For the past dozen years I have been writing narratives of each of our prescribed burns, with records of personnel, timing, procedures, etc. These narratives go in the Pleasant Valley Conservancy files, where I can access them any time. With GIS I have been able to determine accurately the acreage of each burn unit. In the early years, our burns were fairly small, but as restoration proceeded we were able to burn larger acreages.
Although some of my notes are sketchy, they are detailed enough for the present purposes. I broke the burn work down into various tasks, recorded the number of people involved with each task, and the number of hours. The total hours is only that expended on the day of the burn. Thus, preparation of fire breaks is not included. Also, fuel cost is not included in this analysis but could be. The final value is total person hours per burn. An example of a typical record is given here.
Nov. 1, 2012 Oak woodland 26 acres
Preparations, which included final touch-up of the fire breaks, assemble equipment, water, drip torch fuel, etc. took 4 people, 2.5 hours, or 10 person hours.
Orientation: maps are passed out, the burn boss explains the burn, radios are distributed, tasks are assigned. 12 people, 0.5 hours, 6 person hours.
The burn itself: 12 people, 3 hours, 36 person hours.
Major mop-up: 12 people, 1 hour, 12 person hours.
Final mop-up: 2 people, 1 hour, 2 person hours
Clean-up equipment etc.: 2 people, 1 hour, 2 person hours
Total person hours: 68
Hours per acre: 2.6
The graph below shows a summary of the burns we did in 2013, plotting person hours per acre versus acres burned. This is a very interesting graph, as it shows that lots fewer person hours per acre are needed for large burns than for small ones. Plug in the hourly wages you are paying your workers and you can calculate the cost of a burn in real money. For the example here, the total cost is $2040 (assuming labor at $30 per hour) or $78 per acre.
The most costly burn in the above graph was not the 140 acre burn but the 3 acre burn we did of the Crane Prairie, which took 6.3 person hours.
I found a similar graph in a publication of the US F and WS for the Northern Great Plains (below). Note that the burn units on some of these Great Plains burns are more than 5000 acres, and the total burn cost is less than $1 per acre. (It is virtually impossible to do such large burns here in Wisconsin.)
Data such as this provide quantitative support for State Natural Areas biologist Matt Zine, who several years ago gave a nice paper promoting the value of doing large burns.
There are lots of other reasons for doing large burns in addition to cost, but that will be the topic of another post.