Successional reversal in biocrust maturity
We found that eight years of precipitation reduction had a significant effect on cover and relative abundance of some biocrust functional groups. Overall, percentage bare soil was higher by 13.1% (F(1,24) = 3.843, p = 0.062), and lightly-pigmented cyanobacterial cover was higher by 17.6% (F(1,24) = 5.267, p = 0.031) with the precipitation reduction treatment compared with ambient precipitation control plots. In contrast, moss cover was lower by 31.6% (F(1,24) = 6.617, p = 0.017) and total late successional biocrust cover was lower by 23% (F(1,24) = 6.319, p = 0.019). No effect was found in the lichen cover (F(1,24) = 1.98, p = 0.172) or in the darkly-pigmented cyanobacterial cover (F(1,24) = 0.872, p = 0.36) (Figure 1, Table S5.).
Out of six morphospecies of mosses encountered in our sites,Syntrichia caninervis was the dominant species with 10.9% and 7.5% mean cover in control and drought plots, respectively, followed bySyntrichia ruralis with 8.8% and 5.4% mean cover, respectively. All the other bryophytes had less than 1% mean cover (Table S6). Lichens showed a richness with 12 morphospecies. The lichens were dominated by Enchylium coccophorum with 1.3% and 1.2% of mean cover in control and drought plots, respectively, followed byEnchylium tenax with 1% and 0.7% mean cover, respectively (Table S7).