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1 A Review of Methods in Natural Diversity Studies: The Need for Standardization
2 Juan-José Ibáñeza, Eric C. Brevikb*
3 a - National Museum of Natural History of Spain, Spanish National Research Council (CSIC), Serrano 115
4 dpdo, 28006 Madrid, Spain
5 b - Department of Natural Sciences, Dickinson State University, Dickinson, ND 58601 USA
6 (*) Corresponding Author: [email protected]
7
8 Abstract
9 There has been considerable interest in geodiversity and pedodiversity studies over the last
10 approximately 30 years. Pedodiversity is considered part of geodiversity. However in practice they
11 involved different experts and traditions. There are many common aspects that could be shared by all
12 natural diversity studies, however, these common aspects have not been adequately studied and
13 debated. Quantitative techniques that were developed and refined by biodiversity researchers over
14 multiple decades of biodiversity studies should also be applicable to geodiversity and pedodiversity
15 studies. Soil scientists studying pedodiversity followed the same techniques as mathematical ecologists,
16 but geologists studying geodiversity focused on the implementation of proposals aimed at preserving
17 geological heritage and popularising it among the general public. Therefore, pedodiversity and
18 geodiversity diverged and it is not currently possible to compare the results of geodiversity and
19 pedodiversity research. To reach a point where these research results could be compared, it will be
20 necessary to (i) follow uniform mathematical procedures in both these fields and their subfields and (ii)
21 develop universal taxonomies that will be followed for each of the natural resources (fossils, landforms,
22 minerals, soils, etc.) being investigated. Geodiversity studies should move beyond the objective of
23 proposing projects to preserve natural areas of geological value for economic and social purposes
24 (geoparks, geotourism) and extend to attempts to quantify and compare biotic and abiotic diversity and 25 its consequences. If we want to move forward, with a view to achieving a more mature discipline and a
26 true new paradigm, both communities of experts must act synergistically.
27
28 Keywords: geodiversity; pedodiversity; biodiversity; standard measures; geoheritage
29
30 Introduction
31 Over the last three to four decades there has been considerable interest in geodiversity and
32 pedodiversity studies (e.g. Ibáñez and Bockheim, 2013; Ibáñez, 2017; Brilha et al., 2018; Krasilnikov et
33 al., 2018). Soil diversity studies followed biodiversity studies, which have a history that goes back as far
34 as the 1700s (Harper and Benton, 2001; Huston, 1997; Naeem et al., 2002). There are many common
35 aspects shared by the studies of biodiversity and pedodiversity that have not been properly debated and
36 studied by the geodiversity community, despite the fact that the most popular concepts of geodiversity
37 include geology, landforms and soil (Sharples, 1993; Gray, 2004). Many of the methodologies and
38 mathematical procedures proposed, tested and corroborated in the study of biodiversity can be applied
39 without problem to the analysis of geodiversity, as pedodiversity experts have shown (e.g. Ibáñez 2017
40 and references there in). The biotic and abiotic nature of biological versus geological systems does not
41 present an obstacle to the use of the same conceptual and mathematical tools in each discipline, barring
42 some logical exceptions, as has been shown in numerous pedodiversity studies (see Ibáñez and
43 Bockheim, 2013, and references therein). The general definition of diversity, as published in a book on
44 biodiversity (Huston, 1994), is also applicable to geodiversity studies. According to Huston, diversity can
45 be conceptually defined as: "The concept of diversity has two primary components, and two unavoidable
46 value judgements. The primary components are statistical properties that are common to any mixture of
47 different objects, whether the objects are balls of different colours, segments of DNA that code for
48 different proteins, species or higher taxonomic levels, or soil types or habitat patches on a landscape. 49 Each of these groups of items has two fundamental properties: 1. the number of different types of
50 objects (e.g., species, soil types) in the mixture or sample; and 2. the relative number or amount of each
51 different type of object. The value judgements are 1. whether the selected classes are different enough to
52 be considered separate types of objects; and 2. whether the objects in a particular class are similar
53 enough to be considered the same type. On these distinctions hangs the quantification of biological
54 diversity" (Huston 1994, p. 65).
55
56 There are a number of quantitative techniques that have been developed and refined by biodiversity
57 researchers over the multiple decades of biodiversity studies. These same techniques should be
58 applicable to all studies of natural diversity and provide a standard set of evaluations that allow for
59 comparison of the diversity of various natural objects, both biotic and abiotic, as well as investigations of
60 potential links between biotic and abiotic systems (Figure 1). However, in the 25-30 years since
61 geodiversity and pedodiversity studies became relatively common, there are no reviews that critically
62 evaluate the techniques that have been adopted and used by the research groups pursuing work in each
63 of these areas. Therefore, this study was undertaken to (i) review research techniques in the
64 geodiversity and pedodiversity communities, (ii) explore the reasons that each community utilizes these
65 techniques, and (iii) make recommendations for future needs in natural diversity studies. In this paper
66 we will try to address these issues in four related topics (i) theoretical and conceptual aspects, (ii) the
67 mathematical treatment of datasets, with special emphasis on diversity indices, (iii) the need to use
68 universal taxonomies, and (iv) the state of art in the preservation of geological heritage, including soils.
