Juan Pablo Lewis

Floristic groups and plant communities of southeastern Santa Fe, Argentina

This paper is a survey of the vegetation of the southeastern departments in the Province of Santa Fe (Argentina). The vegetation was analyzed following Braun-Blanquets approach modified by Mueller-Dombois & Ellenberg (1974). The most relevant species of the region were placed in 25 groups according to their requirements or general behaviour. Most of the communities are herbaceous, and apart from the woody and some other miscellaneous ones they were grouped into three ecologically and floristically defined sets. The first set, the Stipa grasslands and related communities, which are characterized by the more or less abundant presence of Stipa hyalina, Stipa neesiana and Stipa papposa, comprises five different communities. The second, the halophilous communities, comprises five communities, the two Spartina ssp. grasslands, the halophilous prairies of Distichlis spicata, the short sedge Scirpus americanus communities and the ‘pela-dales’. The third, the hygrophilous communities, comprises nine communities which are not so well defined as the ones in the other sets. Besides, two further communities have been included, the Paspalum quadrifarium and the Melica macra tall grasslands.

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

A survey is presented of the vegetation of the central region of the Santafesinian Chaco (Argentina), a scarcely populated flat area of 20 000 km2, 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 areSpartina 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.

Dynamics and Development of Floristic Richness in the Vegetation of a Large Depressed Area of the Great Chaco

Summary In the present paper the dynamics of the vegetation of the Subermeridional Lowlands of the Great Chaco is discussed. The whole area is in a steady-state defined by edaphic conditions and the disturbance regime. Recurrent floods and fires shape the structure of the communities. The most important communities are ordered along a smooth gradient related to elevation, and they shift along this gradient as a result of irregular cycles of wet and dry years. Strong dominance depresses floristic richness, but a large number of species, most of them rarities, are recorded in each community. These species thrive in microsites created by the interaction between matrix development and disturbance. Ant-hills also provide microsites which increase floristic richness. Hygrophilous communities have a very Gleasonian nature, but around temporary ponds and lakes there seems to be a successional trend.

DEMOGRAPHIC RESPONSES TO FIRE OF SPARTINA ARGENTINENSIS IN TEMPORARY FLOODED GRASSLAND OF ARGENTINA

Population characteristics of Spartina argentinensis after fire were analyzed. Field experiments were done in temporary flooded tall grassland, dominated by S. argentinensis at the Reserva Federico Wildermuth (Argentina), on burnt and non-burnt plots. The following variables were analyzed: soil seed bank, potential and real establishment of seedlings and the effect of fire on them, percentage of tillers that continue growing after fire, emergence and survival of tillers, number of tillers that differentiated panicles, and production and predation of propagules. Plants resprouting after fire produced a larger number of tillers with greater tiller emergence, recruitment, and survival than tillers of those of the non-burnt plants. The proportion of tillers with panicles and number of full spikelets per plant was greater in burnt plants than in non-burnt plants, but individuals caryopses unitary weight as well as germination percentage and viability were not affected by fire. Caryopses were severely predated and they did not build up a permanent seed bank. In spite of the high output of caryopses, seedling establishment was almost negligible under most circumstances. Fire and environmental conditions provided very limited “windows of opportunity” for seedlings recruitment. Asexual reproduction was the main process of population maintenance and growth, and fire triggers off the output and eventual establishment of sexual propagules.

Relación entre la vegetación y el banco de semillas de un espartillar de Spartina argentinensis

S.R. Feldman, C. Alzugaray, and J.P. Lewis. 2007. Relationship between the soil seed bank and vegetation of tall grassland of Spartina argentinensis. Cien. Inv. Agr. 34(1):41-48. Tall grass communities of Spartina argentinensis Parodi are the most widespread plant communities in a large saline depression in Santa Fe, Argentina. The vegetation and soil seed bank for these communities have been studied. However, there is no information about the relationship between them. We worked with previous data obtained from the Federico Wildermuth Reserve, Colonia Bel Grano, Departamento San Martin, Santa Fe, Argentina (31°57’ S; 61°23’ W) and used the cover-abundance of the plant species and density of the soil seed bank for 1998 and 1999. The relationship between plant types C3 and C4 (C3/C4) and annual/perennial functional groups were determined. At the same time, the similarity index and the relationship between cover-abundance and density of the shared species was determined. According to results obtained, plant species relationship between of type C3 were more frequent in the soil seed bank, while plant species of type C4 were more abundant in the vegetation. There was no signifi cant correlation between cover-abundance in the vegetation and soil seed bank density of the common species. The similarity index was very low due to the fact that the number of species common to vegetation and soil seed bank was very low. In conclusion, there was a low relationship between species of the soil seed bank and vegetation with plant species type C3 and C4 as predominant species, respectively.