State Forest Service — Assistant Conservator of Forests (state PSC exams) · India · State Public Service Commissions (e.g. TNPSC, MPPSC, UPPSC, HPPSC, KPSC, MPSC)
Original practice questions written to the published syllabus · not past papersMeasuring single trees, logs and stands: diameter, height, form, volume, biomass and growth, with the instruments and formulas used in the field.
In the exams: IFoS Forestry Paper II Section A (forest mensuration); ICAR AICE-JRF 59 Unit 4; ICAR AIEEA-PG Group 09 (forest mensuration); PRC Forest Resource Management; SAF Certified Forester; state forester and RFO exams
State Forest Service (ACF) and Range Forest Officer exams, India
Short numerical problems: girth to diameter, basal area per hectare, log volume, quarter-girth volume, form factor volume, MAI and PAI, and definitions of top height and site quality.
How our questions for State Forest Service spread across the units of Forest Mensuration. Difficulty: 15 easy, 24 medium, 2 hard.
| Log volume formulas: Huber, Smalian, Newton | 6 | |
| Growth and increment: CAI, MAI and their relationship | 5 | |
| Basal area and its uses | 4 | |
| Volume of standing trees: form factor and form quotient | 4 | |
| Height measurement: principles and hypsometers | 3 | |
| Volume tables: local, general and form-class; construction and use | 3 | |
| Stand measurement: stems per hectare, basal area, top height, stand volume | 3 | |
| Angle-count (Bitterlich) sampling and relascopes | 3 | |
| Age determination and stem analysis | 3 | |
| Site index and site quality curves | 3 | |
| Diameter and girth measurement: breast height conventions, calipers, tapes | 2 | |
| Bark thickness and crown measurements | 1 | |
| Tree biomass and allometric equations | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
From a point 25 m (horizontal) from a tree, the angle to the top is 40° above horizontal and to the base 5° below. What is the height?
A. 23.2 m
H = D(tan α + tan β) = 25 × (tan 40° + tan 5°) = 25 × (0.8391 + 0.0875) = 23.2 m. Subtracting the tangents gives 18.8 m and is used only when both readings are on the same side of the horizontal; using sines in place of tangents gives 18.2 m.
Why is basal area per hectare widely used to prescribe thinnings?
C. It joins tree number and size, is quick to measure, and tracks volume and competition
Basal area integrates number and size, can be estimated in seconds with an angle gauge, and is closely related to volume (G × height × form factor) and to competition. It does change after thinning — that is the point of using it.
A 6-m log has diameters of 40 cm at the base, 34 cm at the middle and 30 cm at the top. What is its volume by Newton's formula?
A. 0.560 m³
Newton: V = (g_b + 4g_m + g_t)/6 × L = (0.12566 + 4 × 0.09079 + 0.07069)/6 × 6 = 0.560 m³. Smalian gives 0.589 m³ and Huber 0.545 m³; a plain average of the three areas (0.574 m³) omits Newton's weight of 4 on the mid-section.
Why is Smalian's formula the one most used to scale logs on a landing or in a stack?
B. It needs only the two end diameters
Log ends are accessible in a stack while mid-points are often buried, so Smalian is practical. It is not exact for butt logs — it overestimates neiloid-shaped butts most — and like all three formulas it needs the length. Those ends are visible on stacked logs.
A volume table entered with dbh alone is called a:
C. Local (one-entry) table
Local tables give volume from dbh only and are valid where the height-diameter relationship matches the construction data. General tables add height; form-class tables add form class. A yield table gives stand values by age and site.
Above-ground biomass of a stand is 100 t/ha and the root-to-shoot ratio is 0.24. What is the total (above- plus below-ground) biomass?
D. 124 t/ha
Below-ground biomass = 100 × 0.24 = 24 t/ha; total = 124 t/ha. Subtracting gives 76; dividing by the ratio gives 416.7.
The main product of stem analysis used in site-quality work is:
A. A height-age curve built from the ages at which the stem reached each disc
Stem analysis gives the age at which the tree reached each sampled height; plotting heights against these ages gives the tree's height-growth history, the raw material of site-index curves.
A stand had 165 m³/ha at 30 years and 240 m³/ha at 40 years. What was its periodic annual increment between those ages?
B. 7.5 m³/ha/yr
PAI = (240 − 165) / 10 = 7.5 m³/ha/yr. 6.0 is the MAI at 40 (240 / 40) and 5.5 the MAI at 30 (165 / 30); 75 is the total periodic increment, not per year.
A tree's volume rose from 0.80 m³ to 1.00 m³ in 5 years. What is its volume increment percent by Pressler's formula, p = (200/n)(V2 − V1)/(V2 + V1)?
C. 4.44%
Pressler: p = (200/5) × (0.20/1.80) = 40 × 0.1111 = 4.44%. The compound-interest formula gives 4.56%; simple interest on the initial volume gives 5.00% and on the final volume 4.00%. The stem names Pressler, so only 4.44% is correct.
In Indian and British yield tables, Site Quality I denotes:
D. The best, most productive site
In these conventions quality classes run from I (best) downwards; classes are defined by ranges of top height at given ages.
Ten here, 41 in the app. The Laisha app has every practice question we have written to State Forest Service in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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