Indirect and expedite assessment of Ilex paraguariensis commercial yield.

A produção de biomassa comercial é uns dos principais indicadores para seleção de progênies e clones de erva-mate. Técnicas tradicionais para se obter tais informações dependem da colheita das árvores e apresentam, dentre outras limitações, elevado custo e reduzida praticidade. Assim, objetivou-se avaliar a eficiência de métodos indiretos, por meio de estimativa de biomassa comercial e escore de produtividade em função de diferentes procedências, sexo e morfotipos. Em um teste de progênies e procedências instalado em 1997, foram avaliadas em agosto de 2015 (dois anos após a última colheita) duas metodologias de análise visual. Para tanto, participaram cinco avaliadores treinados que determinaram, para cada planta, uma estimativa de biomassa comercial (kg), e uma nota, com base em um escore de produtividade (0-10). Para avaliação da produtividade pelas técnicas tradicionais, todas as plantas foram podadas e tiveram sua biomassa comercial (folhas e ramos finos menores de 7 mm de diâmetro) colhida e avaliada por meio de pesagem (Kg.planta-1). As avaliações foram realizadas em experimento instalado em blocos ao acaso, com cinco repetições, sete procedências e 126 progênies, totalizando 5292 plantas avaliadas. Os métodos avaliados foram eficientes na estimativa da biomassa comercial. Os avaliadores apresentaram boa acuidade nas estimativas, expressando de forma eficiente a maior produtividade determinada por comparação de médias entre as procedências, sexo das matrizes e morfotipos. As maiores correlações foram verificadas na análise geral das médias e a estimativa de biomassa comercial é a melhor metodologia para estimar a biomassa comercial aferida em plantas adultas de erva-mate.

Modeling and Mapping Agroforestry Aboveground Biomass in the Brazilian Amazon Using Airborne Lidar Data.

Agroforestry has large potential for carbon (C) sequestration while providing many economical, social, and ecological benefits via its diversified products. Airborne lidar is considered as the most accurate technology for mapping aboveground biomass (AGB) over landscape levels. However, little research in the past has been done to study AGB of agroforestry systems using airborne lidar data. Focusing on an agroforestry system in the Brazilian Amazon, this study first predicted plot-level AGB using fixed-effects regression models that assumed the regression coefficients to be constants. The model prediction errors were then analyzed from the perspectives of tree DBH (diameter at breast height)?height relationships and plot-level wood density, which suggested the need for stratifying agroforestry fields to improve plot-level AGB modeling. We separated teak plantations from other agroforestry types and predicted AGB using mixed-effects models that can incorporate the variation of AGB-height relationship across agroforestry types. We found that, at the plot scale, mixed-effects models led to better model prediction performance (based on leave-one-out cross-validation) than the fixed-effects models, with the coefficient of determination (R2) increasing from 0.38 to 0.64. At the landscape level, the difference between AGB densities from the two types of models was ~10% on average and up to ~30% at the pixel level. This study suggested the importance of stratification based on tree AGB allometry and the utility of mixed-effects models in modeling and mapping AGB of agroforestry systems.

Plasticity in leaf-level water relations of tropical rainforest trees in response to experimental drought.

The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change.

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests.

The seasonal climate drivers of the carbon cy- cle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combina- tion of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measure- ments and 35 litter productivity measurements), their asso- ciated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonal- ity in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rain- fall is < 2000 mm yr-1 (water-limited forests) and to radia- tion otherwise (light-limited forests). On the other hand, in- dependent of climate limitations, wood productivity and lit- terfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosyn- thetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest pro- ductivity in a drier climate in water-limited forest, and in cur- rent light-limited forest with future rainfall < 2000 mm yr-1.