The structure of a forest stand is characterized by: (a) species composition, (b) age, (c) size (diameter and height), and (d)
spatial (horizontal and vertical) arrangement of the trees. Depending on the species, site, and disturbance history, the
stand structure varies with time, thus providing a snapshot of a particular development stage.
Research on growth and stand structure has shown that the spatial distribution of trees is one of the key determinants of
stand productivity. Forest inventories and ecological surveys carried out in British Columbia (BC) have shown that the
structure of naturally established, unmanaged stands varies from simple (single-species, single-storied, and even-aged) to
complex (multi-species, multi-storied, and uneven-aged). Only a few studies have quantitatively characterized this range
of structural complexity, with nearly all studies focusing on old-growth stands.
BC forest policy requires that harvested areas be regenerated with a mixture of tree species whenever a mixture is suited
to the site. This policy is based upon the assumption that under appropriate conditions, increases in stand productivity,
reliability, and/or biodiversity can be attained in mixed-species stands. This assumption has not yet been tested for forest
ecosystems. One mechanism by which different tree species can reduce crown competition for light is through vertical
separation (the development of multiple canopy strata). Canopy stratification is not easily recognized in mixed-species
stands, particularly when species have similar shade tolerance and height growth patterns, and no quantitative methods
have been developed to detect stratification.
The diameter frequency distribution of two-storied stands have been characterized by inverted J-shaped as well as modal
curves. Although it would be more appropriate to characterize stand structure by height frequency distributions, these
distributions have not been developed. We suggest that (i) a stand is stratified if there are distinct, quantitatifiable modes
in the size distribution; either diameter, height, or crown height, and (ii) height or crown height distributions will be the most
sensitive measures.
To characterize the structure of western hemlock (Tsuga heterophylla (Raf.) Sarg.) (Hw) and western redcedar (Thuja
plicata Donn ex D. Don in Lamb.) (Cw) second-growth stands, and to investigate its influence on tree growth, we (1)
described and compared size (diameter, height, and crown height) frequency distributions in single- and mixed-species
stands, (2) determined whether mixed-species stands develop a stratified canopy, and (3) examined whether interactions
between hemlock and redcedar affect tree growth.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/708 |
| Date | January 2001 |
| Creators | Klinka, Karel, Varga, Pal, Montigny, Louise E. M. de, Chourmouzis, Christine |
| Publisher | Forest Sciences Department, University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Relation | Scientia Silvica extension series, 1209-952X, no. 35 |
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