EDINB. J. BOT. 58(1):123–137(2001) 123 STUDIES IN MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL: I. A FOREST OF BROSIMUM RUBESCENS TAUB B. S. Marimon*, J. M. Felfili† & M. Haridasan‡ Theoccurrenceofamonodominant tropicalforestdominatedbythetreespecies BrosimumrubescensTaub.(Moraceae)inthetransitionzonebetweenthecerradoregion andtheAmazonianrainforestsalongtheAraguaiavalleyinthestateofMatoGrosso inBrazilisreported.A6000m2(40×150m)arealocatedinthecentralportionofa forest(14°50∞47◊S,52°08∞37◊W)ontheEldoradoFarminNovaXavantinawassampled todeterminethestructure,phytosociologyandsoilproperties.Atotalof44treespecies was foundintheforest,withaShannondiversityindex(H∞)of2.37andthePielou evennessindex(J∞)of0.63.Thesevaluesweresimilartothosereportedbyotherworkers inanAmazonianmonodominantforestdominatedbyPeltogynegracilipes.Averagetree densityequalorgreaterthan((cid:8))5cmdbhwas1066ha−1andbasalarea37.46m2ha−1. Deadstandingindividualsrepresented7.03%ofthetotaldensityandlianas8.12%.The mainfamilieswereMoraceae,Rubiaceae,Burseraceae,Hippocrateaceaeand Leguminosae–Caesalpinioideae.Thespecieswiththehighestimportancevalueindices wereB.rubescens(124.55),Amaiouaintermediavar.brasiliana(32.97),Cheiloclinium cognatum(22.41),Tetragastrisbalsamifera(19.58)andProtiumpilosissimum(16.64). Brosimumrubescensaloneaccountedfor85.5%oftheindividuals(cid:8)30cmdbh,80.35% ofthose(cid:8)20cmdbh,57.33%ofthose(cid:8)10cmdbh,and35.85%ofthose(cid:8)5cmdbh. Theforestwascomposedofupper,middleandlowerstoreys.Diameterdistributionwas unbalancedforthecommunityandforthemainspecies,suggestingthatestablishment hasbeenepisodic.Thesurfacesoilwasacid,withhighexchangeableAllevelsandlow fertility,asisthecaseformost cerradosandAmazonianforests.TheavailabilityofK was inthe rangeofadequacy,ascomparedwithmostnativesoils.However, concentrationsofavailableMginthesoilwashigherthanthatofavailableCa,with Mg/Caratiosabovethree,unlikemostcerradosandAmazonianforests,but similarto the soilsofmanymonodominanttropicalforestsreportedintheliterature.Soilswere characterizedbyhighconcentrationsofavailableFe.BesidesthehighMg/Caratios,a highproportionofKascomparedwiththebivalentcationsCaandMg,andtoxicities ofFeandMnduetostrongaciditycouldbefactorsinfluencingtheoccurrence of speciesinthisforest. Keywords. Brazil,Brosimumrubescens,floristics, monodominanttropical forest,soils, structure. Introduction Thehighspeciesdiversityoftropicalforestsiswellknown(Richards,1952;Gentry, 1982; Connell et al., 1984) and the successional processes in these forests have been linked with gap dynamics (Denslow, 1980; Clark & Clark, 1992). Occurrence of * DepartamentodeBotaˆnica,UniversidadedeBras´ılia,70919-970Bras´ıliaDF,Brazil.Presentaddress: DepartamentodeCieˆnciasBiolo´gicas,UNEMAT,NovaXavantinaMT,Brazil. † DepartamentodeEngenhariaFlorestal,UniversidadedeBras´ılia,70919-970Bras´ıliaDF,Brazil. ‡ DepartamentodeEcologia,UniversidadedeBras´ılia,70919-970Bras´ıliaDF,Brazil. 