Guilherme C. Abdala1, Linda S. Caldas2, M. Haridasan1 & George Eiten2

1Departamento de Ecologia and 2Departamento de Botânica, Universidade de Brasília, Brasília, DF. Brazil



The aboveground and belowground biomass and soil carbon were measured to a depth of 6 m in a typical cerrado (sense strict) located near Brasília, DF, Brazil, on a well drained dark red latosol (Haplutox). A phytosociological survey of tree and shrub species, as well as ground-layer vegetation, was carried out. There were 3,300 trees and shrubs per hectare, with a total basal area of 14.5m2 ha-1, cylindrical volume of 68.4m3 ha-1, and aboveground biomass of 26,020kg.ha-1. The ground-layer presented an average aboveground biomass of 5,580kg.ha-1 (4,130kg.ha-1 grasses and 1,450kg.ha-1 non-grasses). The litter was estimated at 5,190kg.ha-1. The underground biomass was estimated at 41,100kg.ha-1, with root crowns contributing 7,800kg.ha-1, and charcoal an additional 1,980 kg.ha-1. The soil organic matter, to a depth of 620cm, was 642,000kg.ha-1, representing 89% of the total organic matter, not including charcoal (724,400kg.ha-1).

Key words: biomass; charcoal; global carbon cycle; savanna; soil organic carbon.



Cerrado vegetation covers approximately 2,000,000km2, 20% of the area of Brazil, in its various physiognomic forms (12). The most widespread is cerrado savanna with a significant woody-layer component. Although some studies have been carried out on the aboveground biomass of the cerrado (37, 39), the only information available on the root systems of natural communities is descriptive, with accounts of roots reaching a depth of 18m in the "camp cerrado" of São Paulo State (32). Because of its extensive area, data on this ecosystem are needed for studies of productivity, energy analysis and contributions of management practices to global carbon cycling.


The occurrence of fire (8), the infertility of the soils (17, 24) and seasonal stress in the upper layer of the soil (28) suggest that the belowground component represents the larger part of the total biomass of cerrado vegetation. These results are in accordance with the theories on acquisition and stocking of resources (5). These theories predict that plants, depending on species and the severity of stress, tend to allocate more energy to the roots in order to reduce water and nutritional stress and as a guarantee in the case of catastrophes such as fire.


The relative lack of information on the belowground biomass in many ecosystems is due to the difficulty of removing the soil, a very laborious and expensive process (45). Exists yet the difficulty of separation and washing of the roots, rootlets and micro-rootlets, which are distributed throughout the soil volume. Emphasis on roots in the soil surface (0 - 100cm) is to be expected given the role of organic-enriched layers in water entry and storage. It is observed in retention and mineralization of nutrients, returned in plant litter and in initial establishment of non-epiphytic species (41). The root biomass data reported in the literature for tropical ecosystems seldom exceeds depths of 2m, with the exception (30) in eastern Amazonian, who present quantitative data on biomass of roots to 6m depth.

Two methods are widely used in studies of root biomass in different ecosystems: excavation of the root systems of individual plants and extraction of soil samples of known volume. The first, which is extremely laborious for large plants, is applicable in studies at the species level, for determination of the structure and distribution of roots and the root/shoot ratio. On the other hand, the method of soil samples measures the composite root mass (19) and is more widely applicable, less destructive and provides data on the root/shoot ratio for the ecosystem as a whole.

The objective of the present study was to determine the above-and belowground biomass, as well as soil organic carbon, in a typical cerrado in Central Brazil, as a basis for further studies.


The field studies were carried out from September 1992 to March 1993, in an area of approximately 20 ha of typical cerrado vegetation near Brasília, DF. (47o48’45"W, 15o47’30"S) at an altitude of 1,080m. The climate of the region is characterized as Cwa, following the classification of Köppen, with two distinct seasons: a rainy season in the summer and a dry winter. The average annual precipitation is approximately 1,500mm, with 80% falling between December and March. Representative water balances for the region register a water deficit in the soil from June to October. The average annual temperature is 21oC; the difference between the average temperature of the coldest month (July) and the warmest month (September) is approximately 4oC.

