Deciphering earth mound origins incentral BrazilPlant and SoilAn International Journal onPlant-Soil RelationshipsISSN 0032...
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Silva et al. 2010a

  1. 1. Deciphering earth mound origins incentral BrazilPlant and SoilAn International Journal onPlant-Soil RelationshipsISSN 0032-079XVolume 336Combined 1-2Plant Soil (2010) 336:3-14DOI 10.1007/s11104-010-0329-y 1 23
  2. 2. Your article is protected by copyright andall rights are held exclusively by SpringerScience+Business Media B.V.. This e-offprintis for personal use only and shall not be self-archived in electronic repositories. If youwish to self-archive your work, please use theaccepted author’s version for posting to yourown website or your institution’s repository.You may further deposit the accepted author’sversion on a funder’s repository at a funder’srequest, provided it is not made publiclyavailable until 12 months after publication.1 23
  3. 3. Authors personal copyPlant Soil (2010) 336:3–14DOI 10.1007/s11104-010-0329-y REGULAR ARTICLEDeciphering earth mound origins in central BrazilLucas C. R. Silva & Gabriel D. Vale &Ricardo F. Haidar & Leonel da S. L. SternbergReceived: 13 October 2009 / Accepted: 15 February 2010 / Published online: 10 March 2010# Springer Science+Business Media B.V. 2010Abstract Mound fields are a common landscape traits should resemble those of the grassland. Allthroughout the world and much of the evidence for markers indicate that the mounds were formed bytheir origin has been of a circumstantial nature. It has erosion. The soil isotopic composition, chemical traitsbeen hypothesized that earth mounds emerge over and texture below the mound resembled those of thegrasslands by termite activity; alternatively, they savanna and not those of the grassland. Moreover,might be formed after erosion. We tested whether a most of the species present in the mound were typicalmound field in central Brazil was generated by of savanna. Concrete evidence is provided that moundtermite activity or erosion. We used soil organic fields in the studied area were produced by erosion ofmatter isotopic composition, soil chemical, physical a savanna ecosystem and not termite activity. The useand floristic composition to determine the origin of a of the techniques applied here would improve themound field. If the mounds emerged by termite assessments of whether analogous landscapes are of aactivity in an established grassland the soil organic biogenic nature or not.matter below the mound should have the isotopicsignature of C4 dominated grassland, which contrasts Keywords Carbon isotope . Soil . Erosion . Savanna .with savanna C3 + C4 signature. Additionally, soil Termites . murundusResponsible Editor: Hans Lambers.L. C. R. Silva L. da S. L. SternbergDepartment of Forest Engineering, University of Brasilia, Department of Biology, University of Miami,Brasilia, DF, Brazil Coral Gables, FL 33124, USAL. C. R. SilvaEmbrapa Cerrados Agricultural Research Center,Planaltina, DF 73310-970, BrazilG. D. ValeLaboratory of Forest Management,National Institute for Research in the Amazon (INPA), Present Address:Manaus, Brazil L. C. R. Silva (*) Global Ecological Change (GEC) Laboratory, DepartmentR. F. Haidar of Environmental Biology, University of Guelph,Department of Forest Engineering, University of Brasília, Guelph N1G 2W1 ON, CanadaBrasília, Federal District, Brazil e-mail:
  4. 4. Authors personal copy4 Plant Soil (2010) 336:3–14Introduction McCarthy et al. 1998; Brossard et al. 2007) in Africa and Australia (Picker et al. 2007; Midgley et al.The campos de murundus (literally ‘mound fields’) 2002; Rahlao et al. 2008) and also in north America,represent one of the several types of savanna where mound fields (prairie mounds) occur fromvegetation typical of the cerrado region in central Saskatchewan to Minnesota and south through IowaBrazil. Savannas in this region, consisting of a and Missouri to Arkansas, eastern Oklahoma, andmixture of woody plants (trees and shrubs) in a the coastal plain of Louisiana and Texas (Ross et al.grassland matrix, are the predominant vegetation type. 1968; Mollard 1982).However, the campos de murundus formation differs Several authors have shown that in Brazil thesefrom the typical savannas by its small, round, earth mound fields frequently occur within ecotone zones,mounds, usually found in areas where seasonal towards forest/savanna boundaries (Eiten 1972, 1984;flooding limits the establishment of woody plants to Furley 1986; Araújo Neto et al. 1986; Oliveira-Filhothese mounds (Resende et al. 2004). This landscape and Furley 1990). This makes the investigation of thistype, with tree-covered mounds in a matrix of flood- ecosystem especially relevant to the understanding oftolerant grasses, occurs extensively throughout the past and present vegetation dynamics such as thecerrado (Fig. 1; Oliveira-Filho and Furley 1990), but riparian forest expansion recently shown in thisthere are analogous formations elsewhere in the region (Silva et al. 2008). There are previousNeotropics (Cox et al. 1989; Ellery et al. 1998; descriptions of the vegetation that typically occur inFig. 