Unit 5 · Topic 5.17 Beta

Sustainable Forestry

Sustainable forestry harvests wood no faster than forests regrow while protecting soil, water and habitat.

Practice 7: Environmental Solutions

Part 1 · Hook

Why this matters

For most of the twentieth century, U.S. forest managers put out every fire as fast as they could. Dead branches, brush and young trees piled up on the forest floor. When fires did escape, they burned so hot that they killed even the big old trees that had survived centuries of smaller fires. Today managers set some fires on purpose, a change that sounds backward until you see why.

Part 2 · Before you start

What this builds on

Part 3 · Prerequisite check

Quick check before you start

1. Which is a cost of clearcutting a hillside?

  1. Bare soil erodes and the stream below warms
  2. Shade over the stream increases
  3. Carbon stored on the site increases
  4. Habitat for mature-forest animals grows
Show the answer

Removing all the trees bares the soil and the stream.

  • Correct: Bare soil erodes and the stream below warms:
  • Shade over the stream increases:
  • Carbon stored on the site increases:
  • Habitat for mature-forest animals grows:

2. What is maximum sustainable yield?

  1. The largest harvest a population can replace each year
  2. The total size of a population at its carrying capacity
  3. The smallest harvest that pays for itself
  4. The harvest taken in one year by clearcutting
Show the answer

It is the largest harvest that can be taken year after year without shrinking the population.

  • Correct: The largest harvest a population can replace each year:
  • The total size of a population at its carrying capacity:
  • The smallest harvest that pays for itself:
  • The harvest taken in one year by clearcutting:

Part 4 · See it

See it first

Three panels. Selective cutting: a few mature trees are cut and most of the forest stands. Reforestation: rows of seedlings are planted where trees were cut. Prescribed burn: a planned, low fire burns dead wood and brush on the forest floor while the large trees survive. Each keeps forest cover, soil and habitat while still producing wood or lowering the risk of a large wildfire.
Selective cutting, reforestation and prescribed burns keep forest cover while producing wood or lowering wildfire risk. LevlPrep original diagram.

Part 5 · Step by step

How it works, step by step

  1. Fires are put out for decadesdead wood and brush build up on the forest floor
  2. A large load of fuel is on the grounda wildfire burns hotter and climbs into the treetops
  3. A crown fire kills large trees and bakes the soilthe forest takes much longer to recover
  4. Prescribed burns clear the fuel under safe conditionslater wildfires stay lower and cooler, and large trees survive

Part 6 · Key ideas

Key ideas

  • Sustainable forestry harvests wood no faster than the forest regrows and protects soil, water and habitat.
  • Selective cutting takes some trees and leaves most standing, so the forest keeps its cover, shade and habitat. It costs more than clearcutting.
  • Reforestation replants or lets trees regrow on cut land. Mixed native species restore more habitat than a single-species plantation.
  • Prescribed burns clear dead wood and brush to prevent hotter wildfires. Using recycled wood and paper, and protecting trees along streams, also help.

Part 7 · Misconception

A common mistake

The wrong idea: The best way to protect a forest is to put out every fire as soon as it starts.

What actually happens: Many forests evolved with frequent low fires. Putting out every fire lets fuel build up, so the fire that finally escapes is far hotter and more destructive. Prescribed burns keep fuel low.

Part 8 · Check yourself

Check yourself

Exam-style questions. Anything you miss goes into your review queue.

1. Which forestry method harvests some trees and leaves most of the forest standing?

  1. Selective cutting
  2. Clearcutting
  3. Prescribed burning
  4. Slash-and-burn
Show the answer

Selective cutting removes chosen trees, often single mature ones, from a standing forest.

  • Correct: Selective cutting: Right: some trees are taken, most remain.
  • Clearcutting: Clearcutting removes all the trees.
  • Prescribed burning: Prescribed burning removes brush, not timber.
  • Slash-and-burn: Slash-and-burn clears land for farming.

2. Why does selective cutting cause less erosion than clearcutting?

  1. Most trees stay, so roots hold the soil
  2. The cut trees are left on the ground to block the stream
  3. Selective cutting is done in winter, when there is no rain
  4. The soil under selected trees is harder, so it does not move
Show the answer

Standing trees keep roots in the soil and leaves over it.

