Incipient soils: New habitats in proglacial areas of the Maladeta massif (Central Pyrenees)

Since the Little Ice Age, the deglaciation of the Maladeta massif (Central Pyrenees) has been almost continuous; since then, the glaciated surface has been reduced by 87.9 % until 2021. This deglaciation has led to an increase in proglacial areas, allowing the development of new habitats. In this study, 86 samples of incipient soils (>5 cm depth) were selected with a large range of different characteristics (elevation, orientation, density of plant cover or soil colour). Geochemical, microbiological and statistical analyses were carried out under the hypothesis that time of deglaciation control the evolution of these incipient soils. The results showed soils with highly variable characteristics, although in general neutral-acid pH (median 5.5), water aggregate stability was relatively high (median 64 %), but they exhibited very low carbon content (median 1 %). In these very incipient soils, the time of deglaciation seems not to be a key factor that determined the development of the soils. In spite of this, the duration of the snow cover (strongly influenced by the topography) is a factor that explains the degree of development of the soils. Moreover, the percentage of silt content has shown to give the soil a higher reactivity, water and nutrient retention capacity and greater stability. A pattern of biological succession was found, from bacteria as colonisers, to fungi in subsequent stages, and finally to plants colonising the habitats. Finally, the impact of mountain tourism in the most transited sector of the Maladeta massif (the Aneto cirque) showed a high concentration of nitrate (>50 mg kg^-1), which favours primary productivity and increases the abundance of microorganisms. This study shows the importance of the microtopography and the presence of silt in the development of very incipient soils in recently deglaciated areas.