Everardo Valadares de Sá Barretto Sampaio

Nutrient and soil organic matter dynamics under shifting cultivation in semi-arid northeastern Brazil

Abstract In subsistence farming systems using shifting cultivation, crop production depends on the natural fertility of the soil and depletion of fertility during cultivation is the cause for land abandonment. During the subsequent bush fallow, fertility levels are improved and the land may be available for further cultivation cycles. In the present study, the effects of cultivation and the regrowth of bush fallow on soil organic matter and phosphorus fertility were evaluated, using adjacent plots with different histories of cultivation and lengths of bush fallow in semi-arid northeastern Brazil. Six years of cultivation with minimal fertilisation resulted in reductions of C, N and organic P by 30%, or about 10 t ha −1 of C. Available N and P were greatly reduced under these conditions. In a fertilised and limed field, this trend was to some extent avoided, but such inputs are usually not an option for local farmers. Eight to 10 years of bush fallow were sufficient to re-establish fertility levels similar to the original uncultivated site. Phosphorus fractionation indicated that the decline in P fertility was not a result of net export of P in the crop, but arises from the mineralisation of organic P and subsequent transformation of the surplus inorganic P to unavailable forms.

Florística e fitossociologia de um remanescente de vegetação caducifólia espinhosa arbórea em Caruaru, Pernambuco

The Deciduous Thorny Vegetation (DTV) that covers the semi-arid area of Northeastern Brazil, called caatinga, is highly diversified as a function of its climatic and morphopedological characteristics. Since little is known of its characteristics in the border of its distribution, as in the Agreste region on the Borborema plateau, a floristic and phytosociological survey was conducted in an area at Caruaru, Pernambuco. All plants > 1m high e > 3cm of stem diameter within 36 plots, 10 × 10m each, had their height and diameter measured. A total of 96 species, belonging to 41 families were found in the area, of which 55 species were included in the phytosociological survey. Most of them are also found in the dry core of the Northeastern semi-arid region, but a few of them occur in places with higher water availability. Total density (3,810 plant ha-1) and basal area (24.9m2 ha-1) and stem diameter distribution were within the range found in other DTV areas but the number of plants taller than 8 m was higher, almost double the previous highest value. The most important species were the same found in other DTV areas but different from those of regional Montane Forests (MF), Deciduous Non Thorny Vegetation (DNTV) and Humid Lowland Forests (HLF), in Northeast. In a cluster analysis, based on flora, HLF formed a separate group and in the other group DTV and MF were more similar than DNTV. Structurally, DTV has less small plants than both MF and DNTV and less large plants than MF but more than DNTV. The vegetation in the Agreste at Caruaru is an arboreal DTV, with tall plants and the presence of a few species more common in more humid areas than the dry core of the Northeast.

Flora e estrutura da vegetação arbustivo-arbórea de uma área de caatinga do Seridó, RN, Brasil

ABSTRACT – (Flora and structure of the tree and shrub vegetation of the caatinga at Serido, Rio Grande do Norte State, Brazil). Aphytosociological survey was conducted at one area belonging to the Serido Ecological Station to test the hypothesis that the vegetationat the Serido region is open and low. All woody plants with stem perimeter at breast height ≥3 cm were counted, within 100 plots,10×10€m, and each one had its height, stem perimeter, and crown projection diameters measured, and its aboveground biomass estimated.Fifteen species were found, belonging to 15 genera and 10 families, with a Shannon diversity index of 1,94 . These values are below thoseof most of caatinga places elsewhere. Mimosoideae was the family with most species (three). All structural variables, except density,(3,250 plant ha -1 , basal area 6.1 m 2 ha , maximum height 9.5 m, maximum stem diameter 37 cm, total crown area 8,723 m 2 ha -1 , biomass25 mg ha -1 ) had lower values than caatinga elsewhere. Aspidosperma pyrifolium

Composição florística e análise fitossociológica do componente arbustivo-arbóreo de um remanescente florestal no Agreste Paraibano

A floristic and phytosociological survey was conducted in a caatinga area in the Agreste (sub-humid) region of Paraiba state. All trees and shrubs ³ taller than 1m and larger than ³ 3cm stem diameter found in 30 plots, 10x20m each, were identified and measured. Standing dead plants were also included. A total of 1952 plants were registered, belonging to 22 families, 38 genera and 54 species. Families with most species were Mimosaceae (6 species), Euphorbiaceae (6), Caesalpiniaceae (5), and Rubiaceae (5). Total plant density and stem basal area were 3253 plant ha-1 and 34.77m2 ha-1. Maximum diameter and height were 63cm and 15m. About half of the plants (45.7%) had a stem diameter between 3 and 6cm. Thiloa glaucocarpa (Mart.) Eichl. was the most important species (highest IVI value). The flora included mostly species already registered in other caatinga areas but also species which are typical from more mesic formations, specially the humid forests of high altitudes in Northeast Brazil.

