Due to the increase in atmospheric CO2concentrations, the ratio of carbon fixed by assimilation to water lost by transpiration through stomatal conductance (intrinsic water-use efficiency, iWUE) shows a long-term increasing trend globally. However, the drivers of short-term (inter-annual) variability in iWUE of tropical trees are poorly understood. We studied the inter-annual variability in iWUE of three South Asian tropical moist forest tree species (Chukrasia tabularis A.Juss., Toona ciliata M. Roem. and Lagerstroemia speciosa L.) derived from tree-ring stable carbon isotope ratio (δ13C) in response to variations of environmental conditions. We found a significantly decreasing trend in carbon discrimination (13C) and an increasing trend in iWUE in all the three species, with a species-specific long-term trend in intercellular CO2concentration (Ci). Growing season temperatures were the main driver of inter-annual variability of iWUE in C. tabularis and L. speciosa, whereas previous year temperatures determined the iWUE variability in T. ciliata. Vapor pressure deficit was linked with iWUE only in C. tabularis. Differences in shade tolerance, tree stature and canopy position might have caused this species-specific variation in iWUE response to climate. Linear mixed effect modeling successfully simulated iWUE variability, explaining 41-51% of the total variance varying with species. Commonality analysis revealed that temperatures had a dominant influence on the inter-annual iWUE variability (64-77%) over precipitation (7-22%) and atmospheric CO2concentration (3-6%). However, the long-term variations in iWUE were explicitly determined by the atmospheric CO2increase (83-94%). Our results suggest that the elevated CO2and concomitant global warming might have detrimental effects on gas exchange and other physiological processes in South Asian tropical moist forest trees.
Tag: carbon dioxide
Hydrometeorological sensitivities of net ecosystem carbon dioxide and methane exchange of an Amazonian palm swamp peatland
Tropical peatlands are a major, but understudied, biophysical feedback factor on the atmospheric greenhouse effect. The largest expanses of tropical peatlands are located in lowland areas of Southeast Asia and the Amazon basin. The Loreto Region of Amazonian Peru contains ~63,000 km2 of peatlands. However, little is known about the biogeochemistry of these peatlands, and in particular, the cycling of carbon dioxide (CO2) and methane (CH4), and their responses to hydrometeorological forcings. To address these knowledge gaps, we established an eddy covariance (EC) flux tower in a natural palm (Mauritia flexuosa L.f.) swamp peatland near Iquitos, Peru. Here, we report ecosystem-scale CO2 and CH4 flux observations for this Amazonian palm swamp peatland over a two-year period in relation to hydrometeorological forcings. Seasonal and short-term variations in hydrometeorological forcing had a strong effect on CO2 and CH4 fluxes. High air temperature and vapor pressure deficit (VPD) exerted an important limitation on photosynthesis during the dry season, while latent heat flux appeared to be insensitive to these climate drivers. Evidence from light-response analyses and flux partitioning support that photosynthetic activity was downregulated during dry conditions, while ecosystem respiration (RE) was either inhibited or enhanced depending on water table position. The cumulative net ecosystem CO2 exchange indicated that the peatland was a significant CO2 sink ranging from −465 (−279 to −651) g C m−2 y−1 in 2018 to −462 (−277 to −647) g C m−2 y−1 in 2019. The forest was a CH4 source of 22 (20 to 24) g C m−2 y−1, similar in magnitude to other tropical peatlands and larger than boreal and arctic peatlands. Thus, the annual carbon budget of this Amazonian palm swamp peatland appears to be a major carbon sink under current hydrometeorological conditions.
Degradation increases peat greenhouse gas emissions in undrained tropical peat swamp forests
Tropical peat swamp degradation can modify net peat greenhouse gas (GHG) emissions even without drainage. However, current Intergovernmental Panel on Climate Change (IPCC) guidelines do not provide default emission factors (EF) for anthropogenically-degraded undrained organic soils. We reviewed published field measurements of peat GHG fluxes in undrained undegraded and degraded peat swamp forests in Southeast Asia (SEA) and Latin America and the Caribbean (LAC). Degradation without drainage shifted the peat from a net CO2 sink to a source in both SEA (− 2.9 ± 1.8 to 4.1 ± 2.0 Mg CO2–C ha−1 yr−1) and LAC (− 4.3 ± 1.8 to 1.4 ± 2.2 Mg CO2–C ha−1 yr−1). It raised peat CH4 emissions (kg C ha−1 yr−1) in SEA (22.1 ± 13.6 to 32.7 ± 7.8) but decreased them in LAC (218.3 ± 54.2 to 165.0 ± 4.5). Degradation increased peat N2O emissions (kg N ha−1 yr−1) in SEA forests (0.9 ± 0.5 to 4.8 ± 2.3) (limited N2O data). It shifted peat from a net GHG sink to a source in SEA (− 7.9 ± 6.9 to 20.7 ± 7.4 Mg CO2-equivalent ha−1 yr−1) and increased peat GHG emissions in LAC (9.8 ± 9.0 to 24.3 ± 8.2 Mg CO2-equivalent ha−1 yr−1). The large observed increase in net peat GHG emissions in undrained degraded forests compared to undegraded conditions calls for their inclusion as a new class in the IPCC guidelines. As current default IPCC EF for tropical organic soils are based only on data collected in SEA ombrotrophic peatlands, expanded geographic representation and refinement of peat GHG EF by nutrient status are also needed.
