Modelagem de biomassa florestal através do padrão espectral no Sudoeste da Amazônia /

Uma relação alométrica publicada para estimar a biomassa seca acima do solo a partir do diâmetro de árvores, elaborada para florestas densa da Amazônia Central, foi adaptada para uso em duas florestas abertas no sudoeste da Amazônia, aplicando duas correções lineares: uma que considera a menor densidade básica da madeira e outra que considera a menor altura de árvores para um dado diâmetro. Estas correções foram aplicadas para estimar a biomassa das duas florestas abertas - uma com e a outra sem o bambu Guadua weberbaueri - usando os inventários de Oliveira (2000). As correções foram derivadas usando dados coletados anteriormente de densidade de madeira de 12 árvores da Amazônia Central e dados inéditos de densidade básica, altura e diâmetro de 348 árvores da Amazônia Central e dados inéditos de densidade básica, altura e diâmetro de 100 árvores derrubdas em cada uma das duas florestas abertas no sudoeste da Amazônia comparado com Amazônia Central, teve forte efeito, reduzindo a estimativa de biomassa das duas tipologias de floresta no sufoeste amazônico. Os pesos secos totais estimados na floresta com bambu e sem bambu, com (sem) as correções, foram de 122 (206) t ha ­¹ e 216 (300) t ha ­¹, respectivamente, para os caules 2,5 cm DAP. Para caules10 cm DAP, a biomassa seca com (sem a correção foi 100 (177) t ha ­¹ na floresta com bambu e 200 (280) t ha ­¹ na floresta sem bambu. Baseado nesse inventário, o bambu, que ocupa uma área de 180.000 km², reduz em 44 - 50% o potencial de estocagem de biomassa nestas classes diamétricas. A biomassa da floresta sem bambu é 28 - 29 % menor do que seria estimado sem as correções. A segunda parte deste estudo relaciona biomassa com o padrão espectral, no local dos inventários e extrapola esta relação para uma área de 90x90 km. Foi estimada a biomassa da cada pixel de floresta madura, em imagem do TM Landsat do ano de 1987, quando o bambu estava maduro e espectramente estável. Todos os valores de reflectância, no espaço de atributos cujos os eixos são as bandas espectrais, foram ordenados ao longo de um eixo (nova banda) entre os dois centróides dos pixels das duas áreas inventariadas: floresta com e sem bambu. Os valores de reflectância ordenados foram escalonados para biomassa de árvores 10cm DAP, fixando os dois extremos do eixo de ordenamento em 100 t ha ­¹ e 200 t ha ­¹. Para aprimorar o modelo , foram executadas algumas etapas de pré-processamento digital na imagem de 1987 como: correção da variação no conteúdo de sombra ao nível de sub-pixel ao longo da varredura, causada pela geometria de iluminação; retificação geométrica; retificação radiométrica para uma atmosfera padrão mais limpa; transformação da radiãncia radiométrica para uma atmosfera padrão mais limpa; transformação da radiância codificada em valores de reflectância topo-de-atmosfera e aplicação de filtro mediana em janela móvel de 7x7 pixels, para reduzir efeitos de sombras topográficas. Na área de 90x90 km, os pixels considerados florestados foram identificados usando três distâncias euclidianas: uma a partir do eixo de ordenamento e duas a partir dos extremos do eixo. A grande maioria dos pixels deste "cilindro de aceitabilidade" são capoeiras, pastos, área urbana, corpos d'água, praias e estradas; estes não foram modelados e constituem 28% da área. Todas as etapas do pré-processamento, criação do cilindro de aceitabilidade e o ordenamento polar foram semi-automatizadas usando comandos de macro, para que o modelo possa ser rodado e modificado com facilidade, com diferentes variáveis de entrada. Na área de 90x90 km, o modelo detectou para as árvores 10 cm de DAP, uma biomassa média praticamente ialterada com e sem aplicação de filtro mediana nas bandas (168 t ha ­¹ versus 167 t ha ­¹, respectivamente). Com o filtro mediana, mais pixels de floresta foram corretamente identificados e incorporados no cilindro de aceitabilidade para modelagem, dentro do espaço-banda

Height-diameter allometry of tropical forest trees

Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account. © 2011 Author(s)

Estimativas de biomassa, do índice de área foliar e aplicação do sensoriamento remoto no monitoramento no estudo da cobertura vegetal em áreas de florestas ombrófila aberta e densa na Amazônia

