Estudio del crecimiento de Prioria copaifera (Caesalpinaceae) mediante técnicas dendrocronológicas

A growth study of Prioria copaifera (Caesalpinaceae) using dendrochronological techniques. The Cativo (Prioria copaifera) forms very homogeneous forests called cativales in the flooded plains of some rivers from Costa Rica to Colombia. For over 70 years Cativo has been the main base of the timber industry in the Colombian Darien area. Because of high productivity and high-dominance of Cativo trees, they represent one of the most prone tropical forests for sustainable forest management. The objective of this research is to model diameter and timber volume growth and growth rates (absolute, mean and relative) of Cativo as a function of age, using tree ring data derived from dendrochronologycal techniques. We evaluated the annual nature of the tree rings by radiocarbon analysis and crossdating techniques. Besides, the diameter and volume growth was modeled using von Bertalanffy’s model. As of our results, we estimated the life span of Cativo in 614 years as the time required to reach 99% of the asymptotic diameter. By the mean value we have found that the mean rate of diameter growth is 0.31cm/y. The species requires 90 years to reach 40cm in diameter, the regulated cut diameter in Colombia. We find that Cativo reaches maximum current annual increment (ICA) in diameter at 40 years and in volume at 90 years with rates of 0.5cm/y and 0.032m3/y per tree, respectively. The maximum diameter mean annual increments (MAI) are achieved at 80 years and for the volume at 140 year, with growth rates of 0.45cm/y and 0.018m3/y per tree, respectively. The generated information is useful for the sustainable management of Cativo forests. Rev. Biol. Trop. 59 (4): 1813-1831. Epub 2011 December 01.

El cativo (Prioria copaifera G.) forma bosques dominados por la especie llamados cativales. Durante más de 70 años el cativo ha sido la base principal de la industria maderera en el Darién colombiano, siendo, por su alta productividad y dominancia uno de los bosques tropicales más fáciles de ordenar sosteniblemente. El propósito de esta investigación es modelar el crecimiento del diámetro y el volumen del cativo en función de la edad así como las tasas instantáneas, medias y relativas, empleando anillos de crecimiento. La anualidad de los anillos se demostró usando el efecto de las bombas nucleares y mediante cofechado. Con base en los anillos de crecimiento radiales se modelo el crecimiento del diámetro y del volumen. Esta especie alcanza 40cm de diámetro en 90 años y presenta crecimiento medio de 0.31cm/año. El lapso vital de la especie es de aproximadamente 614 años. El incremento corriente anual máximo del volumen a los 90 años es 0.033m3/año, e iguala al incremento medio a los 145 años con 0.018m3/año. La tasa media de crecimiento absoluta es 0.021m3/año. Los resultados aquí obtenidos sirven como base técnica para el manejo sostenible de los cativales.

Paleoclima de La Guajira, Colombia; según los anillos de crecimiento de Capparis odoratissima (Capparidaceae)

Paleoclimate of La Guajira, Colombia; by the growth rings of Capparis odoratissima (Capparidaceae). There is great concern about the effect of climate change in arid and subarid areas of the tropics. Climate change combined with other anthropogenic activities such as deforestation, fires and overgrazing can accelerate their degradation and, consequently, the increases in losses of biological and economic productivity. Climate models, both local and global, predict that rainfall in the arid Peninsula of La Guajira in the Colombian Caribbean would be reduced and temperature would be increased as a result of climate change. However, as there are only suitable climate records since 1972, it is not possible to verify if, indeed, this is happening. To try to verify the hypothesis of reducing rainfall and rising temperatures we developed a growth ring chronology of Capparis odoratissima in the Middle Peninsula of La Guajira with 17 trees and 45 series which attain 48 years back. We use standard dendrochronological methods that showed statistically significant linear relationship with local climatic variables such as air temperature, sea surface temperature (SST), annual precipitation and wind speed; we also reach to successful relationship of the chronology with global climatic variables as the indices SOI and MEI of the ENSO phenomenon. The transfer functions estimated with the time series (1955 and 2003) do not showed statistically significant trends, indicating that during this period of time the annual precipitation or temperatures have not changed. The annual nature of C. odoratissima growth rings, the possibility of cross-dated among the samples of this species, and the high correlation with local and global climatic variables indicate a high potential of this species for dendrochronological studies in this part of the American continent. Rev. Biol. Trop. 59 (3): 1389-1405. Epub 2011 September 01.

gran preocupación por el efecto del cambio climático en las regiones áridas y semi-áridas tropicales. Los modelos climáticos tanto locales como globales predicen que la precipitación pluvial de la árida Península de La Guajira en el Caribe colombiano se reduciría, y las temperaturas tanto del aire como superficial del mar aumentarían como consecuencia del cambio climático. Para tratar de verificar estas hipótesis construimos una cronología del ancho de los anillos de crecimiento de Capparis odoratissima en la Media Península de La Guajira. La cronología mostró relaciones lineales estadísticamente significativas con las variables climáticas locales: temperatura del aire, temperatura superficial del mar (TSM), precipitación anual, velocidad del viento y variables climáticas del fenómeno ENSO (índices SOI y MEI). Las series de tiempo que calculamos mediante la función de transferencia entre 1955 y 2003, no mostraron tendencias estadísticamente significativas que demostraran que en ese período de tiempo la precipitación anual o las temperaturas han cambiado. La naturaleza anual de los anillos de crecimiento de C. odoratissima, la posibilidad de realizar datación cruzada entre muestras de esta especie y la alta correlación con las variables climáticas locales y globales, señalan un alto potencial de esta especie para realizar estudios dendrocronológicos en esta parte del continente americano.

