DRY FORESTS OF TENNESSEE VALLEY REGION". 



81 



Pines are almost totally absent in this valley, and it is only at its 

 western limit, and chiefly south of the Tennessee River, in Colbert and 

 Franklin counties, where deposits of sandy loams and gravels overlie 

 the Subcarboniferous strata, that the character of the forest flora 

 changes b}' the appearance of the short-leaf pine among the hardwood 

 trees. The climate of the valley is somewhat extreme. According to 

 the observations of the United States Weather Service at Huntsville 

 (altitude 650 feet), made during a period of fourteen years, the mean 

 annual temperature is 59.9° F. ; for the winter, 41'^; spring, 59.9°; 

 summer, 75°, and for the fall, 59.7°. The lowest temperature once 

 during this period was 9° below zero; the highest, 96°. The average 

 of annual minimum temperatures is 11°; the average of the highest 

 temperatures, 92i°. The range of temperature throughout the year is 

 most clearly exhibited in the following table: 



Absolute and average minima and maxima of temperature for each month. 



The mean annual precipitation is 54.1 inches; for the winter, 14.68; 

 spring, 15.41; .summer, 15.16; fall, 8.85.^ 



VEGETATION OF THE TABLE-LANDS AND HIGHER RIDGES. 



XerojpKile forests {cedar glades). — The limestone strata of the foot- 

 hills which form the lower terraces of the higher ridges, undermined 

 and dislocated by the action of water, are almost bare of soil. On 

 these rugged grounds the red cedar {Junip&rus virginiana) predomi- 

 nates, but a few other trees gain a foothold. Among them is the blue 

 ash {Fraxiniis quadrayigidata)., a fine timber tree of the Alleghenian 

 area, which reaches its southern limit here, where it is of stunted 

 growth, being rarely more than a tree of medium size. A peculiar 

 varietal form of the white ash {Fraxinus americana curtissii) is not 

 infrequently found w ith the last. It is readily distinguished by its 

 low habit of growth, almost always beginning to branch below a height 

 of 8 to 12 feet, the spreading branches .somewhat drooping, the foliage 

 pale, and the fruit smaller. In this locality the seeds have the embryo 

 well developed. This tree has also been found bj^ Curtiss in the cal- 

 careous hills of Eufaula, on the eastern border of the State, and is 

 apparentl}^ not rare in the cedar brakes of central and southeastern 

 Tennessee. 



' P. H. Mell, Climatology of Alabama, bulletin 18, Alabama Experiment Station, 

 new series, 1890, p. 23. 

 15894 6 



