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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Organism-environment interactions / Fire-vegetation feedback and savanna-forest states

Fire-vegetation feedback and savanna-forest states

Grass fuel carries fire that keeps trees from closing the canopy, while a closed forest canopy shades out grass and stops fire; the two self-reinforcing states make savanna and forest alternative stable biomes across a wide rainfall range.

Boundary: where this process starts

Starts with: Open grassy ground builds continuous fine fuel

Boundary: where it ends

Ends after: Fire rarely spreads, and forest trees grow into the canopy; Frequent fire kills tree seedlings and saplings and keeps the canopy open

PARTICIPANTSRESOURCESTreesFireGrassesClimatePlant litterHeatLightWaterImpact +3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.fuel carries fireImpact +4 of 5. Click for details and evidence.↻ reinforces · strong · 0.4 open canopy keepImpact 03 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.canopy closesImpact -4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.↻ reinforces · strong · 0.4 shade persistsImpact 02 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Open grassy ground builds continuous fine fuel: makes Plant littermakesOpen grassy ground builds continuous fine fuel: uses LightFrequent fire kills tree seedlings and saplings and keeps the canopy open: uses up Plant litteruses upFrequent fire kills tree seedlings and saplings and keeps the canopy open: uses HeatClosed tree canopy shades out the grass layer and removes fuel: uses LightClosed tree canopy shades out the grass layer and removes fuel: uses WaterFire rarely spreads, and forest trees grow into the canopy: uses Plant litterFire rarely spreads, and forest trees grow into the canopy: uses HeatDisturbance or climate shift pushes the system over a tree-cover threshold: uses HeatDisturbance or climate shift pushes the system over a tree-cover threshold: uses Waterbuilds continuous finefuelPlant litter: builds continuous fine fuelreaches open grassygroundLight: reaches open grassy groundconsumed by firePlant litter: consumed by firekills seedlings andsaplingsHeat: kills seedlings and saplingsblocked before reachingthe groundLight: blocked before reaching the grounddrawn up by canopy rootsWater: drawn up by canopy rootsburns as fuelPlant litter: burns as fuelkills seedlings duringthe fireHeat: kills seedlings during the firewarming stress pushesthe shiftHeat: warming stress pushes the shiftdeficit tips tree coveroverWater: deficit tips tree cover overStart: Fire-vegetationfeedback andsavanna-forest statesSTARTStart: Fire-vegetation feedback and savanna-forest statesEnd: Fire-vegetationfeedback andsavanna-forest statesENDEnd: Fire-vegetation feedback and savanna-forest statesOpen grassy groundbuilds continuous finefuel📄1Open grassy ground builds continuous fine fuelFrequent fire killstree seedlings andsaplings and keeps t…📄1 ↗1Frequent fire kills tree seedlings and saplings and keeps the canopy openClosed tree canopyshades out the grasslayer and removes fuel📄1Closed tree canopy shades out the grass layer and removes fuelFire rarely spreads,and forest trees growinto the canopy📄1Fire rarely spreads, and forest trees grow into the canopyDisturbance or climateshift pushes the systemover a tree-cov…📄1Disturbance or climate shift pushes the system over a tree-cover threshold
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Open grassy ground builds continuous fine fuel
GrassesPlant litterLight
Evidence (1) · added by Loopa
  • Staver, Archibald & Levin 2011, The global extent and determinants of savanna and forest as alternative biome states, Science, doi:10.1126/science.1210465: Grass fuel carries surface fires. (confidence 0.8)
Frequent fire kills tree seedlings and saplings and keeps the canopy open
FireTreesHeatPlant litter
Evidence (1) · added by Loopa
  • Staver, Archibald & Levin 2011, The global extent and determinants of savanna and forest as alternative biome states, Science, doi:10.1126/science.1210465: Fire suppresses tree recruitment. (confidence 0.8)
Closed tree canopy shades out the grass layer and removes fuel
TreesGrassesLightWater
Evidence (1) · added by Loopa
  • Staver, Archibald & Levin 2011, The global extent and determinants of savanna and forest as alternative biome states, Science, doi:10.1126/science.1210465: Forest shade excludes grasses. (confidence 0.8)
Fire rarely spreads, and forest trees grow into the canopy
FireTreesHeatPlant litter
Evidence (1) · added by Loopa
  • Staver, Archibald & Levin 2011, The global extent and determinants of savanna and forest as alternative biome states, Science, doi:10.1126/science.1210465: Lack of fire stabilises forest. (confidence 0.8)
Disturbance or climate shift pushes the system over a tree-cover threshold
ClimateFireTreesWaterHeat
Evidence (1) · added by Loopa
  • Staver, Archibald & Levin 2011, The global extent and determinants of savanna and forest as alternative biome states, Science, doi:10.1126/science.1210465: Bistability exists over a range of mean annual rainfall. (confidence 0.8)