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Understanding the impacts caused by invasive plant species, especially in regions where studies are scarce, is of great importance to the development of management and conservation strategies. Amongst the biomes present in Brazil, the Caatinga (Dry Tropical Forest) stands out for having had few studies dealing with biological invasions by plants and animals. An evaluation of scientific production can provide a means by which the progress of invasion-related studies can be assessed, as well as identify research gaps and provide a broad overview of the importance of invasions in this biome. Thus, the objective of this study was to perform a scientometric analysis to evaluate the development of scientific research over the years on exotic and invasive plant species in the Caatinga. We found 46 papers dealing with invasive plants in the Caatinga published over a 14-year period. The main objectives of most of the papers focused on identifying the main strategies used by plants in the process of invasion and characterising the invaded environment. A total of 28 species were cited as invasive for the Caatinga, with Prosopis juliflora (Sw.) DC., Cryptostegia madagascariensis Bojer, Calotropis procera (Aiton) W.T.Aiton and Parkinsonia aculeata L. being the most cited species. Although studies on the subject are incipient, there is already important information about the dynamics of the invasiveness of plant species in the Caatinga, which can serve as a basis for new studies, as well as for the development of management policies, based on consistent information. Biological invasion, dry forest, exotic species, northeast Brazil, scientometry, semi-arid

Unlike well-known global patterns of plant species richness along altitudinal gradients, in the mountainous areas of the Brazilian Caatinga, species richness and diversity reach their maxima near mountain tops. The causes of this unusual pattern are not well understood, and in particular the role of edaphic factors on plant community assembly along these gradients has not been investigated. Our goal was to assess the role of edaphic factors (fertility and soil texture) on plant community composition and structure on two mountains of the Brazilian semi-arid region. In 71 plots (Bodocongó site, twenty-one 200-m2 plots, 401–680 m asl; Arara site, fifty 100-m2 plots, 487–660 m asl) we recorded 3114 individuals representing 61 plant species; in addition, at each plot we collected composite soil samples from 0–20 cm depth. Significant altitude-related changes were observed both for community structure and composition, and edaphic variables. A canonical correspondence analysis allowed the distinction of two groups of plots according to species abundances, indicating a preferential habitat distribution of species depending both on altitude and soil variables. Although soil fertility was lowest at the highest altitudes, these areas had high richness and diversity. Conversely, the more fertile foothills were characterized by the dominance of generalist pioneer species. Despite the relatively short altitudinal range that characterizes the studied mountains, this study elucidates the role of edaphic factors on the floristic composition and species richness patterns on the mountains of the Brazilian semi-arid region.

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The Cactacea family comprises 128 genera and 1450 species with predominantly neotropical distribution. Cacti are commonly found in arid and semi-arid regions and have great ecological relevance due to their interactions with animals and other groups of plants. Abiotic interactions, such as topography, altitude, rainfall, temperature and soils, also influence the composition and distribution of cacti. The objective of the present study was to assess patterns of species composition and distribution for cacti along an elevation gradient in Brazilian Caatinga vegetation. Four transects (composed by 25 plots of 100 m² each) were established at each of two mountain sites. The topographic variables of elevation, slope, rockiness and soil depth were evaluated to determine if they affect the distribution of richness and abundance of cacti along the elevation gradient using Spearman's (rs) correlation coefficient. A total of 554 individuals of five cacti species (Pilosocereus gounellei, Pilosocereus pachycladus, Tacinga palmadora, Tacinga inamoena and Melocactus zehntneri) were sampled. Cacti richness and abundance were found to be negatively correlated with elevation, slope and rockiness, and positively correlated with soil depth (p<0.05). All species exhibited aggregate spatial distribution patterns, which may be related to different environmental conditions produced by interactions among topographic variables (slopes, rockiness and soil depth), that synergistically influence the patterns of species richness and abundance along the elevation gradient.

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Texture, base saturation, organic carbon content, and water storage availability of soil are drivers of plant physiognomy and composition of communities. Soil properties in ecotone areas are still poorly studied, and the transition between dry, moist, and semideciduous forests is defined only by climate parameters. The objective of this study was to describe the soil properties of a moist-dry forest ecotone in Northeastern Brazil. Seven soil profiles were dug in a pristine semideciduous forest known as “Agreste”. Four more pedons were described to represent soils of dry forests. Morphology, reactivity, texture, organic matter content, and water storage capacity of the soil horizons were determined. The soils of the study area are derived from granites and granitoids, rocks highly resistant to weathering. Soils of dry forests are loam, neutral to alkaline, and hypereutrophic. Soils of semideciduous forest are sandy, acidic, dystrophic, and have up to 65% higher C content. The rocks act as impermeable layers to water, and consequently, most soils develop stagnic properties in semideciduous forests. Soils are dystrophy and have low CEC and loam texture. These properties are attributed to ferrolysis. Umbrisols and Stagnosols with higher water storage capacity than dry forests soils sustain semideciduous forests in Northeastern Brazil.

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