  • Correct: Most trees stay, so roots hold the soil: Right: roots and canopy remain.
  • The cut trees are left on the ground to block the stream: Logs in streams are not the reason.
  • Selective cutting is done in winter, when there is no rain: Logging season is not what limits erosion.
  • The soil under selected trees is harder, so it does not move: Soil hardness is not the reason.

Model or diagram

Three sustainable forestry practices

Three panels. Selective cutting: a few mature trees are cut and most of the forest stands. Reforestation: rows of seedlings are planted where trees were cut. Prescribed burn: a planned, low fire burns dead wood and brush on the forest floor while the large trees survive. Each keeps forest cover, soil and habitat while still producing wood or lowering the risk of a large wildfire.
LevlPrep original diagram.

3. In the reforestation panel, what is shown?

  1. Rows of seedlings planted on cut land
  2. A few mature trees cut from a standing forest
  3. A low fire burning brush under large trees
  4. Large trees standing with no young trees
Show the answer

The middle panel shows small trees planted where trees were cut.

  • Correct: Rows of seedlings planted on cut land: Right: seedlings planted.
  • A few mature trees cut from a standing forest: That is selective cutting.
  • A low fire burning brush under large trees: That is a prescribed burn.
  • Large trees standing with no young trees: The middle panel shows young trees.

4. In the prescribed burn panel, why do the large trees survive the fire?

  1. The fire is low, below the large trees' crowns
  2. The large trees are cut down before the fire is set
  3. The fire is set in the treetops, away from the trunks
  4. The large trees are sprayed with water by the fire crew
Show the answer

The flames are drawn low on the forest floor, below the crowns.

  • Correct: The fire is low, below the large trees' crowns: Right: a low ground fire spares the crowns.
  • The large trees are cut down before the fire is set: The trees are standing in the panel.
  • The fire is set in the treetops, away from the trunks: The flames are on the ground.
  • The large trees are sprayed with water by the fire crew: No water spraying is shown.

5. Which panel's practice best matches the idea of maximum sustainable yield?

  1. Selective cutting, matched to the yearly growth
  2. Prescribed burn, because it produces the most timber
  3. Reforestation, because seedlings can be harvested in a year
  4. Neither, because sustainable yield applies to fish and not trees
Show the answer

Taking only a portion of the trees, matched to growth, keeps the forest producing year after year.

  • Correct: Selective cutting, matched to the yearly growth: Right: harvest matched to growth.
  • Prescribed burn, because it produces the most timber: Prescribed burns do not produce timber.
  • Reforestation, because seedlings can be harvested in a year: Seedlings take decades to reach harvest size.
  • Neither, because sustainable yield applies to fish and not trees: Sustainable yield applies to any renewing population, including trees.

Data

Wildfire in burned and unburned forest plots

A wildfire swept through a pine forest where some plots had prescribed burns in the past 5 years and others did not (invented data for practice)
MeasurePlots with prescribed burnsPlots without prescribed burns
Fuel on forest floor before the wildfire (metric tons per ha)840
Average flame height (m)1.212
Large trees killed (%)1075

6. Write the setup for the percent change in fuel on the forest floor from the unburned plots to the plots with prescribed burns, then give the answer.

Type the setup as on the exam, with brackets and units, then the answer.

Show the answer

8−4040×100=−80%\frac{8 - 40}{40} \times 100 = -80\%: prescribed burns removed 80% of the fuel.

  • Setup: 8−4040⋅100\frac{8 - 40}{40} \cdot 100; answer -80 %

7. A 5,000-hectare forest grows 4 m³ of new wood per hectare each year. To harvest sustainably, how many cubic meters of wood can be cut each year at most?

Type a number, then its unit (m3). Scale words (2.5 million) and powers of ten (2.5 × 10^6) are read.

Show the answer

Yearly growth: 5,000ha×4m31ha5{,}000\,\text{ha} \times \frac{4\,\text{m}^3}{1\,\text{ha}}=20,000m3= 20{,}000\,\text{m}^3. Cutting no more than that keeps the forest from shrinking.

  • Answer: 20,000 m3

Part 9 · Summary

Summary

Sustainable forestry harvests wood no faster than forests regrow while protecting soil, water and habitat. Selective cutting keeps most trees standing; reforestation replants cut land; prescribed burns remove fuel so wildfires stay cooler; and reusing and recycling wood lowers demand. Each method trades some cost or timber for a forest that keeps producing.

Part 10 · Up next

What comes next

Part 11 · Connections

Connections

Share to Google Classroom (opens in a new tab)

Question set for this topic