Plant communities and phytogeographical position of a large depression in the Great Chaco, Argentina

Abstract

A survey is presented of the vegetation of the central region of the Santafesinian Chaco (Argentina), a scarcely populated fiat area of 20 000 km 2, with seasonal flooding. Soils have a strong halo-hydromorphic character and vegetation is basically halophilous. Trees are scarce and most communities are savannas, grasslands or swampy vegetation. Twenty-three communities are described, some of them with several variants. The most widespread communities are Spartina argentinensis grasslands, Elyonurus muticus savannas and a complex of hygrophilous communities. The most important communities are distributed in relation to a topographical gradient, and their structure is shaped by recurrent flooding and fire disturbance. Most of the area is virgin land with very little human interference. The phytogeographical position of the area is discussed.

Three levels of floristical variation in the forests of Chaco, Argentina

“…trees and Spartina argentinensis grasslands characterize the Submeridional Lowlands (Lewis et al 1990). Von Humboldt (Moss 1910) recognized 'pure associations' of temperate regions and 'mixed associations' of tropical forests, thus implying a floristic enrichment of vegetation from high to low latitudes.…”

Soil salinity determines the relative abundance of C3/C4 species in Argentinean grasslands

“…1), across almost 5° of latitude in the Santa Fe province, Argentina, according to the limits already established by Lewis (1981). Within each of these phytogeographical provinces, two sets of relevés were chosen from previous vegetation studies, corresponding to halophyte and non‐halophyte communities (Collantes & Lewis, 1980; D’Angelo et al ., 1987; Lewis et al ., 1990). The salinity of the soil corresponding to each group of communities was estimated through the aqueous solution conductivity in siemens per metre (S m −1 , n = 6 for each community).…”

“…The original data for each community had been taken in 4 m × 4 m plots employing the usual Braun-Blanquet coverabundance subjective scale ranging from + and values of 1-5, representing the percentage of soil coverage (+, very rare, insignificant coverage; 1, very sparse, up to 5% coverage; 2, abundant, from 5% to 25% of soil coverage; 3, any number of individuals, from 25% to 50% soil coverage; 4, numerous, from 50% to 75% soil coverage; 5, very numerous, from 75% to 100% Figure 1 Map of the Santa Fe province indicating the phytogeographical provinces (1, Paranense; 2, Chaquenian; 3, Espinal; 4, Pampean), the three counties were the sampling sites were located, and the waterdeficit isolines (modified from Cáceres, 1980). Lewis et al, 1990) Tallgrass prairie of Leptochloa chloridiformis, 'aibal' of Elionurus muticus (n = 79) 'Espartillar' of S. argentinensis, 'espartillar' of S. densiflora, meadow of Paspalum vaginatum (n = 102) soil coverage; Braun-Blanquet, 1979). These data were transformed to the Mueller-Dombois & Ellenberg percentage scale (+ = 0.1; 1 = 2.5; 2 = 15; 3 = 37.5; 4 = 62.5; and 5 = 87.5%; Mueller-Dombois & Ellenberg, 1974).…”

Structural features of species of Asteraceae that arouse discussions about adaptation to seasonally dry environments of the Neotropics

“…The Chaco encompasses about 800.000 km 2 throughout the north and central regions of Argentina, eastern Paraguay, southeastern Bolivia and extreme western Brazil (Adámoli et al 1990;Lewis et al 1990;Prado 1993). The Brazilian portion of the Chaco is restricted to southwest region of the Pantanal and occupies approximately 7 % of the Nabileque sub-region (Prado et al 1992) (Fig.…”

“…The South American sedimentary plain of the Chaco (or Gran-Chaco), is one of the most extensive seasonally dry Neotropical environments and the largest continuously semi-arid dry forest (Adámoli et al 1990; Lewis et al 1990;Prado 1993). Distinctly Chaquenian phytophysiognomies vary according to climatic and edaphic gradients, and possess a great diversity of environmental and species heterogeneity compared to other arid and semi-arid environments (Adámoli 1987;Spichiger et al 1991).…”