RESUMO Considerando a importância do Silício (Si) para as plantas, nas últimas décadas muitos estudos avaliaram a capacidade do elemento em aliviar o estresse abiótico em diferentes espécies, a maioria delas de interesse agrícola. Para todas as espécies, o Si oferece uma gama de benefícios às plantas na redução dos efeitos do estresse biótico e abiótico, estando especialmente associado a aumentos na biomassa das plantas. No entanto, quando realizamos uma revisão quantitativa sistemática de estudos que relacionam o Si ao alívio do estresse abiótico em plantas, demonstramos que há uma redução dos efeitos do Si ao longo do tempo e que os efeitos do silício foram menores nos estudos mais recentes. Além disso, descobrimos que plantas sob diferentes tipos de estresse tiveram respostas semelhantes ao Si, sugerindo que os mecanismos de alívio do estresse abiótico nas plantas podem ser comuns entre as condições de estresse hídrico, salinidade e metais pesados – os principais estresses ambientais estudados na literatura. Nosso estudo pode direcionar estudos futuros, que não devem se limitar a simplesmente avaliar a existência de quaisquer efeitos de alívio de estresse do Si, mas também compreender a variação que existe nesses mecanismos e que depende do tipo de estresse e dos fatores envolvidos na redução desses efeitos.

ABSTRACT Considering the importance of Silicon (Si) for plants, many studies have focused to evaluate the ability of the element to alleviate abiotic stress in different species, mainly of agricultural interest. For all species, Si offers a range of benefits in reducing the effects of biotic and abiotic stress, being especially associated with increases in plant biomass. However, after performed a systematic quantitative review of studies linking Si to the relief of abiotic stress in plants, it was demonstrated that there is a reduction in the effects of Si over time and that the effects of Si were smaller in recent studies. Furthermore, was found that plants under different types of stress had similar responses to Si, suggesting that abiotic stress relief mechanisms in plants may be common among conditions of water stress, salinity, and heavy metals – the main environmental stresses studied in the literature. This study can guide future research, which should not be limited to simply evaluating the existence of any Si stress-relieving effects, but also to understand the variation that exists in these mechanisms and considered that they depend on the type of stress and the factors involved in reducing these effects.

ABSTRACT The vegetation cover is the result of many biological and abiotic interactions. To identify the different factors that cause changes is crucial when defining future sustainable development and protection of natural resources. In the Brazilian semiarid region, the vegetation cover has been subjected to drastic deforestation and land use at centennial-scale that has led to desertification. Pollen analysis is an efficient tool to reconstruct the different processes of degradation of the vegetation cover over time. We built a referential data set for the vegetation cover using 48 pollen surface samples collected in the reservoirs of the Ceará. We used satellite images for comparison with the pollen signatures and defined an alteration score to express the correlation between terrestrial pollen and anthropic cover. Our results showed our surface samples to be generally representative of the vegetation cover and of the general degradation of the landscape. Our study areas can be considered as degraded as the initial categories “preserved” or “intermediary” are not reflected in the pollen assemblages, in agreement with results of botanical surveys and the historical background. The on-going process of desertification is climate-independent and was initiated many decades or centuries ago by intensive land use for agriculture and grazing.

ABSTRACT Background: Factors determining the coexistence of species have been recognized since Darwin, but empirical studies have brought the relationship between niche similarity and competition into question. Knowing the mechanisms of coexistence makes it possible to predict biological invasions and determine better species combinations for the restoration and recovery of degraded areas. The aim of this study was to test the competition-relatedness hypothesis for semiarid tree species. Thus, an experiment was carried out with a phylogenetic gradient of tree species, planted in pairs. The phylogenetically closest pair consisted of congeneric species of the same clade, the intermediate pair comprised congeneric species of distinct clades, and the more distant pair were species of the same family. Results: Our results show that the phylogenetically closest and the more distant pairs corroborated the competition-relatedness hypothesis, but the presence of one species with high competitive ability in the intermediate pair caused an unexpected pattern. Conclusion: Niche differences are important for coexistence, but it is necessary to know the competitive ability of each species and the specific associations that are more productive to improve the efficiency of restoration programs and to reveal the degree of aggressiveness in the case of invasive species.

