INFLUENCE OF EDWARDS PLATEAU TIMBER. 27 



earth, therefore, the thirsty air soon takes most of it up again, rapidly 

 diying out the earth to a depth fatal to an}^ but very deep-rooted 

 plants. More extreme is this dr3^ing out when the surface is covered 

 by loose stones, as is the case with most of the limestone country, 

 especially west of the timber belt. It is true that a forest evaporates 

 much water from the foliage, but it draws this largeh^ from the lower 

 soil levels; so that, even if the total loss of water from a forest area 

 were equal to that on an exposed area, the earth would not be baked so 

 dry, nor would shallow-rooted herbaceous vegetation be so effectuall}^ 

 excluded. 



PL 11, fig. 1, illustrates the value of heavy timber covering in this 

 direction. The canopy of foliage itself is heavy. Beneath, there has 

 been an accumulation of organic debris to the depth of from 8 to 15 

 inches, the lower laj^ers of which are decomposed into pure humus 

 soil. In such places flourish moisture-loving plants which are alto- 

 gether wanting on similarly situated naked slopes. (See PI. Y.) 



For all these reasons forests tend to conserve the water supph^ and 

 to maintain full springs and an even flow of streams. 



ILLUSTRATIONS OF THE EFFECTS OF THE EDWARDS PLATEAU FOREST. 



Conditions in the vicinit}^ of Austin furnish an unexcelled oppor- 

 tunity to observe both the eflfect of heavy timber upon the behavior 

 of precipitated water and the results of rainfall on bare slopes. Begin- 

 ning at the site of the old Austin dam, there is a series of deep gorges 

 which extend for 10 miles up the river, and head in the high hills of 

 the divide between the Colorado and Barton Creek. Two such gorges 

 lead down from Lone Tree Hill (PL V, figs. 1 and 2). The head of 

 each gorge spreads out in slopes which lead upward to the summits of 

 the hills like an amphitheater, and, by their convergence below, act as 

 a funnel to direct the water into the channel of the stream. The 

 slopes of the southernmost of these gorges, though well timbered 

 below, have been almost denuded farther back, especiall}^ over the part 

 likened to an amphitheater (PL Y, fig. 1). The northernmost gorge is 

 heavily timbered throughout (PL Y, fig. 2). The slopes of the south- 

 ern gorge are denuded of soil down to the rock and adobe, and are 

 never covered with more than a scant}^ growth of drought-enduring 

 plants, which do not suflfice to hide the white, arid slopes. The chan- 

 nel of this gorge is swept clear of organic debris and even of the finer 

 rock debris, leaving a rough, stony channel. 



On the slopes of the northern gorge, under an almost impenetrable 

 growth of cedar and mixed timber, there has accumulated a deep 

 layer of rich soil covered b}" an unreduced debris of fallen leaves and 

 twigs. Loose stones, which even a moderate flood would sweep down- 

 ward, lie on the slopes, as well as the loose leaf litter — striking evidence 

 of the difference in conditions between this and the southern gorge. 