Biomass equations for Brazilian semiarid caatinga plants

Equacoes alometricas foram desenvolvidas para estimar a biomassa aerea viva (B) e a area de projecao da copa (C) de dez especies da caatinga, com base na altura da planta (H) e/ou do diâmetro do caule ao nivel do solo (DNS) ou a altura do peito (DAP). Trinta plantas de cada especie, cobrindo a faixa usual de diâmetros (3 a 50 cm), foram medidas (C, H, DNS, DAP), cortadas na base, separadas em partes, pesadas e subamostradas para determinacao da biomassa seca. A densidade (p) da madeira dos caules e galhos maiores foi determinada. B, C, H e p variaram de 1 a 500 kg, 0,2 a 112 m2, 1,3 a 11,8 m e 0,45 a 1,03 g cm-3. A biomassa das 10 especies, separadamente ou em conjunto (exceto pela especie de Cactaceae), foi estimada com alto coeficiente de determinacao (R2), usando a equacao de potencia (B = aDNSb) e DNS, DAP ou combinacoes de diâmetro, altura e densidade. A melhora com a multiplicacao de DNS ou DAP por H e/ou p foi pequena. A equacao de DAP (valida ate 30 cm) para o conjunto das nove especies teve a = 0,173 e b = 2,295, semelhantes aos valores das medias das equacoes encontradas na literatura, mas um pouco abaixo dos referidos para vegetacao tropical umida. A projecao das copas foi significativamente relacionada com diâmetros do caule, alturas e biomassas.

Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

Our review focuses on the projections of climate change in the Brazilian semiarid region, the Caatinga, based on recent publications about global climate change and biology. We found several vulnerable points in the initial estimates, the main one being that the data were collected and analyzed without a multidisciplinary knowledge. This review discusses several studies that show the current knowledge in many semiarid regions around the world. Some of these studies argue for the increase in vegetation greenness responses even under severe and prolonged drought, based on the high resilience the Caatinga native species show under severe drought conditions over the years. Additionally, we include in this review recent data produced by our group on key ecophysiological variables under drought conditions. We also show successful examples of deforested areas recovery in the semiarid region of the Central America. It is critical that the recovery of semiarid areas is coupled with the implementation of socio-environmental policies, engaging the local population and providing subsidies for life wealth improvement. These are key aspects for a long-term recovery and conservation of the Brazilian dry tropical forest.

Nutrient availability in soil samples from shifting cultivation sites in the semi-arid Caatinga of NE Brazil

Abstract Soil fertility differed substantially among three neighboring sites representing different stages of a shifting cultivation cycle on a deeply weathered Oxisol on the Chapada de Araripe in the semiarid region of NE Brazil. Samples taken from a native thorn forest area (Caatinga), from a recently slashed and burnt area (Burnt) and from a site abandoned after five years of manual cultivation to cassava (Abandoned), were compared using subtractive and additive fertilization greenhouse trials and incubations for C and N mineralization. The effect of burning was to increase soil nutrient content relative to the Caatinga area samples, followed by decreases of N and organic P by 20%, available P by 70%, and exchangeable bases by 55%, on average, after abandonment. The unfertilized control of the missing-element trial gave the lowest dry matter (DM) yields, but still those of the Burnt were twice as large as those of the Abandoned area samples. The relative yield ratios were not changed by nutrient addition, although total yields were increased by a factor of 5. In all three areas, the most severe nutrient limitation was of P, followed by N. The N deficiency somewhat increased relative to P in the Abandoned samples. Addition of 25 mg P kg−1 soil produced 4 to 5-fold dry matter increases in the Caatinga and 7 to 8-fold increases in the Burnt area samples. Further increasing P levels improved yields only marginally and only at high additions of N and K. In samples from the abandoned area, 25 mg P kg−1 not even doubled the dry matter yield, and no additional effects were observed for higher N and K rates. Carbon mineralization during the 12 week incubation followed the order Caatinga > Abandoned > Burnt, whereas the order for N removed in 13 leachings was Caatinga > Burnt > Abandoned. Accordingly, organic matter mineralized from the abandoned soil had a higher C:N ratio. In addition to the nutrient limitations of this Oxisol, samples from the Abandoned area exhibited further limitations resulting in yield reductions, which were not explained by any of the factors examined. This indicates that alternatives to long-fallow shifting cultivation will require further refinement of methodologies to measure and predict soil quality.