The study area has been floristically and physiognomically well conserved in spite of its proximity to urban residential area in Brasília, DF. It had suffered the effects of erosion from road construction 30 years earlier, which led to the formation of two deep gullies, up to 15m wide and 8m deep. Further erosion had recently cut and broadened these gullies, which had natural vegetation growing up to their margins. The experimental plots were located on both sides of one of these gullies, within an area of 2ha.




Two 20m x 50m plots were marked, one on each side of the gully, within 10m of the edge, in areas where the vegetation was typical of the plots which were excavated for belowground biomass. In each plot, all woody individuals with circumferences larger than 6.0cm at 30cm up the trunk from the soil level (C30) were identified to species, and circumference (C30) and oblique height (from the soil level accomplishing along the curving trunk to the base of the crown. It came from there vertically through the crown up to the level of the heights point) were


measured. The Wisconsin importance percentage of each species was calculated (11). The principal genera of theground layer vegetation were determined based on frequency measurements by the line intercept method of Cox (9) within 40m on each side of the gully.

Based on the distribution of the number of woody-layer individuals in circumference classes, the quotient "q" (obtained by dividing the number of individuals in a class by the number in the previous class) was obtained (27). This expresses the percent of individuals, which are recruited from a class to the immediately superior. A community is considered "balanced" when "q" is more or less constant along the distribution.

Aboveground Biomass

The aboveground biomass of each woody-individual in the two 20m x 50m plots was estimated from an allometric equation, obtained from data of 112 cerrado trees and shrubs (G. Eiten & G.C. Abdala, unpublished). In which the cylindrical volume calculated as the product of the basal area at C30 and the oblique height, are used as the independent variable. The equation is as follows:

Log (y) = 0.9967 log (x) + 2.587 (r = 0.91, P << 0.001)

Where y = total dry weight of the individual (g) and x = cylindrical volume (dm3).

The aboveground biomass of the ground layer, including the woody plants with circumference less than 6cm at 30cm height, was determined in 35 plots measuring 1m x 1m. In these plots, all standing biomass, including dead material, was cut at the soil level, separated into grasses and non-grasses, and dried at 70,167ºC. These samples were taken in September 1992, at the end of the dry season, and March 1993, near the end of the rainy season. The distribution of the sample plots was semi-random, with 7 samples taken near the edges of the gully and 28 at distances varying from 4 to 16m from the edges. No distinction was made between plots beneath the crowns of the trees and those in more open situations, although none of the plots were within 1.5m of the trunks of trees whose circumference was more than 30cm at 30cm height. Litter was also collected from these sample plots; fallen branches and trunks with circumference greater than 6cm were not included.

Belowground Biomass

Two types of excavations, blocks and tanks, were made, differing in depth of sampling, volume of soil collected and treatment applied to the samples.

Soil blocks, or monoliths, of known volume were collected at different depths, with average dimensions of 21dm3 (30cm x 35cm surface area x 15-20cm depth), by manually cutting out the soil sample. Each sample volume was measured exactly after extraction, based on the dimensions of the resulting hole. Roots remaining after removal of the soil were cut and added to the sample. Blocks were thus collected at 16 different points, always starting within a 1m x 1m plot in which the aboveground biomass of the ground layer had been harvested. Seven of these sites were located on the edges of the gully and 9 at a distance of 4 to 16m from the edges. In the case of sampling at the edges of the gully, the samples were taken at least 200 cm from the edge to a maximum depth of 620cm. The other, internal plots were sampled to a depth of 100cm. The number of blocks sampled at each depth and the total volume of soil sampled are presented in Table 1.


Table 1. Number of blocks sampled and the total volume of soil collected for subsamples A1 + A2 at different depths.


The soil from each block was sieved through a wire screen (2mm mesh) in the field. The entire root and xylopodium segments retained on the screen were collected as sub-sample A1. The finer material which passed through the screen was homogenized and a sub-sample of 2dm3 (2 liters) was collected as sub-sample A2. From the soil remaining after sieving, small samples were taken for chemical analysis.

