Fjölrit RALA - 15.06.2004, Síða 150

Table 1 gives the mean annual soil temperature, the mean summer and winter temperatures
and the isotivity (difference between summer and winter temperature) for each plot. Although
all the soils under natural vegetation are located within the same climate strip, the higher
altitude of site 3 is reflected in the lower (2°C) mean annual soil temperature. Despite this, in
all three cases the soil temperature regime is isomesic, although the isotivity being much more
pronounced in the site 1. Modification of the plant cover has led to a notable change in the
soil temperature regime of sites 2 and 3, which became thermic under the fems and in the
cultivated area of site 2, and mesic in the deforested area of site 3. In both sites the change of
use has led to an increase of over 2 °C in the mean annual soil temperature and also to a
greater seasonal contrast (increase of 2.2 °C). Conversely, in site 1 the different temperatures
and the soil temperature regime remain constant despite the change in vegetation.
Table 1 Seasonal and annual soil temperature (° C) for the study plots
Site Site 1 Site 2 Site3
Land use Cloud forest Pine forest Woodland (heath) Herbaceous Crop Pine forest Deforested
Mean annual 14.1 14.5 14.4 15.5 16.8 11.6 13.7
Mean summer 15.3 15.6 17.3 18.5 20.8 14.2 17.6
Mean winter 13.0 13.4 12.0 12.8 13.3 9.4 10.6
Isotivity 2.3 2.2 5.3 5.7 7.5 4.8 7.0
We attribute these results to the influence exerted by the different types of vegetation in
creating a special microclimate, which is formed as a result of the action of the trade winds.
The ‘laurisilva’ and pine forests and, to a lesser extent, the woodland have a high capacity to
draw the moisture from the winds. This occurs throughout the year, particularly in summer,
and leads to very homogenous environmental conditions, which determine the isomesic
regime and the isotivity of these natural zones. The crops and the herbaceous plants that
emerged after the trees were cleared do not have the aforementioned capacity and hence the
temperatures are higher and the contrasts greater. The differences between the natural plots on
the three sites may also be due to their location. The modifications to the soil temperature
regime brought about by the change in land use will also have repercussions, in some cases,
on the characterisation of the soil moisture regimes and, consequently, on the classification of
the soils.
References
Soil Survey Staff. 1999. Soil Taxonomy. Second ed. Nat. Resour. Conserv. Serv., USDA
Agric. Handb. 436, Washington, DC.
Tejedor, M., Jiménez, C., Rodríguez-Paz, M., and Hemández-Moreno, J.M. 2003. Soil
temperatura regimes in the island of Tenerife. Altitudinal sequence. ASA-CSSA-SSSA
Annual Meetings. Changing Sciences for a Changing World Building a Broader Vision.
Denver.
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