We conducted a preliminary assessment of the age structure of a previously unmanaged IDFxh forest 15 km NW of Kamloops BC (Isobel Project site) to determine if the uneven sized stems found in most dry-belt IDF forests are indicative of an uneven aged stand history, or if this structure reflects different growth rates. The uneven sized structure could reflect multiple cohorts arising periodically following disturbances (e.g. low severity wildfires), and/ or during periods when soil moisture and seedfall combine to promote seedling establishment. Alternatively, these stands may largely arise as a single cohort, and size differentiation is the result of different growth rates relating to stand density or microsite condition. The perception of an uneven-aged stand structure needs to be closely examined since there may be several management and/or economic consequences associated with maintaining a multi-layered stand. For example, during a western spruce budworm attack understory trees are severely defoliated and either die or have poor growth form. Should the latter be true, this would support the more widespread use of heavier basal area removal systems representing either variable retention, seed tree or shelterwood cuts. We collected tree sections from about 250 stumps in October 2003 (trees harvested in January-March 2003) and from about 150 smaller stems (<17.5 cm dbh) to examine the age of stems across a range of diameter classes. All sections were prepared for aging by sanding with progressively finer grit sizes, and of these, 105 sections were chosen at random for age determination. The following two figures summarize the overall pattern of recruitment, and the relationship between age and diameter at stump height. Further analyses on recruitment patterns in relation to site type (mesic or xeric) will be conducted when the remaining tree sections are aged. Figure 1. The regeneration pattern of trees collected at the site (n=105). Figure 2. The relationship between tree age and the diameter at stump height (n=105).
Forest Investment Account (FIA). 2004. Assessing pre-harvest age structure and diameter at stump height in relation to local area density in a dry-belt Douglas-fir forest: [Walt Klenner]. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2004MR087
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Trees, Growth, Research
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