THE DISTRIBUTION OF WOODY LEGUMES IN NEOTROPICAL DRY FORESTS: THE PLEISTOCENE ARC THEORY 20 YEARS ON*

V Y Mogni,D E Prado,L J Oakley

doi:10.1017/s0960428614000298

Abstract

The Pleistocene Arc Theory (PAT) suggests that present-day disjunct fragments of dry forests in central tropical South America give evidence of a previously more continuous distribution during the Pleistocene that has been disrupted by dry-cold vs. humid-warm climatic cycles. This Arc extends from NE Brazil to NE Argentina and eastern Paraguay, through the Chiquitanía to NW Argentina and SW Bolivia and into the dry inter-Andean valleys in Peru and Ecuador, with intrusions into the Great Chaco. Seasonally Dry Tropical Forests (SDTFs) are floristically and physiognomically dominated by woody legumes, mostly deciduous in the dry season. In the last two decades field collection and research on legume taxa has greatly increased, with a significant number of taxonomic revisions and molecular phylogenetic studies, together with some paleoclimatic modelling studies. The evidence accumulated in the last 23 years has confirmed the integrity of the Chaco and Caatingas phytogeographical provinces, with an impressive and increasing level of botanical endemism discovered. The PAT pattern has also been supported, specifically through the mapping of five selected woody Leguminosae species (Anadenanthera colubrina, Enterolobium contortisiliquum, Pterogyne nitens, Amburana cearensis and Piptadenia viridiflora). The pre-existing nuclei of South American SDTF (Caatingas, Misiones and Piedmont) are now increased to four with the postulation of the Chiquitanía Nucleus in south-eastern Bolivia and bordering Paraguay. Some new endemisms are compiled from recent literature and mapped for the Misiones and Chiquitanía nuclei. The need for more botanical collections and further taxonomic, phylogenetic and demographic studies of South American legumes is emphasised.

Highlights

The seasonally dry areas of the tropics, their ecosystems and vegetation types, have received scant attention from the natural sciences, especially when compared to that given to tropical rain forests (Janzen, 1988; Mooney et al, 1995)
Chaco endemics In South American biogeography the Gran Chaco comprises the thorny vegetation that covers the vast rolling plains of north-central Argentina, western Paraguay and south-eastern Bolivia (Fig. 1), entering Brazil as a narrow strip following the course of the river Paraguay in Mato Grosso do Sul
More than 20 years since the formulation of the Pleistocene Arc Theory, the Chaco and the Caatingas provinces are confirmed as distinct phytogeographical entities

Summary

Introduction

The seasonally dry areas of the tropics, their ecosystems and vegetation types, have received scant attention from the natural sciences, especially when compared to that given to tropical rain forests (Janzen, 1988; Mooney et al, 1995). In recent times has this tendency been partially reversed Pennington et al, 2006; Dirzo et al, 2011).

Methods

Results

Conclusion