Phenology, seed dispersal and difficulties in natural recruitment

13 páginas, 5 figuras, 2 tablas.commercial species. This study focused on a widely exploited Neotropical canopy species, Pachira quinata (Malvaceae), at the southernmost, wettest limit of its natural distribution, in the Colombian Amazonia. We studied phenological patterns, seed production and natural densities; assessed the importance of seed dispersal and density-dependent effects on recruitment, using field experiments. At this seasonal forest P. quinata was overrepresented by large adult trees and had very low recruitment caused by the combination of low fruit production, high seed predation and very high seedling mortality under continuous canopies mostly due to damping off pathogens. There was no evidence of negative distance or density effects on recruitment, but a clear requirement of canopy gaps for seedling survival and growth, where pathogen incidence was drastically reduced. In spite of the strong dependence on light for survival of seedlings, seeds germinated readily in the dark. At the study site, the population of P. quinata appeared to be declining, likely because recruitment depended on the rare combination of large gap formation with the presence of reproductive trees nearby. The recruitment biology of this species makes it very vulnerable to any type of logging in natural populations.We thank Carlos Mejía for continuous support during field work. Ramiro Montealegre shared with us his knowledge on local P. quinata. Mauricio Alvarez initially planted the seedlings that served us for two-year monitoring. Financial support was provided by a WCS-FES-Instituto von Humboldt undergraduate research grant to MCC.Peer reviewe

Patterns of Plant Species Richness Within Families and Genera in Lowland Neotropical Forests: Are Similarities Related to Ecological Factors or to Chance?

22 páginas, 3 figuras, 3 tablas.We compared information on 26 lowland Neotropical florulas, in order to assess which processes are correlated with the patterns of floristic similarities, based on plant species richness within families and genera. The results at the family level indicated that floristic similarity is significantly correlated with ecological factors (e.g., rainfall patterns, temperature and the distance to young mountains as a proxy of sedimentation processes), but is not correlated with geographical distance. At the genus level, again, ecological factors were highly correlated with floristic similarity. However, at this level geographical distance was also significantly correlated with floristic similarity. These quantitative results support Gentry’s theory which states that floristic affinities, in terms of patterns of species richness, are determined mainly by ecological factors. However, stochastic processes seem to play a minor but significant role, given that the most species-rich genera were similar between close-by areas, as predicted by neutral models. Our findings and an accumulating body of evidence show that forest composition does change along environmental gradients, in spite of the occurrence of widely distributed species along Neotropical forests.We thank the department of Biological Sciences and the Faculty of Sciences at Universidad de Los Andes, for the support to conduct this investigation. We thank Diana Guzman for comments and corrections.Peer reviewe

DIVERSIDAD Y COMPOSICIÓN FLORÍSTICA DE TRES TIPOS DE BOSQUE EN LA ESTACIÓN BIOLÓGICA CAPARÚ, VAUPÉS

The Amazon forests are among the most diverse ecosystems in the planet. Although some countries of the Amazon Basin have a fairly complete record of their plants, in Colombia much effort is still needed to have a good idea of the plant diversity patterns and floristic composition. Three one hectare vegetation-land plots (dbh 10 cm) were established in Vaupés, Colombia, regarding three types of forest: Colina, Terraza (Terra Firme forests) and Igapó (periodically flooded). Plant diversity was estimated and floristic composition was described classifying the most important families and species. The highest diversity was found in Colina (Fisher's = 160.3), followed by Terraza ( = 78.4) and Igapó ( = 44.7). Fabaceae s.l. was the most important family of all plots, but in Terraza forest the importance of Arecaceae was similar to that of Fabaceae. Floristic composition was also remarkably different amongst the three forest types, especially Igapó, which was the most dissimilar. However, both Terra Firme forests showed strong floristic differences, which may be caused by differences in abiotic factors (i.e. soils). High plant diversity reported in this study agrees with the hypothesis that central and western Amazon forests are the most diverse of the Amazon Basin.Los bosques amazónicos han sido incluidos entre los más diversos del planeta. Aunque en algunos países de la Amazonía existe un amplio registro de sus plantas, en Colombia hace falta un mayor esfuerzo para tener una buena idea de su diversidad y composición florística. Se levantaron tres parcelas permanentes de vegetación (dap 10 cm) de una ha en el Vaupés colombiano, en tres tipos de bosque: Colina, Terraza e Igapó (los dos primeros de Terra Firme y el tercero inundable). El objetivo fue cuantificar la diversidad y describir la composición florística en términos de índices de importancia para familias y especies. La parcela más diversa fue la de Colina ( de Fisher = 160.3), seguida por la de Terraza ( = 78.4) y por la de Igapó ( =44.7). La familia Fabaceae s.l. fue la más importante en las tres ha, pero en el bosque de terraza la importancia de Arecaceae fue similar a la de Fabaceae. También en composición florística los tres tipos de bosque resultaron considerablemente distintos, siendo el inundable el más disímil de los tres. Sin embargo, también encontramos diferencias importantes entre los dos bosques de tierra firme, que pueden deberse a características abióticas (i.e. suelos diferentes). La alta diversidad reportada en este estudio coincide con la hipótesis que indica que las zonas más diversas de la Amazonía son la occidental y la central