Diversidade de herbáceas em microhabitats rochoso, plano e ciliar em uma área de caatinga, Caruaru, PE, Brasil

Objetivou-se avaliar a influencia da heterogeneidade micro-espacial no aumento da fitodiversidade herbacea em uma area de caatinga de Caruaru, Pernambuco, Brasil. Microhabitats rochosos, planos e ciliares foram selecionados, e nesses foi realizado um levantamento quali-quantitativo das herbaceas ocorrentes em 35 parcelas de 1 m2, em cada microhabitat. Todas as ervas nas parcelas foram contadas, marcadas e identificadas, coletando-se tambem outras especies herbaceas ocorrentes entre as parcelas. A riqueza taxonomica total de herbaceas foi mais elevada ao se considerar o conjunto dos microhabitats. A flora total foi de 62 especies, 42 destas ocorrendo no microhabitat rochoso, 32 no plano e 39 no ciliar. O indice de similaridade floristica de Jaccard entre os microhabitats variou de 42% (plano × ciliar) a 57% (rochoso × plano). Isoladamente, as riquezas de especies nos microhabitats plano, rochoso e ciliar foram de 3,09; 3,88 e de 4,18 especies (ln ind.)-1 e as diversidades, pelo indice de Shannon-Wiener, foram de 2,08; 2,09 e de 2,52 nats.ind.-1, respectivamente. Malvaceae, Euphorbiaceae e Poaceae apresentaram maior numero de especies. A densidade total de herbaceas foi de 4.009 ind.105 m-2, sendo 1.749 individuos do microhabitat rochoso, 1.020 do ciliar e 1.240 do plano. Cerca de 19% das especies eram trepadeiras e foram consideradas como um grupo importante para conservacao da biodiversidade local. Evidenciou-se a importância da inclusao das herbaceas dos diferentes microhabitats, para a determinacao da riqueza floristica da caatinga.

A model of litterfall, litter layer losses and mass transfer in a humid tropical forest at Pernambuco, Brazil

Data on litterfall, litter layers accumulated on top of the mineral soil and layer mineralization collected for three years in a tropical rain forest at Pernambuco, Brazil, were implemented on a simulation model. Litterfall was collected biweekly using 11 collectors 1 × 1 m. Every three months, 20 litter mat samples, 0.5 × 0.5 m, were collected, divided into the L, F and H layers and the CO 2 evolution from each litter layer was determined in the laboratory. Litterfall, in the three years, averaged 7.8, 8.3 and 8.2 Mg ha -1 y -1 , most of it leaves. Litter mat masses varied widely from place to place (15–90 Mg ha -1 ) and the overall averages were 5.6, 7.6 and 26.1 Mg ha -1 for the L, F and H layers, with CO 2 evolution averages of 2.27, 0.507 and 0.123 mgC g litter C -1 day -1 . According to the model, the L layer had a high turnover rate, losing 4.7 Mg ha -1 y -1 through mineralization and 3.4 Mg ha -1 y -1 transferred to the F layer. Values for the F and H layers were 1.4 and 1.2 mineralized and 2.0 and 0.8 Mg ha -1 y -1 transferred. Thus, it would take 2.1, 6.7 and 39 years for newly fallen leaves to be mostly fragments, to be transformed to humus and to be incorporated to the soil organic matter, respectively. Variations of litterfall throughout the three years would have little effect on the system which was not very sensitive to litterfall changes, except for the top layer.

Water budget in a soil with food crops in the semi-arid region of northeast Brazil.

Considering that water is a limiting factor and there are few studies on water balance in the semi-arid Northeastern Brazil, an experiment was established at Coxixola, PB, Brazil, with four treatments (corn and beans crops, bare soil and soil covered with mulch), in plots of 7.7 x 10 m and plant spacing of 1.1 x 1.0 m. Rainfall, evaporation (Class A tank) and soil water (neutron probe) were monitored. Low (212 mm) and irregular rainfall resulted in water deficit towards the final period of the experiment and was responsible for the low water use efficiencies and low productivity of corn (grain and total biomass, 282 and 1141 kg ha-1) and beans (166 and 558 kg ha-1). Bare soil and mulch had similar results, with high water losses, 1.57 and 1.48 mm day-1, respectively, and only small increases in stored soil water (28 and 35 mm, respectively) were observed at the end of experiment. Mulching does not seem to be a promising practice in the area due to this small increase and the difficulty in obtaining plant residues.