A Geobotanical Approach to the Tropical Rain Forest Environment of the Carajás Mineral Province (Amazon Region, Brazil), Based on Digital TM-Landsat and DEM Data

IN PE- 9030 - PRE/ 1030

INT. J. REMOTE SENSING, 1994, VOL. 15, NO. 8, 1633-1648

A geobotanical approach to the tropical rain forest environment of the Carajás Mineral Province (Amazon Region, Brazil), based on digital TM-Landsat and DEM data

W. R. PARADELLA National Institute for Space Research (INPE), 12201-970- São José dos Campos, S. Paulo, Brazil

M. F. F. DA SILVA, N. DE A. ROSA Paraense Emílio Goeldi Museum, 66000-Belém, Pará, Brazil

and C. A. KUSHIGBOR INTERA Technologies Ltd, Ottawa, Ontario, Canada, K1Z 8R9

( Received 27 November 1992; in final form 15 July 1993)

Abstract. Digital TM Landsat images integrated with elevation model variables were used to evaluate the potentiality of geobotany for lithological unit discrimi- nation in the tropical rain forest environment of the Carajás Mineral Province, Brazilian Amazon region. The data set was analysed through digital image processing techniques (enhancements and non-supervised classificatidn). The investigation has shown that the Up-Land rain forest vegetation in the area is mainly controlled by elevation and slope which refiect variations in the geology. Botanical verification has also indicated that the physiognomy (density and stratification), would be the most important vegetation attribute which infiuences the remote sensing responses. The research has provided useful information for the geological model of the area. Thus, by understanding the relationships among vegetation, terrain descriptors and geology, geobotanical remote sensing provides an additional tool for geological exploration in this kind of environment.

1. Introduction The extraction of geological information in rain forest environments based on optical remote sensing (RS) data is always problematic. Papers dealing with this theme are rare in the literature and are restricted either to spatial attribute analysis (Erb 1982) or to application related to specific site conditions where latentes cause changes in the biomass density which results in spectral contrasts (Taranik et al. 1978). The possibility of using vegetation spectral response to infer bedrock characteristics is an interesting alternative that must be investigated. However, the complexity of the environment and the assumed poor relationship between rock and vegetation, have been considered important factors that do not favour the spectral RS performance in such difficult terrain (Birnie 1982).

0143-1161/94 $10.00 () 1994 Taylor & Francis Ltd 1634 W. R. Paradella et al.

The research described here was designed to address the kind of pertinent RS questions which are faced by geological exploration in tropical rain forest environments, such as, whether it is possible to infer characteristics of the substratum through spectral responses detected from the rain forest vegetation canopies, or, which are the main variables involved in the process? The strategy pursued in this investigation takes into consideration the fact that one of the factors that controls the distribution of plant communities in the tropical rain forest environment is the topography (Ab' Sáber 1986). In addition, geology is a fundamental parameter that controls topography. Thus, the hypothetical link vegetation-rock should be sought through the analysis of the relationship between terrain attributes (elevation, slope, etc.) and vegetation parameters that control spectral response (flora, cover density, stratification, etc.). This issue could be properly clarified through a geobotanical model based on orbital RS and terrain descriptors obtained from Digital Elevation Model (DEM).