1 a Locations of grass-land (campo) (G), savanna(cerrado sensu stricto) (S),soil cores at the Universityof Brasilia ExperimentalStation, Federal District,Brazil. The earth moundssampled for soil cores arenumbered from 1 to 5 andfor floristic compositionfrom 1 to 11. The lowerpanel b shows a close up ofa typical earth mound at thesite
  5. 5. Authors personal copyPlant Soil (2010) 336:3–14 5the campos de murundus, where the mounds were substances within the soil, including organic carbon,found mostly populated by savanna tree species, even cations and anions, as well as in the soil physicalthough forest species also occur (Eiten 1984; Furley and properties. Chemical traces could, however, be sub-Ratter 1988; Oliveira-Filho and Furley 1990; Resende et ject to change because some of these components areal. 2004). However, the question of which processes highly mobile. In addition to leaving traces in the soilcreated this landscape is not yet settled. The lack of chemistry and texture, these hypothetical processesquantitative evidence in support to previous circumstan- would also leave different floristic traces. We wouldtial explanations for the origins of this ecosystem expect that the differential erosion of the savannahinders comparisons both within the cerrado and with would leave the mounds mostly occupied by speciesanalogous vegetation elsewhere. Deciphering earth already present in the mounds and vicinity, i.e. speciesmounds origins would allow such comparisons, serving commonly found in the savanna. These species wouldthe interests of ecologists and soil scientists. persist through time, since they provide the most There are two main hypotheses that attempt to abundant seed rain by their proximity. On the otherexplain the genesis of earth mounds in central Brazil. hand, if the mounds originated in grasslands borderingThe first proposes that termite nests, often associated forests, they would be open to establishment by newwith the mounds, were responsible for raising the species. Therefore, one could expect that the abun-microtopography above the grassland vegetation (Eiten dance of forest species occupying the mounds may be1984, 1990; Oliveira-Filho 1992; Ponce and Cunha related to the distance from the forest and its seed rain.1993). These termite nests, being above the flood We investigate here soil isotopic, chemical andlevels of the surrounding grassland during the wet physical markers, and floristic evidence, in a typicalseason, then became populated by flood-intolerant campos de murundus located in the Federal District inwoody vegetation. The second hypothesis proposes Central Brazil in an attempt resolve the question of itsthat differential erosive processes produced the micro- origin. Specifically we test the following hypotheses.topography typical of the campos de murundus 1) The carbon isotopic composition of SOM below(Araújo Neto et al. 1986; Furley 1986). Specifically, the earth mounds, at the level of the surroundingthis hypothesis proposes that the locations where the grassland, shows an isotopic signature similar tocampos de murundus formed were once typical that of the surrounding grassland.savannas and that erosion left behind the mounds on 2) The soil physical and chemical properties belowwhich savanna vegetation persisted. The surrounding the mound resemble those in soils of theareas where erosion occurred became increasingly surrounding grassland.flooded and only sustained flood-tolerant grasses. This 3) Mounds that are closer to the neighbouring forestlast hypothesis does not exclude the possibility that the have a greater number of species from the forestpresence of termite mounds in the slightly sloping compared to those farther from the forest.savanna created the initial microtopography, which inturn led to differential erosion and mound formation. Confirmation of the above would support the The two hypothetical processes leading to mound hypothesis that mounds were formed in grasslandsformation would, however, leave distinct traces in the by the build-up of the microtopography via termitesoil chemistry and the floristic composition of the activity. On the other