Abstract Despite growing knowledge on the distribution and functioning of dryland vegetation types, their internal biodiversity structure (i.e., subregions) is much less studied. In the delineation of subregions, the use of species occurrence or abundance data may reveal different aspects of metacommunity structure. We revisit the issue of the bioregionalization of the woody flora of the Caatinga, the largest block of the dry forest and woodland biome in Latin America, using abundance data. We also evaluated the drivers of the spatial distribution of plant subregions: historical, current environmental and human effects. Using a K-means partition on interpolated NMDS axes, we identified 10 abundance subregions. Aridity, topography and soil, biome stability since the Pleistocene, and historical indigenous effects were retained by a Multinomial Logistic regression model, and their combined fractions explained most of the abundance variability in subregions. The subregions we present may support spatialized conservation and management decisions in the lack of detailed local data. The present results confirm the Caatinga woody flora broad composition patterns uncovered using presence-absence data in previous studies. Additionally, we found larger subregions than those identified with presence and absence data, suggesting the existence of oligarchies of dominant species in distinct parts of the Caatinga biome.

Una variedad de factores ambientales y bióticos determinan el crecimiento de la vegetación y afectan la acumulación de biomasa vegetal. Desde la temperatura hasta la composición de especies, en los ecosistemas forestales el almacenamiento de la biomasa aérea se ve influenciada por una serie de variables, razón por la cual generalmente presenta una alta variabilidad espacial. De acuerdo a esto, el objetivo del estudio es analizar las variables que afectan la biomasa área (en Inglés, aboveground forest biomass - AGB) en los bosques húmedos subtropicales del sur de Brasil y analizar su distribución espacial. Para el estudio se utilizaron los datos de un inventario forestal realizado en el estado de Rio Grande del Sur, sur de Brasil. Se evaluaron bosques de hoja ancha (Broadleaf forests) y bosques mixtos de hoja ancha y coníferas (Mixed Coniferous-Broadleaf forests). Además, se tomaron muestras de 38 parcelas de 1 ha y para la estimación de la biomasa se incluyeron todos los árboles con DAP ≥9.5cm. Los valores para la biomasa aérea se obtuvieron con ecuaciones alométricas publicadas. Las variables ambientales y bióticas (altitud, precipitación, temperatura, suelo, densidad de los troncos y diversidad de especies) se obtuvieron de la literatura o se han calculado a partir del conjunto de datos. Para el conjunto de datos, el AGB medio fue 195.2Mg/ha. Las estimaciones difieren entre los bosques de hoja ancha y los bosques mixtos de hoja ancha y coníferas: el AGB promedio fue menor en los bosques de hoja ancha (AGB BF=118.9Mg/ha) en comparación con los bosques mixtos (AGB MF=250.3Mg/ha). Hubo una alta variabilidad espacial y local en la base de datos, incluso dentro de los tipos de bosques. Esta condición es normal en los bosques tropicales y por lo general se atribuye a la presencia de grandes árboles. La regresión múltiple fue influenciada principalmente por la altitud y explicó 50.7% de la variación en AGB. La densidad, diversidad y materia orgánica también influyeron en la variación de biomasa. Los resultados mostraron una relación positiva entre la biomasa sobre el suelo y la altitud. Por lo tanto, los valores más altos de AGB se encuentran en altitudes mayores y se someten a temperaturas más bajas y un clima más húmedo. Parece que hay una importante contribución de las coníferas Araucaria angustifolia en las parcelas de bosques mixto, ya que tienen una biomasa significativamente mayor que las especies de angiospermas. En Brasil, esta especie en peligro de extinción es parte de un bosque de gran diversidad (Bosque de Araucaria) y tiene el potencial de almacenamiento de la biomasa. Los resultados del presente estudio muestran la variabilidad espacial y local de la biomasa aérea en los bosques subtropicales, destacan la importancia de estos ecosistemas en el almacenamiento global del carbono, y estimulan la mejora de futuras estimaciones de biomasa.

