Ecology and the Challenge of a Multifunctional Use of Soil
Total Page：16
File Type：pdf, Size：1020Kb
Ecology and the challenge of a multifunctional use of soil Patrick Lavelle(1) (1)Institut de Recherche pour le Développement, Centro Internacional de Agricultura Tropical (Instituto TSBF), Apartado aereo 6713, Cali, Colombia. E‑mail: [email protected] Abstract – Soil zoology and soil ecology have become very active fields of research since the early 1990s. A search in the ISI Web of Science databases showed a steady increase in publications about that theme over the last two decades, and 3,612 bibliographic references were found for that theme for the period of 2004 to 2008. The researches covered mostly soil environmental issues, toxicology and ecology. The issue of theoretical development in soil ecology is discussed, and arguments are presented against the idea that the soil ecology theory is deficient. Finally, the need for a general model of soil function and soil management is discussed and some options are presented to reach this goal. Index terms: auto organization, panarchy, soil ecology, soil zoology. Ecologia e o desafio do uso multifuncional do solo Resumo – A zoologia e a ecologia do solo tornaram-se áreas de pesquisa muito ativas a partir do início da década de 1990. Uma busca realizada na base de dados ISI Web of Science mostrou um gradual aumento no número de publicações sobre o assunto nas últimas duas décadas, tendo sido encontradas 3.612 referências bibliográficas para o período de 2004 a 2008. As pesquisas abordaram principalmente assuntos ambientais, toxicologia e ecologia. O desenvolvimento da teoria em ecologia do solo é discutido, e são apresentados argumentos contra a ideia de que existe deficiência na teoria em ecologia do solo. Finalmente, é discutida a necessidade de um modelo geral de funcionamento e manejo do solo, e são apresentadas algumas opções para atingir esse objetivo. Termos para indexação: auto-organização, panarquia, ecologia do solo, zoologia do solo. Introduction paradigms and theories that address soil function in its entirety and are linked with social and economic Soil zoology and ecology cover a fast-growing sciences, in order to identify and implement the best field of scientific research, from basic biology and possible compromises for soil management. its molecular developments, through ecology and environmental sciences, and the still-burning question Scientific domains and production of the dynamics and functions of biodiversity and the Scientific production in soil zoology has increased threats to ecosystem services. The XVth Colloquium exponentially since the early 1990s (Figure 1). A simple on Soil Zoology held in Curitiba (Brazil) in September search of the ISI Web of Science system performed 2008 provided an opportunity to review the advances with the keywords soil fauna, soil invertebrates, in research and identify forthcoming challenges in soil earthworms, termites, soil ants, Collembola and soil ecology. Acari revealed 3,612 references for the 2004–2008 This paper describes the scientific fields and questions period. These could be distributed within 29 variably currently covered by this discipline at the onset of the overlapping “thematic fields” (Figure 2). Biology and 21st century, and addresses the status of soil ecology soil issues were the most commonly found keywords, in general science, highlighting the peculiarities of the just before toxicology and environmental sciences. discipline within mainstream ecology, and as a field This highlights the priorities set by soil ecologists on where general ecological laws often do not apply. It issues of soil management and conservation. Ecology also explains the need for a shift in our conceptual followed, with significant contributions to community background, for the development of truly adapted ecology, biodiversity, models and several related themes Pesq. agropec. bras., Brasília, v.44, n.8, p.803-810, ago. 2009 804 P. Lavelle on trophic and nontrophic relationships. Microbiology, Theoretical developments in soil ecology landscape ecology and global change were other themes Soil ecology has a long tradition of scientific with important inputs. production and many great names associated to it. Another interesting issue is the kind of journals in Aristotle, who once described earthworms as the which soil zoologists publish their work. The largest “intestine of the Earth”, may not have acknowledged proportion was published in soil biology and ecology himself as a soil ecologist; but perhaps Darwin would journals (736), followed by ecotoxicology (206), general have, given his life-long work on earthworms (Darwin, ecology (130), microbiology (60), and soil science (50). 