|
Stand structure data from multi-cohort stands is needed as a foundation for studies of the biological processes of tree growth and for modelling. The Pothole Creek Study Area was selected as a suitable site for collection of detailed site, stand
and history information to help reconstruct past growth and yield. The site is located in a
patchy multi-cohort Douglas-fir stand that was diameter-limit logged around 1964-1966
and is typical of IDF problem forest types in the Merritt
Timber Supply Area.
A permanent sample plot
within the 5-hectare Pothole Creek Study Area is providing essential growth and yield data through repeated measurement.
The Permanent Sample Plot
A square, fixed-area permanent sample plot (PSP) slightly larger than one hectare (10270 m2)
has been established at a mid-slope position within the stand. It is centred on a significant gap created by a skid trail during the most recent
harvest. This location was chosen to represent the range of canopy closure and vertical structure typical of the forest type. Low-level 70 mm air stereo photographs of the plot and surrounding area were taken, and the plot boundaries mapped and tied
into a 25 m by 25 m reference grid established throughout the 5 ha study area. The corners of the plot are marked with
rebar and white PVC pipe.
Most of the trees taller than 1.5 m were mapped with a laser surveying device and given numbered permanent tags. Standard mensurational data (diameter, height, damage, etc.) were recorded for all trees above 6 cm dbh. In addition, crown radii in
four cardinal directions were recorded for all trees taller than 7 m. The diameter and height of all
stumps and taper of the lower bole of large trees was measured at 10 - 20 cm intervals from the base to 1.3 m height. Increment cores of all plot trees are currently being measured and will provide frequency and spatial distribution of tree ages,
and, together with the stump measurements, an approximation of the stand structure at the time of logging.
A 30-m x 30-m subplot was established at the centre of the 1 ha PSP in which light attenuation measurements were taken (see: Light Modelling) and all trees from the tagging limit in the large plot down to 10 cm height
are monitored every two years for ingrowth and mortality. Crown radii were measured for all trees between 1.3 m and 7 m in the subplot. To replicate subplot measurements, two more 20-m x 20-m subplots were established at random locations elsewhere
within the 1-hectare plot. Ingrowth, height, diameter and mortality have been measured on all trees taller than 10 cm within the two smaller subplots.
Initial stand and stock tables and stem maps of both the 1-hectare plot and the 30-m x 30-m subplot have been produced. The structure was simulated with the TASS model to examine the model's ability to mimic the open structure and unique
stem/crown proportions typical of these multi-cohort stands. (See: Stand
Projection.)
A ten-year remeasurement of the main plot and all subplots was completed in
2006. A summary of the results is available in Extension Note 85: "The
Pothole Creek Study Area: Dry uneven-aged Douglas-fir stand development". Retrospective Studies
Natural regeneration on the study site is distributed in distinct patches and patches of advanced regeneration dominate the understory. Twelve
of these patches of various
shapes, sizes and estimated ages were identified for destructive sampling outside of, but near, the permanent sample plot. Each tree taller than 10 cm was mapped and numbered. Three to five trees were removed in 2-3 m intervals along the main clump
axis for detailed stem analysis which included: the total height, crown length, diameter at breast height, the distance between whorls, the number of whorls between the terminal bud and the base of the tree and the total age as determined by tree
ring count at the base. Other trees that were not destructively sampled were measured for height, crown length and DBH.
Total tree age varies within and between clumps but spans a range of about 20 to 60 years. Height/age
curves indicate that most of the trees were suppressed during early growth. Logging appeared to have only a slight release effect on some clumps and increased height growth did not really occur until five to ten years after logging. (Adapted from:
A study of the age structure and regeneration patterns of interior Douglas-fir at Pothole Creek by C. Halenda, 1997.)
Retrospective analysis of height and branch growth of 32 larger trees from outside the PSP
was completed in 2000. See: Canopy Modelling and Stem Analysis.
Research Branch contact: Catherine Bealle Statland.
|
