Fjölrit RALA - 15.06.2004, Side 149

Influence of land use changes in the soil temperature regime of Andisols
C. Jiménez, M. Tejedor and M. Rodríguez
University La Laguna, Tenerife, Canary Islands
Soil temperature is a parameter that influences various processes occurring in soils. Some of
these processes are related to the formation of the soil, while others have to do with biological
activity and crop development. The fact that some soil classification systems, particularly
those in which greater importance is attached to soil use, the choice of this parameter, in the
form of soil temperature regime, as a taxonomy criterion illustrates its importance. One such
case is the Soil Taxonomy (Soil Survey Staff, 1999), which takes temperature into account at
virtually all levels of hierarchy, either directly or indirectly through, for example, soil
moisture regimes. In this system, regimes are defined on the basis of the mean annual
temperature of the soil at 50 cm. The present paper examines how changes in land use can
affect the soil temperature regime. In the case studied, vegetation was modified on three
Andisols on the island of Tenerife (Canary Islands, Spain).
The island, which is located near the Tropic of Cancer and has a maximum height of 3,718
m.a.s.l., has a wide range of microclimates depending on factors such as altitude, orientation,
the influence of the trade winds, etc. The following altitudinal sequence has been described
provisionally for the north side of the island (Tejedor et al., 2003): hyperthermic (0-80
m.a.s.l.), isothermic/thermic (800 m.a.s.l.), isomesic (800-1400 m.a.s.l.), mesic (1400-3200
m.a.s.l.), frigid (> 3.200 m.a.s.l.). The altitudinal strip between 800-1400 m.a.s.l. is influenced
by the trade winds, which discharge their moisture and thus add to the amount of water
obtained through rainfall (which is approximately 650 mm/year). This extra water can be
quite substantial, according to some authors. The corresponding surface soils, formed on
volcanic materials, are Andisols of different types. Three sites were chosen in a zone where
the original vegetation was modified such that in each there were plots with natural plant
cover and others where the cover had been altered. In each plot, temperature was measured
monthly over a period of three years (2001-2003) at 50 cm, using thermistors. Between four
and six measurements were taken each time.
The site 1 soils, located at 870 m.a.s.l., are Ultic Fulvudands, non-allophanic andisols with
an abundance of organic matter (10%) which is well incorporated in the profile, where
halloysites were dominant. The natural vegetation entirely covering the soil is cloud forest -
“Laurisilva” -, the main species being Laurus azorica, Erica arborea, Erica scoparia and
Myrica faya, which reach varying heights between 1-8 metres. One zone was cleared and
replanted in the 1970s with Pinus radiata, which have grown to around 15-20 metres. The
soils of site 2. also at 870 m.a.s.l. but at the opposite end of the same face of the island, are
Hapludands. These too are rich in organic matter (7 %) and have a predominance of allophane
in the fine fraction. The original vegetation was gradually modified to allow cropping.
Coexisting here are plots of natural tree-heath woodland: Erica arborea, with Chamaecytisus
proliferus, Cystus symphytifolius, with a covering of 60-80% all years and reaching 3-4 m
height; plots with herbaceous plants: Pteridium aquilinum, Cystus symphytifolius, Rumex
maderensis, Rubus ulmifolius, with a covering of over 80% in summer and less than 20% in
winter, reaching 0.8-lm in height; and cultivated plots (no irrigation); Solanum tuberosum. In
site 3, located at 1370 m.a.s.l., the natural soils are Hapludands, again with abundant organic
matter and short-range-order products. The natural vegetation is Pinus canariensis with little
undergrowth. During the 1960s, in one of the plots the pine trees were replaced by eucalyptus
trees. However, these were cut down at approximately the same time as our study commenced
and, during the course of the study, herbaceous plants, especially fems, have grown there.
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