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Tropical forests play a critical role in the global carbon cycle, storing 40–55 % of terrestrial plant carbon and significantly contributing to primary productivity. However, uncertainties persist in estimating carbon stocks and fluxes, exhibiting variation across the Neotropics, Africa, and Asia tropical forest regions. Despite hosting some of the most densely sampled forests, significant uncertainties persist in biomass and forest carbon stock estimates in the Neotropics. Although the Southwestern Amazon (SWA) forests span over 20 million hectares, no specific biomass or above- and below-ground carbon model has been calibrated for this region thus far. In our study, we conducted direct forest inventories in the SWA to address the following question: Do the allometric patterns, biomass, and carbon stocks observed in the Southwestern Amazon differ from those found in other regions of the Amazon or Pantropical? Our research reveals substantial differences in water and carbon content, biomass stocks, above- and below-ground oven-dry biomass ratios, and allometric patterns between SWA forests and other Amazonian and Pantropical forests. We have demonstrated that these differences result in overestimations of forest biomass when applying allometric equations developed for other Amazonian and Pantropical regions to the open forests of Southwestern Amazonia. This overestimation can reach up to 37 % when using equations from the eastern Amazon, and between 26 % and 46 % depending on the applied Pantropical equation. The use of an inappropriate factor for the root-to-shoot ratio in the Southwestern Amazon (SWA) can lead to overestimates of belowground oven-dry biomass by up to 20 %. To reduce uncertainties related to estimates of forest carbon stock and flux in Neotropical forests, it is necessary to enhance the density of direct biomass measurements, particularly in southwestern Amazonia. • Improvement of tropical forest carbon stock estimates depends on increasing the direct biomass measurements. • We developed the first set of allometric equations for Southwestern Amazon (SWA) Forests. • The allometric patterns of the forests of the SWA are distinct from the Pantropical regions. • Equations derived from other regions may overestimate SWA forest biomass by up to 46 %. • Our results fill a significant gap in biomass estimation for SWA Forests. [ABSTRACT FROM AUTHOR]

The tension between the large global demand for tropical timber, and ecological sustainability and local socioeconomic development in the fragile natural ecosystems of the Amazon region has challenged many generations. In this case study, carried out in an ecotone forest in the northern Brazilian Amazon, we seek to demonstrate how forest management can became more sustainable through silvicultural prescriptions that reduce forest degradation and soil erosion. We evaluated the effects of the sustainable forest management (SFM) on tree diversity, timber volumes, and carbon stocks. A continuous forest inventory was carried out in nine 1-ha permanent plots (900 subplots of 100 m²), distributed in three treatments with three repetitions: T1 = control without selective logging, T2 = SFM, and T3 = SFM + silvicultural treatment of thinning release by tree girdling and poisoning. SFM was carried out with an average of three commercial timber trees harvested per hectare with DBH (diameter at breast height) ≥ 50 cm, corresponding to a timber volume of 20 ± 6 m3 ha-1, equivalent to the removal of 7 ± 2 Mg C ha-1 (5% of the original C). The formation of clearings (gaps) arising from the falling of exploited trees (0.12 ± 0.09 ha) resulted in greater impacts on the forest structure than the construction of 4 m skidder trails (0.06 ± 0.04 ha), with an average of 7 ± 4 damaged trees ha-1 and 5 ± 3 dead trees ha-1. Although six trees species became locally extinct, tree diversity was little altered, and timber volumes and forest carbon volume stocks remained essentially constant at this average logging intensity. Based on our results, sustainable forest management can become an efficient model for land use in the Amazon when harvesting is carried out using this average logging intensity. However, long-term monitoring studies using permanent plots in ecotone forests in the Brazilian Amazon will still be necessary. Quantifying, evaluating, and reporting impacts related to forest management will enable the formation of an empirical basis to support sustanaible forestry practices and for updating environmental legislation, contributing to local socioeconomic development, and maintaining the environmental services provided globally by tropical forests. • We evaluated the effects of selective logging and silvicultural treatments. • The mean intensity of logging (20 ± 6 m3 ha-1) did not alter tree diversity. • The greatest impact came from clearings created by falling commercial timber trees. • Forest carbon stock may alter depending on the selective logging intensity. [ABSTRACT FROM AUTHOR]

Abstract: Precise estimation of biomass at a regional scale is required for evaluating forest carbon stocks throughout the Amazon. We examined six types of allometric models to identify the best estimator of biomass in primary forests (terra firme) in the northwestern sector of the Brazilian Amazon. We also tested six regression models for estimating tree height. We developed each allometric model using measurements of 101 trees excavated in a primary forest distributed along the upper Rio Negro. A simple power function with stem diameter at breast height D as a single variable was selected as the best model for estimating each biomass component, i.e. above-ground total mass AGW, below-ground total mass BGW, and whole individual mass. Among models developed to estimate tree height H from D, we selected a regression model with a coefficient corresponding to an asymptotic height as the best fit. The D–AGW relationship at our study site differed significantly from models developed previously for other regions of the Amazon. We explain this regional variation in part by regional differences in D–H relationships of sample trees. The D–BGW relationship at our site also differed significantly from that in the central Amazon. However, AGW–BGW relationships were consistent between the upper Rio Negro forest and other forests in the central Amazon, in that the BGW–AGW ratio was constant as 0.136 regardless of tree size. On the basis of D-based allometry and census data from 23 plots established in the upper Rio Negro region, we estimated a stand-level total biomass (dry mass) of 252.6Mgha−1. This estimate is at least 73% lower than the potential stand biomass for the region previously suggested by several meta-analyses. [Copyright &y& Elsevier]

• Surface soil recovery of bulk density in 23 years at 5 cm depth. • Fine root biomass no different in skid trails and controls at 13 years. • Higher CEC and organic C in skid trails when compared to control after 19 years. • Elevated levels of exchangeable Al still in skid trails after 26 years. • Soil compaction persists in skid trails 19 years after logging in a clay Ferralsol. Each year, thousands of km2 of humid tropical forest are logged in the Brazilian Amazon. Many of these areas are underlain by clay soils dominated by non-expansive kaolinite. Logging operations often entail the use of heavy machinery to drag logs through the forest on skid trails, which causes substantial soil disturbance. Therefore, the objective of this study was to investigate if soil recovery occurs over time in the studied Ferralsol. The hypothesis is that soil recovery has indeed occurred and that the trend of recovery is observable. In this endeavor, a chronosequence was established composed of four logging units that were logged 13, 19, 23, and 26 years ago, as well as a control in undisturbed old-growth forest. Samples in the upper topsoil were collected for soil bulk density (BD), fine root biomass (FRB) and various soil chemical properties. Results indicated a sequential recovery. Prior to the study period of 13–26 years after logging operations, FRB recovered. The predicted recovery of the cation exchange capacity was at approximately 15 years, which was followed by soil organic carbon at 20 years. Lastly, BD was recovered within 25 years. Overall, soil organic carbon demonstrated the greatest associations with recovery variables as it accumulated over time. Although surface soils in skid trails did indeed recover, it was a lengthy process that occurred over several decades. In this context, skid trails should be planned to minimize soil disturbance in the logging area to the greatest extent feasible. [ABSTRACT FROM AUTHOR]