Resumo Afloramentos rochosos são relevos residuais montanhosos que ocorrem em regiões tropicais, subtropicais e temperadas de todo o mundo. Nesse trabalho, nossos objetivos foram entender os padrões de riqueza e similaridade florística de plantas trepadeiras em afloramentos rochosos no nordeste do Brasil, bem como, compreender aspectos morfológicos e formas de dispersão dessas espécies. As análises foram realizadas utilizando uma lista florística de plantas trepadeiras registradas em inventários de afloramentos rochosos, nos estados da Paraíba e Pernambuco. Foram identificadas 143 espécies, 66 gêneros e 25 famílias. Quanto ao aspecto morfológico, 72% das espécies são trepadeiras herbáceas e 28% são lenhosas (lianas). O mecanismo de ascensão mais frequente foi o volúvel (66%) e a síndrome de dispersão mais representativa foi autocoria (44%). A riqueza de trepadeiras herbáceas e lenhosas foi positivamente correlacionada com a altitude e negativamente correlacionada com a distância do litoral e a temperatura; correlação negativa também foi observada entre a riqueza de trepadeiras herbáceas e a precipitação, enquanto para as lenhosas a riqueza se manteve constante nessa variável. A análise de similaridade florística resultou na formação de três grupos, sugerindo uma composição florística característica da matriz circundante, influenciada por fatores abióticos e tipos vegetacionais onde os afloramentos rochosos estão inseridos.

Abstract Rocky outcrops are residual reliefs mountainous that occur in tropical, subtropical and temperate regions from all over the world. In this work, our objectives were to understand the richness patterns and floristic similarity of climbing plants, in rocky outcrops in Northeast Brazil, as well as to understand morphological aspects and dispersion forms of these species. The analyzes were carried out using a floristic list of climbing plants recorded in inventories of rocky outcrops, in the states of Paraíba and Pernambuco. We identified 143 species, 66 genera and 25 families. As for the morphological aspect, 72% of the species are herbaceous climbers and 28% are woody climbers (lianas). The most frequent ascending mechanism was the voluble (66%), and the most representative dispersion syndrome was autochory (44%). The richness of herbaceous and woody climbers was positively correlated with altitude, and negatively correlated with distance from the coast and temperature; negative correlation was also observed between richness of herbaceous climbers and precipitation, while for the woody the richness remained constant for this variable. The analysis of floristic similarity resulted in the formation of three groups, suggesting a floristic composition characteristic of the surrounding matrix, influenced by abiotic factors and vegetation types where rock outcrops are inserted.

Abstract The biota of the humid mountain ranges of the Brazilian semiarid is still poorly understood. In order to fill this scientific gap, we carried out an extensive survey along altitudinal ranges (400m - 1,000 m) on both the windward and the leeward slopes of the Baturité Mountain Range, in the state of Ceará state. We registered 400 plant species and 92 families. The Myrtaceae (36 spp.), Fabaceae (25 spp.), Rubiaceae (20 spp.) and Bromeliaceae (15 spp.) families predominated on the windward slope; while Fabaceae (19 spp.), Myrtaceae (14 spp.) and Euphorbiaceae (11 spp.) were the most abundant on the leeward slope. As we expected, the species richness of trees, shrubs, subshrubs, epiphytes and terrestrial herbs was positively correlated with the altitude (R2 > 0.60). Above 800 m, we registered 273 species exclusive to the windward slope, 81 exclusive to the leeward slope, and 46 shared species. Therefore, management actions must consider the spatial heterogeneity, distribution and taxa richness.

RESUMO Diferenças heteroespecíficas nas taxas de crescimento em altura, na produção de biomassa e na área foliar entre espécies coocorrentes são formas de medir a ocorrência de interações: facilitação ou competição. Com base no conceito mais amplo de facilitação, este tipo de interação positiva tem sido relatado para explicar a coocorrência de espécies em ambientes com alta limitação de recurso, a exemplo de climas árticos e áridos. O objetivo deste estudo foi avaliar se a facilitação pode favorecer o desenvolvimento inicial das populações de Mimosa caesalpiniifolia e Bauhinia cheilantha, duas espécies típicas da região da Caatinga, em casa de vegetação. As plântulas de Mimosa caesalpiniifolia Benth e de Bauhinia cheilantha (Bongard) foram cultivadas em vasos por 120 dias, nas proporções de 4:1; 3:2; 2:3; 1:4; 5:0; 0:5. Também foram realizadas avaliações na estrutura e em alguns teores (nitrogênio e fósforo) de nutrientes no solo e na folha das plântulas. Os resultados de crescimento, alocação de biomassa e concentrações de nitrogênio e fósforo nas folhas de Mimosa caesalpiniifolia foram influenciados positivamente com o aumento da densidade de indivíduos de Bauhinia cheilantha (Bongard) Steudel. No entanto, esta última espécie teve a menor taxa de crescimento de competição intraespecífica. Se for adotado o conceito mais amplo de facilitação, pode-se afirmar que houve interações positivas. Por se tratar de duas espécies de Fabaceae que podem apresentar associações com fungos micorrízicos e com bactérias diazotróficas, o principal nutriente limitante para o bom desempenho na coocorrência destas duas populações deverá ser o fósforo, pois não houve diferenças na quantidade de nitrogênio disponível no solo entre o início e o final do experimento.