A variety of environmental and biotic factors determine vegetation growth and affect plant biomass accumulation. From temperature to species composition, aboveground biomass storage in forest ecosystems is influenced by a number of variables and usually presents a high spatial variability. With this focus, the aim of the study was to evaluate the variables affecting live aboveground forest biomass (AGB) in Subtropical Moist Forests of Southern Brazil, and to analyze the spatial distribution of biomass estimates. Data from a forest inventory performed in the State of Rio Grande do Sul, Southern Brazil, was used in the present study. Thirty-eight 1-ha plots were sampled and all trees with DBH ≥9.5cm were included for biomass estimation. Values for aboveground biomass were obtained using published allometric equations. Environmental and biotic variables (elevation, rainfall, temperature, soils, stem density and species diversity) were obtained from the literature or calculated from the dataset. For the total dataset, mean AGB was 195.2Mg/ha. Estimates differed between Broadleaf and Mixed Coniferous-Broadleaf forests: mean AGB was lower in Broadleaf Forests (AGB BF=118.9Mg/ha) when compared to Mixed Forests (AGB MF=250.3Mg/ha). There was a high spatial and local variability in our dataset, even within forest types. This condition is normal in tropical forests and is usually attributed to the presence of large trees. The explanatory multiple regressions were influenced mainly by elevation and explained 50.7% of the variation in AGB. Stem density, diversity and organic matter also influenced biomass variation. The results from our study showed a positive relationship between aboveground biomass and elevation. Therefore, higher values of AGB are located at higher elevations and subjected to cooler temperaturas and wetter climate. There seems to be an important contribution of the coniferous species Araucaria angustifolia in Mixed Forest plots, as it presented significantly higher biomass than angiosperm species. In Brazil, this endangered species is part of a high diversity forest (Araucaria Forest) and has the potential for biomass storage. The results of the present study show the spatial and local variability in aboveground biomass in subtropical forests and highlight the importance of these ecosystems in global carbon stock, stimulating the improvement of future biomass estimates. Rev. Biol. Trop. 62 (1): 359-372. Epub 2014 March 01.

O presente trabalho teve por objetivo descrever a estrutura e composição do estrato arbóreo de uma Floresta Ombrófila Mista na Floresta Nacional de São Francisco de Paula, Rio Grande do Sul utilizando métodos analíticos mistos de fitossociologia tradicional e de rarefação por unidades amostrais. Os dados, amostradas 29 parcelas de 10x10 m, são apresentados através de critérios de inclusão de diâmetro à altura do peito (DAP) mínimo de 5,0 cm e 10,0 cm, curvas de rarefação baseadas em amostras e estimadores não paramétricos de diversidade, de modo a ampliar seu potencial comparativo com outras comunidades. Segundo o critério de inclusão DAP > 5,0 cm, foram identificadas 41 espécies (índice de Shannon-Wiener (H’) = 1,2 nats.ind ') distribuídas em 32 gêneros, pertencentes a 18 famílias. Segundo o critério de inclusão DAP > 10,0 cm, foram identificadas 35 espécies (índice de Shannon-Wiener (H’) = 1,2 nats.ind') distribuídas em 26 gêneros, pertencentes a 17 famílias. Araucaria angustifolia foi a espécie dominante em densidade e freqüência segundo ambos os critérios de inclusão. Os estimadores não-paramétricos estimaram a riqueza mínima da comunidade variando entre 41,1 e 48,7 espécies (DAP > 5,0 cm) e 35,4 e 47,4 espécies (DAP > 10,0 cm). Devido à abordagem analítica utilizada, estes resultados podem ser diretamente comparados aos resultados obtidos em outros estudos que empreguem a mesma abordagem, o que não é possível com a maioria dos estudos similares feitos no Brasil.

In this paper we describe tree community structure and composition of a Mixed Ombrophilous Forest in São Francisco de Paula National Forest, Rio Grande do Sul, using both traditional phytosociological analyses and plot-based rarefaction methods. Data were collected in 29 1 Ox 10 m plots. Results are presented according to the inclusion criteria of diameter at breast height (dbh) of 5.0 cm and 10.0 cm, through sample-based rarefaction curves and non-parametric richness estimators, in order to make quantitative comparisons with other studies valid in the future. Considering individuals with minimum dbh > 5.0 cm, there were 41 species (Shannon-Wiener (H’) = 1.15 nat.ind') distributed in 32 genera and 18 families. There were 35 species with minimum dbh > 10.0 cm (Shannon-Wiener (H’) = 1.22 nat.ind-1) distributed in 26 genera and 17 families. Araucaria angustifolia was the dominant species according to both inclusion criteria. The non-parametric richness estimators yielded minimum estimates of species richness for the whole community varying from 41.1 to 48.7 species (dbh > 5,0 cm) and from 35.4 to 47.4 species (dbh > 10,0 cm). Dueto the analytical approach we used, these results can be directly compared to results obtained in other studies and presented in similar analytical ways, which is not possible in the majority of related results reported in Brazil.