2. Concepts Geobotany deals with the relationship between vegetation and environmental factors. Since the mid-nineteenth century, it has been recognized that distinct plant associations exist on different geological substratum and this might be used to characterize the geology of the area concerned (Karpinsky 1841, in Brooks 1972). Thus, geobotany should not only be understood as a way of prospecting with the purpose of detecting induced mineral stress in vegetal species. Emphasis should also be put in terms of its usage as an alternative tool for geological mapping. For a heavily dense vegetated area, data collected from orbital optical sensors is related to a mixed assemblage of plants (i.e., to the plant communities). So, the influence of the structure and the composition of the communities in the response detected should be more emphasized than the spectral behaviour of individual leaves or isolated canopy species (Saraf and Cracknell 1989). More obvious spectral changes detected from plant communities in low spectral resolution data, (such as MSS and TM-Landsat), tend to be related to the physical property variations of soil/bedrock (moisture content/texture) rather than to the chemical variations (Milton and Mouat 1984). For dense vegetation cover environments, successful geobotanical applications based on orbital RS data have been restricted to the relatively homogeneous forest from the northern hemisphere (Green et al. 1985, Defeo et al. 1986, Bell et al. 1991, among others). Tropical rain forests however, present particular difficulties for geobotanical applications. First, the identification of species is not easy due to the scarcity of access for field observations, height of trees, their unsocial fashion distribution and distinct stratification. Secondly, due to nutrition and aeration reasons, the species are normally shallow-rooted, bear flowers and fruits at irregular intervals and shed them onto the ground where they are decomposed (Cole 1971, Jordan 1982, Pires and Prance 1985). Thus, species identification is sometimes almost impossible from ground levei. Finally, due to the high complexity of the environment, a greater number of species can be found in a few hectares of the Amazon rain forest as opposed to all the identified ones in the cold and temperate forests (Schubart 1986). At cold latitudes, a regional (background) geobotany approach has been developed to geological exploration (Bruce and Singhroy 1984, Bruce and Hornsby 1987). It is based on the hypothesis that the nature and the distribution of plant A geobotanical approach to lhe Amazon rain forest 1635 communities occur as a result of environmental conditions and therefore, variations in distribution from the established norm of an area may be indicative of changes in the geology. The concept has focused on community levei and has been tested through digital image processing of orbital RS data and elevation model variables (Hornsby et ai. 1988). Carajás, the most important Brazilian mineral province, is located on the easternmost border of the Amazon Region. The Province, with an area of 120 000 square kilometers is marked by mountainous terrains, deep chemical weathering which produces thick oxisols ('latosols) and few outcrops. Vegetation cover is typical of the Up-Land tropical rain forest communities with complex and multi- levei canopies and numerous species. Since this region can be considered an excellent test site, a long term remote sensing research programme has been implemented. The project encompasses aspects of remote sensing application such as multi-source data integration, visual methods of extraction of information, digital image processing and geobotanical model developments. This paper presents the final results of a five-year geobotanical investigation that was carried out by the authors in the Pojuca area, a metamorphic belt with various Cu-Zn deposits in the Carajás Province.

3. Study area A 230 square kilometre test area was selected for the investigation, centred on the Pojuca mine camp and located in the northern border of the Carajás Province (figure 1). The area has been receiving attention in regional exploratory programmes since 1974 when geochemical surveys indicated Cu-Zn anomalies in the Pojuca stream. The test-site is inserted in a wide regional sinistral shear zone (Itacaiimas shear belt) characterized by both ductile and brittle deformations aligned on a W-N-W trend (Araujo et ai. 1988). This zone is marked by tangential (low angle) strains that in Pojuca area are vertical due to Carajás transcurrent fault system. Costa and Hasui (1991) have studied regionally these mega-structures and proposed an origin for the metavolcanic and metasedimentary rocks from the area associated to transtension (tectonic basins), followed by granitoid intrusions and to transpression along the Carajás transcurrent system. The geology of the study area is incompletely mapped. Areas around the copper deposits have been mapped in detail (1 : 5000 and 1 : 10000), but much of the rest of the area has only been studied on a regional scale. The geologic maps shown in figures 2 and 3 were generalized from a detailed map published by the mining company Docegeo (Docegeo 1984) and from a recent regional mapping carried out by the Pará Federal University (Macambira et ai. 1990), respectively. According to these authors, the oldest Archean rocks in the area are known as the Xingu Complex, a sequence of tonalitic, granodioritic and granitic gneiss which occurs in the northeastern portion of the region and is related to rounded hilly low relief (altitudes from 150 up to 250 m). The Igarapé Pojuca Group is also Archean in age and occurs in tectonic discordance with surrounding Xingu rocks. It is a volcano-sedimentary sequence with a N7OW structural trending and characterized mainly by schists, banded iron formations and amphibolites. This Group is represented at the surface by a set of parallel ridges and valleys trending W-N-W and altitudes of 250 up to 500 m. This 1636 W. R. Paradella et al.

