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Abstract: Anthropogenic understory fires have affected large areas of tropical forest in recent decades, particularly during severe droughts. Yet, the mechanisms that control fire-induced mortality of tropical trees and lianas remain ambiguous due to the challenges associated with documenting mortality given variation in fire behavior and forest heterogeneity. In a seasonally dry Amazon forest, we conducted a burn experiment to quantify how increasing understory fires alter patterns of stem mortality. From 2004 to 2007, tree and liana mortality was measured in adjacent 50-ha plots that were intact (B0 – control), burned once (B1), and burned annually for 3 years (B3). After 3 years, cumulative tree and liana mortality (≥1cm dbh) in the B1 (5.8% yr−1) and B3 (7.0% yr−1) plots significantly exceeded mortality in the control (3.2% yr−1). However, these fire-induced mortality rates are substantially lower than those reported from more humid Amazonian forests. Small stems were highly vulnerable to fire-induced death, contrasting with drought-induced mortality (measured in other studies) that increases with tree size. For example, one low-intensity burn killed >50% of stems <10cm within a year. Independent of stem size, species-specific mortality rates varied substantially from 0% to 17% yr−1 in the control, 0% to 26% yr−1 in B1, and 1% to 23% yr−1 in B3, with several species displaying high variation in their vulnerability to fire-induced mortality. Protium guianense (Burseraceae) exhibited the highest fire-induced mortality rates in B1 and B3, which were 10- and 9-fold greater than the baseline rate. In contrast, Aspidosperma excelsum (Apocynaceae), appeared relatively unaffected by fire (0.3% to 1.0% mortality yr−1 across plots), which may be explained by fenestration that protects the inner concave trunk portions from fire. For stems ≥10cm, both char height (approximating fire intensity) and number of successive burns were significant predictors of fire-induced mortality, whereas only the number of consecutive annual burns was a strong predictor for stems <10cm. Three years after the initial burn, 62±26Mgha−1 (s.e.) of live biomass, predominantly stems <30cm, was transferred to the dead biomass pool, compared with 8±3Mgha−1 in the control. This biomass loss from fire represents ∼30% of this forest''s aboveground live biomass (192 (±3)Mgha−1; >1cm DBH). Although forest transition to savanna has been predicted based on future climate scenarios, our results indicate that wildfires from agricultural expansion pose a more immediate threat to the current carbon stocks in Amazonian forests. [Copyright &y& Elsevier]

A time-series of Landsat and SPOT sensor data was used to approximate the age of tropical forests regenerating on abandoned agricultural land north of Manaus, Brazil, and to estimate the period of active land use prior to abandonment. Based on field data, two distinct regeneration pathways, dominated by the pioneer genera Cecropia and Vismia, respectively, were described, with the former regenerating on the least intensively used sites. Forests of mixed species composition and lacking numerical dominance by pioneer species were also observed. Transformed Divergence Analysis of Landsat Thematic Mapper (TM) radiance data revealed that forests of varying age and following different regeneration pathways were best discriminated using mid infrared (1.55-1.74μm) wavelengths. As rates of carbon sequestration by forests vary with age and regeneration pathway, the potential exists for refining spatial estimates of the carbon balance of tropical forests regenerating on abandoned agricultural lands. [ABSTRACT FROM AUTHOR]

The study aimed to map several stages of tropical forest regeneration across the Brazilian Legal Amazon using 1.1 km NOAA AVHRR data. Regenerating forest extent was defined using an unsupervised classification of AVHRR channels 1, 2 and 3 and the Global Environment Monitoring Index (GEMI). A method for discriminating four forest regeneration stages was then developed, based on relationships between AVHRR channels 1, 2 and 3 and forest age. This method was applied to AVHRR data to map forests associated with Stages I (early colonization phase, open canopy, < 5 years), II (closed, singlelayered canopy, 5-9 years), III (closed canopy with structural development, 9-20 years) and IV (closed multilayered canopy, > 20 years). The maps provided new regional estimates of regenerating forest for the Legal Amazon and indicated that, over the period 1991 to 1994, approximately 35.8% (157 973 km2) of the total deforested area of 440 186 km2 (estimated for 1992) supported regenerating forest, with 48% of these forests aged at less than 5 years. The study concluded that AVHRR data has an important role in mapping and monitoring tropical forest regeneration. The datasets generated provide valuable input to models of regional carbon flux. For example, Grace et al . (1995a, b) reported net annual CO2 absorption 8.5 2.0 moles m 2 for mature forests in south-west Amazonia suggesting. [ABSTRACT FROM AUTHOR]