69
70 A brief historical review
71 The early objectives of biodiversity studies were more ambitious than those currently shown in the
72 geodiversity literature (e.g. Magurran, 1988; Huston, 1994; Rosenzweig, 1995): (i) detect the spatial 73 patterns/regularities of species assemblages within and between ecosystems (theoretical ecology and
74 biogeography); and (ii) use of the acquired knowledge to preserve species and the ecosystems that
75 house them (conservation biology). Amazingly enough research into pedodiversity preceded
76 geodiversity research (Ibáñez et al., 1990, 1995; De-Alba et al., 1993; Ibáñez, 2017) and suggested that
77 the same patterns found in pedodiversity could occur with landforms diversity and perhaps
78 lithodiversity. It is paradoxical that in general the geodiversity literature omits the pedodiversity findings
79 published by pedologists in the last 27 years (see Ibáñez and Bockheim, 2013, Ibáñez, 2017, and
80 references therein). It is difficult to explain the divorce between pedodiversity and geodiversity scholars
81 because soils are part of geodiversity, or are at least included in its definition (Sharples, 1993; Gray
82 2004). A historical analysis of both concepts and applications sheds light on this paradox.
83
84 The researchers who developed and applied the pedodiversity concept focused a great amount of their
85 efforts on the spatial pattern analysis of soils and soilscapes using, in general, the mathematical tools
86 previously developed by mathematical ecologists. In contrast, a major goal of experts in geodiversity has
87 been to preserve geological heritage and its popularisation among citizens (McKeever et al., 2010;
88 Nowlan et al., 2010; Kikuchi et al., 2011; Farsani et al., 2014). Thus, the trajectories of the two groups
89 diverged with time. Some years later pedologists began to study and discuss the challenges concerned
90 with the preservation of pedological heritage as well as the design of networks of soil reserves
91 (pedoheritage) in the same way that ecologists did, using quantitative procedures (e.g. McBratney,
92 1992; McBratney and Minasny, 2007; Ibáñez et al., 1995, 2008, 2012, 2015). So there are several
93 contributions that quantify endangered and extinct soil types or pedotaxa (e.g. Amundson et al., 2003;
94 Ditzler, 2003; Drohan and Farnham, 2006; Zhang et al., 2007; Bockheim and Haus, 2013), soil endemisms
95 or minorities (e.g. Bockheim, 2004; Bockheim and Schliemann, 2014), criteria for the evaluation of
96 pedosites (Costantini and L'Abate, 2010) as well as future projections of pedodiversity loss (e.g. Lo Papa 97 and Dazzi, 2013; Lo Papa et al., 2011; Costantini and L'Abate, 2009, 2010, 2016; Costantini et al., 2013)
98 and so on. In contrast, since 1992 most of the geodiversity literature has focused on criteria for the
99 selection of areas to be protected, such as geoparks (UNESCO, 1999, 2014). This fact has pros and cons
100 in that criteria that are not strictly scientific are necessary to designate a geopark, which makes it
101 difficult to measure progress made by geoparks towards the preservation of the geodiversity of our
102 planet. On the other hand, designation of geoparks has the possibility to stimulate local economies and
103 engage the public in the preservation of geoheritage (Farsani et al., 2010; McKeever et al., 2010), which
104 has definite benefits from the perspective of promoting geodiversity.
105
106 Current state
107 Lessons from biodiversity findings and its relation with geodiversity and pedodiversity studies
108 Pedodiversity analyses have not only shown interesting aspects about the spatial patterns of soil, but
109 also allow investigations into whether or not pedodiversity follows the same patterns as biodiversity
110 (see Ibáñez and Bockheim, 2013 and references therein as well as Ibáñez, 2017). Furthermore, some of
111 these studies have found close correlations between pedodiversity, lithodiversity and diversity of
112 landforms (De Alba et al. 1993, 1994; Toomanian, 2013) (Figure 2). It is notable that De Alba et al. (1993)
113 quantified the diversity of soils, lithology and landforms in a study area and coined the term “landforms
114 diversity” in the same year that Sharples proposed the term geodiversity in the scientific literature.
115 However, the findings of pedologists have not received much attention from geodiversity experts over
116 the last twenty years (e.g. Zwoliński et al., 2018; Ibáñez et al., in review) with a few exceptions (e.g.
117 Hjort and Luoto, 2010). Even stranger is the case where the geodiversity of the Iberian Peninsula was
118 analyzed using basically the same mathematical tools that are used in biodiversity and pedodiversity
119 research (Benito-Calvo et al., 2009) but (i) pedodiversity was sidestepped and (ii) bibliographic
120 references to pedodiversity analyses were omitted. This was done despite the fact one of the co-authors 121 of Benito-Calvo et al. (2009) was also a co-author of the pedodiversity studies mentioned above and
122 carried out by De alba et al. (1993) and Ibáñez et al. (1994) in which lithodiversity, landforms diversity
123 and pedodiversity were analyzed, estimated and compared. Nobody doubts that soils, geomorphology,
124 lithology and climate condition terrestrial ecosystems and species diversity. The most widely accepted
125 definitions of geodiversity include three of the four factors mentioned above. Likewise, there is strong
126 evidence that biodiversity and pedodiversity follow similar spatial patterns (e.g. Ibáñez and Feoli, 2013;
127 Ibáñez et al. 2014; 2016a), while some evidence suggests that the same could be true with lithodiversity
128 and geomorphological diversity (De-Alba et al., 1993; Ibáñez et al., 1994, 2016a). Consequently, it is not
129 unreasonable to investigate the possible existence of a unified theory of natural diversities as was
130 suggested by Ibáñez et al. (2012). Furthermore, to detect biodiversity patterns mathematical ecologists
131 and biodiversity experts consider the absence of any kind of mathematical regularity as their null
132 hypothesis (Enrico Feoli, personal communication). As we can see above, biodiversity and pedodiversity
133 analyses refute this assumption, justifying future research regarding lithodiversity and geomorphological
134 diversity to conclusively investigate if they follow similar trends as the evidence to date suggests.
