ABSTRACT The need for grassland restoration in the State of Rio Grande do Sul (RS), Brazil, has become evident in the last two decades, when more than 1 million hectares were converted to other uses only in the Pampa region. Since then, studies have started to verify the most suitable ways to restore subtropical grasslands. Around the world, species introduction is one of the principal restoration techniques. We investigated the availability of seedlings and seeds of native grassland species in the local market and the legal framework regarding the restoration of grassland vegetation in RS. We found, in total, only seven companies that sold seedlings or seeds of nine native species from grasslands, a very limited number given the great biodiversity of South Brazilian grasslands. In addition to that, we found no criteria and procedures for grassland conversion or obligatory replacement established in legal norms for grasslands to Pampa region, as there are for forest vegetation. Without legal requirement, a market for seeds and seedlings likely will not develop and, without a market, there will be no producers, and restoration will remain limited. Our results support the need to create initiates and legislation with basic guidelines for the grassland conversion and restoration in RS.

RESUMO Áreas ribeirinhas são foco recorrente de restauração ecológica, devido a sua importância para a manutenção de serviços ecossistêmicos. Entretanto, poucos estudos têm de fato avaliado o sucesso de intervenções ativas em restaurar funções ou processos ecossistêmicos. A regeneração natural é um processo sucessional, cuja avaliação pode indicar o estado e o potencial de resiliência do ecossistema em áreas sob restauração. O presente estudo comparou padrões de regeneração natural de uma área de restauração ecológica (com plantio de mudas nativas há 10 anos) com a mata ciliar de referência, em Cachoeirinha, Rio Grande do Sul, Brasil. Para tanto, foi realizado o levantamento das espécies arbóreas e arbustivas presentes no estrato superior (DAP ≥ 5 cm) e inferior (altura > 30 cm e DAP < 5 cm), em 40 parcelas de 100 m² cada, considerando o plantio (restauração) e a mata ciliar remanescente (referência). Cada estrato e tratamento (referência vs. restauração) foi avaliado quanto aos descritores fitossociológicos, padrões de estrutura e composição, riqueza e similaridade entre as comunidades. Os resultados demonstraram que a área de restauração apresenta composição de espécies e estrutura diferenciada com relação à referência, especialmente para o estrato superior. No estrato inferior (regeneração natural), o número de indivíduos, a altura média e a riqueza de espécies já não diferiram da referência. A composição de espécies em regeneração ainda foi distinta, porém, esta foi mais similar entre si do que as demais comparações entre estratos, indicando que espécies não plantadas foram capazes de se estabelecer nas áreas de restauração.

ABSTRACT Riparian areas are a recurrent focus of ecological restoration due to their importance for the maintenance of ecosystem services. However, few studies have evaluated the success of active interventions in restoring ecosystem functions and processes. The natural regeneration is a successional process and its evaluation might reveal the state and the potential of the ecosystem resilience in forest areas undergoing restoration. The present study aimed to compare natural regeneration of a riparian area that is undergoing restoration (planting of native trees, 10 years ago) with a reference forest area, in Cachoeirinha, Rio Grande do Sul state, Brazil. We conducted a survey of trees and shrubs in the upper stratum (DBH ≥ 5 cm) and the lower stratum (> 30 cm in height and DBH > 5 cm) in a total of 40 plots (100 m2 each), within the planting (restoration) and the remnant forest (reference). For each stratum and treatment (reference vs. restoration) we analyzed phytosociological parameters, patterns of structure and composition, and similarity among plots. The results showed significant differences in relation to structure and species composition, especially for the upper stratum. For the lower stratum (natural regeneration), abundance, height, and species richness were similar between the restoration and the reference areas. Species composition in regeneration remained distinct. However, its similarity value was higher than any other comparison among strata, indicating that species that were not planted were able to establish in the planted areas.

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.