Forest Stand Dynamics

Mature ICH forest Understanding the many factors which affect the natural development of a forest helps predict the consequences of different stand management practices such as spacing, thinning and partial cutting.  This study was undertaken to determine how the forests at Date Creek have evolved through time.  Initial results suggest that the development of these mixed-species forests is much more complicated than originally thought.  Other studies examined the development, structure and function of individual trees.
Mature (135 yrs) ICH forest at Date Creek
Stem sectioning Digital ring counter
Sectioning sample tree for stem analysis Microscopic measurement of tree growth rings

Available Literature:

LePage, P. 1995. The structure and development pattern of mixed-species forest stands in the Interior Cedar-Hemlock zone: Moist Cold subzone of northwestern British Columbia. MSc thesis. Oreg. State Univ., Corvallis, Oreg. 91p.
Abstract: A field study was established to explore stand structure and development patterns of mature, mixed-species forests in the Interior Cedar-Hemlock (ICH) zone: moist cold subzone of northwestern British Columbia. The species of interest in the study area were: western hemlock (Tsuga heterophylla (Raf.) Sarg.), western redcedar (Thuja plicata Donn), lodgepole pine (Pinus contorta var. latifolia Engelm.), hybrid spruce (Picea glauca (Moench) Voss x sitchensis (Bong.) Carr.), subalpine fir (Abies lasiocarpa (Hook.) Nutt.), and paper birch (Betula papyrifera Marsh.). Eighty stand structure plots, 150 to 600 m2 in size, were used to assess the species, size and age variation within the study area. Three representative plots, 1,000 m2 in size, were then selected for destructive sampling. Stand reconstruction techniques were used to: 1) characterize the existing species, age and height / diameter structure, 2) describe and quantify the historical height development pattern, 3) describe the development stage and spatial pattern of the stand and it’s different components and 4) determine the influence of the above characteristics on the current stand composition and structure.

The study stand is 135 years old and originated after a stand destroying wild fire. The resulting mixed-species stand had a very long recruitment period and is currently near the end of the stem exclusion stage of development. Because of the variety of growth patterns exhibited by the different species, neither individual tree height nor diameter were good indicators of stand age structure. The age structure and stage of development were much better defined by direct measures of age, stand density, the diameter distribution / mortality relationship or the overall spatial pattern.

Although partially influenced by age structure and spatial arrangement, the developmental pattern of the mixed-species stand was most strongly related to individual height growth characteristics and inter-tree competition. While lodgepole pine, hybrid spruce, western redcedar and paper birch developed in height along characteristically predictable lines, western hemlock exhibited a number of different growth patterns. Subalpine fir followed an atypical, aggressive height growth pattern, developing more like a pioneer species. The variety of height growth patterns frequently allowed younger trees to overtop older individuals, both within and between species. This resulted in numerous shifts in height dominance by different species during the first 80 years of stand development.

Forest structure is intimately related to disturbance type and intensity, site quality and the availability of seed or propagules for regeneration. This study examined the structure and development pattern of one type of mixture of tree species common to the ICH zone of northwestern British Columbia. Any difference in the factors listed above would likely produce a different species mixture and therefore a different structure and development pattern. Because most silvicultural operations are tied to the different structures at various stages of stand development, a more complete understanding of these patterns will allow managers to better predict the growth impacts of a variety of treatments and work with, rather than against the natural system.

Ashton, P. Mark, S.,  Lydia P. Olander, Graeme P. Berlyn, Rajesh Thadani and Ian R. Cameron. 1998. Changes in leaf structure in relation to crown position and tree size of Betula papyrifera within fire origin stands of interior cedar-hemlock.  Can. J. Bot. 76:1180-1187.
Abstract: Dimensions of anatomical and morphological attributes of leaves can influence physiological response to changes in environment over time.  Linking structural attributes of leaves to crown position and tree size within naturally developing cohorts of trees can provide a clearer understanding of changes in crown morphology for a species.  This study examined leaf anatomy and morphology of Betula papyrifera Marsh growing in two stages of stand development of interior cedar-hemlock forest, northern British Columbia.  Anatomical and morphological measurements of leaves located at six different positions within the crown were made on trees selected from stands that originated 15 y (small tree size) and 145 y (large tree size) after catastrophic fire.  Leaf area and mass were measured in the field.  Microscopic measures were made in the laboratory of thicknesses of leaves, cuticle, upper and lower epidermis, palisade and spongy mesophyll.  Stomatal density and stomatal aperture lengths were also determined.  Leaf anatomy and morphology varied significantly with position in the crown and among size classes of trees.  Changes in leaf anatomy observed among positions within the crown reflect the changing availability of light and moisture experienced during crown development.  For both size classes of tree the largest anatomical dimensions of leaves were at the outer and uppermost parts of the crown, whilst the smallest were at the lower and innermost parts.  Foliage of large trees (145 y) exhibit leaf attributes characteristic of the sun-shade dichotomy reported in the literature, but this was not shown for foliage of young saplings (15 y).  For the small trees (15 y) the largest leaves were located at the top of the crown while the smallest were located at the bottom.  This has been reported for many tropical pioneers but is in contrast to the usual sun shade dichotomy of temperate pioneers.  The large trees (145 y) followed the typical pattern with the smallest leaves at the top of the crown. Information from this study contributes to our understanding of foliar development of tree crowns by demonstrating how leaf structure changes with crown position and tree size under stand competition.

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