Enhancing plant diversity in secondary forests

Dispersal, recruitment and establishment limitations are crucial processes shaping forest composition. In secondary forests these mechanisms may operate differently than in mature forests, because young and isolated secondary forests may suffer stronger limitations due to a lack of suitable dispersers and harsh environmental conditions— such as the elevated competition of exotic grasses. To assess establishment limitations in these forests, we undertook transplant experiments involving seeds and seedlings along a chronosequence of secondary forests in tropical Australia. The experiments included six species that varied in seed size (6–50 mm in length) and successional status (early to late successional). Seeds of five species were placed in one of three treatments: (1) exposed seeds, (2) fenced seeds, and (3) buried seeds, and multiple seedlings of six species were transplanted in block treatments. After 14–17 months, seed from all plant species germinated across all ages of secondary forests. However, in young secondary forest sites (4–12 years) fewer germinated seeds survived. The highest survival rates were observed for buried seeds (27.2%) compared to the low survival of exposed seeds (6.0%). Planted seedlings (6 spp) had the greatest overall survival (63.1%) and the highest growth rates in older secondary forests. We found that species identity was important for growth and survival in both experiments, but detected no effect of successional status or seed size. A crucial finding of this study was that the buried seeds of all species germinated and had relatively high survival irrespective of variation in site conditions or successional status, suggesting that seed availability may be a greater barrier to recovery of secondary forests in the region than the establishment limitations imposed by environmental conditions

Determinantes de la Composición Florística y Efecto de Borde en un Frangmento de Bosque en el Guaviare, Amazonía Colombiana

fragmentation generates changes in biotic and abiotic factors of remnants. The aim of this study was ti describe the floral composition of a forest fragment in Guaviare, Colombia, in relation to the edge effect and abiotic factors. Ten plots of 100m x 10 m were sampled. The importance value index showed that the most important species in the fragment were Iriartea deltoidea, Croton matourensis, and Pourouma minor. Additionally, it was established that the species found near the edge were mainly pioneer plants (small seeded species) while the species away from it corrsponded primarily to mature forest plants (small seeded species) while the species away from it corresponde primarily to mature forest plants (with large seeds). An odination demostrated that each plot had a relatively different floristic composition, which could not be explained by soil composition or temperature. However, humidity seems to play an important role. The distance between plots was not a good predictior of floristic affinities, suggesting that when the seed dispersal vectors are maintained, dispersal limitation has weak effects at the spatial scales studied.The fragment exhibits typical elements of a succesional process, although in harbors a high especies diversity from the original forest. We conclude that fragmentation has caused changes in terms of floral composition, and its necessary to take measures to stop this process in order to maintain part of the floristic composition and the ecological processes of the native forest.La fragmentacón de un bosque genera cambios en muchos aspectos bióticos y abióticos de los pares remanentes. En este estudio describe la composición florística de un fragmento de bosque en el departamento del Guaviare, Colombia, analizando el efecto de borde y factores abióticos. Se establecieron diez parcelas de 100 x 10 m se muestrearon todas las especies delos árboles con DAP >= 10 cm. El índice de importancia mostró que las especies con mayores valores fueron Iriartea deltoidea, Croton matourensis y Pouroma minor. Se estableció que las especies cercca al borde corresponden mayormente a plantas pioneras (de semillas pequeñas) y las especies lejos de éste son principalmente de bosque maduro (de semillas grandes). Una ordenación demostró que cada una de las parcelas posee una composición florística relativamente diferente, que no se explica por factores como característica del suelo o temperatura, aunque la humedad parece jugar un papel importante. La distancia entre las parcelas tampoco fue un buen predictor de la composición florística, indicando que, cuando se mantiene los dispersores de semillas, la disperción limitada o opera fuertemente a las escalas espaciales estudiadas. El fragmento a las escalas espaciales estudiadas presenta una composición con muchos elementos típicos de un proceso de sucesión, aunque conserva una gran diversidad de especies de los bosques originales. Concluimos que la fragmentacón ha ocasionado cambios en términos de la composición florística y se recomiendo adoptar medidas para detener esteproceso, con el fin de mantener parte ed la composición y los procesos ecológicos de los bosques nativos

Biomass accumulation and population dynamics of a flooded forest in the Magdalena Basin (Colombia)

