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We evaluated the importance of small (<5 ha) forest patches for the conservation of regional plant diversity in the tropical rainforest of Los Tuxtlas, Mexico. We analyzed the density of plant species (number of species per 0.1 ha) in 45 forest patches of different sizes (1-700 ha) in 3 landscapes with different deforestation levels (4, 11, and 24% forest cover). Most of the 364 species sampled (360 species, 99%) were native to the region, and only 4 (1%) were human-introduced species. Species density in the smallest patches was high and variable; the highest (84 species) and lowest (23 species) number of species were recorded in patches of up to 1.8 ha. Despite the small size of these patches, they contained diverse communities of native plants, including endangered and economically important species. The relationship between species density and area was significantly different among the landscapes, with a significant positive slope only in the landscape with the highest deforestation level. This indicates that species density in a patch of a given size may vary among landscapes that have different deforestation levels. Therefore, the conservation value of a patch depends on the total forest cover remaining in the landscape. Our findings revealed, however, that a great portion of regional plant diversity was located in very small forest patches (<5 ha), most of the species were restricted to only a few patches (41% of the species sampled were distributed in only 1-2 patches, and almost 70% were distributed in 5 patches) and each landscape conserved a unique plant assemblage. The conservation and restoration of small patches is therefore necessary to effectively preserve the plant diversity of this strongly deforested and unique Neotropical region.

To evaluate the impact of fragmentation on forest regeneration, I measured the abundance of shade-tolerant, mature-phase tree seedlings (individuals 5-100 cm tall) in unfragmented and fragmented vegetation in three sites near Manaus, Brazil. The habitats studied were (1) continuous forest (control, n ϭ 5); (2) 100-ha fragments ( n ϭ 2); (3) 10-ha fragments ( n ϭ 4); and (4) 1-ha fragments ( n ϭ 5). For 10-and 100-ha fragments, seedling density was measured in the center, the edge, and the corner of the fragments, and at 20-m intervals up to 100 m away from the fragment's edge. The density of seedlings declined significantly from continuous forest to forest fragments. Corners of 100-ha fragments had lower densities of seedlings than plots in centers and edges. In both 100-and 10-ha fragments, edge seedling density increased toward forest interior, but the increment was significant for only one site. Edge effects were more important than area effects per se in affecting seedling abundance. Overall, the centers of larger fragments (100 ha) did not have significantly higher densities of tree seedlings than smaller ones (10 and 1 ha). I suggest that a decrease in seed rain produced by increased tree mortality, reduced seed output and dispersal, high seed predation, and lower seedling establishment might explain the lower seedling numbers observed in forest fragments and fragment edges. These results suggest that forest fragmentation at Manaus may affect the regenerative potential of the forest. Impacto de la Fragmentación Forestal en la Abundancia de Plántulas en un Bosque Tropical LluviosoResumen: Para evaluar el impacto de la fragmentación sobre la regeneración de la selva, utilizé la abundancia de plántulas (individuos entre 5 y 100 cm de altura) de árboles tolerantes a la sombra o de bosque maduro, como indicador de la alteración. Censé la abundancia de plántulas en sistemas no fragmentados y fragmentados en tres sitios (A, B, y C) al norte de Manaus, Brasil. Los hábitats estudiados fueron: (1) selva virgen (control, n ϭ 5); (2) fragmentos de 100 ha ( n ϭ 2); (3) fragmentos de 10 ha ( n ϭ 4); y (4) fragmentos de 1 ha ( n ϭ 5). Para los fragmentos de 100 y de 10 ha la densidad de plántulas se midió en el centro, el borde y en la esquina de los fragmentos y también, a intervalos de 20 m, hasta 100 m del borde. La densidad de plántulas (número de plántulas ր m 2 ) decreció significativamente de la selva virgen a los fragmentos de diferentes tamaños. Las esquinas de los fragmentos de 100 ha tuvieron menor número de plántulas que los centros y los bordes. En los fragmentos de 100 y 10 ha, la densidad de plántulas aumentó del borde hacia el interior del fragmento, pero éste incremento fue significativo únicamente para el Sitio B. Los efectos de borde parecen tener un impacto mayor sobre la abundancia de plántulas que el tamaño del fragmento. Los centros de los fragmentos de mayor tamaño (100 ha) tuvieron una densidad de plántulas similar a los menores (10 y 1 ha). La información existente y los resultados obtenidos en e...