124 B. S. MARIMON ET AL. many species with low relative densities is the main characteristic of such forests. The most abundant species constitute no more than 10% of the total number of individuals invariousforestcommunitiesstudied (Oliveira-Filhoetal.,1994;Felfili, 1995; Silva Ju´nior, 1995). However, there exist exceptions, where a single species shows50–100%ofdominance.Suchmonodominantforestshavebeenreportedfrom diVerent continents (Davis & Richards, 1934; Beard, 1946; Connell & Lowman, 1989; Hart et al., 1989; Milliken & Ratter, 1989, 1998; Hart, 1990; Johnston, 1992; Martijena & Bullock,1994; Nascimento,1994;Read et al., 1995;Isaacs et al., 1996; Nascimento et al., 1997). An important question on the dynamics of these mono- dominant communities is whether they represent a successional stage or a climax. The Araguaia Valley in eastern Mato Grosso state is an ecotonal region between the Amazonian forests and the cerrado (savanna) region of central Brazil, where a mosaicofphytophysiognomiesexist(Ratteretal.,1973).Theoccurrenceofapatch of a monodominant forest of Brosimum rubescens Taub. (Moraceae) on a lateritic soilinthisregionwasreportedbyFelfilietal.(1988,1998).Theforesthadastructure resembling a plantation, containing mostly even-sized, tall trees with straight boles. Brosimum rubescens has been intensively logged in the region. Local people use thehardwoodforbuildings,furnitureandfences.Itsnaturaldurabilitycanreach30 years.TheseforestsarealsoimportantforthelocalXavanteIndians.Thehardwood is used to make their traditional weapon, a heavy club called a borduna, and for crosses to mark graves. The fruits are eaten by the Indians and are important to them because they attract wildlife. The fruiting season of B. rubescens is considered to be the best time for hunting tapir and other game by the Xavantes. The floristic composition and structure of this forest are described in this study. The availability of soil nutrients was investigated to determine whether soil fertility played a role in the dominance of a single species in this forest. Study Site The study site (14°50∞47◊S, 52°08∞37◊W) was located within a 5000ha area of dry forestontheEldoradoFarminthemunicipalityofNovaXavantinaineasternMato Grosso,Brazil.Averagealtitudewas350mabovesealevel.Thesitewasundisturbed although logging activities were starting nearby. The climate of the region is Aw in the Ko¨ppen classification (Camargo, 1963), with six to eight wet months per year; climatic data are given in Fig.1. The soil at the experimental site was a dystrophic tropofluvent overlying consoli- dated andunconsolidated sedimentsbelonging tothe sedimentarycover of Bananal (RADAMBRASIL, 1981). The soil was deep, well drained and loamy in texture. Methods The field-work was conducted from July 1996 to July 1997. The sampling of veg- etation was systematic, following Philip (1994). A 40×150m grid containing sixty MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL 125 FIG. 1. Meanmonthlyprecipitation,insolation,relativehumidity,evaporationandtempera- tures for the Nova Xavantina region in Mato Grosso, Brazil (average of 30 years for the nearby Aragarc¸asclimatologicalstation). nested 10×10m plots was located in a representative portion of the forest, giving a total sampling area of 0.6ha. All individuals (cid:8)5cm dbh (diameter at breast height) were identified to the species or morphospecies level and their dbh and height recorded. The dbh measurements were made with a calliper, and the height of trees up to 15m with a telescopic measuring rod; taller trees were measured with a Haga altimeter. Natural regeneration of Brosimum rubescens (individuals with dbh less than5cm)wasrecordedinsubplotslocatedalongsidethemiddlelineofthesampled area. The size of these subplots varied according to the height of the individuals sampled: 1×1m for those 0–30cm; 2×2m, 31–60cm; 5×5m, 61–200cm; 10×10m, above 200cm. Voucher herbarium specimens were deposited at UB and IBGE. Foursurfacesoilsamples(0–10cm)werecollectedatrandomfromeach10×10m plot,andmixedtogethertoformacompositesampleforchemicalanalyses.Thesoil samples were air-dried, sieved through a 2mm mesh sieve and the percentage gravel determined. SoilpHwas measuredina1:2.5soil–watersuspensionaswellasin1M KCl. ExchangeableCa,MgandAlweredeterminedin1MKClandavailableP,K, Fe, Mn, Cu and Zn in Mehlich’s solution (0.0125M H SO +0.05M HCl). 