Fire 1.pdf - Fire Ecology

What is ecology: The study of biotic and abiotic factors that interact with the ecosystem Ecology term is from the 1866 How does fire fit into ecology? Adaptations and evolution Disturbance ○ Functions as a disturbance ○ These can happen occasionally and result in changing ecosystems and populations...

What is ecology: The study of biotic and abiotic factors that interact with the ecosystem Ecology term is from the 1866 How does fire fit into ecology? Adaptations and evolution Disturbance ○ Functions as a disturbance ○ These can happen occasionally and result in changing ecosystems and populations ○ Can shift community structure ○ Even the removal of fire is a disturbance since it occurs naturally Succession ○ Functions to reset succession ○ Succession = patterns of change of these communities ○ Primary or secondary Primary = think about the colonization from bare rock; no existing community Secondary = think about the colonization from soil or existing community present. Change after a disturbance goes through. Fire Ecology: VERY recent field of study ○ Ecology: 1866(Haeckel) ○ Ecosystem: 1935 (Tansley) Tall Timbers Fire Ecology course 1962 = 1962 when the idea of fire and ecology were coined together and thinking of it as a discipline ○ First time fire and ecology were combined Few fire ecology courses exist in the state ○ ABAC, UWG, UGA (grad only) What is fire? Combustion: ○ High-temperature exothermic redox chemical reaction Chemical chain reaction If there is enough heat, it will continue to propagate. Rapid oxidation Focus on the oxidation side of things Taking the fuel and oxidizing it rapidly Exothermic reaction Releases heat Similar: Rusting, decomposition ○ The big difference is what? ANSWER: These are SLOW; fire reactions are fast! Because it is so slow, it does not allow for the build-up (the heat dissipates) of heat like fire does = not that hot as fire Necessary components for combustion ○ Fuel, Oxygen, and Heat --> Leads us to the fire triangle Fire Triangle: Not just a triangle; there is a fire icon inside the triangle Fuel Oxygen Heat Fire: Oxygen, fuel, heat are the legs of a stool The seat of a stool is the chain reaction Fuel: Burnable material Any state of matter (liquids, solids, gases) ○ Solids and liquids generally break down first Into volatilized gasses --> These gasses are the only one that creates flames ○ Only gas creates flames Oxygen: Source? ○ Atmosphere Needs 16% ○ Percent of O2 in the atmosphere is about 21% ○ If it is less than 16% it will not burn ○ If you increase the O2 percentage, it becomes a lot easier for things to burn and the hotter they will burn O2 has not been at constant levels in a very long time! This has a huge role in combustion Heat: Dries material ○ Think about how water can effect this. ○ If you have a wet heat, it will not burn. It will dry off first by evaporating the water. Begins breakdown ○ Once it is dry, breakdown begins Ignition source? ○ Examples? Lightening Sun (if focused) Matches or lighters Where does the heat come from to continue combustion? ○ From the previous reaction --> Which reactants? The O2 ○ This has to do with the types of bonds in the fuels and the O2 Heat from combustion: Energy release from combustion mainly comes from O2 ○ O=O is relatively weak; Contained 498 kJ/mol ○ H-O-H or O-C-O bonds are stronger; less potential energy, therefore less energy is released ○ Combustion releases 418kJ/mol O2 (100 kcal/mol) regardless of fuel you are using The more O2 in the reaction = more O2 breaking = more heat produced ○ Phases of Combustion: Pre-ignition / pre-heat ○ Endothermic: Takes in heat --> You need to build up the fuel so that you can kick off the reaction ○ Warming of material ○ Dehydration ○ Volatilization = taking a liquid and bringing it to a gas stage ○ Pyrolysis = thermal degradation of fuel into smaller components that go on to be volatilized and eventually burn. Results in: Gases Tar (semi-volatile= some go off as gasses and some don’t) Char (Solid= think charcoal) Ignition ○ The transition to combustion ○ When it is on fire = when it is In this stage ○ Exothermic stage Combustion ○ Heat from combustion continues the cycle! ○ Exothermic stage ○ Flaming = most obvious form of combustion ○ Smoldering : Not enough vapors remain, but smoke still present Oxidation on surface but there is not enough gas for a flame ○ Glowing : No smoke Oxidation on surface but there is not enough gas for a flame This case does not even have smoak like smoldering does Extinction ○ When there is not enough heat to maintain combustion PICTURE EXAMPLES Why did some of this burn and some not burn? Some could be more wet --> Not enough fuel to create heat to dry out the vegetation to then have it burn Also, some could be more live vegetation rather than dead vegetation (live vegetation is more wet than dead) The part of that one branch did not burn all the way? Volume things and moisture related things What kinds of combustion are occurring? Flaming occurring in the back Smoldering combustion = smoke but no flame Glowing is also occurring Extinction too, because it stopped glowing Note: Not enough heat to completely combust all the material --> Not everything burns What type of combustion? Smoldering Whenever the wind would blow, there would be a flame! ○ Why? The O2 is flowing to create the flame.. When the wind stopped so did the flame Type of combustion? Smoldering Flaming Not obvious glowing from the video Anything interesting? Transitions between flaming and smoldering --> The flames drop out and you get the smoke that has shifted to the smoldering Active flaming going on in the back At the edge, the flames move really slow and it starts to slow down At the back left corner, there is a fire that is small but then it gets large! Because the saw palmettos were preheating until it ignites Methods of Heat Transfer: Radiation ○ Think about standing next to a fire and feeling the heat Conduction ○ The heat transfer through contact ○ Occurs below a flame ○ Transferred to the soil --> Soil has moisture = you might not get out of the pre-warming stage Convection ○ The heat transfer via fluids and air ○ When the wind blows over fire, it pushes the heat to the next shrub ○ What a lot of this is driven by Combustion Complex and Variable: Wood combustion stages and products Focuses on wood and how particular woods might go through the process as temperature increases ○ Different materials and different woods all have different specific heats for this Low temps and warming = pre heat stage (dehydration stage) up to a certain point before you have a material to go through pyrolysis --> Then you transition to flaming. Then you go into the char combustion and followed by that is ash Since wood is made of cellulose and lignin, we want to see how that effects the process