Sub-sample A1 was washed in the laboratory. The roots and detritus from sub-sample A2 were extracted by agitating the soil sample in a large volume of water for 20 min and collecting the floating material on a fine nylon sieve with 0.5mm mesh. No separation was made between roots of woody and non-woody plants, nor of living and dead material.




Washed roots were dried at 80oC. Roots from sub-samples A1 were separated into three size classes before weighing fine, diameter less than 2mm; medium, diameter between 2 and 10mm; and thick, diameter greater than 10mm. Large fragments of charcoal (> than 2mm) encountered in the samples were weighed separately, as well as the rhizomes of grasses found in the most superficial soil samples. The material from sub-samples A2 was classified as very fine. The proportion between the volume of the sub-sample taken to the laboratory and the total volume of the sample in the field was used to estimate the total biomass of this fraction in the sample. Due to the difficulty of separating charcoal fragments in some fine and very fine sub-samples, a visual estimate was made of the minimal percentage, which the charcoal represented with respect to the mass of the roots.



Tanks: In order to determine the biomass of the root crowns of the trees, two excavations of this type were carried out. Each plot, selected to include a relatively large number of medium-sized and tall trees, measured 5m x 20m. The aboveground biomass of the trees and shrubs was determined and the root crowns and roots with diameters greater than 10mm were collected, to a depth of 100cm. All the material was weighed in the field and sub-samples taken for drying in the laboratory. The weights obtained were compared with the results of the equation, which relates the weight of the root crown, whose roots were cut off at the base, to the basal area at 30cm height (1):

Y = 0.0688 x + 1.385 (n = 84, r = 0.81, P << 0.001)

Where y = dry weight of root crown without roots (kg) and x = basal area (cm2)

Soil organic material: The percentage of soil organic carbon in the samples collected at different depths was determined by the method of Allison (2). The constant 1,724 to convert to percentage of organic material multiplied this value. The weight of organic material per volume of soil was calculated from the bulk density (g.cm-3) measured at different depths from 34 cylindrical samples of 132cm3, dried at 105oC.



The physiognomy of the area was a typical cerrado sense strict, with tree crown coverage of 35%. In the two 1,000m2 plots, 71 species were identified with circumference at 30cm height (C30) greater than or equal to 6cm. The 40 principal species, based on Importance Percentage (IP), are listed in Table 2, and are in accordance with the composition of other areas in the Federal District. The first three species, Caryocar brasiliensis, Qualea grandiflora and Ouratea hexasperma, make up 26% of the total IP, although they represent only 4% of the species, whereas the 20 species of lowest IP, representing 27% of the total number of species, make up 4% of the total IP. The species ranked in positions 1, 2, 4, 13 and 15 (Caryocar brasiliensis, Qualea grandiflora, Qualea parviflora, Pterodon pubescens and Dalbergia violacea, respectively), which are the five species with the largest cylindrical volumes, make up more than 64% of the total cylindrical volume. The tallest tree in the area was an individual of Dalbergia violacea, measuring 12m, and the greatest circumference was that of Pterodon pubescens, measuring 106cm.

Table 2. Wisconsin importance percentage (IP) of the 40 principal species whose circumference at 30cm height was greater than 6cm. IP = (RD + RBA + RF) /3, where RD is relative dominance; RBA, relative basal area; RF, relative frequency and RCV, relative cylindrical volume (oblique height x basal area at 30cm up). Dead standing trees not included

* In the Federal District, certain botanists use other names for some of the species listed above: Orate castaneifolia for O. hexasperma, Vellozia flavicans for V. squamata, Styrax ferruginea for S. ferrugineus, Dalbergia miscolobium for D. violacea.

** For calculating absolute frequency (AF) of each species, the individuals were listed in the order in which they were encountered in the field (zigzag), then the list was sub-divided into groups of 20 neighboring individuals. The relative frequency (RF) was calculated as RF = 100 AF / S AF.