135
136 For geodiversity experts this should not be considered trivial. Most experts in geodiversity have paid
137 attention to one side of the geodiversity coin, the preservation of geological heritage. However, a
138 scientific and worldwide quantitative estimate of geodiversity offers opportunities with great added
139 value, the most important being its inclusion in the mainstream of theoretical ecology, conservation
140 biology, biogeography, and climate change, opening new ways and research lines such as the
141 mathematical detection of spatial patterns of regularity for all the Earth surface systems. All these items
142 are complementary to the current emphasis on conservation issues. In our opinion we cannot talk of a
143 geodiversity paradigm (Gray, 2008) without building a solid unified foundation.
144 145 There are a plethora of papers and books concerning the relationships between soils and landforms
146 (e.g. Ollier and Pain, 1996; Birkeland, 1999; Brevik and Fenton, 1999), soils and lithology (e.g. Zinck et al.,
147 2016), lithology and landforms (e.g. Bridges, 1990; Zinck, 2013), geology and plants (e.g. Kruckeberg,
148 2004), geology and soils (e.g. Kolay, 2010; Brevik and Miller, 2015; Zinck, 2016), landforms and
149 vegetation (e.g. Howard and Mitchell, 1985; Stallins, 2006), and soils and vegetation (e.g. Jobbagy and
150 Jackson, 2000; Eyre, 2013; Ibáñez et al., 2016b). In these cases studies have shown strong relationships
151 between soils and landforms, soils and lithology, etc., to the point that study of one has allowed better
152 understanding of the other. For example, Brevik and Fenton (1999) were able to identify areas along an
153 ancient glacial lake’s shorelines that could be strandlines using soil maps, and Ibáñez et al. (2016b) were
154 able to identify areas where soil studies should be focused based on vegetation mapping. The close
155 relationships noted in studies such as these support the idea that soils and landforms, soils and
156 vegetation, etc. may have similar diversity relationships. On the other hand, the literature reporting the
157 relationships among the respective diversities of these natural bodies is scarce and recent. However,
158 most papers show exciting relationships of pedodiversity with aboveground and soil biodiversity,
159 landforms, lithodiversity and so on (see bibliography in Ibáñez and Bockheim, 2013; Parker, 2017;
160 Ibáñez, 2017).
161
162 Key concepts and needs
163 Problems and non-operational concepts
164 There are no clear and universally accepted concepts of biodiversity, geodiversity and pedodiversity
165 (e.g. Serrano and Ruiz-Flaño, 2007; Petrişsor et al. 2010; Gray, 2004, 2008, 2018, among many others).
166 This fact is a challenge to the operational concept (e.g. Hurlbert, 1971; Ricotta, 2005; Ibáñez, 2017),
167 making it very difficult or impossible to reach scientifically sound mathematical formulations. This issue
168 also occurred decades ago in the field of biological diversity, being critiqued by many reputed ecologists 169 with terms such as “clusters concepts”, “atheoretical concepts”; “omnibus concepts” and “non
170 concepts” (e.g. Hurlbert, 1971; Peters, 1991). With time experts made use of different terms with
171 disparate purposes beyond quantitative biodiversity estimations. However, when the focus is to analyse
172 biodiversity itself, the vast majority of the literature is based on the Linnean hierarchy/taxonomy and
173 especially on the concept of species. The history of pedodiversity studies followed the same path (see
174 Ibáñez and Bockheim 2013 and Ibáñez et al., 2017). In general pedologists made use of two universal
175 classifications proposed by the USDA and FAO, respectively. However, the concept faces other difficult
176 obstacles in addition to those already mentioned, as will be shown below.
177 The need for universal taxonomies
178 Diversity quantification requires classification of the study objects in a rigorous way, that is, it requires
179 the development of taxonomies. Universal classifications / taxonomies allow experts to make use of the
180 same language to compare the results of different studies, areas and environments. Such a situation
181 does not occur with national classifications or those made "ad hoc" for specific research and/or sites. A
182 universal taxonomy is the full/global inventory of the diversity of the studied object. From a scientific
183 perspective it is not permissible to compare results obtained using classifications with different numbers
184 of hierarchical ranks and classes. One of the problems inherent to most of the natural resource sciences
185 is that there are not many disciplines that enjoy the availability of universal taxonomies that are widely
186 accepted by the concerned community of experts. Without this cognitive construct it is not possible to
187 step forward in the quantification of geodiversity. Ad hoc classifications only permit comparisons in
188 areas that use the same taxonomic-constructs with the same databases and resolution scale. At present
189 this set of conditions only occurs in some nations or regions within them.
190
191 A full categorization of geodiversity includes analysis of data that has been generated from disparate
192 disciplines. Some of these disciplines have reached universal classification consensus among their 193 practitioners (e.g. minerals, biological fossils), but this is not true for most, such as geomorphology,
194 hydrology, lithology, hydrology, etc. Based on Huston’s (1994) definition of diversity, without universal
195 classifications it is not possible to compare results among different areas, environment and scales.
