Local environmental context drives heterogeneity of early succession dynamics in alpine glacier forefields

Glacier forefields have long provided ecologists with a model to study patterns of plant succession following glacier retreat. While plant-survey-based approaches applied along chronosequences provide invaluable information on plant communities, the space-for-time approach assumesenvironmental uniformity and equal ecological potential across sites and does not account for spatial variability in initial site conditions. Remotesensing provides a promising avenue for assessing plant colonization dynamics using a so-called real-time approach. Here, we combined 36 yearsof Landsat imagery with extensive field sampling along chronosequences of deglaciation for eight glacier forefields in the southwestern EuropeanAlps to investigate the heterogeneity of early plant succession dynamics. Based on the two complementary and independent approaches, we found strongvariability in the time lag between deglaciation and colonization by plants and in subsequent growth rates and in the composition of early plantsuccession. All three parameters were highly dependent on the local environmental context, i.e., neighboring vegetation cover and energyavailability linked to temperature and snowmelt gradients. Potential geomorphological disturbance did not emerge as a strong predictor of successionparameters, which is perhaps due to insufficient spatial resolution of predictor variables. Notably, the identity of pioneer plant species was highlyvariable, and initial plant community composition had a much stronger influence on plant assemblages than elapsed time since deglaciation. Overall,both approaches converged towards the conclusion that early plant succession is not stochastic as previous authors have suggested but ratherdetermined by local ecological context. We discuss the importance of scale in deciphering the complexity of plant succession in glacier forefieldsand provide recommendations for improving botanical field surveys and using Landsat time series in glacier forefield systems. Our work demonstratescomplementarity between remote sensing and field-based approaches for both understanding and predicting future patterns of plant succession inglacier forefields.

Automated summary

Glacier forefields have been used as a model for studying plant succession patterns after glacier retreat. Through plant surveys and field sampling, we found that the time lag, growth rates, and initial plant community composition of early plant succession varied significantly depending on the local environmental context. Our study demonstrates the complementary nature of remote sensing and field-based approaches in understanding and predicting plant succession patterns in glacier forefields.