Giants of the Amazon: How does environmental variation drive the diversity patterns of large trees?

For more than three decades, major efforts in sampling and analyzing tree diversity in South America have focused almost exclusively on trees with stems of at least 10 and 2.5 cm diameter, showing highest species diversity in the wetter western and northern Amazon forests. By contrast, little attention has been paid to patterns and drivers of diversity in the largest canopy and emergent trees, which is surprising given these have dominant ecological functions. Here, we use a machine learning approach to quantify the importance of environmental factors and apply it to generate spatial predictions of the species diversity of all trees (dbh ≥ 10 cm) and for very large trees (dbh ≥ 70 cm) using data from 243 forest plots (108,450 trees and 2832 species) distributed across different forest types and biogeographic regions of the Brazilian Amazon. The diversity of large trees and of all trees was significantly associated with three environmental factors, but in contrasting ways across regions and forest types. Environmental variables associated with disturbances, for example, the lightning flash rate and wind speed, as well as the fraction of photosynthetically active radiation, tend to govern the diversity of large trees. Upland rainforests in the Guiana Shield and Roraima regions had a high diversity of large trees. By contrast, variables associated with resources tend to govern tree diversity in general. Places such as the province of Imeri and the northern portion of the province of Madeira stand out for their high diversity of species in general. Climatic and topographic stability and functional adaptation mechanisms promote ideal conditions for species diversity. Finally, we mapped general patterns of tree species diversity in the Brazilian Amazon, which differ substantially depending on size class.

Viabilidade e longevidade de sementes de Tabebuia aurea Benth. & Hook. submetidas a diferentes métodos de armazenamento / Viability and longevity of seeds Tabebuia aurea Benth. & Hook. under different storage methods

As sementes de Tabebuia aurea (sin. Handroanthus aureus Mattos), apresentam baixas taxas metabólicas, o que favorece o seu armazenamento em condições de temperaturas negativas e quando armazenadas em temperatura ambiente, há uma progressiva queda em sua viabilidade. Portanto, o objetivo é verificar a viabilidade e longevidade das sementes de Tabebuia aurea submetidas a diferentes métodos de armazenamento. Foram utilizadas no experimento 6100 sementes. Em geladeira foram armazenadas 2400 sementes, das quais 1200 foram acondicionadas em saco plástico transparente e 1200 em saco de papel Kraft. Outras 3600 sementes foram acondicionadas em temperatura ambiente, sendo 1200 sementes em saco plástico transparente, 1200 em saco de papel Kraft e 1200 em bandeja aberta. Para cada tratamento foram utilizadas quatro repetições de 25 sementes, por 12 meses, com delineamento inteiramente casualizado. As médias de germinação, plântulas normais e índice de velocidade de germinação foram transformados em (x +1)-1/2. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5%. Também foram modeladas regressões polinomiais para as variáveis estudas em função dos períodos de armazenamento das sementes. As sementes armazenadas em geladeira à 13 ºC mantiveram elevada germinação, plântulas normais e índice de velocidade de germinação durante os 360 dias de avaliação. O método indicado para o armazenamento de sementes de Tabebuia aurea é em geladeira, à 13 ºC, tanto em saco plástico quanto de papel.

Seeds Tabebuia aurea (syn. Handroanthus aureus Mattos), The seeds of Tabebuia aurea (syn. Handroanthus Mattos aureus), have low metabolic rates, which favors their storage conditions and freezing temperatures when stored at room temperature, there is a progressive decline in viability. Therefore, this study aims to determine the viability and longevity of seeds of Tabebuia aurea subjected to different storage methods. There were used 6100 seeds. In 2400 seeds were stored refrigerator, which in 1200 placed in transparent plastic bag and 1200 in Kraft paper bags. 3600 Other seeds were placed in room temperature and 1200 seeds in clear plastic bag, 1200 in Kraft paper bags and tray open in 1200. For each treatment, four replicates of 25 seeds for 12 months, with design was completely randomized. The average germination, normal seedlings and speed germination index were transformed into (x+1)-1/2. The data were submitted to ANOVA and means compared by Tukey test at 5%. Also regressions polynomials were modeled for the variables study in function of the periods of storage of the seeds. The seeds stored in the refrigerator at 13 °C maintained a high germination rate and normal seedling germination rate during the 360 days of evaluation. The method suitable for the seed storage of Tabebuia aurea is in the refrigerator at 13 °C, both in plastic and paper.

Trioecy in Coccoloba cereifera Schwacke (Polygonaceae), a narrow endemic and threatened tropical species

Trioecy, the co-occurrence of the males, females, and hermaphrodite morphs in natural populations, is a rare and poorly studied breeding system. It is expressed in Coccoloba cereifera, an endemic, and endangered species from the rupestrian fields of Serra do Cipó, southeastern Brazil. Male individuals produce staminate flowers but no fruits. Female individuals produce pistillate flowers and set fruits. Both staminate and pistillate flowers present non-functional organs of the opposite sex that simulate perfect flowers. Hermaphrodite individuals produce two different perfect flowers, each one belonging to distinct individuals, and set fruits. Perfect flowers differ in the amount of pollen produced, in pollen viability, and in some morphological traits. Two Hymenoptera species visited the flowers sporadically. The low natural fructification indicated a limited pollination, while the fruit set recorded in bagged pistillate flowers indicated agamospermy. Female individuals represent more than 40 percent of the population studied and must be the result of agamospermic seeds.

A trioicia, a coocorrência, em população natural, de indivíduos masculinos, femininos e hermafroditas, é um sistema reprodutivo raro e pouco estudado. Coccoloba cereifera (Polygonaceae), espécie endêmica e em perigo de extinção dos campos rupestres da Serra do Cipó, sudeste brasileiro, apresenta esse sistema. Indivíduos masculinos produzem flores estaminadas e não frutificam. Indivíduos femininos produzem flores pistiladas e frutificam. Ambas flores estaminadas e pistiladas apresentam órgãos não-funcionais do sexo oposto, tornando-as semelhantes às flores perfeitas. Indivíduos hermafroditas produzem dois tipos de flores perfeitas, cada um pertencente a indivíduos distintos, e ambos frutificam. As flores perfeitas diferem entre si na quantidade de pólen produzido, na viabilidade do pólen e em algumas características morfológicas. Duas espécies de Hymenoptera visitaram as flores esporadicamente. A baixa frutificação natural indicou uma polinização limitada, ao passo que a frutificação registrada em flores pistiladas, isoladas por sacos, indicou agamospermia. Indivíduos femininos representaram mais que 40 por cento da população estudada e devem ser resultantes de sementes agamospérmicas.