hand, rejection of the abovemound. For example, a grassland origin of the hypotheses and the presence of isotopic, chemical andmounds by termite activity would be reflected by soil floristic signatures typical of the savanna wouldorganic matter (SOM) having the carbon isotopic support the erosive origin of the mounds.signature typical of the C4-rich grassland at depthsbelow the mound (Fig. 2). However, if the moundsoriginated in a savanna, the stable carbon isotopic Materials and methodssignature of SOM typical of savanna previouslymeasured in this area (Silva et al. 2008) would persist Site descriptionin soil layers below the mounds (Martinelli et al.1996; Silva et al. 2008; Victoria et al. 1995). Traces of Measurements were taken in an undisturbed camposthe mounds’ origin would also be found in chemical de murundus site on a grassy slope, having lower than
  6. 6. Authors personal copy6 Plant Soil (2010) 336:3–14Fig. 2 Two possible waysof mound formation:a erosion and b termiteactivity that would lead to ccurrent mound field, and theexpected soil profiles of soilorganic matter (SOM)carbon isotope ratios. Thesolid and stippled linesrepresent the expectedcarbon isotope profile withdepth in the mound and inthe grassland, respectively,for each hypothetical moundformation process. Carbonisotope ratio values belowthe horizontal solid line forthe mound profile representshypothetical SOM valuesbelow the mound (∼100 cmdepth). Slope has beenexaggerated to illustrate thepossible processes ofmound formation5° inclination and bordering a savanna/gallery forest seasonally flooded grassy areas can have higher fertilityecotone, at the University of Brasilia Experimental and organic matter content (Eiten 1990). The area ofStation (FAL-UnB), Federal District, Brazil (Fig. 1; each mound was estimated by using perimeter meas-15° 56′ 40.17″ S and 47° 54′ 36.35″ W). This mound urements, taken by metric tape from the intersectionfield contained mounds averaging 1.1±0.14 m in between the bases of the mounds with the grassy areaheight above the grassland and an average perimeter level, considering their shapes as perfect circles. Theof 32 ± 11 m. These mounds often had termite distance from the forest was also determined for eachcolonies of the species Armitermes cerradoensis mound, by measuring the shortest straight-line distance(Mathews). The average annual temperature for this from each of them to the forest border.region is 22.5°C and average annual rainfall 1,426 mm(1993–2002). Rainfall is seasonally distributed, with Soil coresmore than 80% falling during the months of Novemberto April. Soils in this savanna can be generally During the dry season of 2007 we sampled the soilcharacterized as deep, well drained oxisols, with low profile with a soil auger to a depth of 2.5 m or less iforganic matter and nutrient contents. Soils in the the water table was reached or the presence of gravel
  7. 7. Authors personal copyPlant Soil (2010) 336:3–14 7impeded further sampling. Three soil profiles were Exchangeable aluminum, calcium and magnesium wereacquired in three savanna sites (Fig. 1; S1, 2 and 3), extracted by 1M KCl solution and their concentrationsthree in the campos de murundus grassland area determined by titulation and atomic absorption. Organic(Fig. 1; G1, 2 and 3) and five in the mounds (Fig. 1; carbon content was determined by wet oxidationmounds 1 to 5). At the savanna profile S2 a gravel (Walkley and Black 1934). Soil texture was determinedlayer at 90 cm depth impeded the ongoing sampling. by the international pipette method (Day 1965).The water table was reached at approximately 75 cmdepth in the grassland area, preventing the sampling Floristic compositionof soil at lower depths. Soil samples were collectedevery 10 cm of depth and dried at room temperature Following the Botany Classification System Angio-after which the fine roots were removed by sieving sperm Phylogeny Group II (Apg II 2003; Souza andthrough a 2 mm mesh. The sieved soil was used for Lorenzi 2005) the floristic census of trees, shrubs andanalyses of isotopic abundance as well as chemical herbs was made in 11 mounds, which were at variousand physical properties. distances from the neighbouring gallery forest (Fig. 1). A species/area curve was generated for theSoil stable isotope analysis woody vegetation (>5 cm circumference at breast height) by adding the new species found on eachCarbon isotope ratios of soil samples were determined randomly selected mound in relation to the cumulativeafter a new sieving through a 0.8 mm mesh at the area. Also, following standard methodology (MagurranLaboratory of Stable Isotope Ecology in Tropical 1988; Kent and