Titre en français : Estimation de la biomasse, de l'indice foliaire et application de la télédétection dans l'étude de la couverture végétale en forêts ompbrophiles ouverte et dense en AmazonieThe Amazon, the largest and most diverse of the tropical forest wilderness areas, shelter 33% of the world's tropical forests. However, the scenario of deforestation and degradation of the Amazon forest has been the subject of worldwide interest, primarily due to the growing contribution of deforestation to global warming. This study was conducted at the Caiabi Farm in Alta Floresta (north of Mato Grosso State) and in the Tropical Forestry Experimental Station (EEST/INPA) in Manaus (Central Amazonia). In this research, the main objectives were the study of the vegetation structure, the stock of dry biomass, the leaf area index (LAI) and the spectral behaviour of the open and dense ombrophilous forests. The field inventory was carried out on 3 samples of primary forest, 9 samples of experimental developed forest with different clear cutting levels and 7 samples of forest in regeneration (5, 8, 11, 23 and 30 years old), which have been cut down and burned, without subsequent use. In each sample of 1 ha, divided into 9 subsamples 20 by 20 m, we have measured and identified, by the vernacular name, all the individuals with DBH ≥ 5 cm (in secondary forests), and with a DBH ≥ 10 cm (in primary and managed forests). In sub-samples, hemispherical photographs were taken at 10 m-intervals to estimate LAI. The florisctic analysis showed that the vegetation of Alta Floresta is less diverse than the vegetation of Manaus. The stock of biomass and carbon increases as the successional stage advances. In the managed forest, biomass values were close to those of primary forest, indicating that these exploited areas recovered the original stock of biomass, 19 years after the selective exploitation. In developed forests, statistical analyses of LAI from Alta Floresta and Manaus areas, suggest also highly significant differences (p < 0.01) between the various succession stages. However, in developed forest, statistical analyses of LAI do not present significant differences between treatments after 19 years. Image processing showed us that the SAVI values made it possible to observe variations among the succession stages. The secondary forests dominated by Cecropia showed the greatest vegetation indices. Statistical analyses of the temporal series of the developed areas suggested that the NVDI, SAVI values and the images fractionsvegetation and fraction-shade change with time. However, the interactions of treatment*NDVI, treatment*SAVI, treatment*fractions vegetation and treatment*fractions shade do not vary significantly over timeA Amazônia abriga 33% das florestas tropicais do mundo, é a maior e mais diversa floresta tropical do planeta. No entanto, o cenário do desmatamento e da degradação da floresta Amazônica tem sido alvo de interesse mundial, principalmente, devido a contribuição do desmatamento no aumento do aquecimento global. Este estudo foi conduzido na Fazenda Caiabi localizada no município de Alta Floresta (norte do Mato Grosso) e na Estação Experimental de Silvicultura Tropical (EEST/INPA) em Manaus (Amazônia Central). Nesta pesquisa, objetivou-se analisar a estrutura da vegetação, o estoque de biomassa seca, o índice de área foliar (IAF) e o comportamento espectral das florestas ombrófilas aberta e densa. O levantamento de campo foi realizado em três parcelas de floresta primária, nove parcelas de floresta manejada sob diferentes intensidades de corte e sete parcelas de floresta secundária (5, 8, 11, 23 e 30 anos) onde sofreram corte raso seguido de queima e abandonadas sem uso do solo subseqüente. Dentro de cada parcela de 1 ha, dividida em 9 subparcelas de 20x20m, foram mesurados e identificados todos os indivíduos com DAP ≥ 5 cm (floresta secundária) e DAP ≥ 10 cm (florestas primária e manejada). Nas subparcelas foram tiradas fotografias hemisféricas a cada 10 m para estimar o IAF. A análise florística mostrou que a vegetação de Alta Floresta tem menor diversidade florística em relação a vegetação de Manaus. O estoque de biomassa e carbono aumenta a medida que o estádio sucessionl avança. Em floresta manejada os valores de biomassa foram próximos dos valores da floresta primária, demonstrando que estas áreas recuperaram o estoque original de biomassa, 19 anos após a exploração seletiva. A análise de variância do IAF entre os sítios de Alta Floresta e Manaus demonstraram que há diferenças significativas (p < 0,01) entre os estádios sucessionais. No caso da floresta manejada, a análise estatística para o IAF não evidenciou diferenças significativas entre os tratamentos 19 anos após exploração. No processamento das imagens verificou-se que os valores do índice SAVI permitiram observar variações entre os estádios sucessionais. As capoeiras dominadas pelo gênero Cecropia apresentaram maiores frações de vegetação. As análises estatísticas para a série temporal das áreas manejadas indicam que o NDVI, SAVI e imagens-fração vegetação e sombra mudam significativamente com o passar do tempo. Porém, as interações entre tratamento*NDVI, tratamento*SAVI, tratamento*fração vegetação e tratamento*fração sombra não variaram significativamente com o passar do tempo

