A definition of land surface geomorphodiversity across different scales
Authors: Burnelli Martina , Melelli Laura , Bucci Francesco , Santangelo Michele , Fiorucci Federica , Alvioli Massimiliano 
Published: March 2024

Geodiversity is &#8220;the variety of abiotic features and processes of the land surface and subsurface&#8221; [1,2]. Consensus is growing that geodiversity is the geosphere counterpart of what biodiversity represents within the biosphere, atmosphere, and hydrosphere [2]. Thus, it is potentially relevant to ecosystem functions and services [2]. Since the introduction of geodiversity, several scholars studied it from the theoretical and practical points of view, with different approaches, assumptions and purposes. Methods to define diversity of the geosphere are quantitative, qualitative, or a combination of the twos, with the occasional addition of heuristics [3].Here, we describe a quantitative derivation of a subset of geodiversity, namely, geomorphodiversity. The effort stems from the need of an objective method, apt to providing easy to understand results, readily available for subsequent applications. To that end, requirements are in order about the data included in the analysis: they should be widely available, to allow reproduction of the analysis in most geographical locations, and they should contain enough information to approximate real-world geodiversity.Geomorphodiversity is one implementation fulfilling the requirements, obtained in the literature by different groups, for different locations [4,5], using simple geomorphometry. Data for the method implemented in Italy [6] are a digital elevation model (EUDEM, 25 m resolution), and a lithological map at 1:100,000 scale [7]. DEM provides derived quantities such as slope, drainage network, landforms [8] and slope units [9], all of which contribute in different ways to produce partial diversity maps. We eventually combine partials into an overall geomorphodiversity raster index, GmI, distinguishing five classes of land surface diversity.The inherent parameter dependence in the existing implementations of GmI, partially resolved in [6], is one issue to overcome. Free parameters are embedded in the size of neighborhoods (moving windows, or focal statistics) used to calculate the variety, the arbitrary output resolution, and procedures to polish the final raster diversity map from artifacts. We suggest a multiple assessment of the variety of partial abiotic parameters with a full range of different neighborhood sizes, and a-posteriori statistical selection of local values of diversity. This results in a parameter-free approach to GmI, also allowing a custom resolution of the output, with the lower bound of DEM resolution.We consider a parameter-free geomorphodiversity as a measure of the potential of morphological evolution of the landscape, useful to investigate natural and human-induced diversity in urban areas [10], in combination with accurate, local mapping of geomorphological landforms [11].&#160;References[1] Gray, (2004) Geodiversity: valuing and conserving abiotic nature. ISBN 978&#8211;0&#8211;470-74215-0[2] Schrodt et al., PNAS (2019) https://doi.org/10.1073/pnas.1911799116[3] Zwoli&#324;ski et al., Geoheritage (2018) https://doi.org/10.1016/B978-0-12-809531-7.00002-2[4] Benito-Calvo et al, Earth Surf Proc Land (2009) https://doi.org/10.1002/esp.1840[5] Melelli et al., Sci Tot Env (2017) https://doi.org/10.1016/j.scitotenv.2017.01.101[6] Burnelli et al., Earth Surf Proc Land (2023) https://doi.org/10.1002/esp.5679[7] Bucci et al., Earth System Science Data (2022) https://doi.org/10.5194/essd-14-4129-2022[8] Jasiewicz et al., Geomorphology (2013) https://doi.org/10.1016/j.geomorph.2012.11.005[9] Alvioli et al., Geomorphology (2020) https://doi.org/10.1016/j.geomorph.2020.107124[10] Alvioli, Landscape and Urban Planning (2020) https://doi.org/10.1016/j.landurbplan.2020.103906[11] Del Monte et al., Journal of Maps (2016) https://doi.org/10.1080/17445647.2016.1187977