FLORISTIC COMPOSITION OF THE CERRADO IN THE PÉ-DE-GIGANTE RESERVE ( SANTA RITA DO PASSA QUATRO , SOUTHEASTERN BRAZIL )

(Floristic composition of the cerrado in the Pé-de-Gigante Reserve (Santa Rita do Passa Quatro, southeastern Brazil)). We studied a 1225 ha area, composed mainly of cerrado, in Santa Rita do Passa Quatro, São Paulo State, southeastern Brazil (21°36-38’S, 47°36-39’W). In three cerrado physiognomies (campo cerrado – a wooded savanna, cerrado sensu stricto – a woodland, and cerradão – a tall woodland), we collected all vascular plants in reproductive stage, and identified them to species level. We found 360 species, representing 236 genera and 69 families. The richest families were: Asteraceae, Fabaceae, Poaceae, and Rubiaceae. The savanna physiognomies were richer than the forest one. The ratio between herbaceous and woody species was approximately 2:1. We analysed the whole flora and its two components separately, woody and herbaceous, comparing them with other disjunct cerrado areas. We obtained similarity values (Sørensen index) from 0.47 to 0.81, which showed that the 3 diversity of the cerrado was higher in the herbaceous component than in the woody one.

The cerrado vegetation is characterized by its wide physiognomic variation.According to Coutinho (1978), the cerrado goes from campo limpo, a grassland, to cerradão, a woodland.The intermediate physiognomies (campo sujo -a shrub savanna, campo cerrado -a wooded savanna, and cerrado sensu stricto -a woodland) are considered ecotones.
Accompanying the physiognomic variation, the cerrado vegetation presents a high floristic richness.Castro et al. (1999) compiled many floristic and phytosociological surveys carried out in cerrado areas and estimated the number of vascular plant species in this vegetation type ranging from 3,000 to 7,000.Mendonça et al. (1998) listed 6,429 species for the whole domain, including, besides the cerrado itself, other associated vegetation types, such as gallery forest, deciduous and semideciduous forest, and floodplain grassland.
The cerrado vegetation has two distinct floras, a woody one and an herbaceous one, which are antagonistic, because both are sun-loving (Coutinho 1978).The importance of the herbaceous flora gradually decreases from the campo limpo to the cerradão, while the importance of the woody flora increases in this direction (Coutinho 1978).Mantovani & Martins (1993) compared some cerrado areas, and they found a species ratio of 1:2 to 1:3 between the woody and the herbaceous floras.Castro et al. (1999) emphasized the almost complete absence of studies that sampled the herbaceous component, in spite of its high richness.
Our aim was to carry out a floristic survey in a disjunct cerrado area, distinguishing its physiognomies.This survey intends to increase the knowledge of the cerrado flora, especially of the frequently neglected herbaceous component, and to contribute to phytogeographical studies.
First, the reserve was mapped with remote sensing techniques, using a vegetation index that measures the green biomass, with which the occurrence of cerrado regions was assigned (Bitencourt et al. 1997, Pivello et al. 1999a).We distinguished the cerrado physiognomies following the "forest-ecotone-grassland" concept (Coutinho 1978).Then, in each cerrado physiognomy, except the campo sujo due to its small extension, we carried out floristic surveys in monthly field trips, each one with 23hr sampling effort, from September 1995 to February 1997, when we collected all vascular plant species in reproductive phase.We lodgeal the collected exsicata in the herbarium of São Paulo Botanical Institute (SP).
P l a n t s were classified in families according to the sys-tem proposed by Judd et al. (1999).The species were classified in life forms in accordance with Raunkiaer's system, adapted by Mueller-Dombois & Ellenberg (1974).We considered the phanerophyte species as belonging to the woody component and the non-phanerophytes species as belonging to the herbaceous one.We calculated the floristic similarity among the different physiognomies at species level, grouping them in clusters, using average-linking as agglomerative algorithm (Jongman et al. 1995) and Sørensen index as distance measure (Magurran 1988).The results were compared in the same way with other floristic surveys, in which similar methods were used (Mantovani & Martins 1993, Batalha et al. 1997).
Of the total collected species, 16 (4.4%)are weeds that does not occur spontaneously in cerrado sites (Mendonça et al. 1998).In this vegetation type, this is mainly a consequence of the fragmentation and edge effect (Pivello et al. 1998(Pivello et al. , 1999b)).Mendonça et al. (1998) listed for the whole Cerrado Domain 289 weedy species, or 4.5% of its total flora, the same proportion observed in the Pé-de-Gigante flora.Plant invasions are a major problem in cerrado fragments, occuring pratically in every one of them, dominating in patches and outcompeting native species (Pivello et al. 1999b).This situation occurs also in the Pé-de-Gigante Reserve, where African grasses, especially Melinis minutiflora P. Beauv.and Brachiaria decumbens Stapf, are spreading fast (Pivello et al. 1999c).
