Moss crusts are the highest developmental stage of biological crusts in arid and semiarid ecosystems worldwide. Under natural conditions, elementary functional units of moss crusts are patches. However, to date, the quantitative features, distribution pattern, ecological effect and relationship with environmental factors of moss patches in desert ecosystems remain unclear. In this study, 3303 moss patches in 22 plots and relevant environmental variables were investigated and quantified in the Gurbantunggut Desert, China. Thirty-six patch classes were defined. Moss crusts accounted on average for 11.7% of the plot area, and the mean moss patch area was 23.4 cm². Small patches dominated, indicating a serious fragmentation of moss crusts. Significant density-dependent effects between patch density and size, humped relationships between patch size and moss plant density, and soil water content under moss patches were observed. The overall distribution of moss crusts showed a tendency of moss patch size and moss plant density decreasing from the southeastern part of the desert to the northwestern part, while moss patch density showed the opposite trend. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of moss patches were dominantly influenced by non-moss crust coverage, sand particle size, latitude, mean annual precipitation (MAP) and mean annual temperature. Of these parameters, fine sand, high MAP and low latitude were beneficial to the development of moss crusts. Consequently, the factors influencing the distribution pattern of moss crusts are complex and contain the soil factor, current climatic conditions and natural and human disturbances.
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