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Fire data and transitions

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  • #1646

    Hello Path experts,

    I have a classified MODIS satellite image representing three vegetation state classes at CFB Suffield:
    1. needle & thread (climax species; C3/cool season species dominant),
    2. blue grama/needle & thread (C3 & C4 species co-dominant)
    3. blue grama (secondary succession; C4/warm season species dominant)
    For each pixel representing a state class, I have a complete 36 year fire history which details when each pixel burned and its unique fire return interval. Unfortunately, I do not have enough data to separate early season fires from late season fires. However, it is clear that those pixels which have burned with high frequency have undergone succession from a needle & thread community (climax) to blue grama (secondary succession).
    I have two structural classes—open canopy, representing no litter and closed canopy representing expected litter biomass. After a fire, the structural class always returns to an open canopy and after a set number of years (which I am still working to define), reverts to a closed canopy. Litter in southern Alberta is important because it reduces evapotranspiration, reduces surface temperatures, and promotes the growth of cool season grasses. In an open canopy, surface temperatures are high, evaporation is high, and warm season grasses are favoured.
    My goal is to explore competing hypotheses for how succession has taken place:
    1. one hypothesis is that fire is a disturbance that slowly kills off the climax species (needle & thread/cool season) one fire at a time. Recovery towards the climax species begins the year after a fire, but is interrupted when another fire strikes. The cover of C4 species is solely dependent on the total number of fires. Structural classes are less important in this scenario because they do not provide feedbacks for succession.
    2. a second hypothesis is that more intense fires (with more time between fires) results in the mortality of the climax species (needle & thread; C3 species). Structural classes are important, in that more litter accumulates from infrequent fire, resulting in higher mortality of the climax species, reducing its cover over time. The cover of C4 species is dependent mostly on the time between fires, as litter biomass accumulates.
    3. a third hypothesis (my hypothesis) is that fire indirectly affects climax species, by promoting an open structural class. The cover of C4 species is mostly dependent on the time that a pixel remains in an open class. Succession back to climax (C3) species can only take place once the site has reached a closed structural state. This concept is also critical to understanding climate change. In our ecosystem, evapotranspiration is predicted to be higher, without an offsetting increase in precipitation. Thus, this type of succession is likely to resemble climate change-based transitions.

    My plan is to simulate (NOT SPATIALLY) the change in state classes during the 36 year fire history (assuming that in year 1 the majority of the area exists as climax), and compare the predicted spatial extents of each state class to those of the classified image. I hope to be able to use the percent area burned from the fire datasets to reconstruct the entire fire history.

    Three landscape strata, based on range sites: BLOWOUTS, LOAMY, SAND
    TOTAL STUDY AREA = 12816 PIXELS (250 x 250 m) 80100 ha/197931 acres
    Final conditions:
    -STCO/BOGR = 1358 PIXELS (84.4 %)
    -BOGR/STCO = 218 PIXELS (13.6 %)
    -BOGR = 32 PIXELS (2 %)
    – STCO/BOGR = 4386 PIXELS (67.7 %)
    -BOGR/STCO = 1043 PIXELS (16.1 %)
    -BOGR = 1052 PIXELS (16.2 %)
    – STCO/BOGR = 3660 PIXELS (77.4%)
    -BOGR/STCO = 945 PIXELS (20.0 %)
    -BOGR = 122 PIXELS (2.6 %)
    My questions are:
    1. how do you enter the fire history information under the Advanced Tab?
    2. What exactly are fire transition groups?
    3. Am I able to throw in drought as a factor? We have had 3 droughts in the last 36 years which likely complicate the trends



    Hi Brent,


    Here are some answers to your questions:


    1.  How do you enter fire history information under the Advanced Tab?


    a.  In the "Scenario Exporer" navigate to the Advanced Tab and the "Transition Multiplier Values" property.


    b. Right click on the grid and select "Export All".  Save the file to a desired location.  and click ok.  Excel will open with a blank template for you to enter your transition multiplier data into.


    c.  For each timestep over the simulation period you want to run and for each wildfire transition type enter the (amount of area burned)/(the average amount of area burned per year across all years).  Set the transition multiplier type to "temporal".


    d. You may need to calibrate wildfire probabilities up and down using a static transition multiplier as well.  Do this by creating a transition multiplier value record for each wild fire type and leaving the timestep and transition multuplier type blank.


    e. Import the transition multiplier values by returning to Path and the scenario editor and right clicking on the grid to import the edited excel file.



    2.  Fire transition groups are no longer used in Version 4 of Path.  My recomendation would be to upgrade the version.  Otherwise, fire transition groups (abandoned in version 3) are to define which transition groups the legacy fire history property would apply to.



    3.  Yes you can also add transion multipliers for drought to force higher drought probabilities for specific timesteps.



    If you have any questions about this let me know and we can have a closer look at your data.




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