BC Ministry of Forests - Research Branch - Forest Productivity Section

Online Presentations: SYLVER Demo/Effects of Pruning


Here's "an operational example" of pruning to convince you that SYLVER really works.
Be aware that plantations won't produce clear lumber without pruning when managed on short rotations (assuming the demand for clear lumber will continue as the harvesting shifts from old- to second-growth forests).


This tree added clear mature wood after being pruned to 2, 4 and 6 m at ages 15, 20, and 25, respectively.
Notice that SYLVER recognizes both "knotty and clear wood".


Look at these recently pruned stands. Which one was pruned at the best time? In the past we've favoured the "late", or even later, option.
But are such decisions based on value? And, if so, how is it defined?


To achieve our objective of maximum monetary VALUE, we take all costs (red) incurred throughout the rotation, and all revenues (blue), and reference them to the same point in time, often the year of planting, which we call "the present".
Present Value recognizes that ten dollars sixty years from now may only be worth a dollar today.
Now take the present value of all revenues from the sale of lumber and chips, i.e. $6,000, and subtract the present cost of harvesting, manufacturing, stand tending and planting, i.e. $5,000 ... leaving a net present value $1,000.
The financial assumptions are flexible. For example, SYLVER ignores planting if it's a cost of harvesting, thus increasing the NPV to $1,500.
You can also adjust the real rate of interest, currently 4%, and escalate the costs or prices over the rotation?


Now let's rephrase the earlier question.
In which of these pruned stands would you prefer to invest you savings?
Let's instruct SYLVER to prune "late", and then evaluate our investment.
Instead of 1 lift at age 20, we'll prune in 3 lifts at ages 15, 20 & 25.


We'll plant 1100 Douglas-fir on a very productive site.
Watch for the 1st lift at age 15 when the average DBH is ?? cm.
It produces some clear wood (blue) by age 20.
We're now ready for lift 2 at 20 years,and lift 3 at age 25.
Look at the clear wood around the knotty core and more clear wood is added as the stand grows to age 60.
Mature wood (yellow) has also appeared.
Now take a closer look at this pruned butt log with ??% clear wood.


It shows that the shell of clear wood, in blue, is too thin to produce much clear lumber (dark blue).


This is confirmed by a decline in NPV due to pruning. That is the premium for clear lumber did not cover the treatment costs.
Obviously, we must prune earlier and constrain the knotty core.


Pruning at ages 13, 15 and 17, looks very promising because the knotty core is now relatively small and cylindrical.
The potential for clear lumber, shown here in dark blue, ...


... is more striking on these end views.
Early pruning produces 80 (75%) board feet of clear lumber vs. 24 (20%) in spite of its smaller diameter (1.6 cm less).


Now look at the benefits in terms of clear lumber and NPV at age 60.
Simply by initiating treatment 2 years earlier (13 vs. 15) and compressing the schedule, we've increased the NPV to $2,300.
Now let's examine the relationship between the age at which we start pruning (12 - 15 years), and NPV.


We see that our potential for profit is large, but the profit window is only open for 2 years (age 13 and 14), which isn't surprising considering that New Zealanders target the optimum month for pruning!
However, we also found that very early pruning (12, 14 & 16) removes too much foliage, impairs growth and even kills trees.
And earlier we found that very late treatment leaves a thin shell of clearwood with little opportunity for clear lumber.


How do you actually use SYLVER.
First, call us for a copy of FAN$Y, and a "library of product files" for various silvicultural regimes.
Next, enter your site variables, such as operating difficulty; financial data, e.g. harvesting costs; and request all treatments of potential interest.
Lastly, run FAN$Y and choose the appropriate silvicultural regime.
If a regime is not in the library, simply contact our support service.
We will also use SYLVER for "special studies" of general interest, or in response to a request from you.

Learn about:

Link to Research Branch.