Cg. Recently seeded in clover.
Disc height: 7.5cm
Mechanical herbicide treatment
Disc height: 5cm
December 2009
Greg Baxter
In 2005 FPInnovations - FERIC completed a survey of grass fuel loads in central and northern Alberta along linear disturbances. A disc metre was used in this survey and a relationship between disk height and fuel loads was established, and the data is also available as input into fire behaviour prediction models. Estimating fuel loads accurately is important in this process and can be difficult to do. Photographs of each sample plot were taken and these photographs will be used in the development of this ‘photo guide’.
Accurately estimating fuel loads visually, in any fuel type, is difficult without a good understanding of the fuel type combined with years of experience. One technique commonly used to assist in estimating fuel loads is the use of ‘photo guides’. Photo guides allow the user to view their sample and at the same time compare that to photographs of similar fuel types with known loads. This photo guide shows both spring and fall pictures of grass fuel loads ranging from 0.9 to 7+ tonnes per hectare (t/ha). Four photographs of each load category are shown – two spring and two fall photos.
A total of 126 grass samples were collected in central and northern Alberta in 2005. These samples allowed FERIC to accomplish four objectives:
• Develop a database on grass fuel loading along linear disturbances in Alberta.
• Calculate mean spring and fall grass loads for use in fire behaviour prediction models.
• Develop a model to estimate fuel loads using a grass disc metre.
• Develop a photo guide for estimating grass fuel loads that may be used in the field.
This report fulfills the fourth objective of the project.
FERIC physically collected 64 spring and 62 fall grass samples through central and northern Alberta along linear disturbances (transmission lines, pipelines, seismic lines, etc.) using a grass disc metre (Trollope and Potgeiter 1986) and destructive sampling procedures. At each site a number of photographs were also taken to document the site.
The accurate prediction of fire behaviour is important in the choice of tactics that will be used to stop or control a wildfire. Fire in dry, cured grass fuels are able to travel rapidly, making them difficult to control at times and allowing fires to move quickly into other stands of trees. Fire intensity is dependant on both head fire rate of spread and fuel loading. Heavy fuel loads and rapid fire spread will limit a direct attack on a fire and thus indirect techniques are required. Choosing the appropriate indirect attack depends on the amount of fuel available to the fire and thus an accurate prediction of the load in question is required.
Two data collection techniques were used in this project. Firstly, a grass disc metre was used. This involves sliding an aluminium disk down a pole until it comes to rest on top of the grass fuel. The height at which the disc rests is then noted. The grass directly under the disc is then clipped down to the ground surface and taken to the lab for oven drying and weighing. The dry weight is then converted to a tons/hectare (t/ha) value. The data is then broken down into 5 cm disc height values and a mean t/ha value is calculated for each height class and a relationship is then calculated. Each site was given a reference number and a minimum of two photographs were taken. One photograph was a close-up of the sampling site and the second showed a broader view of the sampling site. Because physically destructive samples were taken at each site, dry-weights determined and we have the associated photo from each sample, we now know what each fuel load ‘looks like'.
The data was broken into eight-fuel load classes based on the data collected. Each class was 1.0 t/ha and the classes ranged from 0 – 1.0 t/ha to greater than 7.1 t/ha. Four photos of each weight class will be shown. Two will show spring fuels and two will show fall fuels so users have a choice depending on time of year. Exact fuel loads (dry-weights) for each photograph are provided.
Two ‘heights' are provided with the photos. Spring grass is usually compressed due to snow press and therefore ‘disc height' is provided. This is the height at which the disc is sitting on top of the fuel. This is used because the user can estimate this height more accurately than predicting the mean height of the standing grass.
For summer or fall grass loads, the mean height of the standing grass is used. This is the average height of grass in the area of interest. This is easier to estimate than a disc height, as predicting how far the disk will slide down and come to rest is difficult.
General descriptions of the grass load are also given.
Cg refers to Calamagrastis species.The grass in these photographs are short and light, with some clover in the top left photo. Photo’s 2 and 3 are the same site at different times of the year. Only one site had a fuel load less than 1.0 t/ha in the fall.
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| Fuel load: 0.69 t/ha Cg. Recently seeded in clover. Disc height: 7.5cm |
Fuel load: 0.99 t/ha Mechanical herbicide treatment Disc height: 5cm |
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| Fuel load: 0.91 t/ha Mechanical herbicide treatment. Mean height: 52 cm |
Snow pressed, light loads characterize the spring photos and short, sparse loads typify the fall loads.
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Fuel load: 1.16 t/ha |
Fuel load: 1.63 t/ha Seeded fescue and clover Disc height: 5 cm |
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Fuel load: 1.63 t/ha |
Fuel load: 1.94 t/ha Cg and other grass species Mean height: 71 cm |
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| Fuel load: 2.77 t/ha 50% cured grass standing. Cg dominant. Disc height: 28 cm |
Fuel load: 2.34 t/ha Wet site. Cg dominant. Disc height: 19.5 cm |
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| Fuel load: 2.86 t/ha Cg dominant. Moist site. Mean height: 82 cm |
Fuel load: 2.49 t/ha Herbicide in spring. Wet site. Mean height: 83 cm |
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| Fuel load: 3.78 t/ha No spraying evident. Cg dominant. Disc height: 13 cm |
Fuel load: 3.43 t/ha Evidence of seeding. Cg dominant. Disc height: 5.5 cm |
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| Fuel load: 3.87 t/ha Evidence of seeding. Cg taking over. Mean height: 83 cm |
Fuel load: 3.16 t/ha Cg dominant. Mean height: 54 cm |
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| Fuel load: 4.65 t/ha No sign of veg. management. Cg. dominant. Disc height: 15 cm |
Fuel load: 4.56 t/ha Powerline appeared to be seeded, but Cg taking over. Disc height: 22.5 cm |
Fall
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| Fuel load: 4.39 t/ha No sign of treatment. Cg dominant. Mean height: 77 cm |
Fuel load: 4.53 t/ha Heavy Cg. Wet area. Mean height: 100 cm |
Spring
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| Fuel load: 5.21 t/ha Evidence of herbicide treatment. Cg. Disc height: 13 cm |
Fuel load: 5.76 t/ha Cg dominant. Disc height: 13 cm |
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| Fuel load: 5.57 t/ha Continuous grass cover. Mean height: 68 cm |
Fuel load: 5.61 t/ha No evidence of treatment. Heavy growth. Mean height: 83 cm |
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| Fuel load: 6.00 t/ha Low site. Heavy growth. Disc height: 21 cm |
Fuel load: 6.38 t/ha Heavy Cg. Low swamp area. Disc height: 17 cm |
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| Fuel load: 6.42 t/ha Heavy Cg growth. Mean height: 68 cm |
Fuel load: 6.40 t/ha |
Very heavy loadings in typically wet areas. Grass tough to walk through. Only one site had a loading greater than 7.0 t/ha in the spring.
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| Fuel load: 7.63 t/ha Continuous Cg. Disc height: 14.5 cm |
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| Fuel load: 7.38 t/ha Seeded with clover. Cg taking over. Mean height: 62 cm |
Fuel load: 13.32 t/ha Tall heavy Cg. Mean height: 95 cm |
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| Fuel load: 21.1 t/ha Tall, continuous Cg. Mean height: 64 cm |