Diversity of Soils

by

J.J. Ibáñez

• LAST REVIEWED: 15 June 2021
• LAST MODIFIED: 23 August 2017
• DOI: 10.1093/obo/9780199874002-0104

Introduction

The earth’s surface is heterogeneous in nature. This feature of the earth’s crust implies that the distribution in space of its natural resources is also varied. Most natural resources vary in a continuum rather than in a discrete way. However, our cognitive system works better in discretely classifying the world that surrounds us. Therefore, we divide all the observed features in nature into non-overlapping categories, through a process called “categorization.” Then we order, name, and group objects previously created in our minds in such categories, producing classifications, either consciously or unconsciously. Most of these classifications are hierarchical (splitting the natural continua in discernible classes by using nested classifications of increasing refinement). A scientific universal taxonomy is a mental construct that inventories the diversity of the universe studied at the global level by experts, such as living organisms, rocks, and soils, conforming to explicit rules. The diversity of a natural resource is based on these grounds. Therefore, the quantification of any diversity always depends on the number of classes and categories of the taxonomy used. As a corollary, the inventory of diversities will always suffer biases and limitations, being provisionally from a historical perspective. At first instance, the notion of diversity of a given natural resource is clear and intuitive. All naturalists recognize that some territories are more diverse than others, regardless of whether they are interested in species, soils, landforms, rocks, etc. Therefore, it is impossible to consider a particular naturalist as the founder of the analysis of diversity. In ecology, the first patterns and theories in biodiversity date back to the first decades of the 20th century. In contrast, the interest of the scientific community in the diversity of the abiotic natural resources began in the last decade of the 20th century, although it is possible to find some exceptional publications before that date. The starting point of this article goes back to the first attempts to operationalize the concept and the first indexes for its estimation.

General Overviews

In contrast with studies of biodiversity, soil diversity (or pedodiversity) analysis is in its infancy, so there are few publications that compile and synthesize the main findings. Ibáñez and Bockheim 2013 is the first study that deals with pedodiversity. Petersen 2008, a doctoral dissertation, describes the state of the art in pedodiversity analysis. The Romanian pedologist Nicolae Florea wrote a book, Florea 2010, in which he presents his ideas on pedodiversity and other aspects of soil sciences. Currently there are no published review papers that capture all the approaches to soil diversity analysis. However, pedodiversity studies make use of many of the same mathematical tools used in biodiversity analysis by ecologists. There are many books and papers that clearly show the application of the most-used mathematical tools to estimate biodiversity and pedodiversity, with only one premise: biotaxa equal pedotaxa (soil types). The number of taxa is termed “richness.” In general, “diversity” indexes take into account the richness as well as the distribution of the number of individuals (or the area covered by them) among the taxa that appear in a given soilscape (“abundance distributions”). Most mathematical tools make use of richness and abundance to calculate the diversity of a given natural resource. May 1975 is a clear and concise review article on this subject. However, this is somewhat dated and does not reflect the progress made over the subsequent decades; Tokeshi 1993 is a more up-to-date review paper. Anna E. Magurran has written and edited several introductory books that synthesize the main findings of their day in biodiversity analysis, among which is Magurran 2004. Some experts study the diversity of soils and their relationships with biodiversity without taking into account the existing literature, often replacing the term “diversity” with “heterogeneity”; see Williams and Houseman 2014, among other studies. Pedodiversity studies are beginning to arouse the attention of other related scientific disciplines, and research on biogeochemical processes, as shown in Quideau, et al. 2013, is an example. In the early 21st century, pedodiversity studies have been considered relevant approaches to soil geography and spatial pattern analysis by the UN Food and Agriculture Organization (FAO) and the Intergovernmental Technical Panel on Soils (ITPS) (see Intergovernmental Technical Panel on Soils 2015).

• Florea, Nicolae. Pedodiversity and Pedocyclicity: Soils in Space and Time. 2d ed. Bucharest, Romania: Academia de Științe Agricole și Silvice, 2010.

  Romanian pedologist Florea presents his ideas on pedodiversity and other aspects of soil science.

• Ibáñez, Juan José, and James G. Bockheim, eds. Pedodiversity. Boca Raton, FL: CRC, 2013.

  DOI: 10.1201/b14780

  A book that synthetizes the state of the art in pedodiversity analysis.

• Intergovernmental Technical Panel on Soils. Status of the World’s Soil Resources: Main Report. Rome: Food and Agriculture Organization of the United Nations, 2015.

  Several paragraphs on the role of pedodiversity analysis appear in chapter 3, section 3.3, titled “Soils, Landscapes and Pedodiversity” (p. 32).

• Magurran, Anne. E. Measuring Biological Diversity. Oxford: Blackwell, 2004.

  A comprehensive and user-friendly book on the main mathematical tools used by ecologists in biodiversity analysis.

• May, M. Robert. “Patterns of Species Abundance and Diversity.” In Ecology and Evolution of Communities. Edited by Martin L. Cody and Jared M. Diamond, 81–120. Cambridge, MA: Harvard University Press, 1975.

  Writing by one of the most well-reputed experts in biodiversity. Describes the most-classic tools used by ecologists over the decades.

• Petersen, Andres. “Pedodiversity of Southern African Drylands.” PhD diss., Universität Hamburg, Institut für Bodenkunde, 2008.

  Begins with an extensive introduction to the study of pedodiversity, with abundant explanations and references. Available online.

• Quideau, Sylvie A., Matthew J. B. Swallow, Cindy E. Prescott, Sue J. Grayston, and Se-Woung Oh. “Comparing Soil Biogeochemical Processes in Novel and Natural Boreal Forest Ecosystems.” Biogeosciences 10.8 (2013): 5651–5661.

  DOI: 10.5194/bg-10-5651-2013,2013

  Key soil biogeochemical processes in a given landscape are pedodiversity dependent.

• Tokeshi, Mutsunori. “Species Abundance Patterns and Community Structure.” Advances in Ecological Research 24 (1993): 111–186.

  DOI: 10.1016/S0065-2504(08)60042-2

  Tokeshi’s review paper updates the contents of the May paper, adding the patterns that characterize the changes of biodiversity that occur over time (ecological succession), as well as the resulting environmental impacts.

• Williams, Brandon M., and Gregory R. Houseman. “Experimental Evidence That Soil Heterogeneity Enhances Plant Diversity during Community Assembly.” Journal of Plant Ecology 7.5 (2014): 461–469.

  DOI: 10.1093/jpe/rtt056

  A typical study in which the terms and mathematical tools in pedodiversity studies are replaced by ad hoc approaches.