ABSTRACT Heteroespecific differences in growth rates in height, biomass production and leaf area among co-occurring species are ways of measuring the occurrence of interaction: facilitation or competition. Based on the broader concept of facilitation, this type of positive interaction has been reported to explain the co-occurrence of species in environments with high resource limitations, such as arctic and arid climates. The objective of this study was to evaluate if facilitation could favor the initial development of Mimosa caesalpinlifolia and Bauhinia cheilantha populations, two species typical of the Caatinga region, under greenhouse conditions. The seedlings of Mimosa caesapinifolia Benth and Bauhinia cheilantha (Bongard) were cultivated in pots for 120 days in the ratios of 4: 1; 3: 2; 2: 3; 1: 4; 5: 0; 0: 5. Evaluations about structure and of some nutrient contents (nitrogen and phosphorus) in the soil and leaf of the seedlings. The results of growth, biomass allocation and concentrations of nitrogen and phosphorus in leaves of Mimosa caesalpinlifolia were positively influenced by the increase of the density of Bauhinia cheilantha (Bongard) Steudel individuals. However, the latter species had the lowest growth rate of intra-specific competition. If we adopt the broadest concept of facilitation, we can affirm that there were positive interactions. As both are species of Fabaceae that may present associations with mycorrhizal fungi and diazotrophic bacteria, the main limiting nutrient for good performance in the co-occurrence of these two populations should be phosphorus, since there were no differences in the amount of nitrogen available in the soil between the beginning and the end of the experiment.

ABSTRACT Variation in environmental conditions during the Quaternary period served as important filters for the maintenance of vegetation types and for determining the composition of the current biota. We analyzed oscillations in the distributions of different vegetation types in Brazil during the Quaternary period using species of the genus Erythroxylum (Erythroxylaceae) because of the vast heterogeneity of habitats in which they occur. We hypothesized that it would be possible to observe geographically distinct distribution patterns of species of Erythroxylum as a result of the climate changes that occurred during the last glacial maximum (LGM) and in the last interglacial period (LIG) of the Pleistocene. We used bioclimatic variables to elaborate distribution models of 11 species under three scenarios: the current climate, LGM, and LIG. We found four plant distribution patterns in humid and semiarid climates. During the LIG, humid patterns were restricted to northeastern and central-western Brazil, while semiarid conditions maintained plant distributions in the same regions of Brazil where they occur today, although with additionanl occurrences in the northern and central-western portions of that country. During the LGM, all distribution patterns exhibited extensions towards the coast due to the exposure of the continental shelf.

Xylem anatomical traits can provide insights regarding the mechanisms affecting the distribution of vascular plants across environmental gradients. In this study, we aimed to investigate the hypothesis that lianas occurring in semiarid environments have characteristics that maximize the xylem resistance to tension-induced cavitation along the root-stem-branch continuum. To gather information regarding the hydraulic architecture of the lianas, we analyzed several anatomical traits of wood: cross-sectional area occupied by the parenchyma (AP), fibers (AF), and vessels (AV); average vessel diameter (d); wood density (WD); pit diameter in the vessel wall (dpit); pit density (Npit), and potential hydraulic conductivity (Kp) in branches, stems, and roots of three congeneric species of lianas that occur in two vegetation types of the semiarid regions of Brazil. We found that lianas in these semiarid environments possess a number of the following xylem traits that may allow resistance to tension-induced cavitation:1) lower vessel diameter, lower Kp, and higher hydraulic safety in roots and branches; 2) Dimorphic vessels, ensuring both hydraulic efficiency and safety; and 3) small diameter of pits (potentially associated with a decrease in the membrane area of the vessel pits). This suite of traits may provide insight into mechanisms allowing lianas to occur in semiarid environments.