196 However, the problem is even thornier. Because there is no single accepted definition of geodiversity,
197 different authors have carried out their geodiversity analysis by addressing different abiotic resources,
198 further complicating efforts to compare results between studies. The current bibliography does not
199 allow us to discern which geographical spaces are more diverse than others. It is impossible to create a
200 quantitative inventory of global geodiversity, or to detect the main hot spots that are rich in “geo-
201 elements”. A datamining study of Geoheritage Journal corroborated these assertions (Ibáñez et al., in
202 review). Thus, universal classifications are needed for all the items related to the quantification of
203 geodiversity as well as international institutions such as EuroGeoSuverys (2010) with interest and
204 funding for the full inventory of all geological natural resources.
205
206 Geodiversity Quantification
207 An example related to diversity indexes
208 In the case of concepts and taxonomies, the provision of new indices to estimate natural diversity gave
209 rise to an immense literature, but not in the case of geodiversity quantification (Brilha, et al. 2018).
210 Various algorithms have been proposed and it is evident that estimating diversity through different
211 mathematical formulations again prevents the comparison of results between sites. However, over time,
212 a small group of indices ended up being the most used (see Magurran, 1988 and references therein). In
213 this way, it is not usually difficult to compare the results of studies conducted by different experts and in
214 different areas. Further, Hill (1974), using Renyi's definition of a generalized entropy, detected strong
215 mathematical relationships among several diversity indexes describing the links between diversity
216 indices and proposed that a “unified concept of diversity is presented, according to which there is a 217 continuum of possible diversity measures”. More recently other authors, such as Feoli et al. (2013),
218 carried out similar studies with success. In a study of the pedodiversity of the global pedosphere,
219 Caniego et al. (2017) made use of singularity spectrums, a mathematical tool usually used in multifractal
220 analysis, and detected strong correlations between many popular pedodiversity indices. It is notable
221 that Renyi's dimensions and singularity spectrums are the tools that are most used to detect multifractal
222 structures in databases, being a fingertip of underlying scaling laws.
223
224 The traditional diversity index works on a single classification and in a given hierarchical level (e.g.
225 species in biology) when all the taxon have the same weight. Mathematical ecologists have spent
226 decades developing and proposing a scientifically sound diversity index that included the taxonomic
227 distance or distinctiveness between the taxa, proposing in the best cases algorithms (e.g. Rao, 1982).
228 There are experts who question the indexes that have been developed because they violate some of the
229 axioms that many ecologists consider unavoidable, such as those proposed by reputed mathematical
230 ecologists such as Pielou (1975) and Laxton (1978). Some examples of these axioms are the following: (i)
231 for a given species number (richness) a diversity index should be maximal if all species occur in equal
232 proportion (e.g. the same number of individual per taxa); (ii) When (i) occurs the diversity index should
233 conformingly increase the richness of the inventory or data set. The Rao diversity index and other “soft
234 indices” that try to incorporate taxonomic distance violate some of these axioms (e.g. Ricotta, 2005). At
235 this date there are no scientific diversity indices that include taxonomic distance and are accepted by
236 most mathematical ecologists.
237
238 It should be noted that these problems arose time and again when attempting to determine the
239 diversity of biological species. Difficulties arose for the following reasons: (i) there are a large number of
240 different indices that may be used; this makes it difficult to compare results between studies that used 241 different indices and detect patterns in them. (ii) Different natural resources are classified using
242 different taxonomic systems, and it is very difficult, if not impossible, to develop indices that are able to
243 integrate results between different taxonomies. Consequently mathematical ecologists did not propose
244 diversity indices that compiled the diversity of several natural resources simultaneously where each
245 resource was classified by different taxonomies (e.g. lithologies, landforms, soil types or pedotaxa). The
246 diversity of each item (e.g. lithotype, landform-type, pedotaxa) should be estimated independently and
247 after that a global geodiversity index should be obtained through some kind of mathematical weighting
248 of the diversities obtained separately for each unique property. Trying to incorporate multiple
249 taxonomies into a single diversity index turns out to be a serious obstacle impeding the progress of
250 geodiversity studies.
251
252 A well-known geodiversity index is the one proposed by Serrano and Ruiz-Flaño (2007) with the
253 following formula to join diversity estimations for geomorphological, hydrological and pedological
254 properties:
255 Gd = Eg R / ln S 256 257 Where Gd = Geodiversity index. Eg = Number of different physical elements (lithological,
258 geomorphologic, hydrological and pedological) of the units; R = Coefficient of roughness of the
259 unit; and S = Surface area of the unit (km2).
260
261 The main problem with this proposal is that the only resource in this list that has a universal
262 classification system available is the soil, with the rest being based on “ad hoc” classifications.
263 Therefore, comparing results from different studies using different information and/or procedures
264 is not possible. Imagine the hypothetical and ideal case where such universal classifications existed for
265 all the natural resources that are part of a widely accepted concept of geodiversity. Even in this ideal 266 case the precision and number of taxa and hierarchical levels of different taxonomies could be quite
267 different. If the classification construct (taxonomy) of one of the “geo-elements” has thousands of taxa,
268 that of another a few hundred taxa and of another only a few tens of taxa, the results will be biased by
269 the natural resources that hold classifications with the highest number of taxa, something unacceptable
270 in a mathematical formula for these purposes. In the same way, the more elements and variables that
271 are included, the more difficult if becomes to analyze an equation designed to interpret the results
272 obtained. In addition, even understanding the reasons the authors included a “coefficient of roughness”,
273 the relief varies continuously. There are many indexes of roughness, and their inclusion in a geodiversity
274 index is intrinsically questionable.
