Seed rain dynamics following disturbance exclusion in a secondary tropical dry forest in Morelos, Mexico

Abstract

Abstract:In most of the legally protected areas in Mexico local inhabitants use natural resources, such as fire wood or cattle grazing. These frequent but low-intensity disturbances have consequences at various levels of the tropical ecosystems and strongly impact forest structure and its regeneration capacity. Despite their importance, the effects of these perturbations in many aspects of tropical forest ecology and in the forest's capacity to recover after disturbance exclusion remain poorly understood. Understanding the impact of these processes on tropical forests is necessary for rehabilitating these forests and enhancing their productivity. In this study, we evaluate the impact of twelve years of exclusion (E) of cattle grazing and fire wood extraction in the composition and dynamics of seed rain, and compare this assessment to a similar analysis in an area where these perturbations continued (without exclusion, WE). We found a strong seasonality in seed rain (96% of seeds fell in the dry season) in both areas. There were no significant differences between E and WE sites in relation to overall seed density, species richness and diversity. However, the distribution along the year of seed species density was significantly different among the E and WE sites. The Jaccard's similarity index between E and WE sites was relatively low (0.57). Barochory was the most common dispersal mode observed among the 23 species in terms of seed species density (48%), followed by anemochory (39%) and zoochory (13%). In relation to seed density, anemochory was the most frequent dispersal mode (88%). Most species in the zone were categorized as small seeds (92%), and there were no significant differences in the distribution of seed size between E and WE. The spatial pattern of dispersal of the four species with the highest relative importance value index, in both areas, was aggregated. Twelve years of disturbance exclusion were not enough to fully restore the seed rain of the area; some differences were already perceptible after this lapse. On the other hand, zoochorous species were almost absent from both sites. The re-introduction of climax and animal-dispersed species may be, in addition to perturbation exclusion, a viable strategy to accelerate ecological restoration in this area. Rev. Biol. Trop. 57 (1-2): 257-269. Epub 2009 June 30.

Seed limitation of woody plants in Neotropical savannas

“…These variations in the seed rain of woody species are consistent with previous studies in cerrado plant communities (Batalha and Mantovani 2000;Munhoz and Felfili 2007) and tropical dry forests (Ceccon and Hernandez 2009). Winddispersed diaspores, however, exhibited a stronger seasonal variation than animal-dispersed diaspores.…”

Intra and inter-annual variation in seed rain in a secondary dry tropical forest excluded from chronic disturbance

“…The influx of forest species and their further establishment into successional areas is affected by phenology, dispersal modes and, presence and abundance of suitable dispersers, life history of tree species and distance to seed sources (old-growth forest). Most tropical dry forest species set flowers and fruits during the dry season (Kushwaha et al, 2011;Janzen, 1967;Borchert, 1996;Ceccon and Hernandez, 2009). Many tropical dry forest tree species are wind dispersed (Gentry, 1995) even though most species in tropical forests have fleshy fruits adapted for animal dispersal (Howe and Smallwood, 1982).…”

Alvaradoa amorphoides germination at low water potential and the role of the antioxidant system

“…Eight individual Alvaradoa amorphoides trees were selected based on their distribution at the site to evaluate the seed germination rates in the field and make comparisons with the seed rain patterns for this species and zone as reported by Ceccon and Hernández (2009). The eight trees were located in different geomorphologies or landscapes, such as foothills or depressions, hillsides, and hilltops, each of which is characterized by different soil humidity conditions or water potentials throughout the year (Table ).…”

“…This tree not only contributes to the structure of the community, but it is also used as firewood by the local people (Ceccon and Hernández, 2009). The A. amorphoides seed has a membranous seminal coat that is permeable to water (Salazar and Soihet,200).…”