Empirical Measurement of Environmental Gradients in Ecological Surveys

Soil temperature, soil moisture and soil fertility were determined empirically at 63 predominantly hill sites in the South Island, New Zealand. Soil temperatures were measured at a depth of 0.5 m in four seasons and gave a standard deviation of mean annual temperature between sites of 2.2-degrees-C. Soil moisture levels, as available water in a 0-0.5 m profile, measured seasonally, gave a standard deviation between sites of 49 mm water. Soil fertility was measured in a common environment as yield of a test species grown in each soil expressed as a percentage of the yield in the same soil given complete nutrients. On this scale the standard deviation between sites was 19%. The trial showed that these environmental factors can be empirically measured in surveys.