275
276 The most popular diversity indexes only consider the richness of taxa and their respective abundances,
277 although taxonomic distance is intended to be included. In another words, classical equations are based
278 exclusively on the information provided by the taxonomies and inventories. However, the index
279 proposed by Serrano and Ruiz-Flaño (2007) does not fulfill this condition. These authors add area and
280 relief to this equation. Biodiversity-area and pedodiversity-area relationships are extremely interesting
281 but are treated separately. The same can be said of physiography as well as relief-area relationships,
282 which also fit a potential law. Furthermore it is arbitrary to include a "coefficient of roughness" because
283 this variable is an intrinsic factor related to the diversity of landforms. As a result, the index includes
284 redundancy and gives more weight to landforms than to geology and soils. It is a type of bias that should
285 not be included in a diversity index.
286
287 Another possibility to quantify geodiversity is the use of some algorithms such as “balancing entropy”,
288 which is based on fractal mathematics and the Shannon entropy index. This proposal delivers a Shannon
289 index, which provides values ranging between 0-1 (e.g. Martín et al., 2005), and could perhaps be used 290 to propose a diversity index for each of the natural classifications. Proceeding in such a way is equivalent
291 to giving the same weight to the diversity of each resource considered in a study. If this initiative is
292 successful it should permit a first comparison of the diversities for all these taxonomies, solving one of
293 the problems previously mentioned. Due to the magnitude of the problem it would be most prudent to
294 apply the same index to each of the taxonomies used by the natural resources separately. As we will see
295 later, the preservation of a natural resource always requires some kind of expert judgment, as shown by
296 Ibáñez et al. (2011).
297
298 Taxonomic considerations: Needs and opportunities
299 The lack of universal lithologic, geomorphological, etc. taxonomies is the first and largest obstacle to
300 achieving global inventories of these resources. Without these universal taxonomies it is impossible to
301 know and quantify the diversity/geodiversity of their respective heritages. Consequently, at the present
302 date, it is impossible to carry out comprehensive, comparable inventories of the objects of study to be
303 preserved. Thus, for example, what is the diversity percentage covered by the current geoparks? As
304 discussed below, the philosophical basis of the criteria used by UNESCO for the designation and
305 protection of geological heritage spaces is not based solely on scientific standards (e.g. Dingwall et al.,
306 2005).
307
308 There are exceptions to this lack of universally agreed on taxonomies, such as mineral taxonomy and
309 inventories as well as fossils where classification is based on biological taxonomies. The International
310 Mineralogical Association as well as the “mindat” database (http://www.mindat.org/) allow
311 comprehensive studies as in the case of pedotaxa and biotaxa. Moreover, the results obtained by some
312 authors show there are many similarities in the spatial distribution of mineral species, biological species
313 and soil types (e.g. Hystad et al., 2015a, b). A deeper investigation of these potential links is merited. 314 The frequency spectrum shows that the typical hollow curve detected in biodiversity and pedodiversity
315 analyses (see Ibáñez and Bockheim, 2013 and chapters there in) is the same as the species accumulation
316 curve where a power law provides a good fit for the mineral species area relationships (Hazen et al.,
317 2015). Life, primarily microbial organisms, has promoted mineral diversification throughout Earth’s
318 history (Grosch and Hazen, 2015). At this date, the International Mineralogical Association has identified
319 5,090 mineral species with about 2,550 being rare, and predicts a minimum global mineral richness of
320 6,394 minerals (Hystad, et al., 2005a, b). It is clear that with universal classification and global data bases
321 we could detect and compare similarities and differences between different natural resources as well as
322 carry out analyses of the spatial and temporal distribution patterns of several diversities, such as
323 biodiversity, pedodiversity and mineral diversity on a scientifically sound basis. After that the
324 identification of sites to be preserved could be done without ambiguity and uncertainty.
325
326 Geodiversity in the ecological literature
327 Ecologists have failed to reach agreement on how to classify habitats, i.e., agree on a universal
328 classification, so the literature on the relationship between biodiversity and habitat heterogeneity is
329 very fuzzy. The desired classification could be achieved if experts in geosciences agreed to utilize
330 universal taxonomies for the abiotic natural resources that currently lack them (e.g., geology,
331 geomorphology and climate). In regions such as the European Union an agreement of cooperation
332 between Progeo and EuroGeosurveys (e.g., Progeo, 2015; Wimbledon and Smith-Meyer, 2013;
333 EuroGeoSuverys, 2010) could be a very interesting and enlightening starting point to be emulated by the
334 international community of experts in geodiversity and geoheritage.
335
336 There is great interest in biotic and abiotic surrogate indicators of biodiversity the scientific literature. In
337 fact, many researchers contend that the exhaustive corroborated diversity-area relationship (that 338 conforms to a power law) hides another more predictive power: biodiversity-habitat heterogeneity
339 relationships (e.g. MacArthur and Wilson, 1967; Harner and Harper, 1976; Johnson and Simberloff,
340 1974; Williamson, 1981; Hupp, 1990; Triantis, 2003; Tews et al., 2003; Ibáñez and Feoli, 2013; Ibáñez et
341 al., 2014, Báldi A, 2008; among many others). Most of these diversity-area relationship datasets also fit a
342 power law (see bibliography in Ibáñez and Bockheim, 2013; Pérez-Gómez et al., 2014; Ibáñez, 2017).
