Effects of Regeneration Abundance on Predicted Development of Interior Douglas-fir Stands By Cornel Lencar Graduate Student, Faculty of Forestry University of British Columbia

Objectives The objectives of my thesis are:  To calibrate the small tree height increment component of Prognosis BC.  To determine regeneration levels and their effect in the development of Interior Douglas-fir stands from the IDFdk1, IDFdk2, and IDFdk3 subzone variants.  To develop working guidelines for natural regeneration stocking levels in IDFdk1, IDFdk2, and IDFdk3.

Interior Douglas Fir Zone in the Kamloops Forest District IDF Zone  In BC, the IDF dominates the low to mid- elevation landscape of the southern Interior Plateau and southern Rocky Mountain trench.  Much of the IDF landscape is occupied by stands of pure Douglas-fir, however mixed stands with lodgepole pine and spruce do occur.  The intricate landscape mozaic that comprise IDF are also characterized by stands with one to four age cohorts.  Irregular size distributions with varying amounts of regeneration, poles and large stems are very frequent.  Stands volume range widely, but reach 250 to 300 m 3 /ha.

Sampling Design  Sampling took place in partially cut stands.  The sample population was stratified based on time since disturbance and residual basal area.  In each selected stand, between 2 and 9 plots were located systematically.  Each plot had a fixed-area of 0.04 ha, with a nested cluster of 5 subplots, each with a radius of 2.07 m, for regeneration measurements.  The cluster of 5 regeneration subplots consisted of 1 plot located in the centre of the main plot and 4 other plots located at m from the centre of the main plot in the cardinal directions.

Measurements (large and small trees)  In the 0.04 ha plot, all trees > 7.5 cm (large trees) were measured for dbh.  Up to 2 trees per species were sampled for height.  All small trees (defined as trees with dbh between 2.0 and 7.5 cm), were measured for dbh in the 0.04 ha plot.  5 small trees per species per plot were sub-sampled for total height and 5 year height increment.

Measurements (regeneration trees)  In the regeneration subplots, all regeneration was counted by species and height class.  4 height classes were used: (1) m; (2) m; (3) m; and (4) > 1.3 m.  Up to 2 “best” trees per species were sub-sampled for height and total age.

Present Data 335 Plots distributed in :  3 ecological zones  sites disturbed 4 to 21 years ago  an elevation range of 700 m  a range of basal area retention  a range of slopes, aspects and elevations

Methodology  A matrix of stands was created,using residual basal area, site conditions and species composition for each subzone.  Average levels of regeneration were calculated for each subzone and grouped by residual basal area and site conditions according to the stand matrix.  Stands disturbed more than 10 years ago were selected from each group of sampled stands defined in the matrix and tree lists were obtained.  For each sampled stand, different levels of regeneration were used as input in the Prognosis BC tree list.  These stands were then projected for 40 years and compared across regeneration levels.

Example of Matrix of Stands Types of Stands as a function of Species Composition, Residual Basal Area Class and Site conditions (Numbers represent sample stands)

Regeneration Summary: Average Regeneration Levels in IDFdk1

Prognosis BC Runs  Input tree list  Select Treatment  Input the regeneration levels  Run the model  Compare results  Draw conclusions (Project must be completed)

IDFdk1-Predicted Volume over a 40 Years Cycle for Different Levels of Basal Area and Regeneration

IDFdk1- Dry Site Series, Low Initial Basal Area and Low, Medium, and High Regeneration Levels

IDFdk1- Dry Site Series, Medium Initial Basal Area and Low, Medium, and High Regeneration Levels

IDFdk1- Dry Site Series, High Initial Basal Area and Low, Medium, and High Regeneration Levels

Conclusions  Little difference was found for the total volumes at different levels of regeneration.  There were considerable differences in the stand structures associated with the different regeneration assumptions.  Species composition and stand structures varied somewhat among subzones and moisture levels, but the trends illustrated here were repeated.

Acknowledgments This research was funded by the BC Ministry of Forests using FRBC funds. Many people, including my supervisory committee, B.C. Ministry of Forests employees, and some of my graduate student colleagues at UBC made this work possible, and more important enjoyable.