NRES 250 Exam 2: Forestry (Fall 2025)

Ecophysiology

Ecology and physiology studied together in the context of the environment

Why is ecophysiology important?

It provides a mechanistic understanding of forest succession, a forest's response to climate change, and atmospheric chemistry in relation to forests

Basic tree biology

Leaves (photosynthesis and respiration), shoots and roots (primary and secondary growth), roots

Tree biology: basic associates

animal seed dispersal, microbe accumulators (root symbiosis), consumers

Tolerance

ability to withstand stress

What is shade tolerance?

the ability to grow well with an amount of shade; "tolerance" is a relative concept

Shade tolerance numeric scale

Very tolerant: 10

Very Intolerant: 1

Very Shade Tolerant trees (around 10)

sugar maple, eastern hemlock (can develop in understory under other trees)

Moderate Shade Tolerant trees (around 6-7)

eastern white pine, northern red oak (can develop in understory under other trees)

Shade Intolerant trees (closer to 1)

aspen, paper birch, red pine (can NOT develop in understory under other trees)

Light Compensation Point

where the rate of photosynthesis is equal to the rate of respiration

What does light compensation point have to do with shade tolerance?

The greater the shade tolerance, the lower the light compensation point. Shade tolerant plants require less light to conduct photosynthesis and balance respiration.

A shade intolerant plant will have a higher light compensation point, demanding more light to balance photosynthesis and respiration.

Carbon assimilation

the process of converting carbon dioxide into sugars during photosynthesis

Shade intolerant plants: have higher carbon assimilation and higher respiration (more photosynthesis, more respiration)

Shade tolerant plants: lower carbon assimilation, lower respiration (less photosynthesis, less respiration); will turn photosynthesis on and off as the receive light

Bulk density of soil

mass per unit volume of soil, usually give grams/cubic centimeters; soil with finer particles (like clay) will have a greater density than soils with larger particles (like sand)

Forest soil (without much rock) has a density around .8 g/cm3

What does bulk density of soils have to do with plants?

Different plants have different root penetration limits and therefore prefer different soil types/

pH scale

0: acidic

7: basic

14: alkaline

pH scale in relation to soils

<5: acidic soil

5.5-6.5: mildly acidic soils

6.5-7.2: becoming alkaline

>7.2-7.3: alkaline

How does soil pH affect the availability of plant nutrients?

Different nutrients become available to plants at different pH levels. Very slightly acidic (near neutral) is considered the "sweet spot"

How does mycorrhizal fungi affect plant growth and survival?

Mycorrhizae grow on plant roots and form a symbiotic relationship. The increase surface area, uptake of water and nutrients (nitrogen and phosphorous)

Site Index

measure of potential tree growth at a site

How is site quality measured?

Site index is calculated based on the average height of dominant and codominant trees of a given species at a given age (uses just height and age, not DBH)

Why do we find site index?

Foresters use site index to assess site quality, plan management activities, and compare the potential of different areas.

Why is the site index base age so important?

Different regions have different patterns of tree growth at various ages. The Lake States use 50 years as a base age while the Southeast uses 25 years and the West uses 100 years.

Silviculture

use of sustainable management practices to establish or guide the development of forested stands in order to fulfill natural resource objectives

Even-aged vs Uneven-aged forests

Even-aged: one age class system (seedling, sapling, pole, mature, old growth)

Uneven-aged: multiple age classes

Even-aged tree regeneration systems: clearcutting/patch clearcutting

most to all trees removed; can be clearcut in patches or different shapes (ie softened edges) for regeneration and aesthetics

Clearcuts are more ideal with shade intolerant species and mimics severe disturbances like fire (often used with pine)

Even-aged tree regeneration systems: seed trees

scattered trees are left after harvest to seed the site (in Wisconsin, often Jack and White Pine, sometimes red pine, paper birch, white spruce)

Problems: seed crop and germination variability (eg good vs bad years for seed production), competition, windthrow

Even-aged tree regeneration systems: shelterwood

a sufficient number of trees are left on the site (denser than seed trees, more aesthetically pleasing); overstory is removed once the understory is established

In Wisconsin, white pine, white birch, oak (density helps because seeds don't spread out as much), red maple, central and northern hardwoods, hemlock, white spruce

Even-aged tree regeneration systems: coppice

trees cut near the ground to stimulate growth and regenerate themselves; root sprouting (aspens) and strum sprouting (red maple, northern red oak)

What are some pros and cons and tradeoffs between natural regeneration and artificial regeneration of even-aged stands?