Wood density in forests of Brazil's 'arc of deforestation': Implications for biomass and flux of carbon from land-use change in Amazonia

Wood density is an important variable in estimates of forest biomass and greenhouse-gas emissions from land-use change. The mean wood density used in estimates of forest biomass in the Brazilian Amazon has heretofore been based on samples from outside the "arc of deforestation", where most of the carbon flux from land-use change takes place. This paper presents new wood density estimates for the southern and southwest Brazilian Amazon (SSWA) portions of the arc of deforestation, using locally collected species weighted by their volume in large local inventories. Mean wood density was computed for the entire bole, including the bark, and taking into account radial and longitudinal variation. A total of 403 trees were sampled at 6 sites. In the southern Brazilian Amazon (SBA), 225 trees (119 species or morpho-species) were sampled at 4 sites. In eastern Acre state 178 trees (128 species or morpho-species) were sampled at breast height in 2 forest types. Mean basic density in the SBA sites was 0.593 ± 0.113 (mean ± 1 S.D.; n = 225; range 0.265-0.825). For the trees sampled in Acre the mean wood density at breast height was 0.540 ± 0.149 (n = 87) in open bamboo-dominated forest and 0.619 ± 0.149 (n = 91) in dense bamboo-free forest. Mean wood density in the SBA sites was significantly higher than in the bamboo dominated forest but not the dense forest at the Acre site. From commercial wood inventories by the RadamBrasil Project in the SSWA portion of the arc of deforestation, the wood volume and wood density of each species or genus were used to estimate average wood density of all wood volume in each vegetation unit. These units were defined by the intersection of mapped forest types and states. The area of each unit was then used to compute a mean wood density of 0.583 g cm-3 for all wood volume in the SSWA. This is 13.6% lower than the value applied to this region in previous estimates of mean wood density. When combined with the new estimates for the SSWA, this gave an average wood density of 0.642 g cm-3 for all the wood volume in the entire Brazilian Amazon, which is 7% less than a prior estimate of 0.69 g cm-3. These results suggest that current estimates of carbon emissions from land-use change in the Brazilian Amazon are too high. The impact on biomass estimates and carbon emissions is substantial because the downward adjustment is greater in forest types undergoing the most deforestation. For 1990, with 13.8 × 103 km2 of deforestation, emissions for the Brazilian Amazon would be reduced by 23.4-24.4 × 106 Mg CO2-equivalent C/year (for high- and low-trace gas scenarios), or 9.4-9.5% of the gross emission and 10.7% of the net committed emission, both excluding soils. © 2007 Elsevier B.V. All rights reserved

Tree height in Brazil's 'arc of deforestation': Shorter trees in south and southwest Amazonia imply lower biomass

This paper estimates the difference in stand biomass due to shorter and lighter trees in southwest (SW) and southern Amazonia (SA) compared to trees in dense forests in central Amazonia (CA). Forest biomass values used to estimate carbon emissions from deforestation throughout, Brazilian Amazonia will be affected by any differences between CA forests and those in the "arc of deforestation" where clearing activity is concentrated along the southern edge of the Amazon forest. At 12 sites (in the Brazilian states of Amazonas, Acre, Mato Grosso and Pará) 763 trees were felled and measurements were made of total height and of stem diameter. In CA dense forest, trees are taller at any given diameter than those in SW bamboo-dominated open, SW bamboo-free dense forest and SA open forests. Compared to CA, the three forest types in the arc of deforestation occur on more fertile soils, experience a longer dry season and/or are disturbed by climbing bamboos that cause frequent crown damage. Observed relationships between diameter and height were consistent with the argument that allometric scaling exponents vary in forests on different substrates or with different levels of natural disturbance. Using biomass equations based only on diameter, the reductions in stand biomass due to shorter tree height alone were 11.0, 6.2 and 3.6%, respectively, in the three forest types in the arc of deforestation. A prior study had shown these forest types to have less dense wood than CA dense forest. When tree height and wood density effects were considered jointly, total downward corrections to estimates of stand biomass were 39, 22 and 16%, respectively. Downward corrections to biomass in these forests were 76 Mg ha-1 (∼21.5 Mg ha-1 from the height effect alone), 65 Mg ha-1 (18.5 Mg ha-1 from height), and 45 Mg. ha-1 (10.3 Mg ha-1 from height). Hence, biomass stock and carbon emissions are overestimated when allometric relationships from dense forest are applied to SW or SA forest types. Biomass and emissions estimates in Brazil's National Communication under the United Nations Framework Convention on Climate Change require downward corrections for both wood density and tree height. © 2008 Elsevier B.V. All rights reserved