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50023 Figure I. Location of the Pojuca site. Area A represents TM-Landsat subscene (512 by 512 pixels) selected for the investigation. B and C are areas covered by regional and detailed geological maps discussed in the text.

unit is also host for severa! Cu-Zn mineral deposits. Docegeo (1987) and Macambira et al. (1990) divided this group into three formations: Bueno, Corpo 4 and Gameleira (figure 3). The Igarapé Pojuca rocks are disconformably overlapped by a widespread low- grade clastic metasediments of Early Proterozoic age named as Rio Fresco Group by Docegeo (1988) or as Igarapé Azul Formation by Macambira et al. (1990). These metasandstones crop out in the southwest comer of the study area and are topographically characterized by a plateau with small hills (altitudes of 500 up to 700 m). Anorogenic granite exposures, with Early Proterozoic age, are scattered through- out the western portion of the test area and have been mapped as Serra dos Carajás granites. Tertiary latente duricrust leveis are common in the top of the plateau and were mapped as a geological unit by Docegeo (1984). Quaternary deposits (alluvium and poorly sorted colluvium) occur along the main drainage channels. The vegetation cover is typical of tropical up-land rain forest. Three major ecological regions can be roughly recognized in the test arca, based on a million scale radar mapping programme (RADAMBRASIL Project) in the seventies (Velloso et al. 1974): (1) Montana Tropical forest associated with the highest altitudes; (2) Sub- Montana Tropical forest with Woodland/Broadleaved forest and (3) Mixed Wood- land forest. A total of 552 plant specimens with 119 species, 89 genera and 39 families were identified from one hectare transect measured near the Pojuca camp (Silva and Rosa 1989). A geobotanical approach to lhe Amazon rain forest 1637

Figure 2. Simplified detailed geological map of the Pojuca area (Source: Docegeo 1984): 1 = alluvial deposits, 2 = latente, 3 = granite, 4= cataclastic breccia, 5= metasandstone, 6 = Igarapé Pojuca Group (indistinct), 7 = Xingu Complex, 8 =drainage, 9 = road, 10 = Pojuca camp.

4. Methodology A Universal Transverse Mercator (UTM)-registered data set was prepared for this research using a Geographical Information System (GIS) based on INTER- GRAPH workstation. The digital analysis was developed on a PC-based software. The Pojuca area is contained within the quadrangle D of a TM-Landsat 5 image (Path 224, Row 64). The image was gathered on 31 May 1984 and was the first TM- Landsat data completely free of cloud cover. This passage was also selected in order to minimize the anthropogenic effects caused by mining activities which have been increasing considerably since 1985. The image was geometrically corrected to a UTM projection based on 50 ground control points from 1: 100 000 and 1: 10 000 topographic sheets and using a first order affine transformation and a bi-linear interpolation scheme. The expected error in position has varied between 8 to 30 m due to non-uniform distribution of the ground control points. The DEM was constructed based on Intergraph Digital Terrain Mapping Package (Intergraph, 1987). Hand digitized contour lines from the topographic sheets were used as input for the DEM generation. A contour-to-grid routine was 1638 W. R. Paradella et ai.

50. 25 .

''Ti";;■ ; N 1 I f O 2 km -

50. 2

11111111111 11111111111 1‘,:;s1 FRT,M1 1 1 1 11 I • I 1 2 3 4 5 6 7 8 9 10

Figure 3. Simplified regional geological map of the Pojuca area (Source: Macambira et 1990): I =granite, 2= gabbro, 3= Igarapé Azul Formation, 4= Gameleira Formation, 5 =Corpo 4 Formation, 6= Bueno Formation, 7= Xingu Complex, 8 = drainage, 9=road, 10 =Pojuca camp.

used to create a grid file with 30 m resolution. This was linearly stretched and elevation, slope and aspect 8-bit images were obtained. A sub-set of 512 by 512 pixel area from the whole TM quadrangle was selected for the digital investigation. As the illumination conditions in the scene vary appreciably from pixel to pixel due to the topography, the analysis was conducted independently in two data sets: (1) original bands, where spectral and spatial attributes could be altogether examined, and (2) band ratios, where topographic effects were minimized and purer spectral products were available. The main steps in the RS analysis are presented in the flow chart of figure 4. The TM original reflective bands were analysed through a combination of enhancements and thematic classification based on EASI/PACE's software (PCI 1988). A feature selection routine-OIF (Optimum Index Factor, Chavez et ai. 1982) was also used to select the best channels for the colour composites. Such channels were enhanced by Frequency Equalization Stretch (FES) and the two best colour composites were selected for visual interpretation. Principal Component Transformation (PCT) was also investigated. The three first components were enhanced by FES and combined as an additional colour composite. Finally, an unsupervised thematic classification based on clustering algorithm (K-means) was applied to the original bands. As the clustering software on the version available supported only four channels as input, the PCT was then A geobotanical approach to the Amazon raia forest 1639

