No abstract

For decades, palynologists working in tropical South America are using the genus Podocarpus as a climate indicator although without referring to any modern data concerning its distribution and limiting factors. With the aim to characterize the modern and past distribution of the southern conifer Podocarpus in Brazil and to obtain new information on the distribution of the Atlantic rainforest during the Quaternary, we examined herbarium data to locate the populations of three Brazilian endemic Podocarpus species: P. sellowii, P. lambertii, and P. brasiliensis, and extracted DNA from fresh leaves from 26 populations. Our conclusions are drawn in the light of the combination of these three disciplines: botany, palynology, and genetics. We find that the modern distribution of endemic Podocarpus populations shows that they are widely dispersed in eastern Brazil, from north to south and reveals that the expansion of Podocarpus recorded in single Amazonian pollen records may have come from either western or eastern populations. Genetic analysis enabled us to delimit regional expansion: between 5° and 15° S grouping northern and central populations of P. sellowii expanded c. 16,000 years ago; between 15° and 23° S populations of either P. lambertii or sellowii expanded at different times since at least the last glaciation; and between 23° and 30° S, P. lambertii appeared during the recent expansion of the Araucaria forest. The combination of botany, pollen, and molecular analysis proved to be a rapid tool for inferring distribution borders for sparse populations and their regional evolution within tropical ecosystems. Today the refugia of rainforest communities we identified are crucial hotspots to allow the Atlantic forest to survive under unfavourable climatic conditions and, as such, offer the only possible opportunity for this type of forest to expand in the event of a future climate change.

Gregório, "Evaluating microfossil content of dental calculus from Brazilian sambaquis" (2010). Karl Reinhard Papers/Publications. 53.

The climatically sensitive equatorial regions provide important information for evaluation of the phasing between high-and low-latitude climate variability. A high-resolution pollen record from northern Brazil demonstrates a significant abrupt and rapid environmental change associated with the Northern Hemisphere Younger Dryas temperature reversal. This finding is consistent with the model in which the Younger Dryas had a stronger influence on temperature in the Northern Hemisphere than south of the equator because of the larger temperature gradient between pole and equator in the Northern Hemisphere than in the Southern Hemisphere. One consequence of the Younger Dryas changes would be the location of the Intertropical Convergence Zone in a southern position, so that even tropical regions would have been under Arctic influence.

Knowledge on juvenile tree growth is crucial to understand how trees reach the canopy in tropical forests. However, long-term data on juvenile tree growth are usually unavailable. Annual tree rings provide growth information for the entire life of trees and their analysis has become more popular in tropical forest regions over the past decades. Nonetheless, tree ring studies mainly deal with adult rings as the annual character of juvenile rings has been questioned. We evaluated whether juvenile tree rings can be used for three Bolivian rainforest species. First, we characterized the rings of juvenile and adult trees anatomically. We then evaluated the annual nature of tree rings by a combination of three indirect methods: evaluation of synchronous growth patterns in the tree-ring series, 14 C bomb peak dating and correlations with rainfall. Our results indicate that rings of juvenile and adult trees are defined by similar ring-boundary elements. We built juvenile tree-ring chronologies and verified the ring age of several samples using 14 C bomb peak dating. We found that ring width was correlated with rainfall in all species, but in different ways. In all, the chronology, rainfall correlations and 14 C dating suggest that rings in our study species are formed annually.