Decline in biological soil crust N-fixing lichens linked to increasing summertime temperatures

Biological soil crusts (biocrusts), comprised of mosses, lichens, and cyanobacteria, are key components to many dryland systems globally. Climate change and other anthropogenic disturbances are thought to cause a decline in late-successional biocrusts cover; yet, few long-term studies exist to track potential shifts in these sensitive soil-surface communities. Using a globally unique long-term observational dataset from a temperate dryland with initial observations dating back to 1967, we examine the effects of 53 years of observed environmental variation and Bromus tectorum invasion on biocrust communities in a grassland never grazed by domestic livestock. Annual observations show a steep decline in the N-fixing cyanolichen cover (dominated by Collema species) from 1996-2002 during a period of extended drought, with Collema communities never able to recover to pre-2000 levels. Declines in chlorolichen species were also observed, both in the number of species present and by total cover, which was attributed to increasing summertime temperatures. Conversely, moss species gradually gained in cover over the survey years, especially following a large Bromus tectorum invasion at the study onset (ca. 1996-2001). These results support a growing body of studies that suggests climate change is a key driver in changes to late-successional biocrust communities. Importantly, results here suggest that warming can partially negate decades of protection from disturbance with biocrusts communities reaching a vital tipping point. The accelerated rate of ongoing warming captured in this study has already resulted in the loss of biocrust lichen cover and diversity, which could have long-term implications for temperate dryland ecosystems globally.