An average of 3,300 individuals with circumference greater than or equal to 6cm at 30cm height were found per hectare, with a total basal area of 14.5m2 ha-1 and a total cylindrical volume of 68.4 m3 ha-1. The frequency distribution of circumference is shown in Table 3. More than 65% of the individuals were less than 2m tall and more than 85% of the individuals were less than 26cm in circumference. If its is accept the definition of trees as individuals with a circumference greater than 10cm at 30cm height and at least 3m tall, the average density of trees in this area was 670ha-1, with the remaining 80% of the individuals belonging to the shrub layer. The trees in this class belong to 39 species.

The large variation in the "q" values shown in Table 3 shows that the sampled cerrado does not have a balanced recruitment in the percent of individuals that survive into the next greater circumference class (27). But the backward "J" shape of the values for absolute number of individuals per class in Table 3 suggests a tendency to equilibrium.

Table 3. Number of trees plus shrub elements per circumference class (at 30cm height above ground, C30) per hectare of the cerrado sense strict. The ratio q = number of individuals in class n / number of individuals in class n-1.

The standing dead represented 7.5% of the total stems (live + dead), 2.1% of the total basal area and 0.4% of the cylindrical volume, indicating that the majority of the dead stems are in the smaller size classes.

In the ground layer, the most frequent genera were Echinolaena, Axonopus, Eragrostis, Trachypogon and Schizachyrium among the grasses; Croton, Merremia, Oxalis, Serjania, Maprounea and Pavonia among the non-grasses. Sprouts of some tree species, such as Dalbergia, Roupala, Davilla, Ouratea and Rapanea, were also present in the ground layer. Ground layer real cover was 95%, with Echinolaena inflexa (Poiret) Chase responsible for more than 70% of the total cover. Axonopus barbigerus (Kunth) Hitchc. was another important grass in terms of ground cover. The non-grasses are negligible in terms of ground cover, contributing less than 5%. The African grass weed Melinis minutiflora Beauv. was present sporadically in the area and was not sampled for biomass measurements.

Aboveground Biomass and Litter

Applying the regression equation of G. Eiten & G. C. Abdala (unpublished) to the values of cylindrical volume found in


the 2000m2 area, a total aboveground biomass of 26020kg. ha-1 was estimated for the woody component with circumference greater than 6cm at 30cm height (6C30). Of this total 12% was composed of shrubs and the rest of trees, as defined above. The leaves made up an estimated 9.7% of the total biomass of the shrubs and 5.2% of the trees. The biomass of the standing dead was estimated at 300kg ha-1.

The average standing dry biomass of the ground layer was 5,580 (+2240)kg.ha-1, with the grasses representing 4,130 (+500)kg.ha-1. The average biomass of the litter was 5190 (+190) kg. ha-1.

Belowground Biomass

By correlating the median depth (in cm) of each of the 106 soil blocks collected with the biomass of the roots per unit volume (mg cm-3), a regression curve was obtained (Figure 1). The correlation between the variables was high, in spite of the variability among samples at the same depth. The high variability was due principally to the variability in the distribution of thick roots, whereas the medium and fine classes showed a much more homogeneous distribution among samples (Table 4).

Table 4 Coefficient of variation (%) of root mass for the classes "very fine + fine" (diameter < 2mm) and total roots in soil blocks sampled at each depth

Integrating the curve in Figure 1, the total root biomass in the interval from 15 to 620cm depths was estimated. For the superficial layer, from 0 to 15cm depth, the average biomass of the 16 soil blocks was used, giving a value of 14460kg. ha-1. Thus the total belowground biomass (living and dead), not including charcoal, was estimated at 33,370 kg.ha-1 to a depth of 620cm.

Figure 1. Total root biomass (dependent variable) as a function of soil depth (independent variable) measured in soil blocks.

The size class distribution of the roots to 100 cm depth is shown in Figure 2, with a marked concentration of roots in the superficial 0-15cm layer where the biomass was 2.2 times that of the next depth (15-30cm). The estimates from the soil blocks indicated that, to 620cm depth, 70% of the biomass was found in the 0-50cm layer and 80% in the first 100cm depth. The rhizomes of grasses made up 5.9% of the total biomass of the 0-15cm layer and only 0.2% in the subsequent depth (15-30cm).

