Reasons for Occurrence of Timberlines and Their Experimental Investigation

Abstract

Though reasons for upper limits of different tree species can vary, including local variations in contributory factors, timberline is ultimately dependent everywhere on the increasingly unfavourable heat balance with rising elevation above sea level. In regions with seasonal climates, increasing cold lengthens the frost period and shortens the frost-free period available for plant production. In addition, whatever adaptation to cold a tree may have, its growth and development is restricted during the vegetative period because heat no longer suffices for completion of the growth cycle. The same applies in principle to trees at the polar treeline. The long winter blockade to life processes is absent in the tropics, but is substituted by inhibition of growth through nightly frosts (Troll, 1966).