To evaluate the impact of fragmentation on forest regeneration, I measured the abundance of shade-tolerant, mature-phase tree seedlings (individuals 5-100 cm tall) in unfragmented and fragmented vegetation in three sites near Manaus, Brazil. The habitats studied were (1) continuous forest (control, n ϭ 5); (2) 100-ha fragments ( n ϭ 2); (3) 10-ha fragments ( n ϭ 4); and (4) 1-ha fragments ( n ϭ 5). For 10-and 100-ha fragments, seedling density was measured in the center, the edge, and the corner of the fragments, and at 20-m intervals up to 100 m away from the fragment's edge. The density of seedlings declined significantly from continuous forest to forest fragments. Corners of 100-ha fragments had lower densities of seedlings than plots in centers and edges. In both 100-and 10-ha fragments, edge seedling density increased toward forest interior, but the increment was significant for only one site. Edge effects were more important than area effects per se in affecting seedling abundance. Overall, the centers of larger fragments (100 ha) did not have significantly higher densities of tree seedlings than smaller ones (10 and 1 ha). I suggest that a decrease in seed rain produced by increased tree mortality, reduced seed output and dispersal, high seed predation, and lower seedling establishment might explain the lower seedling numbers observed in forest fragments and fragment edges. These results suggest that forest fragmentation at Manaus may affect the regenerative potential of the forest. Impacto de la Fragmentación Forestal en la Abundancia de Plántulas en un Bosque Tropical LluviosoResumen: Para evaluar el impacto de la fragmentación sobre la regeneración de la selva, utilizé la abundancia de plántulas (individuos entre 5 y 100 cm de altura) de árboles tolerantes a la sombra o de bosque maduro, como indicador de la alteración. Censé la abundancia de plántulas en sistemas no fragmentados y fragmentados en tres sitios (A, B, y C) al norte de Manaus, Brasil. Los hábitats estudiados fueron: (1) selva virgen (control, n ϭ 5); (2) fragmentos de 100 ha ( n ϭ 2); (3) fragmentos de 10 ha ( n ϭ 4); y (4) fragmentos de 1 ha ( n ϭ 5). Para los fragmentos de 100 y de 10 ha la densidad de plántulas se midió en el centro, el borde y en la esquina de los fragmentos y también, a intervalos de 20 m, hasta 100 m del borde. La densidad de plántulas (número de plántulas ր m 2 ) decreció significativamente de la selva virgen a los fragmentos de diferentes tamaños. Las esquinas de los fragmentos de 100 ha tuvieron menor número de plántulas que los centros y los bordes. En los fragmentos de 100 y 10 ha, la densidad de plántulas aumentó del borde hacia el interior del fragmento, pero éste incremento fue significativo únicamente para el Sitio B. Los efectos de borde parecen tener un impacto mayor sobre la abundancia de plántulas que el tamaño del fragmento. Los centros de los fragmentos de mayor tamaño (100 ha) tuvieron una densidad de plántulas similar a los menores (10 y 1 ha). La información existente y los resultados obtenidos en e...

Abstract:This study tested whether the reduction in the number of large-bodied seed dispersers is correlated with shifts in the taxonomic and functional (e.g. dispersal mode and seed size) traits of the seeding communities within small fragments of semi-deciduous forest, southern Mexico. In five fragments (2.3–640 ha) and one continuous forest site we sampled tree and seedling species in 40 (20 × 20 m) and 120 (3 × 3 m) plots respectively, and recorded the incidence (presence/absence) of the disperser fauna (three common large-birds and >500-g mammals). Tree and seedling species were categorized according to dispersal mode, seed size and whether they originated from local (i.e. from dropped) or immigrant (i.e. from actively dispersed) seeds. Fragment size negatively correlated with number of species of medium to large vertebrate seed-dispersers and number of seedlings of large-seeded species, but had no influence on functional traits of the adult-tree community. Between 41% and 61% of all seedlings were considered as immigrants and the proportion of immigrant seedlings of large-seeded tree species was negatively correlated with forest size. The results suggest that biased defaunation in small forest fragments may seriously reduce recruitment of large-seeded tree species (>1.4 cm length) dispersed by vertebrates, negatively affecting successional trajectories of small forest fragments.

Aims: Across tropical regions, large forest areas have been converted to different agricultural land uses. These uses impose ecological disturbances affecting forest regeneration potential after field abandonment. Finding ways to identify those agricultural land uses limiting forest regeneration is a critical issue for conserving biodiversity in human-modified landscapes. Here, we developed a fast and inexpensive index, useful for quantifying ecological disturbance regimes associated with agricultural land uses, and tested its power to predict forest regeneration potential.Location: Municipality of Marqu es de Comillas, southeast Mexico.Methods: Interviews were conducted with local farmers to quantify disturbance components (size, duration and severity) associated with agricultural land uses. The scaled values of these disturbance components were added in a simple ecological disturbance index (EDI). In each one of nine recently abandoned fields representing a wide range of EDI values, two 10-m 2 plots, one close to and one far from nearby forest remnants, were established. On each plot, all woody plants of 10-100 m in height were counted, identified and measured in four 1m 2 subplots, at the time of field abandonment and 2 yr later. In addition, at each plot, 18 site condition (microclimate and soil) attributes were quantified at the time of abandonment. Plant density, biomass, species richness and species diversity were used as regeneration variables, and EDI and site condition attributes as independent ones.Results: Two years after abandonment, most regeneration variables declined exponentially with EDI. Biomass was not explained by EDI but changed positively with light availability. EDI was strongly correlated to vapour pressure deficit, which also predicted regeneration potential (except biomass).Conclusions: EDI is a cheap and easy tool for quantifying the ecological disturbance produced by a wide range of agricultural land uses. The index predicted several regeneration variables as well as or better than direct measurements of the site condition at the time of abandonment. EDI can be used to identify biodiversity-friendly agricultural land uses in human-modified landscapes.