of tall fescue in the United States (West, 1998).
Tall fescue is the primary cool-season perennial forage grass adapted to the east-central and mid-southern United States (see Chapter 3). Abiotic stresses in this zone include mineral nutrient deficiencies and drought and high temperature stresses during summer. Nutrient imbalances occur because upland soils, in much of the range in which tall fescue is adapted, tend to be highly weathered and eroded. Field trials showed that E+ stands yielded more and persisted longer than E- stands in the southern portion of the adaptation zone, including Texas (Read and Camp, 1986), Louisiana (Joost and Coombs, 1988), Arkansas (West et al., 1993), and Georgia (Bouton et al., 1993).
Endophyte helps tall fescue persist south of the dashed line shown on the tall fescue adaptation zone map (Fig. 4-1). The line represents a transition, from north to south, of increasing summer water deficit caused by high evaporative demand and low soil water-holding capacity. For example, erodible, rocky soils predominate in the Ozark Highlands of southern Missouri and northern Arkansas, where summer temperatures are high. Similar soil limitations occur in the southern Appalachian Mountains and adjoining regions; however, summer temperatures, and thus evaporation rates, are lower at the higher elevations in the Appalachians than in the Ozarks.
Local zones of stress-prone soils occur north of the dashed line, where endophyte aids persistence, and deep, loamy soils occur south of the line, where E- tall fescue can persist. Endophyte and associated antiherbivory characteristics of infected plants help tall fescue compete and survive when growing where conditions favor the growth of other plant species.