A total of 272 species were found in the campo cerrado; 308, in the cerrado sensu stricto; and 148, in the cerradão (Tab.2).Following the "forest-ecotone-grassland" concept (Coutinho 1978), the ecotonal physiognomies are expected to be richer, because they contain species from both the herbaceous and the woody components.Indeed, the existing ecotonal physiognomies in the Pé-de-Gigante Reserve, campo cerrado and cerrado sensu stricto, were richer than one of the extremes, cerradão.The woody to herbaceous species ratio for all three physiognomies together (cerrado sensu lato) was approximately 1:2 (Tab.2).This ratio increased from cerradão, in which the number of woody species was higher than those of herbaceous species, to campo cerrado (Tab.2).Once again, this is expected according to the "forestecotone-grassland" concept (Coutinho 1978)  which predicts a gradual decrease in the number of woody species from cerradão to campo limpo.In Brasília (Ratter 1980), this ratio was also 1:2, while in Lagoa Santa (Warming 1892) and Moji Guaçu (Mantovani & Martins 1993) it was 1:3.In Santa Rita do Passa Quatro and Brasília, there is a predominance of closed cerrado physiognomies (cerrado sensu stricto and cerradão).In Lagoa Santa and Moji Guaçu, on the other hand, open cerrado physiognomies (campo sujo and campo cerrado) prevail, explaining the higher proportion of herbaceous species in these two areas.
In the three cerrado physiognomies sampled in the Pé-de-Gigante Reserve, the highest similarity was between campo cerrado and cerrado sensu stricto (0.803).Between cerrado sensu stricto and cerradão, the similarity value was 0.592 and between campo cerrado and cerradão, this value was 0.519.The same pattern was also observed in Itirapina (Mantovani 1990), where campo cerrado and cerrado sensu stricto were the most similar physiognomies and the campo cerrado and cerradão, the most dissimilar ones.
Comparing the Pé-de-Gigante Reserve with cerrado sites in Campininha Farm and Emas, 76 families, 287 genera and 516 species occur in Campininha Farm (Mantovani & Martins 1993) and 69 families, 229 genera and 358 species in Emas (Batalha et al. 1997).Despite its larger area (1269 ha), the Pé-de-Gigante Reserve presented a floristic richness similar to that found in Emas (16 ha) and lower than that found in Campininha Farm (342 ha).This could be a consequence of recent human impact on the reserve, such as timber explotation and cattle-raising, and the invasion of weeds (Pivello et al. 1999a(Pivello et al. , 1999b)), but also of the prevalence of open physiognomies in Emas and Campininha Farm.Besides, differences on sampling effort could have contributed also to these results.The similarity index values between the Péde-Gigante Reserve and Campininha Farm and between the Pé-de-Gigante Reserve and Emas were 0.558 and 0.659, respectively.Between Campininha Farm and Emas, this value was 0.629 (Fig. 3).
The Campininha Farm distinguished itself from the Pé-de-Gigante Reserve and from Emas by its greater floristic richness.This variation existed mainly at species level, since the genera and families remained approximately constant, as stated previously by Mantovani & Martins (1993).
Herbaceous component -The 236 herbaceous species comprised 65.6% of the flora as a whole.The families represented only in this component accounted for 40.6% of the total number of families, a value lower than those obtained in Campininha Farm (44.7%) (Mantovani & Martins 1993) and Emas (49.7%) (Batalha et al. 1997).The richest families in this component were: Asteraceae, Fabaceae, Poaceae, Rubiaceae, Bignoniaceae, Malvaceae, Apocynaceae, Euphorbiaceae, and Malpighiaceae, representing 66.5% of the total number of herbaceous species.These families are also the most representative ones in this component in other cerrado sites, such as Campininha Farm (Mantovani & Martins 1993) and Emas (Batalha et al. 1997).
The similarity index values between the Péde-Gigante Reserve and the Campininha Farm and between the Pé-de-Gigante Reserve and Emas were 0.472 and 0.609, respectively.Between Campininha Farm and Emas, this value was 0.580 (Fig. 3).The much higher richness found in Campininha Farm (391) contributed to separate it from Pé-de-Gigante and Emas (236 and 250 species, respectively).
There are few studies including the herbaceous species of the cerrado flora (Castro et al. 1999).The seasonality of the epigeal portion of the herbaceous species, that lasts from a few months to two years, contributes to the poor knowledge of this component.As a consequence of the short epigean cycle of many species and depending on fire frequency and intensity, the herbaceous component composition changes a lot throughout the year (Mantovani & Martins 1993).
Woody component -The 124 woody species represented 34.4% of the whole flora.Of all sampled families, 29.0% had species only in the woody component, a value between those found in Campininha Farm (34.7%) (Mantovani & Martins 1993) and Emas (24.6%) (Batalha et al. 1997).
In this component, 108 species were sampled in Emas and 125 in Campininha Farm.The similarity index values between the Pé-de-Gigante Reserve, Campininha Farm and Emas were all between 0.77 and 0.81 (Fig. 3).The similarity index values in this component were higher than those found in the herbaceous one, showing that the heterogeneity is higher in the herbaceous than in the woody flora.This higher heterogeneity of the herbaceous component was evident only at species level, since at genus and especially at family levels there was no pronounced difference between the two components.Castro et al. (1999) made an extensive compilation of many floristic and phytosociological studies carried out in cerrado vegetation and elaborated a check-list of woody species.Of the species sampled here, only Myrcia guianensis (Aubl.) A. DC.(Myrtaceae) was not reported by these authors.