Juliano Morales de Oliveira

Detecting ecological groups from traits: a classification of subtropical tree species based on ecological strategies

We evaluated the frequently assumed but rarely tested hypothesis that in tropical and subtropical forests species form discontinuities along gradients in trait variation, which can be detected to classify species into ecologically meaningful and statistically defined groups. We also tested the hypothesis that the dominant conifer Araucaria angustifolia have a contrasting trait syndrome from the pool of angiosperms. Data were collected in subtropical mixed conifer-hardwood forests in southern Brazil. Eleven trait variables (relative growth rates, growth rates under favourable conditions, annual mortality rates, seed length, seed dispersal mode, wood density, maximum height, crown depth, stem slenderness, specific leaf area, and leaf blade length) were measured for 66 large tree species. The conifer Araucaria angustifolia differed significantly in most traits and vital rates from the angiosperm distributions. The Simple Structure Index criterion was used to identify the optimum number of non-hierarchical k-means groups. This index was largest for a solution with five groups. Non-hierarchical groups were more strongly related with the resource capture and height gradients than groups formed by hierarchical clustering. We propose the recognition of seven ecological species groups in the studied forests depending on growth rates, leaf size, wood density, height, stem slenderness, dispersal, and crown depth: Conifers, Palms, Pioneers, Large-seeded Pioneers, Wind-dispersed Large trees, Large shade-tolerant trees, and Small Shade-tolerant trees. The classification produced was coherent with the ecological strategies present in the community and represents a subdivision of Westoby’s leaf-height-seed plant strategy scheme.

Chuva de sementes de espécies lenhosas florestais em mosaicos de floresta com Araucária e campos no Sul do Brasil

Mechanisms of seed dispersal and recruitment avoid intraspecific competition and allow plants to colonize new habitats. In transition areas between forest and grassland, these processes are not spatially random, but are often associated with isolated woody individuals in the grassland or with areas of continuous shrub cover. In southern Brazil, Araucaria forest forms a mosaic with grassland (Campos) and advance of forest over grassland is observed. This study aims to evaluate the pattern of diaspore dispersal of woody plants associated with ecotones between Araucaria forest and grassland and with isolated woody individuals in the grassland matrix. The study was carried out at the Centro de Pesquisas e Conservacao da Natureza Pro-Mata PUCRS, in Sao Francisco de Paula, in grassland vegetation excluded from fire and grazing for 16 years, and which is surrounded by forest. Diaspore dispersal was evaluated for eight months by using collectors positioned in forest-grassland ecotones with different physiognomies and under isolated woody individuals in the grassland matrix. The different types of environment were compared by univariate and multivariate analysis of variance to verify seed-rain patterns. The results indicated that seed dispersal occurs preferentially associated with isolated woody individuals of Araucaria angustifolia and with continuous patches of Baccharis uncinella. We suggest that these habitats would function as extensions of more similar forest conditions within the grassland matrix.

South Brazilian Forest-Grassland Ecotones: Dynamics Affected by Climate, Disturbance, and Woody Species Traits

The southernmost part of Brazil is characterized by extended grasslands—the southern Campos. In some parts of the region, these grasslands occur in close contact with different forest types of the Atlantic forest biome or riparian forests, forming mosaics. Otherwise, they form large and continuous areas toward south and southwest, where they reach the Pampa grassland of Uruguay and Argentina. Throughout this region, forest expansion and/or shrub encroachment can be observed and have been related both to site conditions (abiotic variables and disturbance regimes) and climatic changes. We know today, based on studies of pollen records from peat profiles, that expansion of woody vegetation throughout the past centuries was driven by changes in the climatic conditions towards a climate increasingly favorable for forest development, and evidence exists that this process is halted or at least slowed down as consequence of land use and disturbances. Current vegetation dynamics in forest-grassland ecotones thus likely are linked both to climatic changes (on the regional scale) and vegetation management and/or disturbance regime (on the local scale).

Dendroecological Studies in the Neotropics: History, Status and Future Challenges

We review a vast literature of Neotropical forest science and wood anatomical research that identifies 220 tree species from 46 botanical families with confirmed annual tree-ring formation. External factors that trigger annual growth rhythms include rainfall seasonality, annual long-term flooding (flood-pulse), soil water salinity (mangroves), and, with increasing latitude and altitude, photoperiod and temperature. Maximum ages for tropical angiosperms derived from tree-ring analyses generally do not exceed 400–600 years; however, at marginal sites characterized by extremely limited growth conditions individual trees might get older. Dendroecological applications provide insights into tree species’ ecology and forest dynamics. Analyses of growth trajectories and age-size relationships of trees highlight considerable variability among individual trees, species, and environments. In recent decades tree-ring studies in neotropical forests have contributed new methods to project timber harvests and to evaluate and adjust management practices to increase the sustainability of forest management. The better understanding of individual- and species-level growth patterns in the Neotropics provides necessary empirical information to conserve and manage tropical forests and the many ecosystem functions and services that they maintain.