Figure 2. Distribution of root diameter classes as a function of depth in the first 100cm, measured in soil blocks. Very fine = material collected by washing/floating sieved soil samples; fine = diameter < 2 mm; medium = diameter 2-10 mm; thick = diameter > 10 mm.

There was an increase in the percentage of biomass in thick roots as depth increased from the soil surface to 40-50cm (Figure 3), with a concomitant decrease in the contribution of very fine and fine roots. Up to a depth of 100cm, 29% of the root biomass was classified as very fine, 30% as fine, 13% as medium and 25% as thick, with the grass rhizomes representing 3%.

Figure 3. Percentage of total root biomass in each diameter class as a function of depth from the surface to 100cm, measured in soil blocks. Very fine = material collected by washing/floating sieved soil samples; fine = diameter < 2mm; medium = diameter 2-10mm; thick = diameter > 10mm.

Thick roots were not encountered in our samples at depths below 100cm from the soil surface, although the medium size class was present in samples to a depth of 420cm, representing 40% of the total biomass in the range of 100 to 620cm depths. The percentage of very fine roots within the class of very fine + fine was fairly constant at all depths, with values between 55 and 65%, with the exception of the surface 0-15cm layer, in which the very fine roots made up 44% of the total.


The two areas of 100m2 sampled as tanks had total basal areas of 1970cm2 and 2380cm2, for individuals with circumference greater than 30cm at 30cm, and 160kg and 212kg of dry weight of root crowns, respectively. Using the equation of Abdala (1), which correlates the dry weight of the root crowns (kg), with the basal area (cm2), the estimates of root crown biomass for the two areas were 154kg and 188kg. These estimates were respectively 3.2% and 11.1% smaller than the actual weights obtained from the field samples, a tolerable limit, which permits the application of the regression equation to other areas. Thus for the average basal area of 10.2cm2 m-2 for individuals with circumference equal to or greater than 30cm at 30cm height, a total belowground biomass for the root crowns of 7,800kg.ha-1 was estimated.

Fragments of charcoal were frequently present in sample blocks to a depth of 200cm, with dry weight 9 to 10 times that of the roots in some samples. These fragments, with volumes no greater than about 1cm3, appeared generally after washing of the samples. The average weights are low but a clear tendency was seen with a peak in the surface layer (0-15cm) and another at 100cm depth (Figure 4a). The importance of the charcoal as a fraction of the total biomass increased at depths of 100 and 210cm (Figure 4b). With a minimum value of 0.05mg of charcoal per cm3 of soil in the range of 120 to 200cm depth, added to the values obtained for the more superficial layers, a total of 1980kg.ha-1 of charcoal can be estimated in the soil from 0-220cm depth.


Figure 4 Distribution of charcoal as a function of depth to 200cm. a) Average dry weight per unit soil volume. b) Charcoal as a percentage of total belowground biomass.


Organic Matter in the Soil

Classified as a dark-red latosol, the soil was yellowish-red (5 YR 4/6) to a depth of 40cm and red (2.5 YR 4/8) from 40 to ca. 500cm. Whitish particles and small fragments of dark colored rocks were visible from 500cm on down, with regolith at 600 to 650cm depths. The soil analysis showed results (Table 5) typical for cerrado soils (14).

The percentage of organic carbon in the soil as a function of depth fit a log-log regression (Figure 5), with a correlation coefficient of r = 0.95 (P<<0.001).

Considering an average value of 0.94g.cm-3 for the apparent density of the soil to a depth of 100cm, gradually increasing to 0.99g,cm-3 at 300cm and to

1.14g.cm-3 at 400cm, then constant to 620cm, the total organic matter in the soil was estimated at 642,300kg.ha-1 to a depth of 620cm, based on the curve of Figure 5 (15 to 620cm depth),

Table 5. Some features of the soil under the cerrado sense strict studied.

The average value of 2.15% organic carbon obtained from the analyses of the soil blocks was used for the 0-15cm layer and the conversion factor of 1.724 to transform organic carbon to organic matter in all calculations. The first 50cm of soil contained only 21% of the soil organic matter and the first 100cm contained 32% of the total, with a large fraction encountered at greater depths.


