Nonannual tree rings in a climate-sensitive Prioria copaifera chronology in the Atrato River, Colombia.

In temperate climates, tree growth dormancy usually ensures the annual nature of tree rings, but in tropical environments, determination of annual periodicity can be more complex. The purposes of the work are as follows: (1) to generate a reliable tree-ring width chronology for Prioria copaifera Griseb. (Leguminoceae), a tropical tree species dwelling in the Atrato River floodplains, Colombia; (2) to assess the climate signal recorded by the tree-ring records; and (3) to validate the annual periodicity of the tree rings using independent methods. We used standard dendrochronological procedures to generate the P. copaifera tree-ring chronology. We used Pearson correlations to evaluate the relationship of the chronology with the meteorological records, climate regional indices, and gridded precipitation/sea surface temperature products. We also evaluated 24 high-precision 14C measurements spread over a range of preselected tree rings, with assigned calendar years by dendrochronological techniques, before and after the bomb spike in order to validate the annual nature of the tree rings. The tree-ring width chronology was statistically reliable, and it correlated significantly with local records of annual and October-December (OND) streamflow and precipitation across the upper river watershed (positive), and OND temperature (negative). It was also significantly related to the Oceanic Niño Index, Pacific Decadal Oscillation, and the Southern Oscillation Index, as well as sea surface temperatures over the Caribbean and the Pacific region. However, 14C high-precision measurements over the tree rings demonstrated offsets of up to 40 years that indicate that P. copaifera can produce more than one ring in certain years. Results derived from the strongest climate-growth relationship during the most recent years of the record suggest that the climatic signal reported may be due to the presence of annual rings in some of those trees in recent years. Our study alerts about the risk of applying dendrochronology in species with challenging anatomical features defining tree rings, commonly found in the tropics, without an independent validation of annual periodicity of tree rings. High-precision 14C measurements in multiple trees are a useful method to validate the identification of annual tree rings.

Flood-promoted vessel formation in Prioria copaifera trees in the Darien Gap, Colombia.

Trees growing in floodplains develop mechanisms by which to overcome anoxic conditions. Prioria copaifera Griseb. grows on the floodplains of the Atrato River, Colombia, and monodominant communities of this species remain flooded for at least 6 months a year. The aims of this study were as follows: (i) to compare variations in tree-ring structure with varying river water levels; and (ii) to reconstruct variations in water levels from the chronology of variations in the porosity of the tree rings. Discs were taken from 12 trees, and the number of vessels along 3-mm-wide radial transects was counted. Standard dendrochronological techniques were used to determine the mean number of vessels over 130 years, between 1877 and 2006; the signal-to-noise ratio was 13.3 and the expressed population signal 0.93. Furthermore, this series of vessel numbers was calibrated against variations in the water levels between 1977 and 2000; positive correlations were found with the mean for both the annual river water level and the level from June to August. The transfer function between the principal components of the mean annual water level and those of chronology allowed us to reconstruct the river levels over 130 years. Our conclusions are as follows: (i) the number of vessels per ring is an appropriate proxy for determining variations in water levels; and (ii) P. copaifera grows thicker and produces more vessels when water levels rise. The probable ecophysiological causes of this interesting behaviour are discussed.

Total carbon accumulation in a tropical forest landscape.

BACKGROUND: Regrowing tropical forests worldwide sequester important amounts of carbon and restore part of the C emissions emitted by deforestation. However, there are large uncertainties concerning the rates of carbon accumulation after the abandonment of agricultural and pasture land. We report here accumulation of total carbon stocks (TCS) in a chronosequence of secondary forests at a mid-elevation landscape (900-1200 m asl) in the Andean mountains of Colombia. RESULTS: We found positive accumulation rates for all ecosystem pools except soil carbon, which showed no significant trend of recovery after 36 years of secondary succession. We used these data to develop a simple model to predict accumulation of TCS over time. This model performed remarkably well predicting TCS at other chronosequences in the Americas (Root Mean Square Error < 40 Mg C ha-1), which provided an opportunity to explore different assumptions in the calculation of large-scale carbon budgets. Simulations of TCS with our empirical model were used to test three assumptions often made in carbon budgets: 1) the use of carbon accumulation in tree aboveground biomass as a surrogate for accumulation of TCS, 2) the implicit consideration of carbon legacies from previous land-use, and 3) the omission of landscape age in calculating accumulation rates of TCS. CONCLUSIONS: Our simulations showed that in many situations carbon can be released from regrowing secondary forests depending on the amount of carbon legacies and the average age of the landscape. In most cases, the rates used to predict carbon accumulation in the Americas were above the rates predicted in our simulations. These biome level rates seemed to be realistic only in landscapes not affected by carbon legacies from previous land-use and mean ages of around 10 years.

[Structural recovering in Andean successional forests from Porce (Antioquia, Colombia)]. / Recuperación estructural en bosques sucesionales andinos de Porce (Antioquia, Colombia).