Analisamos a variação funcional entre espécies decíduas (ED) e sempre verdes (ESV) para compreender as divergências nas estratégias de tolerância e evitação à seca. O estudo foi realizado em um fragmento de floresta tropical sazonalmente seca, localizada no munícipio de Pentecoste (3°47'S, 39°16'W), Ceará, Brasil. Mensuramos 17 traços funcionais foliares em 17 ED e cinco ESV, sendo 12 morfofuncionais, um fenológico e quatro fisiológicos. Verificamos que as ED exibiram maior taxa de fotossíntese por massa (Amassa), menor longevidade foliar (LF) e massa foliar específica (MFE) quando comparadas às sempre verdes. Esses traços foram considerados traços-chaves preditores das estratégias de evitação e tolerância à seca. As ED e ESV apresentaram uma demanda conflitante entre tolerância à seca e taxa fotossintética, pois a LF foi negativamente correlacionada com à Amassa. Embora tenham demonstrado diferenças claras na MFE e LF não observamos diferenças significativas na Aárea e gs, consequentemente, ED e ESV não diferiram na eficiência no uso da água durante o período chuvoso. Apesar da variabilidade substancial dentro do grupo, todas as ED exibem estratégia de evitação à seca enquanto que ESV exibem um conjunto de traços funcionais foliares relacionados a estratégia de tolerância à seca.

We analyzed the functional variation between deciduous and evergreen species to understand the differences across the strategies of avoidance and tolerance to drought. Our study was carried in a fragment of seasonally dry tropical forest located in the city of Pentecoste (3°47‘S, 39°16’W), Ceará, Brazil. We measured 17 functional leaf traits in 17 deciduous and five evergreen species, being 12 morphofunctional, one phenological and four physiological. We found that deciduous species exhibited greater Amass, lower leaf lifespan (LL) and leaf mass per area (LMA) than evergreen species. These traits were considered key predictor traits of avoidance and drought tolerance strategies. Deciduous and evergreen species showed a trade-off between drought tolerance and photosynthetic rate, LL was negatively correlated with Amass. Although we have shown clear differences in LMA and LL not observed significant differences in Aarea and gs, consequently, deciduous species and evergreen species did not find significant differences in WUEi and WUE. Despite substantial variability within the group, all deciduous species fall predominantly in the drought avoidance strategy, while evergreen species display a suite of traits related to drought tolerance.

A presença cada vez mais disseminada de organismos exóticos (muitos dos quais se tornam invasores) nas diferentes regiões do planeta levou ao surgimento de uma linha de pesquisa na ecologia voltada às invasões biológicas. E para permitir a comunicação entre autores também foi desenvolvido um arcabouço terminológico. Mas, apesar disso, a terminologia relativa às bioinvasões tem sido ignorada por boa parte dos botânicos no Brasil. Há uma boa dose de confusão entre botânicos sobre o que seja uma espécie exótica, naturalizada, invasora, daninha e ruderal, levando ao uso inconsistente da terminologia. Além disso, diferentes autores têm adotado posturas praticamente opostas ao lidar com espécies exóticas em suas áreas de estudo, seja na preparação de tratamentos taxonômicos, seja na publicação de levantamentos florísticos e fitossociológicos. Enquanto alguns pesquisadores incluem em floras mesmo espécies cultivadas que não se reproduzem, outros excluem plantas invasoras comuns e conspícuas. Nós apresentamos aqui, em português, os principais conceitos relativos ao tema da bioinvasão e chamamos a atenção dos autores brasileiros para a necessidade de utilizar de modo consistente o arcabouço terminológico já existente na literatura. Também propomos a adoção de rótulos claros para informar quais espécies são exóticas na área estudada, diferenciando-as das nativas, e sugerimos critérios para ajudar botânicos a decidirem quando uma planta exótica deve ou não ser incluída em tratamentos taxonômicos ou levantamentos de florística.