Coker 1995), we determined total basalEcosystems at the University of Miami. Soil samples area, density and diversity for the woody vegetation(10 mg) were loaded in tin cups (3 mm diameter and over all the 11 inventoried mounds. Diversity was8 mm height; Elementar Americas Inc, NJ, USA), determined by Shannon’s index (H’) based on the totalwhich were placed in an automated elemental number of individuals and relative abundance ofanalyser (Eurovector, Milan, Italy) connected to a woody species, as:continuous flow Isoprime isotope ratio mass spec- S Xtrometer (Elementar, Hanau, Germany). Soil samples H0 ¼ À pi ln pi ð2Þwere not pretreated with acid to remove carbonates i¼1since these soils were acidic and do not contain where S is the number of species and pi is the relativeinorganic carbon. 13C abundances are expressed as abundance of each species, calculated as the proportionδ13C values: of individuals of a given species to the total number of 13 RSAMPLE individuals. 1 *1000 The floristic composition of the nearby savanna and RPDB forest areas were gathered from previous studies (Felfili and Silva Júnior 1992, 1993; Felfili et al. 1993; Felfili 1995; Andrade et al. 2002; Silva Júnior 2004; Ribeiro ð1Þ and Tabarelli 2002; Guarino and Walter 2005). A detailed floristic composition inventory was not donewhere RSAMPLE and RPDB represent the 13C/12C ratios for surrounding grassland, as it was mostly dominatedof the sample and PeeDee standard, respectively. The by grasses of the genera Axonopus and Andropogon.precision of analysis was ± 0.1‰ (±σ).Soil chemical and textural characterization ResultsThe soil pH was determined in a water suspension(2:1, v.v.). Total nitrogen was determined by the Carbon isotope ratiosKjeldahl method (Bremner and Mulvaney 1982).Available phosphorus and potassium concentrations Carbon isotope ratios of soil organic matter (SOM) ofwere determined by the method of Mehlich (1953). the surface layer (0–10 cm) from three of the mounds
  8. 8. Authors personal copy8 Plant Soil (2010) 336:3–14Fig. 3 Soil organic matter(SOM) carbon isotopecomposition (δ13C) for fiveearth mounds, three savannaand grassland profiles at theUniversity of BrasiliaExperimental Station,Federal District, Brazil.Numbers above the curvesrepresent location of theprofiles as shown on Fig. 1.The dashed line representsthe average depth of themounds(mound 1, 3 and 4) were distinctly more negative than Soil chemical and physical propertiesthose of the other two mounds (Fig. 3; mound 2 and5). Carbon isotope ratios of the SOM profile at depths All profiles studied here showed acid soils (pH4 to 6),below 25 cm from all mounds, however, increased to with high Al concentration and low nutrient contentvalues between −22‰ to −17‰, typical of savanna (Fig. 4). They can thus be classified as dystrophicSOM at these depths (Victoria et al. 1995; Martinelli soils according to the Brazilian Soil Classificationet al. 1996; Pessenda et al. 1998; Sanaiotti et al. 2002; System (Embrapa 1999). The soils had less thanSilva et al. 2008). With the exception of the S3 1 cmol (+) dm−3 of exchangeable Ca, and general lowsavanna profile, δ13C values of SOM for the mound K and Mg concentrations, leading to base saturationand savanna profile represent a strong C3 contribution values below 50%. The mound profiles had the lowestto the SOM isotopic signature. The δ13C values of the pH values as well as the greatest Al concentration; buttop 100 cm of the S3 savanna profile are clearly layers deeper than 125 cm showed acidity and Aldistinct from those observed at the mounds and other content equal or very similar to savanna profiles. Thesavanna profiles (S1 and 2), but similar to the values savanna profiles had the greatest P and the lowest Nregistered in the soil profiles from the grassland area content at depths between 0 cm and 75 cm. While(G1, 2 and 3), in which we found δ13C values above mounds had slightly higher P than grassland for the−17‰. This isotopic signature represents a greater surface soil, there was a complete absence ofcontribution of C4 plants to SOM compared to the available P in the mound profile until 125 cm depth,other savanna profiles and to those reported inprevious savanna studies (Victoria et al. 1995;Martinelli et al. 1996; Pessenda et al. 1998; Sanaiotti Fig. 4 Soil chemical and textural characteristics for five earth„et al. 2002; Silva et al. 2008). However, δ13C values mounds, three savanna and grassland profiles at the University of Brasilia Experimental Station, Federal District, Brazil. Thereof the S3 savanna profile abruptly changed to those were three replicates for the grassland and savanna profile andtypical of the savanna vegetation at depths below five replicates for the mound profile. Error bars represent ± 1150 cm (Fig. 3). standard deviation
