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We evaluated the composition, structure, and dieback of a montane forest in relation to soils and physiography of an important biogeographic region that has been sparsely studied. Our objectives were to (1) describe the forest composition and structure; (2) assess the current extent of dieback; and (3) relate tree composition, structure, and dieback proneness to edaphic and physiographic measures. We enumerated all live and dead standing plants ≥3 cm dbh, in thirty 20 × 15 m2 overstory plots. We measured all regeneration ≤1 m height in subplots, sampled soils and measures of physiography, and visually rated the proportion of crown dieback, and recorded standing dead trees. Woody plants belonged to 58 species and 25 families, of which 5% were dead. The plant families Lauraceae, Myrtaceae, and Symplocaceae represented over 50% of the basal area; Rubiaceae alone represented 25% of the stems. Multiple regressions revealed measures of edaphic and physiographic factors are associated with tree species richness and diversity, structure (e.g., basal area and stem density), and tree dieback and standing dead trees. Canopy openness and measures of soil toxicity from metals (Al and Cu) on clay‐based soils showed a predictably negative relationship with tree species richness and diversity. Basal area and stem density are positively associated with aspect and slope, and predictably negatively associated with canopy openness. Lastly, dieback and standing dead trees of the dominant canopy tree species are both positively associated with south and southwest aspects. The forest is now in a period of regeneration recovery with high numbers of regenerating secondary successional species. We propose the primary underlying factors that caused the dieback of this forest was a drought during 1970–1980 compounded by accumulations of salts and metals in the soil conveyed by winds from the sea (sodium) and from an ancient period of metallurgy downwind of the forest. However, our results are only suggestive of these causative factors and further study is necessary to confirm or refute these speculative causes for dieback. [ABSTRACT FROM AUTHOR]

The Amazon harbors one of the most diverse tree floras on earth, and most species depend on mutualists for pollination and seed dispersal. This makes them susceptible to reproductive decline in fragmented forest because many of these mutualists suffer area‐related extinction in fragments. It remains unknown, however, whether this highly biodiverse tree flora will reproduce and ultimately persist in fragmented forest. We conducted a 2‐yr study of seed fall in an experimentally fragmented, highly diverse Central Amazonian forest. We determined the effect of fragment size (1, 10, 100 ha and continuous forest control) on the density, species richness, functional diversity and functional composition of seeds separated into two data sets: dispersed tree seeds, and undispersed tree seeds. Our results show a 3× reduction in the density of undispersed, non‐pioneer tree seeds in fragments of all sizes, indicating reduced seed production of the non‐pioneer tree community. The density of dispersed tree seeds was reduced by 6× in fragments of all sizes, while species richness was reduced by 6× in 1‐ha fragments and by 3× in 10‐ and 100‐ha fragments compared to intact forest. This provides evidence of reduced community‐wide seed dispersal, which became more pronounced with declining fragment size. The functional diversity (FRic) of dispersed tree seeds was reduced 9.6× in small fragments, and significant shifts in the functional composition for 8 of the 10 reproductive and ecological traits studied were identified, suggesting compromised ecosystem functioning. These functional compositional shifts provide evidence for disrupted mutualistic processes in fragments, which include loss of pollination by bees, especially small eusocial (meliponid) bees, and loss of dispersal by primates and large birds, which reduced the frequency of large‐seeded tree species. Fragments also lost rare and mature‐forest species, and collectively these changes suggest that future tree communities in fragmented Amazonian landscapes will retain a taxonomically and functionally impoverished species pool with a biased functional composition unless efforts are undertaken to conserve dispersal by large frugivores and pollination by meliponid bees. [ABSTRACT FROM AUTHOR]