Figure 5. Percentage of organic carbon (dependent variable) in the soil is a function of depth (independent variable).

A summary of the distribution of organic material in the cerrado is presented in Figure 6. The total belowground biomass, excluding charcoal and soil organic matter, divided by the total aboveground biomass, including litter, presents a ratio very close to 1.


Figure 6. Stocks of biomass in different compartments of the cerrado sense strict. Aboveground biomass includes standing dead. Root diameter classes are as follows: Very fine = material collected by washing/floating sieved soil samples; fine = diameter < 2 mm; medium = diameter 2-10 mm; thick = diameter > 10 mm. Rhizomes of grasses were included in the class of medium size roots. Humus refers to soil organic matter.


The large percentage of individuals of the woody layer in the first stem circumference class (over 60%) is common in the cerrado (40). It is can be explained by the occurrence of fire, at intervals of not more than 3-4 years, as well as the genetic potential of many species, which occur only as small individuals. The literature (40) cites that found a non-balanced statistical structure in the stem diameters of the cerrado on the Experimental Station at Paraopeba, Minas Gerais State, Brazil, explaining this as due to selective cutting. In our cerrado, fire and selective cutting explain the imbalance, although the backward "J" of the circumference classes shows a tendency to equilibrium, typical of non-planted forests.

The phytosociological analysis of the woody layer shows a pattern very common in the cerrado of the Brasília, Federal District in terms of dominant species (15). The only difference is the dominance of Caryocar brasiliensis, which, although important, is not usually dominant as in our area. Perhaps, this is due to the conservation of Caryocar when firewood is collected because of its fruit, much appreciated in this region.

The estimate of 2450g.m-2 (24,520kg.ha-1) of the wood component of the woody-layer biomass in our area is slightly more than the average (39), which was 2025.g.m-2. Other study (37) reported values from 1,180 to 3,670g. m-2, with an average of 2,260g.m-2, in 38 plots of 10 x 10m each of typical cerrado. This variability can be explained by the high spatial heterogeneity of aerial biomass per unit area commonly observed in savanna areas in what is essentially the same stand (12, 33). Compared with other savanna, types the aerial woody biomass of our cerrado approximates that of the Andropogonae open shrub Savannah of the Ivory Coast, 2,190g.m-2 (26). Although this has larger trees and fewer shrubs, and is more than that of the Nylsvley Savanna of South Africa, 1,490g. m-2 (33).

The 12% of the total aerial biomass of woody plants of 6C30 or more (trees plus thicker-stemmed shrubs) that is in the shrub class alone are closed to the 11.5%, in the Nylsvley Savanna (33). He included all individuals with diameter greater than 1cm at 20cm above the ground and considered individuals with heights of less than 2.5m as part of the


shrub layer. In Nylsvley the standing dead woody biomass was 11.5% of the total biomass of trees and live scrub including leaves, found 7% of the biomass in standing dead in a cerrado sense strict (39). In the present study the small percentage of standing dead biomass (1.1%) is probably due to the selective harvesting of firewood in the area.

In the ground layer, the total of 1,080g.m-2 (including litter) is closed to the value of 990g.m-2, in a cerrado close to Brasília, DF (18). These authors estimated the ground layer biomass excluding litter at 455g.m-2 with grasses representing 62%. In the present study, 74% of the ground layer biomass excluding litter was composed of grasses. Other studies in areas of cerrado in Brasília, DF. showed proportions of grasses ranging from 50 to 80% (4, 37), depending on variations in the density of tree cover, sampling season and time after fire. In the Lamto Savanna of the Ivory Coast, 79% of the ground layer biomass corresponded to grasses (22), whereas in Trachypogon savannas in Venezuela, the grasses comprise 80 to 100% of the total aboveground biomass (36).

The high concentration of the roots in the superficial layers of the cerrado soil is in accordance with observations in other tropical ecosystems (7, 26, 38, 42). However, the percentage of total root biomass in these layers depends on the total depth sampled. For example, if it considers only the first 100cm in the present study, the root biomass in the first 30cm is 75% of the total, instead of the value of 60% obtained for the whole profile to 620cm depth. In studies of nutrient sources, sinks and losses, the relative contribution of a soil layer was assumed to be in some degree proportional to its fine root density.