Figure 4. Flow chart with the main steps in the analysis of the RS data (0IF=Optimum Index Factor, PCT =Principal Component Transformation, FES =Frequency Equal- ization Stretch).

used as a dimensionality-reduction prior to the classification. The four first components from the six original reflective channels were used in the classification. The visual analysis of the enhanced colour composites plus the thematic classification have provided the first four vegetation class maps. As the effects of the atmospheric path-radiance are noteworthy in the TM data, particularly in the visible bands, the Minimum Histogram subtraction method (Chavez 1975) was used to minimise atmospheric effects in the generation of the ratio data. A total of 15 ratios were investigated based on the visual quality of the products. To make the analysis easier, they were grouped into three sets: (1) simple ratios—(3/2), (4/1), (4/3), (3/5), (7/4), (5/4), (2) complex ratios I—(4-3)/(4+ 3), (5-4)/(5 +4), (7-4)/(7 +4), (5-7)/(5 + 7) and (3) complex ratios II—(4/(4 +5+ 7), 5/(4+ 5+7), 7/(4 + 5+ 7), (3/2)/(4/3). The OIF was calculated for each group with the determination of the best three band-ratio combinations for colour composites. The channels were enhanced by FES and the colour composites were further visually analysed. As a result, three additional vegetation class maps were also obtained. Finally, as an attempt to obtain enhanced products with maximum spectral information contained in isolated ratio bands, PCT was also applied to ratio inputs in two situations: (1) six simple ratios as discussed above (3/2), (4/1), (4/3), (3/5), (7/4), (5/4), and (2) the same six simple ratios plus the three best complex ratios indicated by OIF—(4 —3)/(4 + 3), (5-4)/(5 + 4), (5-7)1(5 +7). The three first components from each transformation were then enhanced by FES and colours were assigned to them. The visual interpretation of these colour composites has provided the last two vegetation maps. These nine preliminary vegetation maps were integrated into a final RS Integra- tion Map. The criterion that was adopted for the integration was to consider only the classes that were detected in most of the products. In addition, their boundaries were extracted from the products on which they were more distinguishable.

1640 W. R. Paradella et al.

The main steps in the analysis of the terrain descriptor data from the test-site are presented in the fiow chart of figure 5. Elevation, slope and aspect images were selected for the analysis. The elevation image was firstly clustered and also classified with slope data. As a consequence, two thematic class maps were obtained showing terrain classes in the area with same elevation and same elevation plus slope. The classification of aspect image has shown very complex patterns that prevented further analysis. The comparison of the RS vegetation maps and terrain descriptors classes has allowed consistent inferences regarding the role of the topography and the geology in the distribution of the vegetation cover in the Pojuca area.

5. Results and discussion Figure 6 is the integration map with the nine vegetation classes detected from digital analysis of TM-Landsat data as discussed above. The contribution of each digital product in the definition of the RS vegetation classes has indicated that the PCT over simple plus complex band-ratios (figure 7) has presented the best performance, followed by the PCT over the original bands. Figure 8 is the result of the clustering classification with eight classes using as input descriptor terrains of elevation and slope. Based on figures 6 and 8, the following class associations can be made: RS thematic class A with topographic class 2 (dark brown), class B with 3 (dark blue), class D with 5 (light yellow), class F with 6 (light green), part of class G with 7 (black). Classes C, E and I have presented no clear topographic relationships. These results indicate that topography represents a fundamental control in the distribution of most of the vegetation classes in the Pojuca area. In addition, elevation constitutes the main terrain parameter in this control since the clustering results from elevation data when taken isolated have presented a class trend closer to elevation plus slope classification. Slope was important in the definition of the class G in figure 6 whose geological correspondence will be discussed later. The visual comparison of the geological maps with the RS vegetation classes also supports interesting geobotanical correlations. Thus, taking into account the geo-

DEM COMPONENT TOPOGRAPH1C MAP

OIGITIZE

DEM

ELEVATION SLOPE

ELEVATION I ELEVATION CLUSTERING I ISLOPE CLUSTERII

THEMATIC CLASS MAP 1 1 THEMATIC CLASS MAP

SUMMARY MAP A Hl PRELIMINARY ASSESSMENT SUMMARY MAP 8

Figure 5. Flow chart with the main steps in the analysis of the DEM data. A geobotanical approach to the Amazon rain forest 1641

