Journal of Arid Environments 122 (2015) 27e29

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Short communication

Termite mounds as dominant land forms in semiarid northeastern Brazil Roy Richard Funch
rio, Av. Transnordestina, s/n, Feira de Santana, Bahia 44036-900, Brazil Universidade Estadual de Feira de Santana e UEFS, Campus Universita

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 October 2014 Received in revised form 6 May 2015 Accepted 22 May 2015 Available online xxx

Open source satellite imagery has allowed the visualization and mapping of remarkable numbers of large, densely-packed termite mounds covering extensive areas in the semiarid region of northeastern Brazil, revealing tens of millions of regularly spaced termitaria (between 2 and 4 m tall, at densities of up to 35/ha). The origin, distribution, and natural history of these mounds are discussed, as well as questions regarding their age and dense packing, their sharing or appropriation by other insects, and why they attained such huge volumes in a dry landscape. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Biogenic mounds Termitaria Bioturbation Mima mounds Landscape

The semiarid northeastern region of Brazil is dominated by semi-deciduous forests and fully deciduous arboreal/shrub, dense, thorny “caatinga” vegetation (Giuliett et al., 2005). This latter vegetation type is often almost impenetrable, and grows on oligotrophic, clayey, acid soils that support little economic activity. As the resolution of Google Earth imagery has improved in this area it has become possible to clearly distinguish very large termite mounds (“murundus”) due to their circular outlines and regular spacing (Fig. 1) e resulting in the capacity to accurately map their distribution over wide areas. A grid survey using Google Earth (at 0.15 degrees of arc; intersect spacing ~16 km NeS and EeW) in central Bahia State and northern Minas Gerais State in northeastern Brazil indicated a corearea (CA) of termite mounds covering 112,000 km2 (Fig. 1A). The degree of bioturbation as a direct result of insect activity in this area is quite impressive, as these roughly conical biogenic structures average 9 m in diameter at ground level and from 2 to 4 m in height (average volume ~24 m3) with densities up to 35 mounds/hectare (Fig. 1B,C,D). The core occurrence area comprises approximately 90 million mounds that represent the removal and re-deposition of ~2 cubic kilometers of earth (equivalent to 900 Great Pyramids) e arguably the greatest example of insect biopedoturbation and ecosystem engineering at a landscape scale yet recorded

E-mail address: [email protected]. http://dx.doi.org/10.1016/j.jaridenv.2015.05.010 0140-1963/© 2015 Elsevier Ltd. All rights reserved.

(Middelburg et al., 2006). These termitaria alter the landscape and soil composition by bringing up sub-soil material, generating mound fields of modified
rrez and Jones, 2006) that fertility (Bruyn and Conacher, 1990; Gutie are shunned for most economic uses except grazing. It was, in fact, this clearing for grazing in recent decades that made the mounds more visible, as they form under low (<4 m), but very dense semiarid vegetation and are not easily seen even from the roadside. These mounds have greater volumes and are very unlike the impressively engineered structures described for some Africa and Australia termitaria, with their complex architecture designs for efficient gas exchange and/or temperature control (Dangerfield et al., 1998; Jacklyn, 1992; Darlington, 1984; Pomeroy, 1977) e being essentially amorphous mounds of subsurface material with some internal chambers (of variable sizes and placements). In that sense they superficially resemble some of the “mima” mounds found in the United States and “heuweltjies” in southwestern Africa, although those term are generic rather than specific, and are applied to structures of both biogenic (gophers, termites, and possibly vegetation-aeolian accretion; see Gabet et al., 2014; Cramer and Barger, 2014; Horwath and Johnson, 2006; Cramer and Midgley, 2015) and purely geological origins (Berg, 1990; Silva et al., 2010). The mounds described here are found in dry environments, are solid, usually sun-baked and extremely hard, and normally covered by vegetation (and penetrated by roots), so they suffer only very

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R.R. Funch / Journal of Arid Environments 122 (2015) 27e29

Fig 1. (A) Location of the core area (CA) of termite mound concentrations in northeastern Brazil; (B) Google Earth© image of a termite mound field in a cleared pasture area surrounded by intact vegetation (with smaller areas in various stages of abandonment and regeneration) in the semiarid region of Bahia State, Brazil. Center-point coordinates: 12
300 0100 S  41
360 5000 W; eye altitude 2.07 km. Scale bar ¼ 290 m. (C) Individual mound, 4 m tall. (D) The same mound field as B, from ground level.

limited erosion by wind or rainfall e and are presumably quite old. The extremely regular spacing (overdispersed) of these termite mounds and the fact that they never touch or overlap indicates scale-dependent feedback between them (Rietkerk and van de Koppel, 2008). The exact natures of these interactions are still unknown, although short-range competition for foraging territory or mound-building resources might explain their consistent spacing of from one to two mound-diameters. The reason for their large volumes and close packing throughout their distribution range is

less obvious, however, but could be related to protection from predation (by large but now extinct, or locally extinct, mammalian predators), from desiccation, occasional flooding, and thermal extremes in this semiarid region, or may reflect their extremely long life spans and continuous and/or sequential occupation, combined with short-range competition (or combinations of those factors). The termitaria described here begin as large mounds erected by Syntermes dirus Burmeister (Isoptera, Termitidae) under the canopies of dry forests growing on clayey soils. These mounds are

R.R. Funch / Journal of Arid Environments 122 (2015) 27e29

initially built and occupied only by S. dirus, until reaching heights of about 1.5 m. Examinations of larger, more “mature” mounds have identified numerous other termite and ant species inhabiting or coinhabiting these structures. Although most of the mounds appear abandoned (especially those found in cleared areas that have been overgrazed for many years), excavations and local informants indicate that essentially all of them are inhabited, although not necessarily by the founding species. Sequential habitation would be expected for the reasons described above. In spite of their impressive volumes, durability, wide distribution, and remarkable influence on the local landscape, these termite mounds were first reported only in 1985 in a popular science magazine published in Brazil (Funch, 1985), with no subsequent published studies. Additional work will be needed to determine the sequences of growth and occupation of these mounds, the ecological requirements and substrate preferences of their builders and subsequent inhabitants, mound ages and age distributions, and their influence on the plant species occupying the mounds and inter-mound areas e but the ability to visualize these structures using open-source satellite images will greatly facilitate that research. Acknowledgments: The author was supported by a DCR grant from FAPESB/CNPq ~o de Amparo a  Pesquisa do Estado da Bahia and the (Fundaça
gico Conselho Nacional de Desenvolvimento Científico e Tecnolo Grant number DCR0001/2012). Thanks to Eliana Cancello of the Zoology Museum-USP, Brazil, for identifying the termite species, and the Chapada Diamantina Foundation for logistic support. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jaridenv.2015.05.010.

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