1881), considered the milestone for future studies While publications were dispersed among a very large on soil ecosystem engineers. Over the last century, number of journals, another remarkable feature is the scientists have regularly added their contributions to very low number of papers published in the four major the building of soil ecological theory (Bornebusch, generalist scientific journals: Science (2), Nature (1), 1930; Gisin, 1943; Omodeo, 1952; Jongerius, 1960; Proceedings of the National Academy of Sciences (4) Wallwork, 1970; Bouché, 1972; Swift et al., 1979; or Trends in Ecology and Evolution (1). This feature has Bal, 1982; Satchell, 1983), and a few recent textbooks lead several authors (Barot et al., 2007; Andrén et al., synthesize the accelerated development of soil ecology 2008) to argue that soil ecology is weak at producing in the last 20 years (Gobat et al., 1998; Lavelle & Spain, general paradigms and theories on which to base its 2001; Coleman et al., 2004; Bardgett et al., 2005). own research and as a source of further inspiration for Soil science and soil ecology in particular deal with non-soil ecologists and other scientists. complex systems, in which biological interactions Nevertheless, this situation may mainly reflect are highly constrained by a number of environmental biases of the top generalist journals towards selected factors. In soils, competition for the capturing of types of research and themes that they consider of a resources, for long a major issue in mainstream greater general interest. ecology (actually largely dominated by above-ground vertebrate, insect and plant studies) is only one of these constraints, probably not the major one. Mutualism is thought to be a widely spread form of interaction among soil organisms in the use of generally low-quality resources (Lavelle, 1997; Wall & Moore, 1999). Physical constraints of the environment, like moving in a compact environment and facing often rapidly variable moisture conditions, impose major restrictions on soil organisms. Therefore, ecosystem engineering that helps adapt to these constraints is a major process, whereby ecosystem engineers create suitable conditions for the existence of other groups, often based on mutualist relationships. Competition and food-web effects observed in experiments and under specific field conditions may not be a dominant process, but rather act as secondary, although important regulators to adjust microbial activity and processes at the meso-aggregates scale (hundreds of micrometers to milimeters). Ecosystem engineers, when they are present, tend to regulate processes via predominantly mutualist interactions at -2 -1 Figure 1. Average yearly number of publications on soil the scales of their functional domains (10 to 10 m) 1 2 invertebrates (source ISI Web of Science; keywords: soil and of the ecosystem (10 to 10 m), the ones that fauna, soil invertebrates, earthworms, termites, soil ants, matter for the delivery of ecosystem services (Lavelle Collembola and soil Acari). et al., 2006). Pesq. agropec. bras., Brasília, v.44, n.8, p.803-810, ago. 2009 Ecology and the challenge of a multifunctional use of soil 805 Furthermore, observations of spatial partitioning forests actually are in a stage of the natural succession of populations that are said to support the hypothesis where litter accumulated and decomposed by fungi of a competitive exclusion among species of ants or and arthropods during more than 60 years has become earthworms (Albrecht & Gotelli, 2001; Decaëns et al., a suitable resource for earthworms. The absence of 2008) might as well be interpreted as the result of a earthworms in other places where succession is at cooperation across time in still unidentified succession other stages is by no means due to their exclusion processes. Bernier & Ponge (1994) showed that by the arthropods that colonize the litter. These patches where earthworms do occur in alpine spruce arthropods and the associated fungal microflora are Figure 2. Publication subjects for the period 2003–2008 (note that one publication may fall under several keywords). Source: ISI Web of Science. Pesq. agropec. bras., Brasília, v.44, n.8, p.803-810, ago. 2009 806 P. Lavelle actually participating in a maturation process that will nontrophic interactions probably explains most features transform litter into a suitable food for earthworms at in soil function (Young & Crawford, 2004; Lavelle a later stage. et al., 2006). These theoretical developments, rooted in Another example of disjointed distributions that slow and time-consuming observations and reflexions might be misinterpreted is provided by endogeic on soil complexity, have had little echo in mainstream earthworms. In the Lamto savannah, two functional ecology, not to speak of soil science itself. They groups of endogeic earthworms that exhibit clear are, however, the basis for a next