The effect of vegetation composition on the fuel load
The plant species that comprise a vegetation differ in their attributes
as fuel. This is not only a result of chemical differences, but also
in the size of plant parts that become available as fuel, and the growth
form.
The composition of the vegetation is the result of complex interactions
that are described by this model. Press 'Restart' in the main
menu to follow the vegetation composition.
Fuel size
Fuel size is to some extent determined
by the growth form of the plants. Herbaceous fuels are, of course,
produced by grasses and forbs. Woody fuels on the other hand, are
produced by trees and bushes of various sizes. Due to smaller diameters
of their stems, shrubs contribute to the smaller fuel classes. Trees
of different sizes will produce larger pieces of fuel that may only be
consumed after a number of fires.
Fuel arangement
The multiple stems of shrubs, coppice and suffrutex plants act as a break
to windblown fuels. Leaves and even very small twiggs that are borne
by the wind are caught by the stems and deposited amongst them.
In this way, fuel accumulates within the plant.
Trees on the other hand, must be considered differently. The thick
trunk, frequently with a fire resistant bark, does not burn readily.
The branches are therefore protected somewhat from ground fire, simply
because they are too high to be ignited by the flames.