Modeling climate change impacts on rangeland productivity and livestock population dynamics in Nkayi District, Zimbabwe
Smallholder farmers in semi-arid areas depend on both cropping and livestock as the main sources of livelihoods. Rangeland productivity varies on both spatial and temporal scales and provides the major source of feed for livestock. Rangeland productivity is expected to decline with climate change thereby reducing livestock feed availability and consequently livelihoods that depend on livestock. This study was carried out to assess the impacts of climate change on rangeland productivity and consequently livestock population dynamics using a 30-year simulation modeling approach. The climate scenarios used in the simulations are built from the localized predictions by General Circulation Models (GCMs). The primary climate variables under consideration are rainfall (+/-7% change), carbon dioxide (CO2 up to 650 ppm) and temperature (+4 °C change). This was done by applying the SAVANNA ecosystem model which simulates rangeland processes and demographic responses of herbivores on a temporal and spatial scale using a weekly internal time step and monthly spatial and temporal outputs. The results show that rainfall levels of less than 600 mm/year have the largest negative effect on herbaceous biomass production. The amount of biomass from the woody layer does not change much during the year. The carbon dioxide (CO2) effects are more influential on the tree and shrub layers (C3 plants) than the herbaceous layer (C4 grasses). The CO2 effect was more dominant than the effects of rainfall and temperature. In the baseline simulations, the shrub plant layer increased significantly over 30 years while there is a three-fold increase in the woody plant layer (trees and shrubs) where biomass increased from a 1980 production to that of 2010. The biomass of the herbaceous layer was stable over the historical period (1980 to 2010) with values fluctuating between 200 and 400 g/m2. Grass green biomass has a variable distribution where most production occurred in the fields and cleared areas while lower levels of production were found in the forested areas. The spatial distribution of shrub green biomass was less directly linked to yearly rainfall. Shrub biomass was mostly found in forested areas, and it showed a steady increase in production. Cattle, donkey, and goat populations rose slowly from 1980 but the rise was disrupted by a dry period during the late 1980s to the early 1990s causing a decline in all populations primarily due to grass unavailability. The populations of cattle goats and donkeys started to rise again from 1995 onwards due to improvements in rainfall. Cattle and donkey populations were rising faster than that of goats while sheep population was not changing much for most of the simulation period, otherwise they declined significantly during the drought of 2002. Similar changes in simulated grass biomass (g/m2) were observed in almost all climate scenarios, except for the peak and low years. The livestock population simulation showed few variations in livestock population under all scenarios. The main conclusion from the study is that CO2 effects on rangeland productivity are much more dominant than the localized effects of rainfall and temperature. This has implications of favoring the growth of the tree and shrub layers over herbaceous layer, which meant that in the long run, the species that are able to use tree and shrub layers may be kept as a livelihood source as they will have a feed source. © 2020 by the authors.
Carbon stocks and effluxes in mangroves converted into aquaculture: a case study from Banten province, Indonesia
Aquaculture is one of the main drivers of mangrove loss across Southeast Asian countries. The conversion of mangroves to aquaculture generates substantial loss of carbon stocks and reduces carbon storage capacity. Here, we present total ecosystem carbon stocks (TECS), carbon dioxide (CO2) and methane (CH4) effluxes obtained from mangrove forests (fringe and interior mangroves), silvofishery aquaculture ponds (dense and sparse mangroves), and non-silvofishery aquaculture ponds in Sawah Luhur, Banten, Indonesia. We found no significant difference in TECS across five land uses, ranging from 261 ± 14 Mg C ha-1 in non-silvofishery ponds to 574 ± 119 Mg C ha-1 in fringe mangroves. Most of these stocks were found in the soil carbon pool (87%) in fringe and interior mangroves. However, the conversion of mangroves to aquaculture ponds resulted in soil carbon loss from -6% to 60%. The highest soil CO2 effluxes during dry and wet seasons were observed in interior mangroves (151 ± 12 mg CO2 m-2 h-1). The highest soil CH4 effluxes were found in fringe mangroves with 0.13 ± 0.04 mg CH4 m-2 h-1. The highest aquatic CO2 and CH4 effluxes were found in dense silvofishery ponds, at 118 ± 7 mg CO2 m-2 h-1 and 0.38 ± 0.04 mg CH4 m-2 h-1, respectively. Our findings suggest that land use that includes mangroves (i.e., mangrove forest and/or silvofishery ponds) tends to have higher carbon stocks, soil, and aquatic CO2 and CH4 effluxes, compared to aquaculture ponds without mangroves. It is therefore crucial to maintain mangroves for natural carbon capture and storage through carbon stock enhancement.