The ever-growing presence of exotic organisms (many of which become invasive) throughout the planet has led to the emergence of biological invasions as a field of study within ecology. To enable communication between scientists in this field, a terminology has developed. However, this terminology has been ignored by many botanists in Brazil where there is confusion regarding definition of exotic, naturalized, invasive, weed and ruderal species, leading to inconsistent use of the concepts. Moreover, different authors have adopted antagonistic positions when dealing with exotic species existing in their study areas, either in the preparation of taxonomic treatments or in floristic and phytosociological surveys. While some authors include in floras cultivated, non reproducing species, others exclude even widespread and common invasives. We present here, in Portuguese, the main concepts related to the theme of bioinvasion and draw the attention of Brazilian authors to the necessity for consistent use of the terminological framework available for biological invasions. We also propose that authors should clearly label exotic plants reported in their work, differentiating exotics from native species. Finally, we suggest criteria to help botanists decide when exotic plants should or should not be included in taxonomic treatments or in floristic surveys.

Recentemente foi proposta a inclusão de fisionomias com Cordia oncocalyx Allemão (Boraginaceae) como um novo tipo/unidade à classificação de caatingas de Andrade-Lima (CFFAL). Porém, nenhum estudo avaliou quantitativamente essa proposta. Este estudo visou descrever a fisionomia e estrutura de uma caatinga com C. oncocalyx comparando-a a outros estudos para verificar diferenças estruturais e fisionômicas. Amostrou-se 1795 indivíduos de 25 espécies, somando uma área basal de 35,26 m². C. oncocalyx e Mimosa caesalpiniifolia Benth. (Fabaceae) representaram 48% do VI total. A fisionomia foi caracterizada pelo predomínio de indivíduos de altura intermediária (3‒4 m) e concentração de área basal nos indivíduos altos (> 8 m). Dentre as cinco espécies com maior valor de importância (VI), apenas uma teve frequência alta dentre as cinco espécies de maior VI de levantamentos compilados (16/35). Desses levantamentos, apenas dois eram comparáveis a este estudo e só um pôde ser classificado conforme a CFFAL, inserindo-se dentre caatingas arbóreas abertas. Nesse caso, a comunidade era densa e dominada por indivíduos finos e baixos, em contraste à caatinga aqui estudada. Os resultados indicam a adequação da inclusão das caatingas com C. oncocalyx dentre caatingas florestais médias e baixas da CFFAL. Porém, o baixo número de estudos comparáveis limita o alcance de generalizações.

Recently, the inclusion of physiognomies with Cordia oncocalyx Allemão (Boraginaceae) as a new type/unit within Andrade-Lima's classification of caatingas (ALFPC) has been proposed. However, no study has quantitatively analyzed this proposal so far. In order to fill this gap, a phytosociological study was conducted in a caatinga with C. oncocalyx, and differences in structure and physiognomy in relation to compiled caatinga studies were verified. 1795 plants from 25 species and a total basal area of 35.26 m² were found. C. oncocalyx and Mimosa caesalpiniifolia Benth. (Fabaceae) had 48% of total importance index (IV). The physiognomy was characterized by the predominance of individuals of intermediate height (3‒4 m) and the tallest ones accounted for the highest fraction of basal area. Of the five species with highest IV, only one had high frequency among the species with highest IV in the compiled studies (16/35). Only two of these compiled studies were comparable to the present study, and only one could be classified according to ALFPC. A contrast between that study and the present one was found, as the first reports a dense community with high number of small diameter individuals accounting for most of the basal area. These findings suggest the suitability of including C. oncocalyx caatingas in low and medium caatinga forests as proposed in ALFPC. However, the low number of comparable studies limits generalizations.

Resumo Para verificar se a composição florística constitui unidades discretas ou contínuas ao longo de um gradiente topográfico foram analisadas três fitofisionomias (caatinga sobre altitudes de 300 a 500 m, floresta decídua sobre altitudes de 500 a 700 m e carrasco sobre atitudes de 700 m) sobre classes de solos distintas no semiárido setentrional do Nordeste do Brasil. Em cada fisionomia foi realizado o levantamento das espécies, as quais foram classificadas em formas de vida e de crescimento. A riqueza de espécies foi maior na floresta decídua (250) do que no carrasco (136) e na caatinga (137). A caatinga apresentou poucas espécies em comum com as fitofisionomias de carrasco ou de floresta decídua (6 e 18 espécies). A maior sobreposição de espécies ocorreu entre a floresta decídua e o carrasco, 62 espécies. Foram exclusivas da caatinga, floresta decídua e do carrasco, 104, 161 e 59 espécies, respectivamente. Quanto às formas de crescimento, nas fisionomias sobre relevo sedimentar com Latossolo e Arenosolo predominaram espécies lenhosas: 124 na floresta decídua e 68 no carrasco. Na caatinga sobre relevo do embasamento cristalino com predominância de Planossolo, a maior riqueza de espécies (69) foi de ervas. Na análise comparativa do espectro biológico com outras formações brasileiras, o de caatinga se destacou dos demais, constituindo uma unidade individualizada pela maior proporção de terófitos e caméfitos. Em relação à flora das três fisionomias, objeto deste estudo, pode-se afirmar que a da caatinga representa uma unidade discreta.

