Long-term evidence for dispersal limitation in arctic primary succession: Consequences for soil carbon

Background/Question/Methods: Climate warming will reduce permanent snow and ice in the arctic, increasing opportunities for primary succession and associated changes of soil properties such as carbon dynamics. The rate at which succession proceeds may depend on the mechanisms that limit the rate of succession. Here we introduce a new approach to assess the long-term role of plant dispersal in limiting the rate of primary succession and coincidental soil development. In three alpine valleys in northern Sweden, we compared primary succession along two types of chronosequences with similar species pools and climates but with contrasting spatial scales: glacial forelands that span several km, and sorted circles (frost boils) that span 2-3 m. Four successional stages (bare ground, cryptogamic soil, herbaceous vegetation, and woody vegetation) were sampled in both forelands and circles in the three valleys.

Results/Conclusions:  Lichen dating showed that successional stages that were achieved in centuries on forelands were arrived at after only decades on circles. Since the relatively small circles are presumably free from dispersal constraints, these age differences strongly suggest that arctic primary succession is constrained by plant dispersal. Surface soil C content (g C /m²) varied significantly among successional stages in both sequences, suggesting that this important ecosystem service is also constrained by dispersal. In conclusion, the rate of primary succession is much faster on small-scale circles than on large-scale forelands, suggesting that arctic primary succession and associated surface soil C dynamics there are influenced by plant dispersal in arctic tundra.