Assessing the ecological value of dynamic mountain geomorphosites

Over the last 15 years, the methodological proposals for assessing the heritage value of geomorphosites have been numerous and varied (Brilha, 2018). While some of the main criteria for assessing the geoscientific value, i.e. the interest for Earth sciences (rarity, representativeness, integrity), are mentioned in most methods, the criteria for assessing additional values (Reynard, 2005, 2009:  aesthetic, ecological and cultural values) are much more heterogeneous (Mucivuna et al., 2019). There is particularly little discussion in the literature about the assessment of the ecological value of geomorphosites. Many case studies suggest to give a high score when “valuable” or “interesting” fauna and/or flora are observed, without explaining the link with a specific geomorphological landform or process. A few authors, such as Bollati et al. (2015), proposed to assess the “ecologic support role”, i.e. the impacts of geomorphological processes and landforms on vegetal and animal diversity or their contribution to ecosystem services. Despite these suggestions, there is still no detailed methodological proposal to assess the ecological value of geomorphosites based on clearly defined criteria.

The bi-directional relationship between geomorphology and biological elements of nature has been the subject of many publications and led to the development of the biogeomorphology, defined as the study of interactions between geomorphological processes and structures and living organisms, like plants, animals and microorganisms (e.g. Knox, 1972; Butler, 1995; Gorbushina, 2007). Compared to other categories of geosites, the activity of processes responsible for their formation and evolution is often a core characteristic of geomorphosites (Reynard, 2009; Pelfini and Bollati, 2014; Coratza and Hobléa, 2018) and this dynamic can have a strong influence on vegetation. This is especially the case in mountain environment, where dynamic geomorphological parameters can have various effects on vegetation distribution and community composition (Giaccone et al., 2019).

The aim of this communication is to clarify and objectivize the assessment of the ecological value of dynamic mountain geomorphosites. A complete evaluation of the ecological value should take into account the impacts of geomorphological processes and landforms on vegetation and fauna diversity. Here we propose to look further into the question of the influence of dynamic mountain geomorphosites on vegetation diversity. We suggest the definition of three criteria – disturbances, microhabitats, types of substrates – that should be used for a more accurate and objective assessment of the ecological value of this category of geomorphosites, with a particular focus on the links between geomorphology and vegetal biodiversity. We finally apply these criteria for the assessment of the ecological value of four mountain geomorphosites situated in the Vallon de Nant (Swiss Alps): a rock glacier, a moraine complex from the Younger Dryas, a side and frontal moraine from the Little Ice Age and a zone of scree slopes and avalanche deposits.