This assumption, plus the difficulty in sampling greater depths, has led to an emphasis on upper soil layers, usually to depths of less than 100cm, in most studies, despite the evidence showing the importance of deep roots in water uptake (41).

The total volume of the soil blocks collected at depths beyond 100cm in the cerrado is probably insufficient to adequately estimate the thick roots, whose distribution is very heterogeneous, but which could be seen, albeit infrequently, in the eroded walls of the gully at depths beyond 400cm. For this reason, the belowground biomass calculated from the equation of Figure 1 underestimates the roots with diameter greater than 10mm. The biomass contributed by this fraction, which does not appear in the equation, should be relatively small, due to the large concentration of roots, including thick roots, in the superficial layers of the soil. Similar conclusions as regards the inadequate number of samples for determining thick roots at greater depths were reached (42).

The total root biomass decreases exponentially with depth in many different ecosystems, however, in certain savannas there is an increase in the root biomass from the surface to a depth of 20-30cm, consistent with the hypothesis in which the stability of the savannas is due to two strata (44). And that trees and herbs of these two strata explore different soil horizons. The gradual increase in the proportion of thick roots as we proceed from the surface to a depth of c. 50cm (Figure 3) demonstrates the competitive interaction between trees and herbs in the cerrado, in accordance with the two-layer hypothesis (44), or with the models of Savanna structure (43).

This pattern has been observed in other savannas (21, 23, 31, 34). Sampling in more detail, with soil layers of only 10cm thickness, for example, should permit a more precise description of the distribution of woody roots along the soil profile in the cerrado.

The proportion of fine plus very fine roots, with diameters less than 2mm, is high in the cerrado, compared to other ecosystems, principally forests.


This difference may be due to the presence of a continuous ground layer in the cerrado with a high proportion of non-woody plants. The vegetation of Accra Plains, consisting of small thicket clumps associated with mounds surrounded by grassland, shows a high percentage of fine root (31).

The other authors (6) showed that the proportion of fine roots (diameter<6mm) increased from 60% to 90% when the percentage of non-woody plants went from 1% to 44% of total biomass in the faces Tall Bana and Open Bana woodland, respectively.

The part of this difference founds in the cerrado may be explained by the method of extraction of the very fine roots by floating in water. This process permits the recovery of very fine roots and root fragments, which would not be harvested by manual separation or sieving of roots from soil samples. This component was a significant fraction of the belowground biomass: 35% of the total belowground biomass, and 60% of the roots with less than 2mm in diameter.

When the belowground biomass of different ecosystems is compared, without considering the differences in methodologies used, a large variation is noted in the order of magnitude of the total root weight (Table 6), as well as in the root/shoot ratio. The majority of perennial herbaceous species, including some grasses, present well developed root systems, with a root/shoot ratio generally greater than 1.0 (26, 45).


Woody plants in their initial growth stages also present a root/shoot ratio greater than 1.0; however, as the plant grows, there is a tendency to invert this ratio (34, 45). Water stresses, whether from flooding or from deficits, can lead to an increased investment in the root system (5, 6, 29, 41). Nutritional stress can lead to a similar modification in the relative development of root and shoot (5, 20, 41) and fire-adapted communities also tend to invest heavily in belowground structures (5, 45).

In the cerrado sense strict studied, with its high density of shrubs, water stress, nutritional stress and fire adaptation are all-present as probable factors leading to increased root/shoot ratio. The root/shoot ratio of 1 can be considered relatively high, compared to other Savanna ecosystems, such as the Andropogonae savanna woodland (r:s = 0.6) (26), and even when compared to dry forests with a total biomass greater than that of the cerrado.

