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1. The effectiveness of global protected areas for climate change mitigation

   https://doi.org/10.1038/s41467-023-38073-9  

   Duncanson, L. ; Liang, M. ; Leitold, V. ; Armston, J. ; Krishna Moorthy, S. M. ; Dubayah, R. ; Costedoat, S. ; Enquist, B. J. ; Fatoyinbo, L. ; Goetz, S. J. ; et al ( June 2023 , Nature Communications)

   Forests play a critical role in stabilizing Earth’s climate. Establishing protected areas (PAs) represents one approach to forest conservation, but PAs were rarely created to mitigate climate change. The global impact of PAs on the carbon cycle has not previously been quantified due to a lack of accurate global-scale carbon stock maps. Here we used ~412 million lidar samples from NASA’s GEDI mission to estimate a total PA aboveground carbon (C) stock of 61.43 Gt (+/− 0.31), 26% of all mapped terrestrial woody C. Of this total, 9.65 + /− 0.88 Gt of additional carbon was attributed to PA status. These higher C stocks are primarily from avoided emissions from deforestation and degradation in PAs compared to unprotected forests. This total is roughly equivalent to one year of annual global fossil fuel emissions. These results underscore the importance of conservation of high biomass forests for avoiding carbon emissions and preserving future sequestration.
2. Variability in above- and belowground carbon stocks in a Siberian larch watershed

   https://doi.org/10.5194/bg-14-4279-2017  

   Webb, Elizabeth E. ; Heard, Kathryn ; Natali, Susan M. ; Bunn, Andrew G. ; Alexander, Heather D. ; Berner, Logan T. ; Kholodov, Alexander ; Loranty, Michael M. ; Schade, John D. ; Spektor, Valentin ; et al ( January 2017 , Biogeosciences)

   Abstract. Permafrost soils store between 1330 and 1580 Pg carbon (C), which is 3 times the amount of C in global vegetation, almost twice the amount of C in the atmosphere, and half of the global soil organic C pool. Despite the massive amount of C in permafrost, estimates of soil C storage in the high-latitude permafrost region are highly uncertain, primarily due to undersampling at all spatial scales; circumpolar soil C estimates lack sufficient continental spatial diversity, regional intensity, and replication at the field-site level. Siberian forests are particularly undersampled, yet the larch forests that dominate this region may store more than twice as much soil C as all other boreal forest types in the continuous permafrost zone combined. Here we present above- and belowground C stocks from 20 sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River, near Chersky, Sakha Republic, Russia. We found that the majority of C stored in the top 1 m of the watershed was stored belowground (92 %), with 19 % in the top 10 cm of soil and 40 % in the top 30 cm. Carbon was more variable in surface soils (10 cm; coefficient of variation (CV)  =  0.35 between stands) than inmore »the top 30 cm (CV  =  0.14) or soil profile to 1 m (CV  =  0.20). Combined active-layer and deep frozen deposits (surface – 15 m) contained 205 kg C m−2 (yedoma, non-ice wedge) and 331 kg C m−2 (alas), which, even when accounting for landscape-level ice content, is an order of magnitude more C than that stored in the top meter of soil and 2 orders of magnitude more C than in aboveground biomass. Aboveground biomass was composed of primarily larch (53 %) but also included understory vegetation (30 %), woody debris (11 %) and snag (6 %) biomass. While aboveground biomass contained relatively little (8 %) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was negatively related to stand age, and soil C density (top 10 cm) was positively related to soil moisture and negatively related to moss and lichen cover. These results suggest that, as the climate warms, changes in stand age and structure may be as important as direct climate effects on belowground environmental conditions and permafrost C vulnerability.« less
3. Droughts, Wildfires, and Forest Carbon Cycling: A Pantropical Synthesis

   https://doi.org/10.1146/annurev-earth-082517-010235  

   Brando, Paulo M. ; Paolucci, Lucas ; Ummenhofer, Caroline C. ; Ordway, Elsa M. ; Hartmann, Henrik ; Cattau, Megan E. ; Rattis, Ludmila ; Medjibe, Vincent ; Coe, Michael T. ; Balch, Jennifer ( May 2019 , Annual Review of Earth and Planetary Sciences)