2 4 Phytosociological parameters were calculated (Curtis & McIntosh, 1950, 1951). Shannon’s (H∞=−S (p ln p) and Simpson’s (l=S [n(ni−1)]/[n(n−1)] indices I i i were used to evaluate species diversity. Pielou’s evenness index (J∞=H∞/ln S) was also calculated (Magurran, 1988). Height and diameter distributions were evaluated. The class intervals (IC) for the forest and its main species (those with at least 10 individuals recorded) were 126 B. S. MARIMON ET AL. calculated according to Spiegel’s (1976) formulae, which minimizes the number of classes that would have no members: IC=A/nc and nc=1+3.3log(n), where amplitude A=maximum value (of either diameter or height) – minimum value; nc=number of classes; n=number of trees. To determine the lower limit of class distribution (I): I=minimum value (of either diameter or height) – IC/2. The ‘q’ quotient was calculated to determine whether the diameter distribution was balanced (Meyer, 1952). This model, based on geometric progression, assumes that in mixed natural forests where equilibrium between mortality and recruitment exists, the ratio between the number of trees in successive diameter classes should be constant. The ratio is obtained by dividing the number of individuals in a class by the number in the preceding class. Results Chemical characteristics of the soils and the percentage of gravel are presented in Table1. Thesoilwas stronglyacidicand high inlevelsofavailableAl. Thelevels of availableCaandMgwerelow.ThelevelofKwasintermediate.Ironconcentrations were high. Shannon’s diversityindex(H∞)was 2.37 and Pielou’sevenness index (J∞)was 0.63 for all plants (cid:8)5cm dbh. These indices were 1.62 and 0.48, considering only the plants (cid:8)10cm dbh. Simpson’s index (l) was 0.36. Floristic composition and phytosociological parameters are given in Table2. The highest IVIs (Importance Value Index=relative density+relative dominance+relative frequency) were for Moraceae, Rubiaceae, Burseraceae, Hippocrateaceae, Lauraceae and Leguminosae–Caesalpinioideae (Fig.2). These six families represented 83% of the total density and IVI of the forest and Moraceae with a single species, Brosimum rubescens, was by far the most important. Brosimum rubescens was the most abundant species with 35.8%of all individuals, 57.3%oftheindividualswithdbh(cid:8)10cm,80.4%oftheindividualswithdbh(cid:8)20cm, and 85.5% of the individuals with dbh (cid:8)30cm. The second most abundant species was Amaioua intermedia var. brasiliana followed by Cheiloclinium cognatum and Tetragastrisbalsamifera.Thetotalbasalareaperhawas37.46m2,71%ofwhichwas accounted for by B. rubescens. The highest IVIs were for B. rubescens (124.6), A. intermedia var. brasiliana TABLE 1. Proportion of gravel and chemical properties of the soil of the monodominant Brosimumrubescensforest. Mean(and standarddeviation) of60samples Gravel pHin pHin Al Ca Mg K P Fe Mn Zn Cu (%) KCl water (cmol(+)kg−1) (mgkg−1) 38.6 3.68 4.26 2.20 0.07 0.21 0.22 2.88 240.7 16.9 1.38 3.46 (19.0) (0.13) (0.10) (0.36) (0.07) (0.17) (0.06) (0.90) (25.3) (8.0) (0.33) (0.61) MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL 127 FIG. 2. Importance Value Indices of the most important families identified in the 0.6ha sampling areaoftheBrosimumrubescensforest. (32.97), C. cognatum (22.41), T. balsamifera (19.58) and P. pilosissimum (16.64). These represented 72% of the total IVI and B. rubescens alone represented 41.5%. Dead standing trees represented 6.31%of the total (Table2). Amongthe 44 species recorded, 17 had only one individual occurring in the sampling area and eight had onlytwoindividuals.Hymenaeacourbarilhadthelargestindividualinthesampling, measuring 105cm dbh. The height distribution for B. rubescens and for the whole forest (all species) is shown in Fig.3. Most of individuals of B. rubescens were in the higher classes with themaximumnumberbetween22.3and25.2m.Thereisadistinctstratificationinthe forest. Trees of the upper storey (such as Brosimum rubescens, Hymenaea courbaril andJacarandacopaia)reachabout28m,thoseofthemiddlestorey(suchasAmaioua intermedia,Tetragastrisbalsamifera,CheilocliniumcognatumandProtiumpilosissimum) 20m, while those of the lower storey (such as Mouriri apiranga, Miconia holosericea, M. tomentosa, Siparuna guianensis and Tetragastris unifoliolata) reach about 10m. The diameter distribution of all individuals and the ‘q’ quotients are given in Fig.4. Almost half of the individuals (41.41%) were in the first diameter class. The quotient ‘q’ varied among classes indicating that this is an unbalanced community. Brosimum rubescens distribution did not show the reversed-J shape expected for balanced populations, it was unimodal, with skewing to the right (Fig.5). There werefewindividualsupto20cm,aconcentrationbetween20and40cmandastrong decrease above 40cm dbh. Amaiona intermedia var. brasiliana had fewer individuals in the first class than in the second (q=1.13). Most of T. balsamifera individuals were up to 15cm dbh. 128 B. S. MARIMON ET AL. TABLE2. PhytosociologicalparametersfortheBrosimumrubescensforest.Absolutedensity (AD),relativedensity(RD),absolutedominance(ADo),relativedominance(RDo),absolute frequency (AF), relative frequency (RF) and importance value index (IVI).Species ranked by IVI Density/ha Dominance/ha Frequency/ha Species AD RD ADo RDo AF RF IVI 1. BrosimumrubescensTaub. 380.00 35.85 26.6183 71.25 98 17.46 124.55 2. Amaiouaintermedia Mart. 151.70 14.31 1.9972 5.35 75 13.31 32.97 var.brasiliana (A. Rich.) Steyerm. 3. Cheilocliniumcognatum 103.30 9.75 0.6389 1.71 62 10.95 22.41 (Miers)A. C.Smith 4. Tetragastrisbalsamifera 68.30 6.45 1.7017 4.55 48 8.58 19.58 (Swartz)O.K. 5. Deadindividuals 60.00 5.66 2.1953 5.88 42 7.40 18.93 6. ProtiumpilosissimumEngl. 81.70 7.70 0.2416 0.65 47 8.28 16.64 7. Liana–Malpighiaceae 45.00 4.25 0.2133 0.57 37 6.51 11.33 8. Hymenaeacourbaril L.var. 5.00 0.47 1.5447 4.13 5 0.89 5.49 stilbocarpa(Hayne)Lee& Lang. 9. Callichlamyssp. 15.00 1.42 0.0665 0.18 15 2.66 5.26 10. Myrciariafloribunda (West 15.00 1.42 0.0727 0.19 13 2.37 3.98 exWilld.) Berg 11. AnthodondecussatumRuiz 13.30 1.26 0.0657 0.18 13 2.37 3.80 &Pav. 12. Nectandracuspidata Nees 10.00 0.94 0.0808 0.22 10 1.78 2.93 13. Ephedranthus parviflorus 8.30 0.79 0.1328 0.36 8 1.48 2.62 S.Moore 14. Nectandrahihua (Ruiz & 13.30 1.26 0.1544 0.41 5 0.89 2.56 Pav.)Rohwer 15. Liana–Rubiaceae 8.30 0.79 0.0506 0.14 8 1.48 2.40 16. Jacarandacopaia(Aubl.) 3.30 0.31 0.2884 0.77 3 0.59 1.68 D.Don 17. MouririapirangaSpruceex 5.00 0.47 0.0221 0.06 5 0.89 1.42 Triana 18. Micropholisvenulosa (Mart. 3.30 0.31 0.1896 0.51 3 0.59 1.41 exEichl.)Pierre 19. Miconiaholosericea(L.) DC. 5.00 0.47 0.0191 0.05 5 0.89 1.41 20. SloaneasinemariensisAubl. 