Phenology of biological soil crusts, annuals and perennials for remotely sensed studies
Biological Soil Crusts (BSC) are distributed across three quarters of Australia. Previous studies mostly neglected, or considered all BSC components in one or two groups, when they were in a dry state. There is considerable similarity between the spectra of dry BSC and dry soil, thus creating a high potential for misinterpretation. This study examined the likelihood of defining bioclimatic and seasonality patterns in which the different phenological patterns of BSC, annuals and perennials could be utilized in multi-temporal remote sensing studies. Analysis of climatic data (n = 80 years) revealed there are three bioclimatic patterns defined as “common”, “dry” and “wet”, with the probability of occurrence of 74%, 14% and 12%, respectively. Based on the results of two years of phenological observations at Middleback Field Centre (South Australia) of BSC, annuals and perennials which shared the “common” bioclimatic pattern there are three periods when images can be selected. 1) Two to four days after a rainfall pulse when the BSC growth can be detected. This usually occurs in late autumn, winter and early spring, 2) peak growth stage of all biological components when synchronized with a rainfall pulse, usually in late pre-spring; July and August and 3) when both the BSC and annuals have dried. This may be associated with any long dry period but occurs mostly in December, January and February. It must be noted that, BSC grow at any time of the year after rainfall and rapidly dehydrate during dry hot periods. Moreover, after rainfall bare soil, litter, and stone will also affected by moisture and this is of concern in the detection process.