Leaf litter decomposition is rapidly enhanced by the co-occurrence of monsoon rainfall and soil-litter mixing across a gradient of coppice dune development in the Chihuahuan Desert

• Coppice Dune volume did not affect decomposition.
• Placement on up and down –wind sides of dunes did not affect decomposition.
• Decomposition was strongly affected by precipitation and soil-litter mixing.
• Solar radiation did not strongly affect decomposition.
• Soil-microbial films formed on litter following monsoons and decomposition.

Shrub encroachment, a common occurrence in drylands over the past 150 years, has the potential to alter the redistribution of soil and soil resources by wind and water. This may affect decomposition via soil-litter mixing (SLM). SLM can accelerate decomposition, but its contributions and relationship with abiotic controls, particularly in the context of shrub encroachment, are unknown. To better understand the spatiotemporal relationships between decomposition and shrub encroachment, we conducted a 24 month decomposition study aimed at understanding how placement of litter on either up or downwind sides of dunes in association dune volume affected litter decomposition. There was little decomposition in the first six months of the experiment, with 97.2% of mass remaining despite high exposure to solar radiation. Decay occurred in synchrony with monsoons and SLM, suggesting precipitation during the monsoon season plays an important role in facilitating both SLM and decomposition. Litter placements across a gradient of shrub volumes had no effect on decomposition rates and SLM, but litter placement on the downwind side of dunes had a positive influence on soil-microbial film development. Ultimately, monsoons rainfall and SLM promoted decomposition across a gradient of shrub encroachment in this dryland ecosystem.