Places subjected to natural or human disturbance can recover forest through an ecological process called secondary succession. Tropical succession is affected by factors such as disturbances, distance from original forest, surface configuration and local climate. These factors determine the composition of species and the time trend of the succession itself. We studied succession in soils used for cattle ranching over various decades in the Porce Region of Colombia (Andean Colombian forests). A set of twenty five permanent plots was measured, including nine plots (20 x 50 m) in primary forests and sixteen (20 x 25 m) in secondary forests. All trees with diameter > or =1.0 cm were measured. We analyzed stem density, basal area, above-ground biomass and species richness, in a successional process of ca. 43 years, and in primary forests. The secondary forests' age was estimated in previous studies, using radiocarbon dating, aerial photographs and a high-resolution satellite image analysis (7 to >43 years). In total, 1,143 and 1,766 stems were measured in primary and secondary forests, respectively. Basal area (5.7 to 85.4 m2 ha(-1)), above-ground biomass (19.1 to 1,011.5 t ha(-1)) and species richness (4 to 69) directly increased with site age, while steam density decreased (3,180 to 590). Diametric distributions were "J-inverted" for primary forests and even-aged size-class structures for secondary forests. Three species of palms were abundant and exclusive in old secondary forests and primary forests: Oenocarpus mapora, Euterpe precatoria and Oenocarpus bataua. These palms happened in cohorts after forest disturbances. Secondary forest structure was 40% in more than 43 years of forest succession and indicate that many factors are interacting and affecting the forests succession in the area (e.g. agriculture, cattle ranching, mining, etc.).

Recuperación estructural en bosques sucesionales andinos de Porce (Antioquia, Colombia)

Structural recovering in Andean successional forests from Porce (Antioquia, Colombia). Places subjected to natural or human disturbance can recover forest through an ecological process called secondary succession. Tropical succession is affected by factors such as disturbances, distance from original forest, surface configuration and local climate. These factors determine the composition of species and the time trend of the succession itself. We studied succession in soils used for cattle ranching over various decades in the Porce Region of Colombia (Andean Colombian forests). A set of twenty five permanent plots was measured, including nine plots (20x50m) in primary forests and sixteen (20x25m) in secondary forests. All trees with diameter ≥1.0cm were measured. We analyzed stem density, basal area, above-ground biomass and species richness, in a successional process of ca. 43 years, and in primary forests. The secondary forests’ age was estimated in previous studies, using radiocarbon dating, aerial photographs and a high-resolution satellite image analysis (7 to >43 years). In total, 1 143 and 1 766 stems were measured in primary and secondary forests, respectively. Basal area (5.7 to 85.4m²ha-1), above-ground biomass (19.1 to 1 011.5 t ha-1) and species richness (4 to 69) directly increased with site age, while steam density decreased (3 180 to 590). Diametric distributions were "J-inverted" for primary forests and even-aged size-class structures for secondary forests. Three species of palms were abundant and exclusive in old secondary forests and primary forests: Oenocarpus mapora, Euterpe precatoria and Oenocarpus bataua. These palms happened in cohorts after forest disturbances. Secondary forest structure was 40% in more than 43 years of forest succession and indicate that many factors are interacting and affecting the forests succession in the area (e.g. agriculture, cattle ranching, mining, etc.). Rev. Biol. Trop. 58 (1): 427-445. Epub 2010 March 01.

Lugares susceptibles a perturbaciones naturales o antrópicas pueden recuperar la cobertura boscosa. La sucesión tropical puede ser afectada por factores tales como perturbaciones, distancia al bosque original, topografía y clima local. Estos factores determinan la composición de especies y la tasa de recuperación de los sitios. Se estudió la sucesión en suelos que habían sido usados para el establecimiento de pasturas ganaderas por varias décadas en la Región Porce de Colombia (bosques Colombianos de los Andes). Se midieron un total de veinticinco parcelas, incluyendo nueve parcelas (20x50m) en bosques primarios y dieciséis (20x25m) en bosques secundarios. Se midieron todos los árboles con un diámetro ≥1.0cm. Se analizó la densidad, área basal, biomasa aérea y riqueza de especies, en un bosque con un proceso sucesional de ca. 43 años y en un bosque primario. Las edades de los bosques secundarios fueron obtenidas en estudios previos usando la datación con carbono catorce (C14), fotografías aéreas y el análisis de imágenes de satélite de alta resolución (entre 7 y >43 años). En total, 1 143 y 1 766 individuos se midieron en bosque primario y secundario, respectivamente. El área basal (5.7 a 85.4m²ha-1), la biomasa aérea (19.1 a 1 011.5 t ha-1) y la riqueza de especies (4 a 69) aumentaron directamente con la edad de los sitios, mientras que la densidad de árboles disminuyó (3 180 a 590). Las distribuciones diamétricas fueron en J-invertida para los bosques primarios y unimodal para los secundarios. Tres especies de palmas fueron abundantes y exclusivas de bosques secundarios viejos y bosques primarios: Oenocarpus mapora, Euterpe precatoria y Oenocarpus bataua. Cohortes de estas palmas aparecieron después de perturbaciones del bosque. La recuperación de la estructura de los bosques secundarios en más de 43 años de sucesión fue 40% e indica que varios factores están interactuando y afectando la sucesión de los bosques en el área (e.g. agricultura, ganadería extensiva, minería, etc.).