Abstract To test whether the flora is organized in discrete or continuous units along a topographic gradient, three physiognomies were assessed on different soil classes in a semi-arid region of northeastern Brazil: caatinga (xeric shrubland) at altitudes from 300 to 500 m, deciduous forest at altitudes from 500 to 700 m and carrasco (deciduous shrubland) at 700 m. In each physiognomy a species inventory was carried out, and plants were classified according to life- and growth-forms. Species richness was higher in the deciduous forest (250) than in the carrasco (136) and caatinga (137). The caatinga shared only a few species with the carrasco (6 species) and the deciduous forest (18 species). The highest species overlap was between the deciduous forest and the carrasco (62 species). One hundred and four species occurred only in the caatinga, 161 only in the deciduous forest and 59 only in the carrasco. Woody species predominated in physiognomies on sedimentary soils with latosol and arenosol: 124 species occurred in the deciduous forest and 68 in the carrasco. In the caatinga on crystalline basement relief with predominance of planosol, herbs showed the highest species richness (69). Comparing the biological spectrum of Brazilian plant life-forms, the caatinga stood out with higher proportion of therophytes and chamaephytes. Considering the flora of the three phytophysiognomies studied here, we can affirm that the caatinga is a discrete floristic unit.

Resumo O crescimento urbano promove redução na cobertura vegetal, introdução de espécies exóticas e tem sérias implicações na conservação biológica. Um fragmento com vegetação savânica (24 ha - 3º47'55"S e 38º29'10"W) localizado na zona urbana de Fortaleza, Ceará, teve sua flora amostrada por coletas assistemáticas e teve um hectare inventariado em um estudo fitossociológico. Para a listagem florística foram coletadas espécies de todas as formas de crescimento presentes no fragmento. Para a descrição da estrutura da vegetação foram alocadas de forma aleatória oito transeções de 5 ´ 250 m totalizando 1ha, nas quais foram medidos os perímetros e altura dos indivíduos lenhosos com perímetro no nível do solo (PNS) maior ou igual a 9 cm. Foram coletadas 151 espécies (138 indígenas e 13 exóticas) no levantamento florístico e 37 (35 indígenas) no levantamento fitossociológico. A densidade e a área basal total da comunidade foram, respectivamente, 1218 ind/ha e 7,34 m2/ha e a altura e diâmetro médios foram, respectivamente, 2,53 ± 1,29 m e 6,68 ± 5,67 cm, o que enquadra a área estudada dentro da amplitude de variações encontradas em áreas de cerrado sensu stricto e campo cerrado. Os resultados alcançados incrementam as poucas informações sobre as savanas costeiras do nordeste.

Abstract Urban growth promotes reduction in the vegetation cover, introduction of exotic species and has serious implications for biological conservation. In the urban area of Fortaleza, Ceará state, a vegetation fragment with savannic physiognomy (24 ha - 3º47'55"S and 38º29'10"W) was sampled for a floristic survey and had 1 ha subjected to a phytosociological inventory. The floristic list of the fragment, considered a priority area for municipal conservation, is showed here. Phytosociological data have also been sampled, providing more information about the savannas from the Brazilian's Northeast coast. For the floristic list, species from all growth forms present in the fragment were collected. For the description of the structure of the vegetation, we assigned randomly eight transects with 5 × 250 m (1ha in total) in which the perimeters at ground level (PNS) and the total height of individual plants were measured for all woody plants with PNS greater than or equal to 9 cm. In the floristic survey we collected 151 species (138 indigenous and 13 exotic) and in the phytosociological study, 37 species (35 native). The density and basal coverage of the community were 1218 ind/ha and 7.34 m2/ha, respectively. The average height and average diameter were respectively 2.53 ± 1.29 m and 6.68 ± 5.67 cm. Although our study site is geographically out of the Cerrado domain, it has structural variables compatible with the ones observed within the range of variations found in other Cerrado areas.