Some authors (6) showed an inverse relation between the aboveground biomass and the root/shoot ratio along a topographic gradient in Low Amazon Caatinga, that is, the root/shoot ratio increased as the proportion of woody plants, in the total biomass decreased, as would be expected. This pattern was also observed by other authors in the Tall Amazon Caatinga (20), and in the Andropogonae savannas of the Ivory Coast (26). For the cerrado sense lato, with its varying densities of woody plants in diverse physiognomies, one would expect a similar relationship, in which the root/shoot ratio decreases as the total aboveground biomass increases.

Table 6. Comparison of belowground or root biomass (R), total biomass (R + S) and the ratio root/shoot (R/S) in different tropical ecosystems.

* Average of open and sub-canopy areas, where the canopy cover amounted to 27.5%.

** Above and belowground peak total biomass.

*** The sum of above + belowground / herbaceous + woody / mean biomass.

References to the quantities of charcoal present in soil have not been found, even in studies in which the areas suffer frequent burning. Although the charcoal represented less than 3% of the total biomass of the roots, its presence in practically 90% of the soil blocks sampled to a 200cm depths, And the increased proportion of charcoal to total belowground biomass with increasing depth (Figure 4b). It indicates that this material is highly resistant to decomposition. The charcoal fragments were frequently encountered in all the samples of a certain depths, 100 a


120cm, for example, and were very rare in the samples at other depths, such as 50 to 75cm.

The soil organic carbon content encountered in the present study is very similar to that reported in the superficial layers of the soil in other cerrado area (14). Compared with other ecosystems, the percentage of organic matter is relatively low; even so, when the organic matter in the soil is included in the total above and belowground biomass. Its can verify that the belowground compartment contains 94% of the total carbon stock in the cerrado (Figure 7), based on calculations to a depth of 620cm. With a ratio between organic carbon/organic matter equal to 0.58, the stock of organic carbon in the first 100cm of the soil would be 11.9kg. m-2. This value is comparable to that of other tropical oxisols (25).

The total area of cerrado on latosol has been estimated as 92 million hectares (16). Using the formula from Figure 5 to estimate the organic carbon to 2m, a total of 16.3.1015g of organic carbon would be present in the cerrado latosol. This value represents 33% of the total organic carbon estimated for all the savannas around the world (3). This proportion would be much higher if the total depth of the latosol, which often reaches 10 to 20m, were considered.

Figure 7. Percentage of total biomass in the cerrado: distribution between the aboveground and belowground compartments, in which the overwhelming contribution of soil organic carbon is evident.


We are grateful to Washington Novaes, former Director of SEMATEC. Francisco Ozanan C. C. de Alencar, head of the Department of Parquets and Gardens of the Brasília Federal District, Rogério Pereira Dias, Oscar A.M. Rosa Filho, Márcio Armando Silveira, Mardocheu P. Rocha, Mara R. B. Chaves and Pedro Caldas, as well as the team of excavators from NOVACAP, for their support.



Matéria orgânica e raizes da superfície e do solo: relação das raizes com os demais componentes da matéria orgânica do cerrado do Brasil Central.

A biomassa aérea e subterrânea e o carbono orgânico do solo foram medidos até a profundidade de 6m em um cerrado típico (sense strict) próximo a Brasília, DF, Brasil, sobre um latossolo vermelho escuro, bem drenado (Haplutox). Um levantamento fitossociológico de espécies lenhosas e da camada rasteira foi conduzido. Um total de 3.300 árvores e arbustos por hectare foram encontradas, com uma área basal total de 14,5m2.ha-1, volume cilíndrico de 68,4m 3 .ha-1, e biomassa aérea de 26.020kg.ha-1. A camada rasteira apresentou uma biomassa aérea média de 5.580kg.ha-1 (4.130kg.ha-1gramíneas e 1.450kg.ha-1 não-gramíneas). A serapilheira foi estimada em 5.190kg.ha-1 e a biomassa subterrânea em 41.100 kg. ha-1, com coroas de raiz contribuindo com 7.800kg.ha-1, e carvão com mais 1.980kg.ha-1. A matéria orgânica do solo, até 620cm profundidade, foi 642.000kg.ha-1, representando 89% do total, excluindo o carvão (724.400kg.ha-1).

Palavras chaves: biomassa; carvão; ciclo global de carbono; savana; carbono orgânico do solo



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