320 research outputs found
Quantifying the role of fire in the Earth system – Part 2: Impact on the net carbon balance of global terrestrial ecosystems for the 20th century
Fire is the primary form of terrestrial ecosystem disturbance on a global
scale. It affects the net carbon balance of terrestrial ecosystems by
emitting carbon directly and immediately into the atmosphere from biomass
burning (the fire direct effect), and by changing net ecosystem productivity
and land-use carbon loss in post-fire regions due to biomass burning and
fire-induced vegetation mortality (the fire indirect effect). Here, we
provide the first quantitative assessment of the impact of fire on the net
carbon balance of global terrestrial ecosystems during the 20th century, and
investigate the roles of fire's direct and indirect effects. This is done by
quantifying the difference between the 20th century fire-on and fire-off
simulations with the NCAR Community Land Model CLM4.5 (prescribed vegetation
cover and uncoupled from the atmospheric model) as a model platform. Results
show that fire decreases the net carbon gain of global terrestrial ecosystems
by 1.0 Pg C yr<sup>−1</sup> averaged across the 20th century, as a result of the
fire direct effect (1.9 Pg C yr<sup>−1</sup>) partly offset by the indirect
effect (−0.9 Pg C yr<sup>−1</sup>). Post-fire regions generally experience
decreased carbon gains, which is significant over tropical savannas and some
North American and East Asian forests. This decrease is due to the direct
effect usually exceeding the indirect effect, while they have similar spatial
patterns and opposite sign. The effect of fire on the net carbon balance
significantly declines until ∼1970 with a trend of 8 Tg C yr<sup>−1</sup>
due to an increasing indirect effect, and increases subsequently with a trend
of 18 Tg C yr<sup>−1</sup> due to an increasing direct effect. These results help
constrain the global-scale dynamics of fire and the terrestrial carbon cycle
HESFIRE: a global fire model to explore the role of anthropogenic and weather drivers
Vegetation fires are a major driver of ecosystem
dynamics and greenhouse gas emissions. Anticipating potential
changes in fire activity and their impacts relies first
on a realistic model of fire activity (e.g., fire incidence and
interannual variability) and second on a model accounting
for fire impacts (e.g., mortality and emissions). In this paper,
we focus on our understanding of fire activity and describe
a new fire model, HESFIRE (Human–Earth System
FIRE), which integrates the influence of weather, vegetation
characteristics, and human activities on fires in a stand-alone
framework. It was developed with a particular emphasis on
allowing fires to spread over consecutive days given their major
contribution to burned areas in many ecosystems. A subset
of the model parameters was calibrated through an optimization
procedure using observation data to enhance our
knowledge of regional drivers of fire activity and improve
the performance of the model on a global scale. Modeled fire
activity showed reasonable agreement with observations of
burned area, fire seasonality, and interannual variability in
many regions, including for spatial and temporal domains not
included in the optimization procedure. Significant discrepancies
are investigated, most notably regarding fires in boreal
regions and in xeric ecosystems and also fire size distribution.
The sensitivity of fire activity to model parameters is
analyzed to explore the dominance of specific drivers across
regions and ecosystems. The characteristics of HESFIRE and
the outcome of its evaluation provide insights into the influence of anthropogenic activities and weather, and their interactions,
on fire activityinfo:eu-repo/semantics/publishedVersio
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The influence of soil communities on the temperature sensitivity of soil respiration
Soil respiration represents a major carbon flux between terrestrial ecosystems and the atmosphere, and is expected to accelerate under climate warming. Despite its importance in climate change forecasts, however, our understanding of the effects of temperature on soil respiration (RS) is incomplete. Using a metabolic ecology approach we link soil biota metabolism, community composition and heterotrophic activity, to predict RS rates across five biomes. We find that accounting for the ecological mechanisms underpinning decomposition processes predicts climatological RS variations observed in an independent dataset (n = 312). The importance of community composition is evident because without it RS is substantially underestimated. With increasing temperature, we predict a latitudinal increase in RS temperature sensitivity, with Q10 values ranging between 2.33 ±0.01 in tropical forests to 2.72 ±0.03 in tundra. This global trend has been widely observed, but has not previously been linked to soil communities
Soil Respiration in Tibetan Alpine Grasslands: Belowground Biomass and Soil Moisture, but Not Soil Temperature, Best Explain the Large-Scale Patterns
The Tibetan Plateau is an essential area to study the potential feedback effects of soils to climate change due to the rapid rise in its air temperature in the past several decades and the large amounts of soil organic carbon (SOC) stocks, particularly in the permafrost. Yet it is one of the most under-investigated regions in soil respiration (Rs) studies. Here, Rs rates were measured at 42 sites in alpine grasslands (including alpine steppes and meadows) along a transect across the Tibetan Plateau during the peak growing season of 2006 and 2007 in order to test whether: (1) belowground biomass (BGB) is most closely related to spatial variation in Rs due to high root biomass density, and (2) soil temperature significantly influences spatial pattern of Rs owing to metabolic limitation from the low temperature in cold, high-altitude ecosystems. The average daily mean Rs of the alpine grasslands at peak growing season was 3.92 µmol CO2 m−2 s−1, ranging from 0.39 to 12.88 µmol CO2 m−2 s−1, with average daily mean Rs of 2.01 and 5.49 µmol CO2 m−2 s−1 for steppes and meadows, respectively. By regression tree analysis, BGB, aboveground biomass (AGB), SOC, soil moisture (SM), and vegetation type were selected out of 15 variables examined, as the factors influencing large-scale variation in Rs. With a structural equation modelling approach, we found only BGB and SM had direct effects on Rs, while other factors indirectly affecting Rs through BGB or SM. Most (80%) of the variation in Rs could be attributed to the difference in BGB among sites. BGB and SM together accounted for the majority (82%) of spatial patterns of Rs. Our results only support the first hypothesis, suggesting that models incorporating BGB and SM can improve Rs estimation at regional scale
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