5.00 0.47 0.0108 0.03 5 0.89 1.39 21. IngaheterophyllaWilld. 6.70 0.63 0.0446 0.12 3 0.59 1.34 22. Chaetocarpusechinocarpus 3.30 0.31 0.1148 0.31 3 0.59 1.21 (Baill.) Ducke 23. Caraipasp. 5.00 0.47 0.0330 0.09 3 0.59 1.15 24. Ourateasp. 3.30 0.31 0.0503 0.13 3 0.59 1.04 25. SacoglottisguianensisBenth. 1.70 0.16 0.2136 0.57 2 0.30 1.02 26. AspidospermadiscolorA.DC. 3.30 0.31 0.0421 0.11 3 0.59 1.02 27. Apuleialeiocarpa (Vog.) 1.70 0.16 0.1890 0.51 2 0.30 0.96 Macbr. MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL 129 TABLE 2. (continued) Density/ha Dominance/ha Frequency/ha Species AD RD ADo RDo AF RF IVI 28. Odontadeniapuncticulosa 3.30 0.31 0.0084 0.02 3 0.59 0.93 (Rich.) Pulle 29. Miconiatomentosa D. Don 3.30 0.31 0.0071 0.02 3 0.59 0.93 30. Unonopsislindmanii 3.30 0.31 0.0065 0.02 3 0.59 0.92 R.E. Fr. 31. Licaniaapetala (E. Meyer) 1.70 0.16 0.0899 0.24 2 0.30 0.69 Fritsch 32. Licaniakunthiana Hook.f. 1.70 0.16 0.0735 0.20 2 0.30 0.65 33. SiparunaguianensisAubl. 1.70 0.16 0.0577 0.15 2 0.30 0.61 34. Physocalymmascaberrimum 1.70 0.16 0.0463 0.12 2 0.30 0.58 Pohl 35. Ormosiaparaensis Ducke 1.70 0.16 0.0218 0.06 2 0.30 0.51 36. Hirtellagracilipes 1.70 0.16 0.0144 0.04 2 0.30 0.49 (Hook.f.) Prance 37. CoccolobaglazioviiLindan 1.70 0.16 0.0072 0.02 2 0.30 0.47 38. MabeafistuliferaMart. 1.70 0.16 0.0068 0.02 2 0.30 0.47 39. Caseariaarborea Urban 1.70 0.16 0.0052 0.01 2 0.30 0.47 40. Xylopiasericea A.St.Hil. 1.70 0.16 0.0047 0.01 2 0.30 0.47 41. MinquartiaguianensisAubl. 1.70 0.16 0.0044 0.01 2 0.30 0.46 42. DuguetiamarcgravianaMart. 1.70 0.16 0.0040 0.01 2 0.30 0.46 43. Pouteriacf. cuspidata 1.70 0.16 0.0040 0.01 2 0.30 0.46 (A. DC.)Baehni 44. Tetragastrisunifoliolata 1.70 0.16 0.0037 0.01 2 0.30 0.46 (Engl.)Cuatr. 45. Erythroxylumsquamatum 1.70 0.16 0.0035 0.01 2 0.30 0.46 Swartz TOTAL 1066.67 100.00 37.4639 100.00 570 100.00 300.00 Seedlings(0–30cmtall)ofB.rubescenswereabundantintheunderstoreyofforest, averaging 14.13 plantsm−2, while seedlings 31–60cm tall averaged 2.59m−2. Figure6 shows the high number of seedlings of B. rubescens in the lower height classes in comparison with other species, and this species practically disappeared after the 2m height class. Discussion Diversity and evenness indices were much lower than in mixed tropical forests in Brazil which reach values of the order of 3–4 for Shannon index log e basis and 0.7–0.9forevenness(Felfili,1995;Walter,1995).Thevaluesinourforestwerelower than those found by Nascimento (1994) for a Peltogyne gracilipes monodominant forest in the Amazon (2.3–2.5 and 0.7–0.8). The Simpson index was similar to that 130 B. S. MARIMON ET AL. FIG. 3. Heightdistribution oftreesin the0.6hasampling area. FIG. 4. Diameter distribution and corresponding ‘q’ quotient ratio of trees in the 0.6ha sampling area. foundbyHartetal.(1989)foramonodominantforestofGilbertiodendroninAfrica (l=0.37). Several studiesin Brazilianforestshave shownthat afew families containagreat proportionofthedensity,basalareaandhenceIVI(Felfili,1995;SilvaJu´nior,1995; MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL 131 FIG. 5. Diameter distribution of Brosimum rubescens, Amaioua intermedia var. brasiliana and Tetragastrisbalsamiferainthe 0.6hasampling area. FIG. 6. Frequency distribution of the height of seedlings and saplings of Brosimum rubescensand otherspecies. 