343 Consequently, there is sufficient evidence to justify researching whether the spatial patterns of diversity
344 are a consequence of mere chance or are a characteristic of abiotic resources. If patterns in
345 anthropogenic activity, climate, and geodiversity are driving forces behind biodiversity patterns, this
346 would open a fascinating and unexplored research field to expand the horizons of geodiversity studies,
347 which are currently restricted to the protection of geological heritage (with a few exceptions). That
348 would make opportunities and funds available to experts in geology, landforms and soils. At this date
349 the bibliography on this topic is in its infancy (e.g. Pemberton, 2007; Parks and Mulligan, 2010;
350 Matthews, 2014; Pérez-Gómez et al., 2014). For example, in some environments and lithological
351 materials rainfall produces soil erosion and eroded sedimentary sequences inducing the development of
352 badlands landscapes, increasing the biodiversity of such sites (Gallart et al. 2013). Some human practices
353 can interfere with badlands formation when these should be preserved as part of biodiversity and
354 geodiversity heritages (Phillips, 1998).
355
356 Geological heritage and its preservation, including pedodiversity
357 We have begun to consider the preservation of geological heritage to be as important as preservation of
358 biological heritage. It is impossible to preserve the world’s biological resources without the preservation
359 of the abiotic habitats that support them. From this point of view it is desirable that biologists and
360 geologists, as much as is possible, use the same language, concepts and methodologies.
361 362 The criteria for the designation of geoparks are to an extent scientific, but they are also focused on
363 education, management, and tourism. Sustainable development, the aesthetics/beauty of the
364 landscapes, respect for the traditions of the local and/or indigenous population, the improvement of
365 human living conditions and so on are all considered in addition to scientific concerns. In a holistic sense
366 this is laudable and desirable. However, in a scientific sense the published papers make it difficult to
367 focus on preserving the diversity of geological heritage because the investigated variables are rarely the
368 same. To provide better understanding of the UNESCO Geoparks rationale (UNESCO 1999, 2014, 2017a,
369 b) it would be healthy to discern the strictly scientific criteria separately from the educational, social and
370 economic ones that can be taken into account by the local, national and international policy makers
371 involved after the scientific criteria have been determined. The UNESCO Geoparks initiative, as currently
372 structured, fails to achieve global and continental scale inventories of the geological heritage that needs
373 to be preserved, but it is useful for educational and tourism purposes (Kikuchi et al., 2011; Farsani et al.,
374 2014).
375
376 The selection of criteria in order to design the networks of reserves in conservation biology is also a
377 matter of debate. However, ecologists are able to get scientifically sound quantitative criteria using
378 rigorous procedures. The design of a network of biological reserves requires measures of diversity to
379 decide “where” and “how” to detect which combinations of available areas could capture the most
380 diversity (Williams et al., 1996). With this background, conservationists can answer the frequently asked
381 question: “How can we choose a small percentage of the total area of a given geographical site to
382 represent the greatest number of species?” (e.g. Csuti et al., 1997).
383
384 Approaches to conserving natural diversity 385 Three approaches are considered when choosing “priority areas” for conservation management, the: (i)
386 hotspots of richness (which simply select the areas richest in taxa); (ii) hotspots of range-size rarity
387 (narrow endemism or, as is the case in pedology, rare occurrences or rare soil assemblages); and (iii)
388 sets of complementary areas (which select areas for the greatest combined species richness) (Williams
389 et al., 1996). The complementary area methods distinguish between irreplaceable and flexible areas,
390 which help planners by providing alternatives for negotiation (Williams et al. 1996). Ibáñez et al. (2008)
391 discuss the pros and cons of the above mentioned alternatives for the preservation of soil heritage. In
392 this respect Gray (2008) mentions hotspots of geodiversity. The three above mentioned criteria are not
393 mutually exclusive. For example, hotspots of richness do not consider taxa, species or "geo-elements"
394 that have a singular value, on the contrary, they consider the hotspots of range-size rarity, selecting for
395 areas that are the richest in species with the most restricted ranges. International initiatives could be
396 developed that elaborate an inventory of the geological heritage of the world on a global scale using a
397 combination of these criteria.
398
399 In the case of pedodiversity preservation there are other initiatives, such as the one used by the Russian
400 School to create a national inventory of so-called soil minorities (Goryachkin, 2004). This term is similar,
401 but not exactly the same, as the concept of the soil endemism used in some states of the USA
402 (Bockheim, 2004; Bockheim and Haus, 2013).
403
404 It is also noteworthy that the most popular definitions of geodiversity (e.g. Gray, 2004) include soil
405 resources as part of geodiversity. Dingwall et al. (2005, p.44) state that: “The question of where soils fit
406 in this process deserves some discussion here. Soils are often included within the definition of
407 geodiversity. Whether or not this is appropriate is an equivocal issue, and one that lacks any rigorous
408 debate or any consistency in approaches to geoconservation. Soils are, in essence, living organic bodies 409 that lie between, and demonstrate the integration of, the physical and biological realms in the
410 landscape. Soils per se have received little attention within the protected areas profession, and it is rare
411 to find protected areas devoted specifically to protection of soils and/or soil features. The New Zealand
412 geopreservation inventory is a rare case in which a soil category is included (Hayward, 1985). Dixon
413 (1966) believes that this may be a consequence of the strength of the international soil conservation
414 movement, which has its focus on the utilitarian values of soils, i.e. agriculture, horticulture, farming,
415 forestry etc. Soils are not singled out for attention as components of natural heritage under the World
416 Heritage Convention, and it is highly unlikely that sites would be either nominated or inscribed primarily
417 for their soil values. For this reason, soils are not discussed in any detail in this report.”