   Tropical woody plants store ∼230 petagrams of carbon (PgC) in their aboveground living biomass. This review suggests that these stocks are currently growing in primary forests at rates that have decreased in recent decades. Droughts are an important mechanism in reducing forest C uptake and stocks by decreasing photosynthesis, elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. Tropical forests were a C source to the atmosphere during the 2015–2016 El Niño–related drought, with some estimates suggesting that up to 2.3 PgC were released. With continued climate change, the intensity and frequency of droughts and fires will likely increase. It is unclear at what point the impacts of severe, repeated disturbances by drought and fires could exceed tropical forests’ capacity to recover. Although specific threshold conditions beyond which ecosystem properties could lead to alternative stable states are largely unknown, the growing body of scientific evidence points to such threshold conditions becoming more likely as climate and land use change across the tropics. ▪ Droughts have reduced forest carbon uptake and stocks by elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. ▪ Threshold conditions beyond which tropical forests are pushed into alternative stable states are becoming more likely as effectsmore »of droughts intensify.« less
4. Deforestation-induced climate change reduces carbon storage in remaining tropical forests

   https://doi.org/10.1038/s41467-022-29601-0  

   Li, Yue ; Brando, Paulo M. ; Morton, Douglas C. ; Lawrence, David M. ; Yang, Hui ; Randerson, James T. ( April 2022 , Nature Communications)

   Biophysical effects from deforestation have the potential to amplify carbon losses but are often neglected in carbon accounting systems. Here we use both Earth system model simulations and satellite–derived estimates of aboveground biomass to assess losses of vegetation carbon caused by the influence of tropical deforestation on regional climate across different continents. In the Amazon, warming and drying arising from deforestation result in an additional 5.1 ± 3.7% loss of aboveground biomass. Biophysical effects also amplify carbon losses in the Congo (3.8 ± 2.5%) but do not lead to significant additional carbon losses in tropical Asia due to its high levels of annual mean precipitation. These findings indicate that tropical forests may be undervalued in carbon accounting systems that neglect climate feedbacks from surface biophysical changes and that the positive carbon–climate feedback from deforestation-driven climate change is higher than the feedback originating from fossil fuel emissions.
5. Greenness trends and carbon stocks of mangroves across Mexico

   https://doi.org/10.1088/1748-9326/ab246e  

   Vázquez-Lule, Alma ; Colditz, Rene ; Herrera-Silveira, Jorge ; Guevara, Mario ; Rodríguez-Zúñiga, María Teresa ; Cruz, Isabel ; Ressl, Rainer ; Vargas, Rodrigo ( July 2019 , Environmental Research Letters)

   Mangroves cover less than 0.1% of Earth’s surface, store large amounts of carbon per unit area, but are threatened by global environmental change. The capacity of mangroves productivity could be characterized by their canopy greenness, but this property has not been systematically tested across gradients of mangrove forests and national scales. Here, we analyzed time series of Normalized Difference Vegetation Index (NDVI), mean air temperature and total precipitation between 2001 and 2015 (14 years) to quantify greenness and climate variability trends for mangroves not directly influenced by land use/land cover change across Mexico. Between 2001 and 2015 persistent mangrove forests covered 432 800 ha, representing 57% of the total current mangrove area for Mexico. We found a temporal greenness increase between 0.003_{[0.001–0.004]}and 0.004_{[0.002–0.005]}yr⁻¹(NDVI values ± 95%CI) for mangroves located over the Gulf of California and the Pacific Coast, with many mangrove areas dominated byAvicennia germinans.Mangroves developed along the Gulf of Mexico and Caribbean Sea did not show significant greenness trends, but site-specific areas showed significant negative greenness trends. Mangroves with surface water input have above ground carbon stocks (AGC) between 37.7 and 221.9 Mg C ha⁻¹and soil organic carbon density at 30 cm depth (SOCD) between 92.4 and 127.3 Mg Cmore »ha⁻¹. Mangroves with groundwater water input have AGC of 12.7 Mg C ha⁻¹and SOCD of 219 Mg C ha⁻¹. Greenness and climate variability trends could not explain the spatial variability in carbon stocks for most mangrove forests across Mexico. Site-specific characteristics, including mangrove species dominance could have a major influence on greenness trends. Our findings provide a baseline for national-level monitoring programs, carbon accounting models, and insights for greenness trends that could be tested around the world.

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