Chapters 2 to 6 gave some of the physical reasons why the upland boreal forest is characterized by large, crown fires which remove large amounts of the forest floor organic matter and recur about every 100 years. In brief, the fire behavior results from the large conifer component of the forest which is an ideal fuel consisting of large numbers of small needles and branches, long canopy lengths, relatively short distances from the forest floor to the lower canopy, low foliage moisture, and a well-aerated forest litter and duff layer made up of small branches, decay resistant needles and cones. The airstream and synoptic weather patterns create the spring and summer temperature and precipitation patterns for fuel drying and lightning for ignition. Although this fire behavior is characteristic of large parts of the North American boreal forest, there are areas where it is not, particularly the maritime regions of Quebec, Labrador and Newfoundland.

This chapter will discuss how the fire behavior characteristics are reflected in tree recruitment and mortality patterns, and these result in a limited number of age distributions.

Some population background for boreal trees

Tree populations are never studied by following the individuals throughout their long lives. Instead, assumptions are made about the population structure and its birth, death and migration processes. These assumptions are validated, often with varying difficulty, and the age distribution then interpreted using these assumed population processes. See the Appendix at the end of this chapter on assumptions about the equivalence of age and survivorship distributions. For a general introduction to the ecology of boreal trees, see Ritchie (1987).