To determine the effect of fire front width on surface fire spread rates, a series of simultaneously ignited experimental fires was carried out in a pine plantation. Fires were ignited in plots with widths ranging from 0.5 m to 10 m and were burned in low wind conditions. Flame lengths were small in all fires, ranging from 20 cm to 60 cm. Since pre-heating of the forest litter from flame radiation is assumed to be an important mechanism in the spread of low intensity, low wind surface fires, it then follows that the width of a flaming front should effect on the heating of the fuel to ignition temperatures. Total flame radiation was also measured at a point 50 cm ahead of the advancing flame front for a number of the fires. Experimental results indicate that a flame radiation measured ahead of the fire stays fairly constant once the flame width is between 2 and 5 m. Theoretical flame radiation calculations confirm this trend. Rates of spread between the 5 and 10 metre width fires also appear to be similar; this indicates that, for the type of fires studied, once flame width is greater than about 2 m, radiation from any extra width of fire front has little effect on spread rate.

A critical parameter for the initiation and propagation of a crown fire in the boreal forest is the height to the base of the live crown. The initiation of a crown fire requires that the surface fire intensity must be sufficient to ''jump'' the gap between the forest floor and the live crown and ignite crown fuels. The greater the height of the live crown base, the more intense the surface fire must be to induce a crown fire. Plantation forest fuels tend to be more structured and have less variability than naturally regenerated areas, allowing prediction of the height of the live crown base to be made from commonly available stand parameters. Plantations of four commonly planted boreal forest species were sampled over a variety of age classes to determine a predictive relationship for height to live crown base. Height to live crown base can be predicted from stand height and density for Pinus banksiana (jack pine), Pinus resinosa (red pine), Picea mariana (black spruce), and Picea glauca (white spruce). In addition to predicting the height to live crown base, parameters within the equations lead to other observations. Crown foliar fuel loading does not change with stand height following crown closure in red pine but in the other three species crown fuel load increases as the stand grows taller.

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