No abstract

Following perturbation, different assemblages that originate under the same abiotic conditions initiate successional pathways that may continue to diverge or converge toward an eventual climax. Forest regeneration in the Central Amazon begins with alternative successional pathways associated with prior land use. In a 12-yr study of secondary forests, initially ranging between 2 and 19 yrs after abandonment, we compared species compositions through time along two pathways, abandoned clear-cuts dominated by Cecropia and abandoned pastures dominated by Vismia; prior results at these sites have not directly evaluated species composition. At all ages, the Chao-Jaccard similarity index of species composition was highest comparing pasture transects to each other, lowest comparing pastures transects to clear-cut transects, and intermediate comparing clear-cut transects to each other. Through time, clear-cut transects became less similar to each other, as did pasture transects. Changes in similarity reflected declining dominance along both pathways, but Cecropia dominance of clear-cut transects declined more rapidly than Vismia dominance of pasture transects. A rich association of species replaced Cecropia in clear-cut transects, resulting in decreased similarity among them. In pasture transects one genus, Bellucia, replaced the lost Vismia, so similarity of Vismia transects was maintained despite some turnover in dominance. Overall, even with turnover of individuals and decline of the dominant pioneers, the alternative pathways exhibited strikingly different species assemblies after two decades of succession, suggesting that the effect of land use persists well beyond initial floristic composition.Abstract in Portuguese is available in the online version of this article.

Efforts to sequester carbon through tree plantations and natural regeneration in the tropics may also provide an opportunity to restore native forest ecosystems. However, the degree to which species composition of native species differs between tree plantations and secondary forests is unknown. In this study, we conducted surveys of woody plants (!2 cm dbh) in 20 secondary forest and tree plantation plots (30 Â 30 m) in a tropical lowland forest landscape. Sites were 8 to 21 years old and were either abandoned cattle pastures (secondary forests) or monoculture tree plantations (Hieronyma alchorneoides and Vochysia guatemalensis) planted for carbon sequestration. We compared species composition, ecological traits, and diversity of woody plants in secondary forests and tree plantations, while accounting for distance from primary forest. Species composition, but not species richness, of the natural regeneration was significantly different in tree plantations and secondary forests. The abundances of understory species, short-lived pioneers, and bat-dispersed species were all higher in secondary forests than in tree plantations. Abundances of canopy species, long-lived pioneers, shade-tolerant species, and dispersal categories besides bats were not associated with forest type. We conclude that tree plantations can alter species composition of regeneration compared with secondary forests perhaps by altering composition of seed disperser assemblages or inhibiting early successional species.

No abstract

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) in seven tree plantation plots and seven secondary forest plots (30 x 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 functional groups. We found that differences between these two forests types in stem density and basal area were declining. We did not find evidence for differences between forest types in the rate of accumulation of species richness when accounting for sample size. Although, 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 functional groups 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.