01111111 11111;1111 "e FJA 1 G. 1 Év-Zid. P1;111 4.1

Figure 6. Final integration map.

logical units previously mapped in detail (figure 2), the following relationships can be established: RS class A with latente duricrust, class D with Igarapé Pojuca Group, class E with granitic rocks, class F with Xingu Complex and class G with alluvium. If the regional geological map is now considered (figure 3), class C could be related to Igarapé Azul Formation and for classes B, H and I no correspondence was noted. Some important aspects deserve attention in this discussion. First, the good adjustment between the vegetation class C with lithologies from the Igarapé Azul Formation as mapped by Macambira et al. (1990) in figure 3, suggests that the metasandstone unit that was mapped by Docegeo (1984) in the southern border of figure 2 without clear stratigraphic position, probably belongs to Pojuca Group. In addition, the aligned contact between the vegetation class C and D with a NNW orientation (line a- b, figure 7), also suggests a structural contact by faults between Igarapé Pojuca Group and Igarapé Azul Formation (or Rio Fresco Group). Secondly, it is also expected that latentes occur over Rio Fresco Group and not over et al. 1642 W. R. Paradella

Figure 7. TM Principal Component colour-composite (PC1, PC2, PC3-RBG, enhanced by Frequency Equalization). Simple plus complex ratios discussed in the text were used as input channels.

Figure 8. Thematic classification by clustering based on elevation and slope images. A geobotanical approach to lhe Amazon rain forest 1643

Igarapé Pojuca Group on the southeastern comer of figure 2 (class A surrounded by C and C surrounded by D in figure 6). The presence of these rocks in this particular region is still controversial taking into account the two published maps. Finally, based on the spectral patterns it was not possible to confirm the sub-division of the Igarapé Pojuca group as proposed in the map of figure 3. Three phases of field work and three helicopter campaigns were carried out from 1989 to 1991 in order to characterize the vegetation classes detected by RS and aiming at clarifying relationships between lithology, topography and vegetation cover. Air observations and photographs from a hand-held camera in a low-flying helicopter combined to botanical ground reconnaissance have allowed the classification of the vegetation in the study area into three principal formations: (1) Dense Ombrophilous Equatorial forest, (2) Open Ombrophilous Equatorial forest and (3) Alluvial forest. The descriptions in table 1 outline the main geobotanical characteristics of the RS class in the Pojuca area. The field-work has also suggested that RS class I is apparently associated with shadows while for class H, the impossibility of access and the lack of consistent geological information prevented any conclusion regarding geobotanical relationships. However, it is important to mention that recent information from Docegeo's geologists that lately visited one of the areas mapped as class H, just 5 km towards the northern part of the Pojuca camp indicated the presence of lithologies very similar to the Igarapé Pojuca Group rocks (Vieira 1991). This similarity could partly explain the mixed Xingu/Pojuca spectral characteristic for this unit. But the distinct relief characteristics of this unit when compared to both groups, reinforces the necessity of more detailed geological and botanical information for a more consistent geobotanical conclusion. The botanical verifications have indicated that the RS classes can be explained mainly through physiognomical rather than floristic basis. Variations in density, coupled with differences in stratification and canopy structure could be the main causes of the spectral TM responses. A model of these variations based on field and helicopter observations is shown as an idealized canopy cross-sections for most of the vegetation classes from the study area in figures 9 and 10. The geological field verification carried out in the southwestern comer of the test site, has also confirmed the dose association of latente duricrusts with areas mapped as RS class A. This seems to be a regional trend on the tops of the Igarapé Azul, (or Rio Fresco Group), plateaus for the whole Carajás Province. In addition, a careful examination of alteration product and unaltered rock samples of drill cores obtained from the Pojuca Leste prospect (4 km southeastern from Pojuca camp), have indicated that the extension of the Igarapé Pojuca towards the southeastern is not so continuous as previously mapped in figure 2. Lithologies from Igarapé Azul Formation must be expected in this region as proposed by Macambira et al. 1990. Finally, in spite of the fact that the field-work did not provide conclusive evidences, it is still suspected that the contact between Igarapé Pojuca and Rio Fresco Groups is controlled by faults.

6. Conclusions The geological characteristics of the area play an important role in the control of the spatial distribution of the tropical rain forest classes detected by orbital RS. 1644 W. R. Paradella et ai.

