Note 9 — Chapter VI · THE BORDER VALLEYS OF THE EASTERN ANDES

Reference to the figures in this chapter will show great variation in the level of the timber line depending upon insolation as controlled by slope exposure and upon moisture directly as controlled largely by exposure to winds. In some places these controls counteract each other; in other places they promote each other’s effects. The topographic and climatic cross-sections and regional diagrams elsewhere in this book also emphasize the patchiness of much of the woodland and scrub, some noteworthy examples occurring in the chapter on the Eastern Andes. Two of the most remarkable cases are the patch of woodland at 14,500 feet (4,420 m.) just under the hanging glacier of Soiroccocha, and the other the quenigo scrub on the lava plateau above Chuquibamba at 13,000 feet (3,960 m.). The strong compression of climatic zones in the Urubamba Valley below Santa Ana brings into sharp contrast the grassy ridge slopes facing the sun and the forested slopes that have a high proportion of shade. 54 represents the general distribution but the details are far more complicated. See also Figs. 53A and 53B. (See Coropuna Quadrangle.)