Resumo O semi-árido brasileiro é dominado pela caatinga. Entretanto, outras formações vegetacionais são encontradas, por exemplo, as florestas decíduas e semidecíduas. Este estudo descreve a fisionomia e a estrutura de uma floresta estacional no planalto sedimentar da Ibiapaba, Ceará. Foi selecionada uma parcela de um hectare e as plantas separadas em três componentes: plantas lenhosas com perímetro ao nível do solo ≥ 9 cm (CLS), plantas lenhosas com perímetro ≥ 3 e ≤ 8.9 cm (CLI), e herbáceas/sublenhosas com perímetro < 3 cm (HSL). No CLS foram encontradas 88 espécies (33 famílias), no CLI 50 espécies (23 famílias) e no HSL sete espécies (cinco famílias). No CLS, densidade total, área basal e altura máxima e média foram 5683 plantas/ha, 47 m2/ha, 18 e 5 m, respectivamente. No CLI, densidade e área basal foram 17500 plantas/ha e 2,8 m2/ha. Em HSL, a densidade foi 9 plantas/m2 e apenas 31% da área amostrada foi coberta por esse componente.

Abstract The Brazilian semiarid region is dominated by caatinga. However, other vegetation formations occur, including deciduous and semi-deciduous forests. This study describes physiognomy and structure of a forest on the sedimentary Ibiapaba plateau. All plants within one hectare were separated into three components: woody plants with perimeter at soil level (PSL) ≥ 9 cm (WCLP), woody plants with PSL ≥ 3 and ≤ 8.9 cm (WCSP), and herb/subwoody plants (HSwC). WCLP included 88 species (33 families), WCSP 50 species (23 families) and HSwC only 7 species (5 families). Total density, basal area, and maximum and average height of WCLP were 5683 plants/ha, 47 m2/ha, 18 and 5 m respectively. Total density and basal area of WCSP were 17500 plants/ha and 2.8 m2/ha, respectively. Density of HSwC was 9 plants/m2 and only 31% of the sampled area was occupied by this component.

No domínio semi-árido brasileiro, a flora das bacias sedimentares ainda é pouco conhecida, mas os levantamentos já existentes indicam que há grande heterogeneidade florística e fisionômica. Mesmo áreas geográficas próximas podem apresentar dissimilaridade florística. Visando testar esta hipótese, a composição florística e o espectro biológico da floresta estacional decídua de Serra das Almas, estado do Ceará, foram analisados e comparados com os de 14 áreas sedimentares no Nordeste. Foram encontradas 104 espécies e 39 famílias em 1 ha analisado. Fabaceae, Euphorbiaceae, Erythroxylaceae e Myrtaceae foram as famílias com maior riqueza e fanerófitos a forma de vida predominante (87%). Arbóreas e arbustivas representaram 72% das espécies, trepadeiras 15%, subarbustos 6% e herbáceas 7%. A análise de agrupamento da composição dos fanerófitos, usando o índice de Jaccard e as médias de grupo a posteriori, indicou a formação de grupos florísticos entre áreas geográficas mais próximas. Porém, não foi significativo pelo teste de Mantel, o que demonstra a ocorrência de alta heterogeneidade florística mesmo entre áreas geográficas próximas. A flora da floresta da Serra das Almas apresentou maior semelhança com as formações encontradas no planalto da Ibiapaba.

In the Brazilian semi-arid region, the flora in the sedimentary basins has been poorly studied, but the few surveys already done indicate great floristic and physiognomic heterogeneity. Even neighboring sites may be floristically different. To test this hypothesis, the floristic composition and the biological spectrum of the seasonal deciduous forest at Serra das Almas, Ceará, was analyzed and compared to those of 14 other northeastern Brazil sedimentary areas. A total of 104 species belonging to 40 families were found at the 1 ha site. Fabaceae, Euphorbiaceae, Erythroxylaceae and Myrtaceae were the families with the most species and phanerophytes the main life form, comprising 87% of the species. About 72% of the species were trees and shrubs, 15% were lianas, 6% understory shrubs and 7% herbs. A cluster analysis of the woody flora of the 14 areas, using the Jaccard index and a posteriori group averages, indicated the formation of groups as a function of geographical proximity of the areas. However, this effect was not significant, according to the Mantel test, demonstrating floristic heterogeneity even in neighboring areas. The flora of the forest at Serra das Almas was most similar to that of the vegetation found atop the Ibiapaba plateau.