Thread: Live fuel moistures
07-05-2000, 01:49 PM #1cbp3Firehouse.com Guest
Live fuel moistures
Alright, how about a little help here. Lately I've gotten a bug in my ear about the utility of measuring live fuel moisture. It is a useful tool for fire managers in the Great Lakes for their Red and Jack Pine, and so it occurs to me that it might be darn handy as a predictor of potential fire behavior in the Pitch Pine we have down here in the Barrens.
Even more importantly, we have extensive Atlantic White Cedar swamps. Now, these do 1 of 2 things when a fire hits them...they either stop the fire in its tracks, or they explode, significantly increasing control problems. The reason is pretty obviously (to me, anyway...) a question of live fuel moisture.
So I'm working on acquiring the equipment to measure and track it, but I've had problems coming up with a methodology for doing it.
So: How's it work? Once a week good enough? Stations 20-30 miles apart okay? Are small twigs okay in the sample, or do we measure only needles? If twigs are okay, how large (or small) can they be before affecting the results? How many samples from one area are good?
Any feedback here would be appreciated. If I can sweettalk my way into federal assistance, then maybe I can "go forth and observe" places like Mich. and Wi. Otherwise, I'll rely on firefighters like you to help. Any pointers?
07-05-2000, 02:02 PM #2bob1350Firehouse.com Guest
I believe out here where fuels are very, very, very, dry, this sort of thing is handled by the US Forest Service or the Colorado State Forest Service. That's who issues the red flag days anyway. I'd say save yourself lots of work and contact the Feds or your State forest service. There is also the web site: www.fs.fed.us
07-06-2000, 10:08 AM #3monteFirehouse.com Guest
Live fuel moistures are used early on to indicate the trend of the season. First, they demonstrate all the potential fuel, or additional available fuel to a fire that starts, kindles, burns in the dead and down. Most live plants have certain moisture thresholds during parts of the season. Like, during greenup or bud break, growth period, growth cessation, dormancy. First find out what those are for your area and plant species. Second, you need to tie in the knowledge of available moisture to the plants during stress periods. That would be what ever drought system indicators you use, like, Keetch Byron, etc. Oddly enough, during 1988 live fuel samples were taken in the Yellowstone area. The live fuel moistures really did not significantly change from normal expectations. However the available soil moisture was extremely depleted, and consequently, live fuels became part of the burning profile quite readily. Lots of crowning and sustained crown runs. If you track live fuel moistures, locations and dates are important, since they will indicate where your growing season is compared to normal. Live fuel moistures may not show you that you are extremely dry, but they will show you you might be several weeks ahead, and therefore moisture stress is greater, and your burning or fire profile will incorporate more live fuels faster. Your local county extension office should have a list of plant species and what is considered normal for live fuel moistures based on dates and growth characteristics. They would also be tracking the drought conditions, and how they measure it and what it means. Live fuel moistures are a good way to track trends and potential. I personally tracked samples of like kind. That is, just needles, just 0-1/4" twigs (live or dead), then I would sample live twigs with foliage on it for 0-1/4", or 1/4"-1". Stay with the 1,10,100,1000 hr. sample designations, then a variety of grasses and forbs and shrubs. Keep all samples segragated, like, all spirea together, all fescues together. I have also used the Computrac moisture analyzer (which is good and quick), but I prefer the drying oven (24 hour drying cycle) because it takes more samples and you can mix sample sizes etc. in the same batch. Hope this helps.
07-14-2000, 10:39 AM #4J.WattFirehouse.com Guest
Good background monte. All I can add is to focus on some type of indicator species. I'm in the northern valley area of CA where we use manzanita as our indicator species. The annuals (one hour fuel)dry out much earlier than the brush (generally a 10 hr. fuel no matter how big the main stems are). By taking samples on a regular basis we not only develop current and historical trends but change tactics based on LFM. When the brush is still flush with LFM we can run grass/range fires into the brush as a natural barrier. Once we see and measure that we've reached our limits for that tactic we often have to try and keep the fire out of the brush. For example, our manzanita just dropped below 100% LFM (equal free water to veg mass) for our low elevation areas about 10 days ago. The mid to high elevation samples were still over 130%. At 100% the manznita will burn with slope, wind or other assistance like dead pine needles draped in the leaves. Below 90% the brush will burn freely when ignited and the leaves will burn hot enough to start spot fires.
We also use the drying oven and scales as our system. A lot of fire behavior prediction is subjective based on experience and observation. Get a feel from each fire as to which burn under different conditions and try to predict what you'll see the next time. There are also some other field measurements you can do. Bend a pine needle between your fingers. Does it bend or snap? That gives a clue for one hr. moisture. Do the same with your 10 hr. live fuels. You can probably correlate a subjective test to observed fire behavior and be a "cosmic fuels guy".
As the previous post mentioned, contact your university extension advisors and USFS folks. There is information available.
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