Rita Mesquita

Secondary forests or " capoeiras " accounted for 20% of the total deforested area in the Brazilian Amazon in 2006. This study relates land use history and biomass accumulation in a chronosequence of secondary forests in the Apuí municipality, one of the deforestation hotspots in the Amazon. Aboveground live biomass (ABGB) was estimated for trees in 16 secondary forests with ages ranging from 3-23 years of abandonment, and subjected to two previous land uses: eight areas were clearcut and used only once for small farm agriculture and then abandoned (low intensity); eight areas were maintained mainly as pasture experiencing several prescribed fires until abandonment (high intensity). Satellite imagery data between 1985 and 2010 was supplemented with landowner interviews in order to define the secondary forests age and their previous land use history. The point-centered quarter method was used for sampling trees in four diametric classes (1<5 cm, 5<10 cm, 10<20 cm, ≥...

Although forest succession has traditionally been approached as a deterministic process, successional trajectories of vegetation change vary widely, even among nearby stands with similar environmental conditions and disturbance histories. Here, we provide the first attempt, to our knowledge, to quantify predictability and uncertainty during succession based on the most extensive long-term datasets ever assembled for Neotropical forests. We develop a novel approach that integrates deterministic and stochastic components into different candidate models describing the dynamical interactions among three widely used and interrelated forest attributes-stem density, basal area, and species density. Within each of the seven study sites, successional trajectories were highly idiosyncratic, even when controlling for prior land use, environment, and initial conditions in these attributes. Plot factors were far more important than stand age in explaining successional trajectories. For each site, the best-fit model was able to capture the complete set of time series in certain attributes only when both the deterministic and stochastic components were set to similar magnitudes. Surprisingly, predictability of stem density, basal area, and species density did not show consistent trends across attributes, study sites, or land use history, and was independent of plot size and time series length. The model developed here represents the best approach, to date, for characterizing autogenic successional dynamics and demonstrates the low predictability of successional trajectories. These high levels of uncertainty suggest that the impacts of allogenic factors on rates of change during tropical forest succession are far more pervasive than previously thought, challenging the way ecologists view and investigate forest regeneration.

Title: Logging On in the Rain Forests. Authors: Gascon, Claude; Mesquita, Rita; Higuchi, Niro;Cabarle, Bruce J.; Hartshorn, Gary S.; Bowles, Ian A.; Rice, Richard E.; Mittermeier, Russell A.; da Fonseca, Gustavo AB. Publication: Science, Vol. 281, Iss. 5382, p. 1453 (1998). ...

ABSTRACT Background: The tradeoff between seed mass and seed number per plant is widely established for different taxa, guilds, and communities. Relative to primary forest species, pioneer species generally produce large numbers of small seeds. Aims: We tested if the relationship between seed mass and seed number was connected to the fruit variables – namely, fruit mass and fruit number per tree – in order to evaluate tradeoffs in seed packaging. Methods: Seed mass and seed number per tree as well as fruit mass and fruit number per tree were measured for 12 pioneer species common to secondary forests in the central Amazon. Results: Seed mass, seed number, fruit mass, and fruit number varied by several orders of magnitude among species. Seed number was explained only partially by seed mass alone (R 2 = 0.55), but nearly completely by the combination of seed mass, fruit mass and fruit number (R 2 = 0.94). The number of seeds per fruit was positively correlated with fruit mass and total seed number per tree and negatively with seed mass and fruit number. Seedling and adult abundances were most dependent on fruit number and fruit mass, not seed number and seed mass. Conclusions: Biomass tradeoffs between seed mass and seed number are partially dependent on seed packaging, specifically seeds per fruit, fruit mass and fruit number per tree for pioneer trees in the central Amazon.

ABSTRACT Background: Plant succession and community assembly following different land-use histories in the Amazon Basin are poorly understood. Aims: Changes in woody vegetation were monitored across chronosequences of abandoned pastures and abandoned clearcuts in order to compare their successional patterns. Methods: In chronosequences, initially 5–19 years old in abandoned clearcuts and 2–11 years old in abandoned pastures, trees (≥ 3 cm dbh) were tagged and recruitment and mortality recorded annually for 12 years. Results: Stem densities exhibited no significant trend during the first 25 years of succession regardless of land-use history. Basal area in abandoned clearcuts increased rapidly in the first decade, outpacing accumulation in abandoned pastures, although basal area on the two pathways converged at 25 years post-abandonment. Transects in abandoned pastures were much more variable in stem density and basal area than those in abandoned clearcuts, reflecting cohort growth and thinning by the dominant genus Vismia in the pastures. Species density, initially similar in the young stands, increased at a much faster rate in abandoned clearcuts than in abandoned pastures, resulting in a large divergence after 25 years. Conclusions: Succession following deforestation in the Amazon exhibits alternative pathways that correspond to prior land use – abandoned clearcuts of primary forest or clearcuts converted to pastures through prescribed burns and later abandoned. The most important divergence in the two successions was the extremely slow accumulation of species over 25 years in abandoned pastures.

The phylogenetic structure of communities can reveal forces shaping community assembly, but the vast majority of work on phylogenetic community structure has been conducted in mature ecosystems. Here, we present an analysis of the phylogenetic structure of three Neotropical rain forest communities undergoing succession. In each site, the net relatedness of the community is initially high and consistently declines during succession. This pattern is evident both when comparing plots of different age classes and when comparing stem ...

Deforestation is occurring at an alarming rate in many parts of the world, causing destruction of natural habitat and fragmentation of what remains. Nowhere is this problem more pressing than in the Amazon rainforest, which is rapidly vanishing in the face of enormous ...

... Jennifer M. Cramer 1,2,* ,; Rita CG Mesquita 2 ,; Tony Vizcarra Bentos 2 ,; Barry Moser 3 ,; G. Bruce Williamson 1,2. Article first published online: 25 MAY 2007. ... 2002), given the paucity of studies (Wright & Duber 2001, Cordeiro & Howe 2003, Dick et al. 2003, Bruna et al. ...