RESUMO

Tropical forests are a key determinant of the functioning of the Earth system, but remain a major source of uncertainty in carbon cycle models and climate change projections. In this study, we present an updated land model (LM3PPA-TV) to improve the representation of tropical forest structure and dynamics in Earth system models (ESMs). The development and parameterization of LM3PPA-TV drew on extensive datasets on tropical tree traits and long-term field censuses from Barro Colorado Island (BCI), Panama. The model defines a new plant functional type (PFT) based on the characteristics of shade-tolerant, tropical tree species, implements a new growth allocation scheme based on realistic tree allometries, incorporates hydraulic constraints on biomass accumulation, and features a new compartment for tree branches and branch fall dynamics. Simulation experiments reproduced observed diurnal and seasonal patterns in stand-level carbon and water fluxes, as well as mean canopy and understory tree growth rates, tree size distributions, and stand-level biomass on BCI. Simulations at multiple sites captured considerable variation in biomass and size structure across the tropical forest biome, including observed responses to precipitation and temperature. Model experiments suggested a major role of water limitation in controlling geographic variation forest biomass and structure. However, the failure to simulate tropical forests under extreme conditions and the systematic underestimation of forest biomass in Paleotropical locations highlighted the need to incorporate variation in hydraulic traits and multiple PFTs that capture the distinct floristic composition across tropical domains. The continued pressure on tropical forests from global change demands models which are able to simulate alternative successional pathways and their pace to recovery. LM3PPA-TV provides a tool to investigate geographic variation in tropical forests and a benchmark to continue improving the representation of tropical forests dynamics and their carbon storage potential in ESMs.

Assuntos

RESUMO

O presente estudo teve como comparar o desempenho das equações obtidas por meio de modelos volumétricos e de função de afilamento para obtenção do volume total individual com casca em povoamentos de Eucalyptus grandis, em Itatinga, SP. Para tanto, foram cubadas 180 árvores pelo método de Smalian. Após isso, foram selecionados e testados seis modelos volumétricos e quatro modelos de função de afilamento, sendo que para a seleção das melhores equações utilizaram-se os coeficientes de ajuste e precisão: R² ajustado, erro padrão da estimativa absoluto e em porcentagem e a análise gráfica da dispersão residual. Os melhores modelos de volumetria e afilamento foram submetidos ao teste qui-quadrado, a um nível de significância com 5% de probabilidade de erro, para verificar se existem diferenças significativas nas estimativas das equações. As equações volumétricas e de afilamento apresentaram bons valores de ajuste, grande maioria com R² ajustado maior que 0,95 e erros inferiores a 13%. As equações obtidas por meio do modelo de Meyer e do modelo Polinomial de 5º grau apresentaram os melhores desempenhos, sendo que após a análise pelo teste qui-quadrado ambos obtiveram valores calculados inferiores ao tabelado, indicando que tanto um quanto outro podem ser utilizados para estimativa do volume total das árvores.

This study had as objective comparing the performance of equations obtained by means of volumetric models and tapering function to obtain the total individual volume with bark of Eucalyptus grandis, in Itatinga, SP. For such, 180 trees were measured through the Smalian method. After that, six volumetric and four tapering functions were selected and tested, and to select the equations that provided the best adjustment indices, adjustment and precision coefficients were used: adjusted R², standard error of the absolute estimate, as well as percentage and graphical analysis of the residual dispersion. The best volumetric models and tapering functions were subjected to the chi-square test at a significance level of 5% to verify if there was significant difference in the estimates of the equations. The volumetric and tapering function equations presented good adjustment values, a large majority with R² adjusted higher than 0.95 while having errors lower than 13%. The equations obtained using the Meyer model and the Polynomial model of the 5th degree showed the best performances, and after the chi-square test, both obtained lower values than the table, indicating that both can be used to estimate the total volume of trees.

Assuntos

RESUMO

O presente estudo teve como comparar o desempenho das equações obtidas por meio de modelos volumétricos e de função de afilamento para obtenção do volume total individual com casca em povoamentos de Eucalyptus grandis, em Itatinga, SP. Para tanto, foram cubadas 180 árvores pelo método de Smalian. Após isso, foram selecionados e testados seis modelos volumétricos e quatro modelos de função de afilamento, sendo que para a seleção das melhores equações utilizaram-se os coeficientes de ajuste e precisão: R² ajustado, erro padrão da estimativa absoluto e em porcentagem e a análise gráfica da dispersão residual. Os melhores modelos de volumetria e afilamento foram submetidos ao teste qui-quadrado, a um nível de significância com 5% de probabilidade de erro, para verificar se existem diferenças significativas nas estimativas das equações. As equações volumétricas e de afilamento apresentaram bons valores de ajuste, grande maioria com R² ajustado maior que 0,95 e erros inferiores a 13%. As equações obtidas por meio do modelo de Meyer e do modelo Polinomial de 5º grau apresentaram os melhores desempenhos, sendo que após a análise pelo teste qui-quadrado ambos obtiveram valores calculados inferiores ao tabelado, indicando que tanto um quanto outro podem ser utilizados para estimativa do volume total das árvores.(AU)

This study had as objective comparing the performance of equations obtained by means of volumetric models and tapering function to obtain the total individual volume with bark of Eucalyptus grandis, in Itatinga, SP. For such, 180 trees were measured through the Smalian method. After that, six volumetric and four tapering functions were selected and tested, and to select the equations that provided the best adjustment indices, adjustment and precision coefficients were used: adjusted R², standard error of the absolute estimate, as well as percentage and graphical analysis of the residual dispersion. The best volumetric models and tapering functions were subjected to the chi-square test at a significance level of 5% to verify if there was significant difference in the estimates of the equations. The volumetric and tapering function equations presented good adjustment values, a large majority with R² adjusted higher than 0.95 while having errors lower than 13%. The equations obtained using the Meyer model and the Polynomial model of the 5th degree showed the best performances, and after the chi-square test, both obtained lower values than the table, indicating that both can be used to estimate the total volume of trees.(AU)

Assuntos