INCIDENCE OF RAIN EVENTS ON PAMPA GRASSLAND, SANTA FE, ARGENTINA

Abstract

The incidence of wet weather events on the structure and functioning of a pampa grassland (32°40’ S, 61°17’ W) was analyzed. Vegetation sampling was done every 30-40 days in 200 ha (March 2006 – November 2010) using a sampler of 0.25 m2. Species were identified and separated in order to determine the dry matter (DM) and calculate the relative proportionality. DM was accumulated per growing season. Rainfall data of the study period were compared with the historical record (RH) of the Agrometeorological Station Zavalla (33°01’ S, 60°53’ W). The events presenting wet precipitation ? 90% RH were selected and grouped into: Autumn, April 2006 (A2006), April 2007 (A2007); and Summer, February 2009 (F2009), February 2010 (F2010). The vegetation data obtained before and after events, and between events were treated by multivariate analysis using Multiple Response Permu- tation Procedures and the Kruskal Wallis test. The events analyzed did not change the proportion of species or the primary productivity of the grassland to the same extent. DM after event for A2006 and A2007 was 1556 kg ha-1 (increased L. multiflorum, S. hyalina, S. neesiana) and 1124 kg ha-1 (increased Cyperáceas and Juncáceas), respectively. DM after event for F2009 and F2010 was 1822 kg ha-1 (L. mul- tiflorum, T. repens, S. hyalina, H. stenostachys) and 1359 kg ha-1 (H. stenostachys and P. dilatatum), respectively. The amount, distribution, intensity, duration, timing of rainfall occurrence and soil water content before the event might have influenced the response of the grassland.