418
419 Soils as an independent natural resource
420 The agronomic bias of soil science has been recognized by many pedologists (e.g. Ibáñez et al. 2005;
421 Havlin et al. 2010; Brevik and Arnold, 2015). However, many pedologists also contend that pedology
422 should be considered a natural resource that is deserving of conservation and being included as part of
423 the overall earth surface system as well as a part of our natural heritage (e.g. Ibáñez and Boixadera,
424 2002; Ibáñez et al., 2005; EuroGeoSuverys, 2010; Gordon and Barron, 2012) (Figure 3). Thus it seems
425 there is a dilemma concerning soils as part of the geological heritage given that some UNESCO
426 documents only mention soil as an afterthought (UNESCO 1999, 2014, 2016). Furthermore, a
427 metanalysis (unpublished data, Ibáñez et al., in review) showed that there are almost no publications
428 that consider soils as a resource to be preserved within the framework of the Geological Heritage
429 Journal. In fact, the term pedodiversity only appears in a single paper among those evaluated. As
430 promoted by Gordon and Barron (2012) and Ibáñez (2017), earth surface systems should perhaps be
431 considered as natural bodies in view that they are a continuum that can and should be studied as a
432 holistic system, including groundwater, regolith and rocks among other “geo-elements” also included in 433 many geodiversity studies. This is the same concept as the Earth Critical Zone that is strongly supported
434 by the USA government (e.g. Amundson et al., 2007; Brantley et al., 2007; Lin and Hopmans, 2011;
435 among many others).
436
437 There is a body of literature related to pedodiversity as well as the preservation of soils as part of our
438 cultural and natural heritage as we saw in the previous section. These papers have not followed the
439 UNESCO criteria for geoparks, but are based on quantitative criteria, georeferenced inventories or
440 databases using universal classification procedures that permit the comparison of results between
441 locations if the scale of resolution level is taken into account (e.g. Costantini and L’Abate, 2016) as well
442 as the intensity of sampling (e.g. Jafari et al. 2013). For example, the studies of Costantini and L’Abate
443 (2009, 2010, 2016) are illustrative of making use of a recent soil map of Italy to quantity the number of
444 soil sites or pedosites in Italy, concluding that there are potentially 726. After that we can make use of
445 the heuristic algorithms (complementary methods) to mathematically prioritize areas that contain a
446 greater diversity of soils (e.g. Csuti, 1997) and / or follow the steps of these Italian authors with a view
447 towards selecting the sites of greatest interest (continental, national, provincial, etc.) according to the
448 principle subsidiarity of the European Union. After obtaining this information, the UNESCO criteria can
449 be applied to proposals for the designation of geoparks. The whole procedure is reproducible for other
450 countries allowing (i) the detection of all pedosites of interest in a geographical space, (ii) analyzing the
451 preservation gaps, i.e. the sites that should be designated as geoparks but still do not have not a
452 geoparks label (national or UNESCO ones); (iii) comparison of the results with those obtained in other
453 territories using the same procedures; and (iv) detecting the weaknesses inherent in the methodology
454 used to improve it. This is a purely scientific process that incorporates the criteria that UNESCO
455 demands exclusively in a final evaluation.
456 457 The need for standardization
458 There are a plethora of concepts, definitions, and quantitative assessments related to geological
459 heritage, geosites, geoconservation, geoparks, etc. (e.g. Brilha, 2016). Furthermore, the preservation of
460 geomorphological heritage has aroused much greater interest than other natural objects included in the
461 concept of geodiversity (e.g. Reynard et al. 2007; Carton et al. 2005; Coratza and Giusti 2005; Tesla and
462 Aldighieri, 2011; Tesla et al., 2013) with some exceptions (e.g. Sá dos Santos et al., 2016). However,
463 quantitative assessments and indices that include strictly scientific data and others that do not obscure
464 the literature about how to quantify geodiversity are needed. We will not be able to eliminate other
465 aspects of geodiversity such as cultural, economic, aesthetic, educational, and so on, and we should not
466 try to do so. In fact, there are considerable opportunities to grow both natural sciences and the social
467 sciences by combining aspects of both (Ramisch, 2004; Moon and Blackman, 2014). However, combining
468 all of these issues into a single geoheratige measure at one time is not necessarily the best approach. A
469 prime example is the aesthetic value, which depends on the observer’s psychology, age, educational
470 training, as well as the cultural values of the society from which the observer comes. It is highly
471 recommended that strict quantification of geodiversity be initially separated from the other
472 nonscientific components related to geoconservation. The wish to preserve geological heritage with
473 international standards and achieve a UNESCO label has become a serious problem for the advancement
474 of the scientific study of geodiversity. The distribution of geoparks recognized by UNESCO (Tables 1, 2)
475 proves it. Very few developing countries have succeeded in obtaining a UNESCO label, unlike emerging
476 and developed ones, and this means the world’s geoparks cannot possibly be effectively protecting a
477 majority of global geo- and pedodiversity. In this respect we encourage geodiversity scholars to follow
478 the Costantini and L’Abate model or the complementary methods previously mentioned in the frame of
479 pedodiversity and soil heritages. However, there is no scientific reason why geodiversity experts should
480 not take into account the preservation of pedodiversity, by definition, and there is no reason that 481 biodiversity, geodiversity, and pedodiversity experts should not be using the same set of quantitative
482 tools to undertake their work.
