Abstract
Abstract The higher flammability of tropical savanna, compared with forest, plays a critical role in mediating vegetation‐environment feedbacks, alternate stable states, and ultimately, the distribution of these two biomes. Multiple factors contribute to this difference in flammability, including microclimate, fuel amount and fuel type. To understand this transition in flammability, we studied fuel characteristics and microclimate across eight savanna–forest boundaries in south‐central Brazil. At each boundary, the environment was monitored for one week with automated measurements of near‐surface wind speed, air temperature, relative humidity and presence of dew. Manual measurements were performed to quantify fuel amounts and fuel moisture. These data were used to parameterize the fire behaviour model BehavePlus5 in order to simulate fire behaviour over the savanna–forest boundary. There were strong gradients across the boundary in all variables with the exception of total fuel load. During the day, savannas had higher wind speed and air temperature, and lower relative humidity and fuel moisture than forests. Although fuel loads were similar in savanna and forest, savanna was characterized by lower fuel bulk density, largely because of the presence of grasses. Based on these measurements, the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest. A sensitivity analysis indicated that the primary cause of these differences was the low fuel bulk density characteristic of grassy fuels, with lesser contributions from wind speed, fuel moisture and total fuel load. These results indicate that the dominance of grassy fuels is the primary cause of the high flammability of savanna.
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Claims 9
Claim · model-written summary
Most variables showed strong gradients across savanna–forest boundaries, except total fuel load.
- Outcome
- gradients across the boundarye0
Not reportedTaxon
Verbatim
e0“There were strong gradients across the boundary in all variables with the exception of total fuel load.”
Claim · model-written summary
Savannas had higher daytime wind speed and air temperature than forests.
Not reportedTaxon
Verbatim
e0“During the day, savannas had higher wind speed and air temperature, and lower relative humidity and fuel moisture than forests.”
Claim · model-written summary
Savannas had lower daytime relative humidity and fuel moisture than forests.
Not reportedTaxon
Verbatim
e0“During the day, savannas had higher wind speed and air temperature, and lower relative humidity and fuel moisture than forests.”
Claim · model-written summary
Fuel loads were similar in savanna and forest.
Not reportedTaxon
Verbatim
e0“fuel loads were similar in savanna and forest”
Claim · model-written summary
Savanna fuel bulk density was lower, largely due to grasses.
Verbatim
e0“savanna was characterized by lower fuel bulk density, largely because of the presence of grasses”
Claim · model-written summary
The model predicted faster savanna fires than forest fires.
Not reportedTaxon
Verbatim
e0“the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest”
Claim · model-written summary
The model predicted more intense savanna fires than forest fires.
Not reportedTaxon
Verbatim
e0“the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest”
Claim · model-written summary
The model predicted greater flame lengths for savanna fires than forest fires.
Not reportedTaxon
Verbatim
e0“the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest”
Claim · model-written summary
Sensitivity analysis attributed most fire behavior differences to low bulk density of grassy fuels, with smaller contributions from wind, moisture and fuel load.
Verbatim
e0“the primary cause of these differences was the low fuel bulk density characteristic of grassy fuels, with lesser contributions from wind speed, fuel moisture and total fuel load”