  9. 9. Authors personal copyPlant Soil (2010) 336:3–14 9
  10. 10. Authors personal copy10 Plant Soil (2010) 336:3–14below which it increased, reaching values higher thanthose encountered at the surface. The grasslandsurface soil had the highest organic matter percentage(9%), which quickly decreased to values similar tothose of savanna, but lower than those of the moundsoil at 30 cm depth (<3%). The organic matter contentin soils of mounds remained greater than that insavanna soil until 80 cm depth and it was similar tovalues of the savanna soil below this depth (Fig. 4). Fertility and organic matter content tended to behigher on the surface soil, decreasing at lower depthsof the soil profile (Fig. 4). However, Ca, Mg and Pwere the exception. The concentration of these Fig. 5 Cumulative number of woody species per cumulativeelements either increased at a lower depth or area in 11 earth mounds studied and in ten 1,000 m2 plots on savanna physiognomy of cerrado sensu stricto and galleryoscillated in concentration throughout the profile. forest in undisturbed gallery forests in the Federal District of Soil particle size properties show strong and Brazil (Felfili 1995)consistent differences between profiles. Soil texturewas sandier on grassland soils compared to moundsand savanna (Fig. 4). At the surface layers (0–10 cm)sand/clay ratios are on average four times higher in represent a total species richness similar to thatgrassland soils than in the savanna or mounds. previously reported for 10,000 m2 of surrounding savanna cerrado sensu stricto vegetation, and lowerFloristic composition than that found in gallery forests of the same watershed (Fig. 5; Felfili 1995; Guarino and WalterThe floristic composition of the eleven mounds 2005). The total density of 6,239 individuals ha−1 isinventoried included 37 families, 64 genera and 83 much higher than that observed in either surroundingspecies, of which 59% were tree species, 24.1% savanna or gallery forest (data not shown). The totalshrubs and 14.5% herbs. The six most frequent basal area of 14 m² ha−1 is twice that observed infamilies were the Melastomataceae (14 species), savanna and three times lower than that in galleryPoaceae (six species), Fabaceae (six species), Myrta- forest, while the diversity of 3.11, estimated byceae (five species), Lauraceae and Euphorbiaceae Shannon’s index, is lower than for either of the two(four species each). Of the species recorded, 61.4% other ecosystems (data not shown).are usually encountered in open savanna vegetation,while 18.1% are characteristic of forests (mostlygallery forests) and 19.3% can be found in both Discussionecosystems. There was no correlation between rela-tive abundance of forest species present in the mound Carbon isotope ratios of the SOM profile below theand distance of the mound from the forest (R2 =0.11, mound (∼1 m) averaging −18.5±1.1‰ (± σ) could notP>0.05). No trees or shrubs were encountered out of be distinguished from those in two of the three savannathe mounds on the surrounding grassland, where cores taken here and were also similar to those ofAndropogon sp. and Axonopus sp. (C4 grasses) were savanna SOM found in a previous study in the samedominant. region (Silva et al. 2008). These values are lower than Over the mounds we found 642 individual woody the average δ13C value of SOM from the C4-dominatedplants representing 54 species in a total area of grassland area surrounding the mound (−15±0.7‰).1,029 m2 (Fig. 5). The cumulative species/area curve The savanna isotopic signal below the mound indicatesshows a high local species richness, where 46 species that this site was a savanna and not grassland beforewere found in the first 500 m2 inventoried. After that, mound formation. Therefore, the isotopic data supportsthe curve stabilized, with an increase of just 8 more the erosion hypothesis. Unfortunately we could notspecies in the next 500 m2 (Fig. 5). These results collect samples from the surrounding grassland to