483
484 Conclusions
485 Both as a science as well as a scientific paradigm, studies of the diversity of a given natural resource
486 began in the disciplines of ecology and conservation biology more than six decades ago. After the Rio
487 Summit, when the neologism biodiversity was popularized, the neologisms geodiversity and
488 pedodiversity were proposed. However, the first quantitative studies on pedodiversity had been carried
489 out and to published before the Rio Summit. Diversity studies have two purposes: (i) the quantification
490 of and mathematical search for regularities in the universe and (ii) the preservation of such diversities.
491 In this respect biodiversity, geodiversity and pedodiversity should face the same challenges and
492 problems. However in practice this has not been the case. While the studies of pedodiversity have
493 followed the path created by biodiversity work, those of geodiversity have largely ignored the biological
494 and pedological diversity literature and blazed their own path. The disinterest of geodiversity experts in
495 pedodiversity and biodiversity findings can be understood but is harmful. Currently the mainstream
496 geodiversity studies are primarily concerned with the preservation of natural heritage, while literature
497 concerning the quantification of geodiversity is scarce and the methodologically dispersed. This
498 complicates attempts to reach any type of consensus among the experts of the various disciplines
499 carrying out natural diversity research.
500
501 The rationale and definitions of geodiversity include soil resources. However, in practice most
502 geodiversity experts ignore the soil resource. As a result geodiversity and pedodiversity research has
503 diverged even though the two should be linked. Consequently, the conservation of pedological heritage
504 has, unfortunately, not been successful, whereas the conservation of geodiversity has been more 505 successful. It can be said that these are two lines of research are almost mutually ignored by the other
506 respective community of researchers. This state of the art has had negative repercussions in both areas
507 of knowledge since the lack of formalization of geodiversity has not given rise to any new paradigm
508 (according to the canons of the philosophy of science). In turn pedodiversity preservation as part of the
509 geological heritage has received neither political attention nor funding.
510
511 On the other hand pedodiversity experts have compared the patterns of soil diversity and biological
512 species diversity, detecting similarities between the biotic and abiotic worlds in different environments,
513 biomes and at various scales, using different classification systems. This fact leaves no doubt that certain
514 mathematical regularities tested are not idiosyncratic of life as ecologists assumed. In fact some
515 pedologists have surmised that perhaps they could move towards a unified theory of diversity that
516 concerns both biotic and abiotic resources. Furthermore, when experts on pedodiversity analysis have
517 carried out quantifications of biodiversity, pedodiversity, lithodiversity and landform diversity they reach
518 intriguing similarities.
519
520 The most accepted concepts of geodiversity, which include soils, demonstrate that the practices for
521 conservation of our natural heritage developed against the rationality of the concept. Consequently it is
522 inexplicable that this divorce is perpetuated against scientific rationality. Experts in both research fields
523 should build a bridge that will benefit both communities of practitioners and the progress of their
524 respective disciplines. Geodiversity studies should be more ambitious, moving beyond the objective of
525 proposing projects to preserve natural areas of geological value for economic and social purposes
526 (geoparks, geotourism) and extending into attempts to quantify and compare biotic and abiotic
527 diversity. On the other hand, pedodiversity experts should pay more attention to the political aspects of
528 geoparks and preservation of our pedological heritage. If we want to move forward, with a view to 529 achieving a more mature discipline and a true new paradigm, both communities of experts must act
530 synergistically. The current situation does not fully benefit either of these groups. To achieve this
531 marriage, geodiversity experts must accept the inescapable inclusion of soil resources in their research
532 agenda and properly document the findings that have been achieved in the fields of biodiversity and
533 pedodiversity. In addition, progress needs to focus on ways to formally reach scientifically sound
534 standards and methods to quantify the so-called habitat heterogeneity that helps us better understand
535 how abiotic diversity conditions biodiversity patterns.
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Table 1. The number of geoparks by country (UNESCO, 2017b) Country Number of Country Number of Country Number of geoparks geoparks geoparks China 35 Hungary* 2 Finland 1 Spain 11 Iceland 2 Malaysia 1 Italy 10 Indonesia 2 Morocco 1 Japan 8 Mexico 2 Netherlands 1 United Kingdom* 7 Norway 2 Northern Ireland* 1 Germany* 6 Republic of Korea 2 Poland* 1 France 6 Slovenia* 2 Romania 1 Greece 5 Brazil 1 Slovakia* 1 Austria* 4 Croatia 1 Turkey 1 Portugal 4 Cyprus 1 Vietnam 1 Ireland* 3 Czech Republic 1 Uruguay 1 Canada 2 Denmark 1 TOTAL 130 Diversity Statistic S or Richness = 35; H or Shannon Diversity Index = 2,8103; E or Equitability = 0.807 * - transnational UNESCO Global Geoparks have been assigned to each of the involved countries
Table 2. The number of Geoparks by continent (UNESCO, 2017b). Continent Number of studies Europe 74 Asia 49 North America 4 South America 2 Africa 1 Oceania 0 Diversity Statistics; Richness =6; H (Shannon Diversity Index) = 0.85623; E or Equitability = 0.47787
Figure
Figure 1. There are numerous links between biotic and abiotic systems and their natural diversity.
Figure 2. There are close correlations between pedodiversity, lithodiversity, and landforms diversity, and all are a part of geodiversity.
Figure 3. Soils are at the center of the earth surface system and cultural heritage. Figure from Ibáñez et al. (2012).