Loud, gigantic, and scary! This was my first impression of a skidder – a heavy vehicle used in cutting trees. Multiple trees are crushed to access one large Amazonian log. This was the logging operations that occurred in the Jamari National Forest in the Rondônia State of Brazil. Logging tropical trees is simultaneously an art and a damaging activity, given that these trees play a crucial role in regulating Earth’s climate. Despite this importance, only a few operations follow certified sustainable forest management plans (SFMPs).
In Brazil, a minimum of SFMPs are underway across 25% of the Amazon forest area managed for timber production. Without SFMPs, these forests are more susceptible to illegal logging and conversion to monocropping systems than their SFMP-managed counterparts. While logging activities in tropical forests under SFMPs are less environmentally destructive than conventional logging, there are essential differences among logging activities across types of SFMPs. In general, SFMPs can still be significantly improved to achieve sustainable development goals (e.g., REDD+).
My research in quantifying logging impacts on Amazonian forests began a decade ago during an in-depth training in tropical forest management provided by Brazil’s National Institute for Amazonian Research (INPA). During a demanding five-week training, I learned that the gaps in forest management knowledge in Amazonia are as gigantic as the importance of this extensive tropical rainforest in a changing climate (Figure 1).
So, I set out to assess the impact of selective logging under SFMP on forest regeneration and litter and soil biogeochemistry in evergreen forests in Central Amazonia. This research has been published in the journal of Science of the Total Environment (Bomfim et al., 2020).
In this study, my co-authors and I conducted extensive fieldwork to estimate canopy cover, record tree seedling density, and collect litter and soil samples from unlogged and logged forests at Precious Woods Amazon-PWA (Itacoatiara, Amazonas State; Figure 2).
PWA’s 35-year polycyclic timber harvesting included reduced-impact selective logging (~17 m3 ha−1 yr−1 or four trees per hectare of ~45 tree species) followed by natural forest regeneration. All operations are conducted in compliance with the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification guidelines (Precious Woods Amazon, 2017). During logging operations, trees were identified and directionally felled, slashed (i.e., cut into lengths), and winched with a metal cable by a track-type tractor with hydraulic winch to the skid trail (pre-winching stage). Later, logs are dragged by a rubber-tired skidder with hydraulic grapples through the skid trail to the nearest landing. At the Jamari location, trees are also directionally felled (Figure 3), but there is no pre-winching stage. As such, a rubber-tired skidder enters the forest to winch the logs to the nearest landing. The lack of a pre-winching state and permanent skid trails are essential differences between Jamari’s and PWA’s logging schemes.
Several aspects need to be taken into account when ranking SFMPs in tropical forests, as forests are typically different in structure, composition, and soils. Here, I attempted to illustrate differences in logging schemes between PWA and Jamari in the Brazilian Amazon.
On one hand, at PWA, skid trails are permanent (i.e., will be used in the next cutting cycles), and the skidder does not transit in the forest, allowing natural regeneration to take place while avoiding the soil compaction caused by skidder transit (DeArmond et al., 2019). At Jamari, on the other hand, skid trails are relatively temporary and are not properly opened. Here, the skidder follows orange ribbons placed on small trees by forest workers to indicate the best route to access a felled log inside the forest (Figure 4). This is repeated for every single felled tree during present and future cutting cycles (Figure 5). The soil compaction caused by the movements of the skidder, which at PWA is limited to trails only, happens inside the forest where natural regeneration will take place after logging operations are completed. This is also where marketable tree species will grow to meet the demands necessary for economic viability. As such, forest management must consider both the short and long-term impacts of the system they use.
Overall, our field study results at PWA support the notion that selective logging operations at Precious Woods Amazon, at least after the first harvest cycle, appear not to compromise litter and soil biogeochemistry, thus, nutrient cycling in the studied forests. We found that litter and soil parameters (i.e. carbon-nitrogen ratio, bulk density, cation exchange capacity and calcium-magnesium ratio) reflected differences in vegetation structure. Still, litter parameters (e.g., carbon stock and carbon-nitrogen ratio) were more sensitive to logging than soil parameters. In particular, we found that sand content and four dynamic litter and soil parameters can be used as indicators of sustainable forest management in upland evergreen forests in Central Amazonia.
We still fall short in our ability to thoroughly compare both logging schemes based on field data. However, recent studies using multi-temporal airborne LiDAR (Light Detection and Ranging) data (Rangel Pinagé et al., 2019) have been contributing to our understanding on the impacts of logging in hard-to-access tropical forests that are privately managed.
Future forests will need to be increasingly better managed. Assessing and improving sustainable forest management plans in tropical forests is a current necessity to ensure their maintenance and functioning in a changing climate.
About the Author: Dr Barbara Bomfim is a Postdoctoral Research Fellow in the Climate and Ecosystem Sciences Division at Lawrence Berkeley National Laboratory. She is a member in the Next Generation Ecosystem Experiments-Tropics, where she currently focuses on predicting tropical forest response to and recovery from wind disturbances. She received her M.Sc. in Tropical Forest Management at the University of Brasilia, Brazil, and her Ph.D. in Soils and Biogeochemistry from the University of California, Davis. Her research aims to advance knowledge on the response of biogeochemical cycling to disturbance in terrestrial ecosystems, with a main focus on integrating field observation, laboratory experimentation, stable isotope tracers, and statistical modeling tools. Her twitter is @BarbaraBomfim18
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