04-For-A4 Forest Management · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Forest Engineering, 04-For-A4 Forest Management, May 2014. Closed book; approved Casio/Sharp calculator only. 3 hours. Seven questions; the instructions call for Questions 1, 2, 3, 6 and 7 plus EITHER Question 4 or Question 5.
Reference texts: Davis, Johnson, Bettinger & Howard, Forest Management: To Sustain Ecological, Economic, and Social Values (age-class regulation, area/volume control, biodiversity planning); Klemperer, Forest Resource Economics and Finance (discounted cash flow, break-even stumpage/rate analysis); Smith et al., The Practice of Silviculture: Applied Forest Ecology (silvicultural systems, natural disturbance regimes); Van Wagner (1978), “Age-class distribution and the forest fire cycle,” Can. J. For. Res. 8 (negative-exponential fire-origin age structure); BC Forest and Range Practices Act and BC Ministry of Forests guidance (Canadian regulatory context).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Given. Figure 1 plots two things against “years from now”: the forecast operable growing stock, which starts at about 8 million m3 today, falls steadily to a minimum of about 4 million m3 at roughly year 30, and then recovers to about 6.5 million m3 by year 100; and the maximum sustainable harvest level, drawn as a horizontal line at about 4 million m3. The two lines meet at the trough: the growing-stock curve comes down to touch the harvest line at about year 30 and never crosses below it.
Find. For each of the six actions, whether it could produce an immediate AND sustainable increase in harvest level, and why.
Approach. Read the constraint off Figure 1 before judging any action. Today's operable inventory is roughly twice the harvest level, so it is not today's stock that limits the cut. What limits it is the trough at about year 30, where the operable growing stock falls to the harvest line: the harvest shown is the highest constant flow the forest can carry through that bottleneck. An action therefore permits an immediate increase in the sustainable harvest level if it adds recoverable operable volume at or before the year-30 bottleneck — either now, or by making currently non-operable stands operable in time to relieve the trough. This is the classic allowable cut effect: because the sustainable harvest is a single sustained flow set by the tightest point of the whole forecast, volume that arrives before that point lets the entire flow, including this year's cut, be raised immediately. Conversely, an action whose volume arrives after year 30 lands on a part of the curve that is already in surplus and does nothing for the binding constraint, however sound the investment. Sustainability is then simply the requirement that the raised flow still clear the trough rather than draw the inventory down below it.
| Management action | Immediate sustainable increase? | Reason |
|---|---|---|
| 1. Black spruce plantations, first operable at age 40 | No | Planted today, these stands first contribute operable volume in year 40 — a decade after the year-30 bottleneck. The growing stock is already recovering by then, so the binding constraint is untouched and the sustainable harvest level cannot be raised now. |
| 2. Fertilize mature (already-operable) stands, +2% increment now | Yes | The added increment accrues from this growing season onward to stands that are operable today — exactly the stands that carry the forest down through the drawdown to year 30. More volume at the bottleneck means a higher flow can be sustained through it, so the harvest level can go up immediately. |
| 3. Space 20-year-old stands, cuts operable age 60→40 | Yes | These stands are 20 years old now, so cutting their operable age from 60 to 40 makes them merchantable in year 20 instead of year 40 — i.e. before the year-30 trough. The extra operable area arrives exactly where the constraint binds, and by the allowable cut effect the whole sustained flow (this year's included) can be lifted at once. |
| 4. Harvest to protect regeneration for higher yield at age 60 | No | The regeneration being protected is age zero today, so the yield gain is realized around year 60 — two decades past the bottleneck, on a part of the forecast that is already in surplus. Good long-term silviculture, but no lever on today's harvest level. |
| 5. Reduce top diameter and stump height, recover more volume/tree | Yes | A utilization change applies to every stand cut from today forward, the trough years included, recovering more merchantable volume from the same standing trees. The gain is immediate, is present at the bottleneck, and repeats every year the standard is held, so it is sustainable by construction. |
| 6. Norway spruce plantations, first operable at age 25 | Yes | Unlike action 1, a 25-year operability age puts this new volume on stream in year 25 — just inside the year-30 bottleneck. It relieves the binding trough, so it too supports an immediate, sustainable increase. The only difference between actions 1 and 6 is timing relative to year 30, and that is precisely what decides them. |
Answer: actions 2, 3, 5 and 6 can; actions 1 and 4 cannot. The six actions sort cleanly on one test — does the extra operable volume arrive at or before the year-30 trough? Actions 2 and 5 deliver it immediately (more increment on, and better recovery from, stands already merchantable). Actions 3 and 6 deliver it in years 20 and 25 respectively, still inside the bottleneck. Actions 1 and 4 deliver it in years 40 and 60, on the far side of the trough where the growing stock is already recovering, so neither relaxes the constraint that sets the harvest level. Note how the paper pairs them: actions 1 and 6 are the same kind of investment (a new plantation) and differ only in operability age, 40 versus 25, and actions 3 and 4 likewise differ only in when the treated stand becomes merchantable — year 20 versus year 60. Timing relative to the trough, not “is it operable today,” is what the question is testing.
All four qualifying actions are also sustainable rather than a one-time draw-down: each raises the volume available at the tightest point of the forecast, so the higher flow still clears the trough and can be carried indefinitely, and the long-run recovery to about 6.5 million m3 leaves headroom beyond it. A candidate who answered “only 2 and 5” has applied the right test to the wrong forest — that is the correct answer when operable growing stock is flat or rising, because then the constraint really does sit at today's inventory.