Little is known about how soil seed banks vary in germination, composition, and density under different land uses after tropical forest conversion. Seed banks can potentially act as one source of regeneration for reforestation of old agricultural lands. Our study documents the composition and density of germinants in soil seed banks from four land uses types surrounding the Sinharaja forest in southwest Sri Lanka. These include: (1) kekilla fern lands; (2) pine plantations; and (3) tea. These were compared to the adjacent (4) mature rainforest. During the 6‐month period of monitoring, we recorded 1,674 germinants (0.036 germinants/cm3 soil), representing 46 species. Germinants of tree and shrub species were restricted to the pine and rainforest soils and all of them are considered pioneers. The soils of the rainforest had the lowest species richness, density, and diversity of germinants; tea lands comprised much higher richness, Shannon diversity, and density. However, almost all germinants in tea were grasses and herbs as compared with other land uses. A multivariate analysis of the germinants of soil seed banks revealed that the four land use types comprise very different compositions and abundances, some of which can be associated with differences in growth habit (trees, shrubs, vines, herbs, grasses). Our results suggest that pine plantations may facilitate some tree and shrub regeneration. However, the seed banks beneath tea and kekilla fern land do not comprise any woody plant species. This may explain why agricultural lands such as tea do not revert back to forest easily. [ABSTRACT FROM AUTHOR]

Few studies have been published that focus on monitoring and investigating the long-term patterns of recruitment and survival of seedlings in the understories of tropical forests. Studies for mixed dipterocarp forest, the dominant tropical forest type for South and Southeast Asia, demonstrate seedlings in the existing forest understory (advance regeneration) play the most important role in forming a new forest after disturbance (e.g., logging, windstorms). Our study monitors the regeneration dynamic across a topographic gradient (ridge, mid-slope, and valley) of the understory for a mixed dipterocarp forest in the Sinharaja MAB reserve in southwest Sri Lanka. We recorded seedling recruitment, growth, and mortality by species in replicated plots on multiple forest understory sites over a ten-year period. Seedling density ranged from 26 to 31 m² with all of it categorized as advance regeneration of canopy tree species. Results show differences in seedling density per species across the topography and over time, with differences driven by changes in species composition from valley to ridge and in recruitment periodicity potentially related to supra-annual variations in climate. Seedling mortality was higher on ridges than valley and midslopes; and disproportionately higher seedling mortality occurs of relatively shade-intolerant late-successional trees species (70% mortality after 8 yr) compared with their more shade-tolerant associates (30% mortality after 8 yr). Our results contradict current selective logging prescriptions for tropical forests that comprise a single cutting cycle and minimum diameter felling for all commercial timber trees. Such harvests give no consideration to timing and manipulation of the forest canopy to favor release of advance regeneration. We recommend careful timing of timber harvests to occur in synchrony to the periodicity of seedling recruitment and silvicultural treatments that both insures their release and that accommodates to differences in seedling composition and density across topography. [ABSTRACT FROM AUTHOR]

We tested alternative hypotheses concerning factors affecting early forest succession and community composition in deforested and abandoned areas invaded by an exotic grass, Saccharum spontaneum, in Panama. We hypothesized three barriers to natural regeneration: (1) Saccharum competition, (2) seed dispersal limitations, and (3) fire. We measured natural tree and shrub regeneration in a factorial experiment combining distances from adjacent forest, mowing treatments of the Saccharum, and a prescribed burn. To determine, the applicability of the general model of neotropical succession and the nucleation model of succession to species composition of forest regeneration in these anthropogenic grasslands in Panama the effect of time since fire and distance to remnant vegetation (isolated trees, shrubs, and large monocots) was measured. Fire significantly affected species composition and decreased species richness because most species had either their resprouting ability or seed germination inhibited by fire; the few species that had regeneration enhanced by fire dominated early successional communities. Sites differed in time since fire, ranging from 1 to 4 yr; the interaction of site and distance from the forest significantly affected community composition and the prevalence of species with different dispersal mechanisms and shade tolerance. At recently burned sites, light-dependent wind-dispersed species predominated; most were found near the forest edge. As time since fire increased, significantly more shade-tolerant, larger-animal-dispersed species were recorded, and the proximity to and species identity of remnant vegetation became more important in affecting species composition of the natural regeneration; no significant effect of distance from the forest was found at sites that were unburned for three or more years. Our results support both successional models; the temporal sequence of species composition corresponded to later stages of the general model, while the spatial distribution of species followed the nucleation model. Our results highlight the importance of effective seed dispersal in structuring successional species composition and distribution and in regaining lost diversity resulting from frequent fires in the Saccharum. [ABSTRACT FROM AUTHOR]