Tectonic control on the stratigraphic framework of Late Pleistocene and Holocene deposits in Marajó Island, State of Pará, eastern Amazonia

The traditional view that the Brazilian Amazonia is located in a tectonically stable area since the Cretaceous is changing in front of the increasing documentation of fault reactivations even during the Holocene. How the sedimentary record has responded to these events is an issue that remains to be approached with basis on field data. This work focuses on the stratigraphic correlation of late Quaternary deposits from eastern Marajó Island, with the goal of demonstrating the role of fault reactivation on the origin and preservation of these deposits. Despite the location in a stable platform of a continental passive margin, three studied stratigraphic units display significant vertical offsets that define two depocenters that are better explained through tectonic displacements. This interpretation is reinforced by several morphostructural features related to faults that occur between the studied drills. Without the influence of tectonics, sediment preservation in this characteristically low-lying terrain would have been negligible. The results of the present work motivate to look for other tectonically-influenced areas in Amazonia, which similarly might have acted as sites for sediment accommodation during the late Quaternary. These sedimentary records have great potential to be the source of valuable information for reconstructing Quaternary geological events in Northern Brazil.

A visão tradicional de que a Amazônia brasileira localiza-se em ma área tectonicamente estável desde o Cretáceo está mudando perante a crescente documentação de reativações de falha, até mesmo durante o Holoceno. Como o registro sedimentar respondeu a esses eventos é um tema que permanece por ser abordado com base em dados de campo. Este trabalho enfatiza a correlação estratigráfica de depósitos quaternários tardios no leste da Ilha do Marajó, com o objetivo de demonstrar a importância de reativações de falha na origem e preservação desses depósitos. Apesar da localização em área de plataforma de uma margem continental passiva, três unidades estratigráficas estudadas mostram significantes rejeitos verticais, que definem dois depocentros, explicados por deslocamentos tectônicos. Esta interpretação é reforçada por várias feições morfoestruturais relacionadas com falhas localizadas entre os poços estudados. Sem influência tectônica, a preservação de sedimentos nesse terreno, caracteristicamente plano, seria imperceptível. Os resultados do presente trabalho motivam a procurar outras áreas tectonicamente influenciadas da Amazônia, que possam ter atuado como sítios de acomodação de sedimentos durante o Quaternário tardio. Esses registros sedimentares têm grande potencial de serem fontes de informações valiosas para auxiliar na reconstrução de eventos geológicos quaternários no norte do Brasil.

A new age to an old site: the earliest Tupiguarani settlement in Rio de Janeiro State?

This paper presents unexpectedly early dates for a Tupiguarani settlement in Southeastern Brazil. One radiocarbon dating of 1740 ± 90 yr BP (1820-1390 cal yr BP) was already available for the Morro Grande site (Araruama, southeastern coast of Rio de Janeiro State). Two new dates, obtained from charcoal samples, are reported here. An age of 2920 ± 70 yr BP (3220-2790 cal yr BP) was obtained from a specialized hearth, probably used for cooking ceramics; a funerary hearth at the same archaeological locus was dated at 2600 ± 160 yr BP (3000-2150 cal yr BP). Both measurements were made independently, indifferent laboratories, arguing for their validity. These results considerably age the arrival time of Tupiguarani populations to the coastal region of Southeastern Brazil. They may have important implications to the hypotheses about the origin and dispersion of these populations from Amazonia, supporting the claim of recent authors who consider that their expansion must have begun well before 2000 yrs BP.

Este artigo apresenta datações inesperadamente antigas para umassentamento Tupiguarani no sudeste do Brasil. Uma datação radiocarbono de 1740 ± 90 anos AP (1820-1390 cal anos AP) já existia para o sítio de Morro Grande, situado no município de Araruama, na costa sudeste do Estado do Rio de Janeiro. Duas novas datações, obtidas de amostras de carvão, são apresentadas neste trabalho. A data de 2920 ± 70 anos AP (3220-2790 cal anos AP) foi obtida a partir de uma fogueira de uso específico, provavelmente destinada a queimar cerâmica; uma outra provém de uma fogueira funerária do mesmo setor arqueológico, datada em 2600 ± 160 anos AP (3000-2150 cal anos AP). As duas medidas foram feitas independentemente, em laboratórios diferentes, o que reforça sua validade. Estas datações mostram que o momento de chegada de populações Tupiguarani à costa brasileira ocorreu muito antes do que se imaginava. Elas podem ter importantes implicações para as hipóteses sobre a origem e a dispersão dessas populaçõesa partir da Amazônia, corroborando a hipótese de autores recentes que consideram que a expansão Tupi deve ter começado bem antes de 2000 anos AP.