RS VEGETATION CLASS1FICATION VEGETATION RELIEF/LITHOLOGICAL CLASS (FORNATION CLASS) CHARACTERISTICS ASSOCIATIONS

A High Dense Ombrophilous Forest associated with high altitudes Plateaus assoclated with latentes. Equatorial forest (plateaus), ciosed crowns, clear understory, canopy height ranging troe 25 up to 30 metem, unciear stratification between canopy and emergents (slIghtly flat top canopy), Jorge trees, no Incidence of bamboos and few lianas. The most common emergent species is time Newtonla suaveolens.

I3 bense Ombrophilous Forest with a clear understory with many Rolling plain up to moderate hIlly Equatorial forest Individuais, common presence of lianas on the terrains of time igarapí Azul Formatlon crown. Newtonla suaveolens is time most common Cor Rio Fresco Group) lithologles . emergent species - ( WIWW height). The dossel is more irregular and ranges near 25 meter height.

C Dense Ombrophilous A slightly moer dense variation of the clame Restrictedtosteep slopes and hilly Equatorial forest 11, with more Irregular dossel, arboreal terralns of time !carece' Azul Individuais near 30 meter height, presence of FormatIon lithologle, lianas, few emergent species and sporadlc na tural clearing with bamboos.

D Open Ombrophilous Forest with a dominant stratum troe 10 up to Parallel valleys and ridges trending Equatorial forest 15 meter height, high frequente of lianas, WNW associated with metavolcanIc rocks teu emergents and presence of undergrowth of the !coroo; Pojuca Group. with lianas and bamboos. Time most common emergent specles are Bertholletia excelsa and Astronium gracIle. The most commonc—EISTjf liana specles is the Memora schomburgkil. This unit presents a marked characteristic In time arca: the locally known .leafy towers. (emergents and dossel covered by lianas on time hillsIdes).

Tipe-Savannah vegetatIon Due to time absence of access, no botanical Hilly terralns related to Serra dos descrIptons are avallable. However, based on Carajás granite, time alr reconnaissance trote time hellcopter, this vegetation class presents physiognomlc and floristic similarities with time Brazillan "cerrado", a type-savannah vegetation (Pires and France 19135). This unit is characterIzed by moderate to iow biomass with natural clearing assoclated to rocky sou l or exposures of rocks.

F Open Ombrophilous Forest with stratifications, given by Loa hilly refle( associated with Equatorial forest scattered emergents (around 35 metem s high), gnelss/migmatltes of the Xingri (Mixed forest) ao arboreal dossel with 25 meters high and Complex. presence of understory (10 meters hlgh) with natural clearings. The most common emergent species is time Bertholletia excelsa.

G Ailuvial forest Forest related to lowlands, indlcating excess Alluvlum of humidity or swampy conditIons, malnly dralnages or flooded arcas. Time dossel is generally Irregular. In places where no natural clearing occurs, the dossel with emergents represents the most important stratum In time blomass. It Is also noted that monocotyiedon species, mainly .açai" (Euterpe oleoraceae) dominate near the drainage, while dicotyledon species, mainly "babaçu. (Orbignya barboslana) are common near time slope,

Table 1. Main geobotanical characteristics of the RS classes.

Botanical verification has shown that the physiognomy of the vegetation cover, mainly density and stratification, would be the most important parameter which influences the detected remote sensing responses. In addition, elevation and subordi- nate slope are the most important terrain attributes that control the geobotanical regional pattern in the Pojuca area. The investigation has shown that orbital RS image when digitally integrated with DEM data constitutes a promising tool for geobotanical approaches in this kind of terrain. Furthermore, the research has also provided new insights into the current geological models of the arca. A geobotanical approach to the Amazon rain forest 1645

Class A

Class B

Class C Figure 9. Schematic physiognomical cross-section for class A, B and C.

Acknowledgments The authors benefited from the reviews by Drs I. Vitorello, J. C. N. Epiphânio and R. Almeida Filho from INPE. The authors would like to acknowledge the scientific supports given by Bill Bruce and Dr Andrea G. Fabbri during the post- doctoral research conducted by the senhor author at CCRS (Ottawa) in 1988. The authors also thank the Brazilian mining company Docegeo and its geologist Eduardo Angelim de Pontes Vieira for the assistance and support during field -works and helicopter campaigns in the Pojuca area. Partial funding for this investigation was provided through a grant from SGTM/PADCT (contract number 1139/87). A geobotanical approach to the Amazon rain forest 1647

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