Pioneer zone geo-ecological change: Observations from a chronosequence on the Storbreen glacier foreland, Jotunheimen, southern Norway

• Contributions are made to chronosequence methodology and geo-ecological succession.
• The focus is on the pioneer stage, which has been oversimplified in previous studies.
• The study emphasises interactions between plants, insects and abiotic habitat factors.
• Drainage, pervection and frost sorting are inferred to be important drivers of change.
• Plant and insect colonizers exhibit a high degree of independence of each other.

The first 33 years of primary geo-ecological succession is investigated in the pioneer zone of the Storbreen glacier foreland using the chronosequence approach. Pitfall trapping of invertebrates and the sampling of higher and lower plants and habitat factors from quadrats were used on three replicate transects across a till plain accurately dated by annually monitored glacier front variations combined with the mapping of annual moraine ridges. Unstable, saturated sediments deglacierized for < 1 year are colonized first by very large numbers of Collembola and a small number of epigeal beetles and spiders. Improved drainage, loss of fine matrix by pervection and frost sorting lead to the development of an active stone pavement after 6–21 years, which is colonized by sparse herbaceous perennials, a slowly-developing cryptogamic crust dominated by mosses, and moderately abundant epigeal beetles, spiders and the glacier harvestman (Mitopus morio). Further soil development and stabilization of the stone pavement lead, via a transition phase (21–26 years), to a fast developing ecosystem (26–33 years) in which the cover of most of the plants and pitfall catches of invertebrate groups are increasing rapidly (including a resurgence in Collembola catches and the spread of Racomitrium moss, terrestrial lichens and shrubs). Spatial heterogeneity reflects gradual successional trajectories related to small variations in physical habitat conditions. The sequence of changes is summarized in a conceptual geo-ecological model in which abiotic and biotic processes combine to drive the pioneer stages of both invertebrate and plant succession with little evidence of highly integrated biotic communities.