Rock Glaciers Vegetation Colonization in Retezat Mountains: Implications for Morphodynamics and Palaeoclimate Reconstruction

Vegetation is an important ecological indicator of rock glaciers' activity as its development marks the transition from active to inactive and relict states. Most rock glaciers in Retezat Massif are covered by vegetation, mostly Pinus mugo shrubs but also herbaceous and forestry vegetation. In this paper, 82 rock glaciers from Retezat are classified into six classes according to vegetation characteristics, rock glaciers' vegetation changes are assessed using old aerial and ground imagery, and the timing of shrubs vegetation growth is investigated by means of dendrochronology methods applied on three rock glaciers. The study's main purpose is to identify what caused the vegetation colonization, climate variation, or rock glacier inactivation. Results indicate that altitude is the dominant factor of rock glacier vegetation cover variability. In most cases, the vegetation patches increased in density and only slightly in surfaces. The last rock glaciers' vegetation colonization initiated in the 18th century, beginning with 1830s on all the three rock glaciers probably after the last local Little Ice Age cold spell. We conclude that the investigated rock glaciers were pseudorelict during the entire Holocene and that recent vegetation settling is not the first one in the Holocene. However, the scenario of rock glaciers inactivation that caused vegetation growth, previously advanced in the literature, cannot be excluded, especially in light of the recent discoveries of rock glaciers activity, and further investigations should be done to come to a less ambiguous outcome.