Soil temperatures inside and outside forested and treeless boulder slopes in the Bolivian high Andes. A test of the hypothesis of Walter and Medina (1969) Article

Kessler, M, Hohnwald, S. (1998). Soil temperatures inside and outside forested and treeless boulder slopes in the Bolivian high Andes. A test of the hypothesis of Walter and Medina (1969) . 52(1), 54-62. 10.3112/erdkunde.1998.01.05

cited authors

  • Kessler, M; Hohnwald, S

abstract

  • In the northern and central Andes, isolated forest patches dominated by Polylepis (Rosaceae) occur at elevations of up to 1000 m above the closed timberline, in many cases growing on boulder slopes. WALTER and MEDINA (1969) proposed (a) that soil temperature determines the upper timberline in tropical mountains and (b) that boulder slopes have higher soil temperatures than fine-grained soils because the open structure of the boulder slope permits warm air to penetrate deeper into the soil, thus allowing trees to grow there. We tested these hypotheses by measuring soil temperatures in 5 cm and 12,5-17,5 cm depth at three sites in forested and treeless boulder areas and in adjacent unforested fine-grained soil at 4050 m a.s.1. in the Zongo Valley, La Paz, Bolivia, in 1995 and 1996. We found that minimum, maximum and average soil temperatures are about 2°C lower within the forested boulder slope and about 1°C lower within the unforested boulder slope than in adjacent fine-grained soil, thus rejecting the hypothesis of WALTER and MEDINA. This suggests that the restriction of Polylepis patches to boulder slopes above the present-day forestline is due to anthropo-zoogenic causes (burning and grazing). While our results do not provide decisive data to judge whether soil temperature is the limiting factor at the Andean timberline, they show that forest can grow at average soil temperatures of 4-5°C (and less than 3°C over periods of several months), which are lower than the limiting value of 7-8°C proposed by WALTER and MEDINA.

publication date

  • January 1, 1998

Digital Object Identifier (DOI)

start page

  • 54

end page

  • 62

volume

  • 52

issue

  • 1