  11. 11. Authors personal copyPlant Soil (2010) 336:3–14 11depths below 1 m. However, the interpretation of the explaining low P and high N, organic matter andcarbon isotope ratios of SOM deeper in the grassland plant density.soil profile may be equivocal since savanna isotopic In contrast, there was a close match betweensignatures could have eroded away during the forma- savanna and mound soil profiles for potassium,tion of the mound field. The slight increase in carbon calcium and magnesium, with the grassland showingisotope ratios with depth at the top 25 cm in all soil a different profile. The soil texture, which may be aprofiles is caused by isotope fractionation during more permanent feature of the soil profile anddiagenetic processes in SOM (Martinelli et al. 1996; therefore more faithfully record the mound genesis,Silva et al. 2008). One particular SOM isotope profile showed a close agreement between mound andin the savanna (S3) was unusual in that it had δ13C savanna profile, with the grassland showing a muchvalues typical of the grassland area and showing a greater proportion of sand compared to the moundstronger C4 component than the other savanna samples and savanna soil profiles (Fig. 4). The sandiness ofat depths between 0 cm and 150 cm depth. We propose the grassland soil compared to those of the mounds isthat this profile is showing the process we hypothesize: further evidence that erosion processes were impor-differential erosion will cause some savanna areas to tant in the formation of the campos de murundus. Webecome grasslands. At depths greater than 150 cm, propose that erosion carried away the smaller andrepresenting the older vegetation, SOM from this core lighter clay particles leaving the remaining soil, wherehas the isotopic signature typical of a savanna. After erosion occurred, rich in the larger and heavier sandthe erosion, however, this site became more populated particles. This is supported by significant correlationswith C4 grasses as evidenced by the shift in the carbon between soil texture and soil moisture found inisotope ratios in SOM at depths shallower than transects from grasslands (higher relative sand con-150 cm. We also note that this savanna soil profile is tent) to riparian forests (higher relative clay content)the closest to the gallery forest (Fig. 1) and probably at the same site studied here (Munhoz et al. 2008).more susceptible to erosion from runoff. Accordingly, The majority of the species found on the moundsthis area may eventually undergo a transition to a are from savanna and only about 18% are of forestcampos de murundus. origin. No correlations between the presence of forest Soil chemical and physical profiles for the most species on the mounds and their distance relative topart matched the savanna profile. Discrepancies the forest were found and the species/area curvebetween savanna and mound profiles were observed within the mounds matches the savanna saturationin soil pH, organic matter, total nitrogen, phosphorus (Fig. 5). All these observations support the presenceand aluminum. The differences, however, did not of a savanna ecosystem prior to mounds formation,indicate that mound profiles were more similar to which supports the erosion hypothesis. However,those of grassland than the savanna profile. Rather, some floristic metrics were quite different comparedthey indicated that savanna and grassland were similar to the savannas. For example, the basal area in theand the mound profiles were unusual. To some extent mounds (14 m2 ha−1) was greater than those of thethis is expected because, with the exception of savanna (7 m2 ha−1), but much lower than in the forestphosphorus, nutrients can be highly mobile and their (42 m2 ha−1), and the diversity on the mounds (3.1 H’)profile may not be conserved during the erosive was lower than those observed in the gallery forestprocess that left the mounds behind. Phosphorus, (3.6 H’) and the neighbouring savanna (3.5 H’). Wehowever, can easily bind to organic matter. The near propose that these contrasting characteristics wereabsence of available phosphorus in the mound profile developed after the mound formation. In other tropicalup to a depth of 100 cm might be explained by its systems, increased tree density and basal area in smallbinding to organic matter observed at higher concen- islands may result from habitat fragmentation due totration in the mounds compared to savanna and changes in dispersion and reduced seeds predationgrassland (Fig. 4). In addition, fauna activity can (Wright and Duber 2001). This along with expectedaffect these nutrient concentrations (Oliveira-Filho increases in seedling recruitment near conspecific1992). Differential nutrient input through termites, species may in time reduce diversity (Wright andbirds and mammals may have increased productivity Duber 2001). Likewise, our results suggest that limitedin the mounds over savanna and grassland, also mound area, or the fragmentation of the savanna, may
