On open sand dunes, there are considerable diurnal and nocturnal temperature variations. In California, on an August day, when the air temperature was above 15.5 °C 1 m above the ground, the soil surface was at 38 °C and soil 15 cm below the surface was at 19 °C. In a Nevada desert, the soil surface temperature reaches 65.5 °C and in Veracruz, in the coastal dunes in the central Gulf of Mexico, the soil surface also reaches 65 °C. These temperatures are critical for seed germination and seedling establishment. Some species, such as hard-coated legumes, need these temperature oscillations over several weeks to break the hard seed coat. They lie on the soil during the dry season, and the temperature fluctuations break the testa. When the rains come, they are ready to germinate. Vegetation cover reduces these temperature oscillations considerably. There are also temperature differences over short distances because of topography and orientation. In the dunes of temperate regions, there are temperature and vegetation differences depending on dune slope orientation.

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