132 B. S. MARIMON ET AL. Walter, 1995; Nascimento et al., 1997), but the degree of dominance by just one species as well as the great concentration of individuals of the species in the higher diameterclassesfound inthis forestis notcommon. Itiscomparableonlywiththat foundinothermonodominantforests(Hartetal.,1989;Martijena&Bullock,1994; Readetal.,1995;Isaacsetal.,1996).Amonodominantspecies(Peltogynegracilipes) studied by Nascimento et al. (1997), on Maraca´ Island in the Amazonian forest, had 23% of all trees (cid:8)10cm dbh and 86% of those (cid:8)30cm dbh. The dominance ofBrosimumrubescensinourforestisaboutthreetimesgreaterthanthisforindivid- uals(cid:8)10cmdbh.Infact,B. rubescenscontainedmostofthetotalbasalareaofthe forest, showing values and pattern for this parameter similar to that found for monodominant forests of Celaenodendron mexicanum Standl. (28.8m2 ha−1) in Mexico (Martijena & Bullock, 1994) and Gilbertiodendron dewevrei (De Wild.) Le´onard in Africa (Hart et al., 1989). A large number of rare species (those with just one or two individuals in the sample) is alsocommonin otherBraziliantropical forestssuch asa monodominant forest in the Amazon (Nascimento et al., 1997), a gallery forest (Felfili, 1994), and a swampy gallery forest in Central Brazil (Walter, 1995). The diameter distribution in our forest is unbalanced with the ‘q’ ratio between successive diameter classes inconstant, suggesting disequilibrium between mortality andrecruitment(seeMeyeretal.,1961;Osmaston,1968).Harper(1977)pointsout thatmosttropicalforestsdonothavebalanceddiameterdistributionsalthoughthey tend towards it. The great disparity between the first and second diameter classes mightindicateeitherhighmortalityofsmallindividualsorapreviouslowrecruitment oftheseedlingsintothefirstclass,orbothevents.Felfilietal.(1988,1998),studying a similar forest type, found the same diameter structure and suggested that the structureandcompositionoftheforestmightchangeinthefuture.Hubbell&Foster (1987) suggested that species with a similar pattern of diameter distribution to B. rubescens could be light-demanding or, at least, partially light-demanding, and mortality caused by low light levels was responsible for the pattern. Hartetal.(1989),inareviewofseveralworksintropicalmonodominantforests, suggested that such forests did seem to be characteristic of situations undisturbed for a long time. They concluded that the dominant species had characteristics in common, such as big seeds, persistent seedlings (with arrested development when shaded), and a low capacity for seed dispersion. Brosimum rubescens conforms to this in having big seeds (1cm diameter) and the presence in stands of many small woody seedlings (under 30cm tall) suggestive of the slow development found in persistent seedlings. The large quantity of seedlings under the mother trees also suggests a low dispersion capacity. Hart (1995) also noticed persistent seedlings in monodominant stands of Gilbertiodendron dewevrei in a forest in Zaire. After 10 years, half of the 123 Gilbertiodendron seedlings (<0.5m tall) tagged in 1981 were still alive but only one had reached 1m height. The Brosimum forest might present a similar pattern. The high number of seedlings of Brosimum under 1m tall as opposed to the low