  12. 12. Authors personal copy12 Plant Soil (2010) 336:3–14lead to higher density and lower diversity of woody Although our results do not support the termite originplants. hypothesis, their association with earth mounds may However, the conclusions raised from the compar- actively alter the physical environment and vegetationison of such floristic data have to be taken cautiously. dynamics. For instance, termite activity (hollowingFloristic composition vary greatly within both savannas out soil, mining clay etc.) may have affected theand forests of cerrado region, thus any extrapolation height or area of the mounds through time, perhapsbased on the particular site studied here would be intensifying differential erosion. Additionally, theinappropriate. Additionally, because different sampling predominance of wind-dispersed species on thedesigns were used on each of these vegetation types regional open savannas (Ribeiro and Tabarelli 2002)(systematic design—continuous strip layout—in the can be replaced by species that depend on bioticforest; sets of randomized plots in the savanna; and agents for dispersal. The fast response of insects tocomplete census in the mounds), comparing vegetation current changes in climate should also be of relevancefeatures may be not as straight forward as one would towards such dynamics. It has been shown inthink. The reason why different designs are used is to southern Africa that termitaria density is positivelyproduce the most representative data set of each given correlated with rainfall (Picker et al. 2007), futher-ecosystem. Considering that each of the above vege- more, they may reach more than 20,000 years in age,tation physiognomies was satisfactorily described becoming a stable part of the landscape (Midgley et(Fig. 5) and that the criteria of inclusion for woody al. 2002) and altering vegetation composition (Rahlaospecies was the same (>5 cm), here the floristic et al. 2008). While a potential association betweenfeatures of these different ecosystems are comparable termitaria and woody species distribution in campos(Felfili 1995). de murundus of central Brazil remains to be investi- The isotopic and chemical signature of the soil gated, there are similar landscapes in Africa andprofile as well as its texture and the floristic Australian savannas, as well elsewhere in the Neo-composition of the mounds all suggest that they were tropics, which may indeed be caused by termite orformed by erosion. This site was most likely a other biotic-mediated activity (Cox et al. 1989; Ellerysavanna site that gradually eroded to the campos de et al. 1998; McCarthy et al. 1998; Brossard et al.murundus landscape with small tree islands in a 2007). In such places the isotopic profiling of SOM asmatrix of seasonally flooded grassland. Much of the used here would certainly improve our confidence inprevious evidence regarding the termite origin of the assessments of whether they are truly of acampos de murundus was circumstantial and only biogenic nature or not.based on the observation of the presence of termitenests on the mounds. However, it is not known Acknowledgements We thank Doyle McKey (Centrewhether the termites became established after mound D’Écologie Fonctionnelle Et Évolutive (CEFE)-CNRS), Norton Polo Benito (EMBRAPA-Cenargen), José Carlos Sousa Silvaformation or were the actual cause of the mound (EMBRAPA-Cerrados) for helpful comments.formation. One study in particular (Oliveira-Filho1992) proposes a succession of different termitespecies in mound genesis, which initiates with ReferencesArmitermes euamignathus (Silvestri), a species moretolerant of moist conditions than other termites. Andrade L, Felfili JM, Violatti L (2002) Fitossociologia de umaAccording to this interpretation, the succession of área de cerrado denso na Recor-IBGE, Brasília-DF. Actatermite species culminates in Cornitermes snyderi, Bot Bras 16:225–240which is least tolerant of moist conditions. Our Angiosperm Phylogeny Group II (2003) An update of the Phylogeny Group classification for the orders and familiesisotopic data do not support the above scenario in of flowering plants: APG II. Bot J Linn Soc 141:399–436that the SOM isotopic signature below the mound is Araújo Neto MD, Furley PA, Haridasan M, Johnson CE (1986)characteristic of savanna and not the moist grassland The “mounds” of the “cerrado” region of Central Brazil. Jrich in C4 grasses. The evidence for erosive processes Trop Ecol 2:17–35 Bremner JM, Mulvaney CS (1982) Nitrogen total. In: Page AL,in mound genesis has also been circumstantial and Miller RH, Keeney DR (eds) Methods of soil analysis:based on the observation that campos de murundus chemical and microbiological properties. American Societyare usually found in seasonally flooded gentle slopes. of Agronomy, Madison, pp 595–624
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