The enduring world forest carbon sink
The uptake of carbon dioxide (CO2) by terrestrial ecosystems is critical for moderating climate change. To provide a ground-based long-term assessment of the contribution of forests to terrestrial CO2 uptake, we synthesized in situ forest data from boreal, temperate and tropical biomes spanning three decades. We found that the carbon sink in global forests was steady, at 3.6 ± 0.4 Pg C yr−1 in the 1990s and 2000s, and 3.5 ± 0.4 Pg C yr−1 in the 2010s. Despite this global stability, our analysis revealed some major biome-level changes. Carbon sinks have increased in temperate (+30 ± 5%) and tropical regrowth (+29 ± 8%) forests owing to increases in forest area, but they decreased in boreal (−36 ± 6%) and tropical intact (−31 ± 7%) forests, as a result of intensified disturbances and losses in intact forest area, respectively. Mass-balance studies indicate that the global land carbon sink has increased, implying an increase in the non-forest-land carbon sink. The global forest sink is equivalent to almost half of fossil-fuel emissions (7.8 ± 0.4 Pg C yr−1 in 1990–2019). However, two-thirds of the benefit from the sink has been negated by tropical deforestation (2.2 ± 0.5 Pg C yr−1 in 1990–2019). Although the global forest sink has endured undiminished for three decades, despite regional variations, it could be weakened by ageing forests, continuing deforestation and further intensification of disturbance regimes. To protect the carbon sink, land management policies are needed to limit deforestation, promote forest restoration and improve timber-harvesting practices.
Key messages
- Regions surrounding the Kahuzi-Biega National Park (KBNP) and other areas of South Kivu Province in the eastern part of the Democratic Republic of the Congo have been losing their natural forests for decades.
- There is a positive correlation between deforestation and CO2 emissions. Our research shows that deforestation increases temperature and negatively impacts rainfall, although not significantly.
- Deforestation and its effects on the local climate are very likely to disrupt local agricultural practices and severely impact the unique biological diversity of the region.
- Understanding the important role of forests in regulating climate not only helps to develop appropriate climate change adaptation and mitigation strategies but also to attain better biodiversity conservation and food security, and to go beyond just carbon sequestration services.
Key messages
- Regions surrounding the Kahuzi-Biega National Park (KBNP) and other areas of South Kivu Province in the eastern part of the Democratic Republic of the Congo have been losing their natural forests for decades.
- There is a positive correlation between deforestation and CO2 emissions. Our research shows that deforestation increases temperature and negatively impacts rainfall, although not significantly.
- Deforestation and its effects on the local climate are very likely to disrupt local agricultural practices and severely impact the unique biological diversity of the region.
- Understanding the important role of forests in regulating climate not only helps to develop appropriate climate change adaptation and mitigation strategies but also to attain better biodiversity conservation and food security, and to go beyond just carbon sequestration services.
Key messages
- Regions surrounding the Kahuzi-Biega National Park (KBNP) and other areas of South Kivu Province in the eastern part of the Democratic Republic of the Congo have been losing their natural forests for decades.
- There is a positive correlation between deforestation and CO2 emissions. Our research shows that deforestation increases temperature and negatively impacts rainfall, although not significantly.
- Deforestation and its effects on the local climate are very likely to disrupt local agricultural practices and severely impact the unique biological diversity of the region.
- Understanding the important role of forests in regulating climate not only helps to develop appropriate climate change adaptation and mitigation strategies but also to attain better biodiversity conservation and food security, and to go beyond just carbon sequestration services.
Key messages
- Regions surrounding the Kahuzi-Biega National Park (KBNP) and other areas of South Kivu Province in the eastern part of the Democratic Republic of the Congo have been losing their natural forests for decades.
- There is a positive correlation between deforestation and CO2 emissions. Our research shows that deforestation increases temperature and negatively impacts rainfall, although not significantly.
- Deforestation and its effects on the local climate are very likely to disrupt local agricultural practices and severely impact the unique biological diversity of the region.
- Understanding the important role of forests in regulating climate not only helps to develop appropriate climate change adaptation and mitigation strategies but also to attain better biodiversity conservation and food security, and to go beyond just carbon sequestration services.