Total Ecosystem Carbon Stocks of Mangroves in Lamu, Kenya; and Their Potential Contributions to the Climate Change Agenda in the Country

Mangroves are carbon-rich ecosystems found in tropical and subtropical areas around the world. However, they are threatened by a combination of natural and human-induced factors. When mangroves are lost or degraded, their co-benefits to human society are greatly diminished along with the ecosystem’s ability to sequester carbon. The current study assessed mangrove cover and cover change, as well as measuring carbon stocks and their emissions levels from the mangroves of Lamu County, Kenya. We sampled above-and below-ground carbon pools, including soil organic carbon (SOC), in 191 plots distributed throughout the study area. Lastly, we evaluated the economics of avoiding mangrove deforestation based on the carbon-offset market. The total carbon stock of mangroves in Lamu was estimated at 20 million Mg C, with an average density of 560.22 ± 79.79 Mg C ha–1. Southern swamps recorded significantly higher carbon densities (p < 0.05) than other mangrove management blocks in Lamu. At least 1,739 ha of mangroves in Lamu were lost between 1990 and 2019 due to anthropogenic activities, representing a decline of 60 ha yr–1. Total emissions from loss and degradation of mangroves in Lamu is estimated at 140.1 Mg C ha–1; which translates to 30,840.1 Mg CO2e yr–1. Assuming an offset price of US$10/Mg CO2e, the estimated costs of avoided emissions in Lamu is US$308,401 yr–1 plus other co-benefits such as fishery functions and shoreline protection. Mainstreaming mangroves and associated blue carbon ecosystems into national development and climate change agenda could accelerate Kenya’s achievements of both Sustainable Development Goals (SDGs) and the Paris Agreement.

Mangrove selective logging sustains biomass carbon recovery, soil carbon, and sediment

West Papua’s Bintuni Bay is Indonesia’s largest contiguous mangrove block, only second to the world’s largest mangrove in the Sundarbans, Bangladesh. As almost 40% of these mangroves are designated production forest, we assessed the effects of commercial logging on forest structure, biomass recovery, and soil carbon stocks and burial in five-year intervals, up to 25 years post-harvest. Through remote sensing and field surveys, we found that canopy structure and species diversity were gradually enhanced following biomass recovery. Carbon pools preserved in soil were supported by similar rates of carbon burial before and after logging. Our results show that mangrove forest management maintained between 70 and 75% of the total ecosystem carbon stocks, and 15–20% returned to the ecosystem after 15–25 years. This analysis suggests that mangroves managed through selective logging provide an opportunity for coastal nature-based climate solutions, while provisioning other ecosystem services, including wood and wood products.

Harvest volumes and carbon stocks in boreal forests of Ontario, Canada

We used models to project forest carbon stocks for a series of harvesting scenarios for 29 boreal forest management units totalling 23.3 million ha in Ontario, Canada. Scenarios evaluated for 2020 to 2050 ranged from a no harvesting option to annual harvesting of 2% of the total merchantable volume present in 2020. For each scenario, we estimated the following carbon quantities: (a) forest ecosystem carbon stocks, (b) sum of carbon stocks in forest ecosystem and harvested wood products (HWP) minus emissions associated with HWP production and decomposition, and (c) net greenhouse gas (GHG) effects of harvesting estimated as (b) combined with emissions avoided by substituting HWP for non-wood materials. The average of each carbon quantity for 2020 to 2050 was linearly dependent on the annual harvest volume. The developed relationships were used to estimate harvest volumes for which the three carbon quantities would equal equilibrium forest ecosystem carbon stocks for a pre-suppression natural disturbance cycle. These estimates indicate the range of harvest volumes for which resulting carbon stocks would equal or exceed those in an unmanaged forest. Also discussed are possible criteria for determining annual harvest volume.

Harvest volumes and carbon stocks in boreal forests of Ontario, Canada

We used models to project forest carbon stocks for a series of harvesting scenarios for 29 boreal forest management units totalling 23.3 million ha in Ontario, Canada. Scenarios evaluated for 2020 to 2050 ranged from a no harvesting option to annual harvesting of 2% of the total merchantable volume present in 2020. For each scenario, we estimated the following carbon quantities: (a) forest ecosystem carbon stocks, (b) sum of carbon stocks in forest ecosystem and harvested wood products (HWP) minus emissions associated with HWP production and decomposition, and (c) net greenhouse gas (GHG) effects of harvesting estimated as (b) combined with emissions avoided by substituting HWP for non-wood materials. The average of each carbon quantity for 2020 to 2050 was linearly dependent on the annual harvest volume. The developed relationships were used to estimate harvest volumes for which the three carbon quantities would equal equilibrium forest ecosystem carbon stocks for a pre-suppression natural disturbance cycle. These estimates indicate the range of harvest volumes for which resulting carbon stocks would equal or exceed those in an unmanaged forest. Also discussed are possible criteria for determining annual harvest volume.

Effects of different management options of Norway spruce on radiative forcing through changes in carbon stocks and albedo

Norway spruce (Picea abies Karst. (L.)) in the boreal zone can be managed as even-aged or uneven-aged stands, or be grown with no management at all. Here, we investigated how these management options affect carbon dynamics, particularly the carbon stocks in the forest ecosystem (trees and soil), and albedo, and their combined effect on radiative forcing compared to a reference case, clear-cut site before planting seedlings. This allowed us to assess the potential of different management regimes to mitigate global warming. We ran long-term simulations under the current climate on a sub-mesic site in central Finland (62oN) using an eco-physiological forest-ecosystem model. Compared to even-aged management, no management (old-growth forest) increased ecosystem carbon stocks by 47 per cent and decreased albedo by 15 per cent, whereas uneven-aged management reduced ecosystem carbon stocks by 16 per cent and increased albedo by 10 per cent. Only the no management option resulted in a significant net cooling effect whereas for even-aged and uneven-aged management, the opposing effects of changes in albedo and carbon stocks largely cancelled each other with little remaining net effect. On the other hand, the latter one even made a small net warming contribution. Overall, maintaining higher ecosystem carbon stocks implied the larger cooling benefits. This was evident even though lower albedo enhanced radiation absorption, and thus warming. Increasing use of the no management option by forest owners may require proper incentives such as compensation for lost harvest incomes.