Natural regeneration: lower cost, dependence on nature and probabilities (too few or many)

Artificial regeneration: higher costs, more site prep, dependable and predictable, more reliable stand and species establishment

What does the land manager really need to watch out for/monitor relative to uneven-aged stand regeneration?

What influences forestry decision making?

landowner societal objectives (how do we manage forests and why), public perceptions (influence what is perceived as aesthetically pleasing/desirable)

Mixed: Pros and Cons

Pros: more niches filled, better crown closure, greater pest resistance, diversity and therefore flexibility with the market, desired by public for aesthetics and recreation, habitat diversity

Cons: higher administrative costs (more details to track), higher harvesting costs and more frequent stand entry for harvest, more frequent damage to remaining trees, more mgmt. skills required, higher road maintenance cost

Pure: Pros and Cons

Pros: can fit valuable species in stand, simple to match site index with tree species, easier stand management, planning, and regeneration, reduced harvest cost and stand entries

Cons: reduces aesthetics, susceptible to insects and disease, decreased diversity and wildlife habitats, less flexibility with the market

Uneven: Pros and Cons

Pros: holds multiple age classes, reduced harvest residue and fire risk, flexibility on harvest options based on markets, steady income with small woodlots, favorable odds with species regeneration

Cons: increased harvest costs (more frequent entry and greater administrative costs), more silvicultural knowledge and management skills required, more road maintenance, increased administration

Even: Pros and Cons

Pros: decreased residual damage, growth rates more uniform, greater wood quality (possibly), more wood harvested each harvest, less complicated to manage, inventory, and harvest

Cons: greater risk of loss due to damaging agent, forest protection can be costly (all trees share same threats, like a highly flammable pine stand), lowers aesthetic and recreational value, desired reproduction is more difficult and costly, longer investment period

Pre-commercial thinning

Often, inputs don't produce products, but act as site preparation: fertilization (increases soil fertility), pruning (removes branches and helps combat disease), thinning (reduces competition)

Revenue is possible, site dependent (outputs): pulpwood, posts, firewood, sawlogs, utility poles

The general goal is Timber Stand Improvement.

Release treatment

Acts to "free" (allow more growth) desirable species by removing competition and therefore freeing resources; best before trees reach pole stage before growth rate will slow

often done via fire, herbicide, mechanical

Improvement cuts/ Timber Stand Improvement (TSI)

done on pole and mature stands (after pole stage); removing "low value" (deformed, infected, etc- depends on desired outcome) trees

"leave the best, cut the rest"

Row thinning

selecting certain rows or strips to be thinned (often every 5th); thinning by spatial design, not crown class; common in even-aged stands; response short-lived and tree growth will soon slow to limiting factors (water, light, nutrients)

Thinning from below

Removing suppressed and intermediate crown classes; very common in US forestry

"leave the best, cut the rest"

Thinning from above

Removing dominant/codominant crown classes to promote growth of remaining trees (aka high thinning); considered good silviculture

High thinning is NOT the same as high grading.

High thinning vs. high grading

High thinning is NOT the same as high grading, as high thinning takes into consideration the health of the future stand. High grading is simply "take the best, leave the rest."

High grading is bad forestry and decreases desirable stand genetics.

Combination thinning

A combination of row thinning and thinning from below at the same time. Combination thinning is a wise choice for a first (pre-commercial) thinning if timber is the objective.

Individual tree selection

Harvesting the best individual product; "surgically" removing certain trees so that others can grow

takes more skill and time, but can make more money

Salvage cut

the removal of dead, damaged, or diseased trees with the intent of recovering value prior of deterioration/harvesting before value declines

Fertilization: Nitrogen

Fertilization: Phosphorous