Postdispersal Seed Fate of Tropical Montane Trees in an Agricultural Landscape, Southern Costa Rica

Variation in postdispersal seed fate is an important factor driving patterns of forest regeneration. Because most previous studies have not tracked final seed fate and have commonly equated seed removal with predation without considering the possibility of secondary dispersal, little is known about individual seed mortality factors in successional and degraded habitats. This study tracked the postdispersal fate of large-seeded tropical montane trees in abandoned pasture, young secondary forests, and small forest fragments during two consecutive years in an agricultural landscape in southern Costa Rica. The incidence of secondary dispersal by animals, scatterhoarding in particular, and the effects of seed burial on germination were measured. Overall, seeds survived through germination more often in secondary forests with high levels of mortality occurring in abandoned pastures and forest fragments. The majority of seed mortality was caused by rodent predation in forest fragments, insects and fungal pathogens in secondary forests, and a combination of desiccation, insects, and fungal pathogens in pastures. Seeds were frequently secondarily dispersed in larger forest fragments, whereas they were only rarely moved in pastures and secondary forests. Burial tended to improve germination in pastures and was important for an often scatterhoarded species, Otoba novogranatensis, in all habitats. The results of this study suggest that: (1) seed mortality factors differ in response to the type of habitat degradation; (2) large-seeded species have high potential for survival when dispersed to young secondary forests; and (3) seed removal is not a reliable proxy for seed predation, particularly in less degraded forest fragments.     

Fauna as passengers and drivers in vegetation restoration: A synthesis of processes and evidence

Efforts to restore terrestrial woody ecosystems to former agricultural land are typically based on plant‐focused actions, often neglecting fauna. However, the processes that maintain or restore the health and integrity of these ecosystems involve many animal–plant interactions. Here, I synthesise information about these relationships and the implications for revegetation practice. Fauna have often been viewed as passengers, responding passively to plant‐focused revegetation. This view involves two surrogacy assumptions: first, that vegetation attributes can indicate habitat sufficiency for fauna; second, that animals will be capable of dispersing to the restored habitat and of establishing populations there. Habitat sufficiency depends on how resources such as food and nest sites can be indicated by vegetation attributes and how they interact with an animal's species‐specific requirements. Dispersal and establishment depend on proximity to source populations in habitat elsewhere, the type of intervening habitat and the intrinsic mobility of different species. Evidence about the effects of age, revegetation type and spatial context in relation to animal communities indicates that it can often be invalid to assume vegetation surrogacy. Fauna can also drive the developmental trajectories of floristic diversity and composition during revegetation, because animal–plant interactions frequently mediate life‐history transitions that determine seedling recruitment. Frugivore‐mediated seed dispersal is the best studied, but animals also directly influence early‐stage tree recruitment, especially through their roles in seed predation, seedling herbivory and indirectly through top‐down cascades that include large carnivores. These processes have been insufficiently recognised or studied, although some recent work highlights their significance. Intervening to alter abundances of functionally important animals could be useful in accelerating the redevelopment of woody vegetation. Further research is needed to clarify animals’ roles as both passengers and drivers during revegetation, especially manipulative experiments and innovative restoration trials, in which animals and plants are considered together from the outset.     

Seed Dispersal by Salvin's Curassow,Mitu salvini (Cracidae), in a Tropical Forest of Colombia: Direct Measurements of Dispersal Distance1

Seed dispersal by Salvin's curassows (Mitu salvini) was studied in a lowland tropical forest at La Macarena on the border of the Macarena and Tinigua National Parks, the Department of Meta, Colombia. Continuous observations were made on the feeding and ranging behavior of a well-habituated pair of birds from 0600 to 1800 h for 19 days. Ibtal observation time was 222 h. The daily distance traveled by the birds ranged from 630 to 3750 m, with a mean of 1959 m (± 776 m). The total home range was ca 34.4 ha. Although curassows were observed consuming fruits of 13 species belonging to the families Rubiaceae, Meliaceae, Moraceae, Burseraceae, Leguminosae, and Lecythidaceae, only seeds of Geophila re fens (Rubiaceae) and Picas spbenophylla (Moraceae) were found in their feces. For G. repens, the mean and maximum retention times were 1 h 52 min (± 1 h 20 min) and 6 h 08 min, and the mean and maximum direct dispersal distances were 245 m (± 164 m) and 633 m. More than half the seeds were dispersed in canopy gaps. For F. sphenophylla, the mean and maximum retention times were 3 h 1 5 mm (± .37 min) and 7 h 08 min, and the mean and maximum direct dispersal distances were 329 m (± 46 m) and 451 m. Nearly 60 percent of the estimated seed intake of G. repens and 92-94 percent of F. sphenophylla were digested or damaged. The retention times and the dispersal distances for Streptogyna americana, which has adhesive burrs, were also measured. The mean and maximum retention times were 1 h 55 min (± 1 h 56 min) and 9 h 11 min, and the mean and maximum direct dispersal distances were 128 m (± 68 m) and 280 m. This is the first study in which direct measurements were made for retention times and dispersal distances of the epizoochory and endozoochory for birds in the field.     

Do Thinning and Burning Sites Revegetated after Bauxite Mining Improve Habitat for Terrestrial Vertebrates?

Thinning and burning forests established on revegetated mine pits in jarrah (Eucalyptus marginata) forests of south‐west Australia is being considered as a management option to accelerate succession in sites with excessive tree densities. To assess the impact of thinning and burning on reptiles and small mammals, we installed trapping grids in eight thinned and burned sites, each paired with untreated controls. Of the eight pairs, four were in rehabilitated sites (planted with nonlocal species) and four were in restored sites (seeded with local species). Thinning and burning had no significant impact on the small mammal community, although Cercatetus concinnus was more abundant in rehabilitated sites. In contrast, thinning and burning significantly increased reptile abundance and species richness, with two species (Morethia obscura and Menetia greyii) only recorded in thinned and burned sites. We concluded that thinning and burning was a successful management option in revegetated mine pits in jarrah forests, particularly because reptile communities created by thinning and burning were more similar to those in unmined forest. Although published studies for comparison are few, we expect thinning and burning to have generally positive effects on reptile communities in forest ecosystems where fire is an important disturbance agent. Our study emphasizes the importance of monitoring revegetated areas over time periods sufficient to detect deviations from desired successional trajectories, so that management options, such as thinning and burning, can be implemented if required.     

Interaction between ants and seeds of a nonmyrmecochorous neotropical tree, Cabralea canjerana (Meliaceae), in the Atlantic forest of southeast Brazil

On the forest floor of two Atlantic forest sites in southeast Brazil, we recorded 26 ant species (12 genera) interacting with the seeds of Cabralea canjerana (Meliaceae), a typical ornithochorous tree whose seeds are covered by a lipid-rich aril. The ants treat the arillate seeds in three different ways: (1) the large ponerine ants Pachycondyla striata and Odontomachus chelifer individually remove the seeds to their nests, (2) many species (Pheidole spp.) recruit workers to remove the aril on the spot, or (3) Solenopsis spp. recruit nestmates and cover the seeds with soil before removing the aril on the spot. The ants remove the aril exceptionally rapidly, and removal greatly facilitates seed germination. Seed predation by insects below fruiting trees is severe, and field experiments using vertebrate exclosures showed that rodents also prey heavily upon seeds found near parent trees. Ponerine ants actively remove seeds from this predation-prone zone. By removing bird-manipulated and naturally fallen seeds, ants can play a key role in the fate of medium-sized seeds like those of C. canjerana.