Effects of experimental lightgaps and topography on enrichment plantings in a central Amazonian secondary forest

Enrichment plantings into secondary forest are an important option in restoring species diversity and ecosystem services. However, little attention has been given to environmental requirements for species performance. This study evaluated the effects of lightgaps and topographic position on the growth and survival of four native tree species (Pouteria caimito, Garcinia macrophylla, Dipteryx odorata and Cynometra bauhiniaefolia) planted into a 26-year old secondary forest originating from abandoned pastures in the central Amazon Basin. Artificial lightgaps and control plots under closed canopy were uniformly distributed on plateaus and bottomlands near water bodies. Seedlings were planted randomly into the plots and monitored for 28 months. Seedling survival rate was high (93%) and did not differ among species. Overall, lightgaps produced a 38% increase in seedling height relative to the controls. Although the four species naturally occur in mature forest, two of the four grew significantly more in lightgaps than in closed canopy secondary forest. Overall, bottomlands facilitated greater seedling growth in height (38%) relative to plateaus, but only one species exhibited a significant increase. This study shows the importance of the environmental variability generated with canopy openings along the topographic gradient, suggesting that both the selection of species and microsite conditions of planting sites have to be considered important criteria in the recovery of degraded areas. (AU)

Successional trajectories of secondary forests and tree plantations in Costa Rican lowlands

Tree plantations used for carbon sequestration or forest restoration often support diverse plant communities. However, it is unknown how rates of successional change in tree plantations compare to secondary forests. In this study, we compared the successional trajectory of tree plantations to that of secondary forests that were between 8 and 23 years old. Censuses of woody plants (≥ 2 cm dbh [diameter at breast height]) in seven tree plantation plots and seven secondary forest plots (30 × 30 m) were conducted over three years (May 2013-July 2016) in a lowland tropical forest. Secondary forests were naturally regenerating from abandoned cattle pastures. Tree plantations were monocultures of two different native species (Vochysia guatemalensis and Hieronyma alchorneoides), planted for carbon sequestration. We measured the change in stem density, basal area, species density, rarefied species richness, and relative abundance of different growth forms and regeneration guilds. We found that differences in stem density and basal area between these two forest types were declining. Nevertheless, we did not find evidence for differences between forest types in the rate of accumulation of species richness when accounting for sample size. On the other hand, even though the successional trajectory in tree plantations was very similar to secondary forests, there were differences between forest types in species composition. The rate of change in relative abundance of different growth forms and regeneration guilds was similar in both forest types. Overall, our results suggest that structural - but not compositional differences - between tree plantations and secondary forests are converging during the second decade of succession.

Las plantaciones forestales usadas para el secuestro de carbono o restauración forestal pueden sostener comunidades de plantas de alta diversidad. Sin embargo, no se sabe si las tasas de cambio sucesionales de plantaciones forestales son comparables con las de bosques secundarios. En este estudio, examinamos las trayectorias sucesionales en plantaciones forestales y bosques secundarios que tenían entren 8 y 23 años de edad. Realizamos inventarios de plantas leñosas (≥ 2 cm dap) en siete parcelas de plantaciones forestales y siete parcelas de bosques secundarios durante un periodo tres años (mayo 2013 - julio 2016) en un bosque tropical de tierras bajas. Estos últimos se regeneraron naturalmente en potreros abandonados, mientras que las plantaciones forestales fueron monocultivos de dos especies nativas (Vochysia guatemalensis y Hieronyma alchorneoides), sembradas para el secuestro de carbono. Medimos el cambio en densidad de tallos, área basal, densidad de especies, riqueza de especies y abundancia relativa de diferentes grupos funcionales. Encontramos que las diferencias en densidad de tallos y área basal, entre los dos tipos de bosques, estaban disminuyendo. No obstante, no hubo evidencia de diferencias entre los tipos de bosques en relación con la acumulación de riqueza de especies cuando se consideró el tamaño de la muestra, aunque había diferencias en la composición de especies, entre los dos tipos de bosque. Asimismo, en ambas zonas, la trayectoria sucesional en plantaciones forestales se parecía mucho. Por otro lado, la tasa de cambio en la abundancia relativa de grupos funcionales fue similar en ambos tipos de bosque. Por lo tanto, nuestros resultados sugieren que la diferencia en la composición de especies entre los tipos de bosque no disminuyó durante la segunda década de sucesión.

Dung beetle communities: a neotropical-north temperate comparison

Dung beetle communities have been compared across north temperate latitudes. Tropical dung beetle communities appear to be more diverse based on studies using different methodologies. Here, we present results from a standardized sampling protocol used to compare dung beetle communities across five neotropical forests in Brazil and Ecuador and two warm, north temperate forests in Mississippi and Louisiana. Species richness in the tropical forests was three to seven times higher than the temperate forests, as would be expected by studies of other taxa across tropical and temperate latitudes. Average body size in the temperate forests was larger than the tropical forests, as predicted by Bergmann's rule. Dung beetle abundance and volume per trap-day were generally higher in Ecuador than Brazil, and higher in Mississippi than Louisiana, but there were no tropical-temperate differences. Species rank-abundance curves were similar within countries and between countries. Rank-volume distributions indicated a smaller range of beetle body sizes in Ecuador versus Brazil or the USA. Community similarity was high within countries and low between countries. Community differences between Brazil and Ecuador sites may be explained by differences in productivity based on geological age of the soils.