Tuesday, August 5, 2008: 1:30 PM
103 DE, Midwest Airlines Center
Cristina Martinez-Garza1, Wolke Tobon2, Julio Campo2 and Henry F. Howe3, (1)Centro de Educacion Ambiental e Investigacion Sierra de Huautla, Universidad Autonoma del Estado de Morelos, Cuernavaca, Mexico, (2)Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico, (3)Biological Sciences, University of Illinois-Chicago, Chicago, IL
Background/Question/Methods A unique study in seed-dispersal limitation and experimental restoration of connectivity through dispersal in a tropical agricultural mosaic was planted in an eroded pasture in southern Veracruz, Mexico in 2006. High mortality of seedlings of 6 early- and 16 late-successional tree species planted in open pasture occurred during a severe and extended dry season in 2007 which lasted beyond the normal end in June and well into July. August was unusually dry as well. Twenty-two species of pioneer and later-successional tree seedlings were planted in 16 fenced 30 X 30 m plots in active pasture during the rainy season of August 2006 - February 2007. Soil depth and gravimetric soil moisture were measured in the dry month of June 2007. Growth and ultimate mortality were measured in July 2007. Results/Conclusions The unsually severe and extended dry season resulted in far higher seedling mortality than in previous experiments at this site. Seedlings experienced more than 70% mortality, reversing previous results in other plantings in the area that averaged ~ 70% survival. Seedling survival for nine months ranged from 0% for Virola guatemalensis to 80% in early successional Heliocarpus appendiculatus, with a global mean of 28.4 ± 6.7%. Plant survival was positively correlated with soil depth, a relationship apparently driven by pioneers with fleshy fruits. Plant survival did not reflect relative gravimetric soil moisture. Species planted early during the rainy season showed higher survival than those planted later, favoring pioneers that were available for planting early in the rainy season (41% pioneer versus 20% non-pioneer survival). Species with higher growth rates showed higher survival, we hypothesize because larger plants developed more extensive root systems. To avoid catastrophic mortality from severe dry seasons in tropical restorations, we recommend planting early in the wet season after several months of cattle exclusion.
