Effect of low vegetation on the recruitment of plants in successional habitat types

I assessed the role of low vegetation (plants ca 1 yr old and <= 50 cm tall) as a biotic facilitator or barrier in the recruitment of different growth forms and species in primary forests, secondary forests, and old-fields (abandoned pastures) in southeastern Mexico. I removed by hand all plants (<= 100 cm tall, including roots) and litter from 20, 0.25 m(2) plots in each habitat. For 1 yr, I counted the number of plant species (5-50 cm tall) recruited, grouped them into different growth forms, and compared them to undisturbed control plots. Prior to manipulation, the standing density of trees and lianas was highest in primary and secondary forests. Shrubs were more abundant in secondary forests, whereas herbs, epiphytes, and hemi-epiphytes were more abundant in old-fields. Herbaceous plants appeared as important components of the community in all habitats. The removal of low vegetation increased total plant recruitment in all habitats. Considering each growth form, the absence of vegetation increased recruitment in primary forests for herbs, in secondary forests for epiphytes and hemi-epiphytes, in old-fields for trees, and for lianas in primary forests and old-fields. In vegetation removal plots, recruitment of species was greater in pastures, lower in secondary forest, and similar in primary forest with respect to control plots. Depending on habitat type, species, and growth form, the presence of low vegetation may act as a recruitment barrier or facilitator for different species, affecting plant community structure, diversity, and composition in different habitats.