Few studies in Colombia have quantified population dynamics on private conservation lands, making it difficult to know whether passive restoration (secondary succession) is a good option to increase forest biomass. We analyzed three permanent plots (0.3 ha) in the Reserva El Paujil (Middle Magdalena Valley, Colombia), in secondary forests, after 8-9 y. We tested whether population changes and aboveground biomass accumulation should be higher in secondary flooded forests than in terra firme forests. We found that mortality rates (7.98/y ± 4.50 DE) were higher than recruitment rates (5.89/y ± 5.29 SD), generating a mean negative change (-2.09/y ± 4.36 SD). However, the growth of surviving individuals was high (0.028 ± 0.019 SD), causing a positive rate of biomass accumulation (3.33 ton/y/ha ± 5.15 SD). This rate was much higher than in terra firme forests in the area (0.10 ton/y/ha ± 1.90 SD), which was associated with soil fertility. The most dominant species with high biomass accumulation was Anacardium excelsum. In contrast, the highest increase in mortality was observed for pioneer species (i.e., Cecropia membranacea and C. peltata), Bauhinia picta, and Guadua angustifolia (which also showed the highest recruitment). Overall, establishing a biological reserve has allowed the growth of large trees, generating carbon stocks equivalent to those from active ecological restoration processes

Forestación de bosques en sabanas de la altillanura colombiana: relevancia de las condiciones ambientales para el establecimiento de plántulas

One way to counteract climate change is to plant forests with high carbon storage capacity. In this study we report the results of a reforestation project in savannas of the Tomogrande Reserve, in Vichada Department, Colombia. We restricted fire in six one-hectare plots: in two seasonally inundated and two highland savannas we planted seedlings of trees found in the Orinoco Basin and nearby gallery forests and in two of them we did not plant seedlings (control plots). Out of 200 seedlings planted in well-drained savannas, only 17 % survived after two and a half years (33 % came from nearby forest and 12 % from other areas). None of the 182 seedlings planted in flooded savannas survived at the end of the study. The main mortality cause in well-drained savannas was wilting. We concluded that in addition to the control of fire, seedling establishment of forest trees in savannas is highly affected by climatic and light conditions and for this reason the trees with highest potential for restoration are the ones already found at the site in the same ecological conditions (e.g. forest edge).Una forma de contrarrestar el cambio climático es la generación de bosques con alta capacidad de almacenamiento de carbono. En este trabajo se reportan los resultados de una iniciativa de reforestación de bosque en sabanas de la rserva Tomogrande. Se crearon barreras contra el fuego en seis áreas: dos inundables y dos no inundables, para sembrar plántulas de bosques de la Orinoquia, y manteniendo dos más como control sin adición de plántulas. De 200 plántulas sembradas en sabanas no inundables, únicamente el 17 % de ellas sobrevivieron por más de dos años (33 % para las especies de bosques aledaños y 12 % para las de otros lugares de la Orinoquia). Ninguna de las 182 plántulas trasplantadas a zonas inundables sobrevivió por más de dos años. La principal causa de mortalidad en sabanas bien drenadas fue el marchitamiento. Se concluye que a pesar de que la ausencia de fuego puede ayudar al establecimiento de árboles, las condiciones climáticas y lumínicas de la sabana disminuyen las probabilidades de que las plantas de bosque se establezcan y las que logran mayor probabilidad de supervivencia son las especies que viven en los bosques de galería aledaños (especialmente en bordes de bosque)

Possible Fruit Protein Effects on Primate Communities in Madagascar and the Neotropics

The ecological factors contributing to the evolution of tropical vertebrate communities are still poorly understood. Primate communities of the tropical Americas have fewer folivorous but more frugivorous genera than tropical regions of the Old World and especially many more frugivorous genera than Madagascar. Reasons for this phenomenon are largely unexplored. We developed the hypothesis that Neotropical fruits have higher protein concentrations than fruits from Madagascar and that the higher representation of frugivorous genera in the Neotropics is linked to high protein concentrations in fruits. Low fruit protein concentrations in Madagascar would restrict the evolution of frugivores in Malagasy communities.We reviewed the literature for nitrogen concentrations in fruits from the Neotropics and from Madagascar, and analyzed fruits from an additional six sites in the Neotropics and six sites in Madagascar. Fruits from the Neotropical sites contain significantly more nitrogen than fruits from the Madagascar sites. Nitrogen concentrations in New World fruits are above the concentrations to satisfy nitrogen requirements of primates, while they are at the lower end or below the concentrations to cover primate protein needs in Madagascar.Fruits at most sites in the Neotropics contain enough protein to satisfy the protein needs of primates. Thus, selection pressure to develop new adaptations for foods that are difficult to digest (such as leaves) may have been lower in the Neotropics than in Madagascar. The low nitrogen concentrations in fruits from Madagascar may contribute to the almost complete absence of frugivorous primate species on this island