Stand Density Basic Concepts

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Stand Density Basic Concepts




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Slide1

Stand Density

Slide2

Basic Concepts

Growth

and

yield

Harvesting

Regeneration

Thinning

Fire

and

fuels

Slide3

Forest Stand Dynamics

Forested 

stands

 are the product of past disturbances and management. Understanding how some 

disturbance

 (for example, fire, harvest, etc.) history has influenced

current

stand

structure

 or how it changes and develops in the future (that is, forest stand

dynamics)

For

example, a

silviculturist

may want to evaluate different management regimes to see how differentiation, the divergence in growth patterns of individual trees, affects the stand structure in terms of 

crown classes 

or how it might influence stand and stock tables.

Slide4

Crown Classes

dominant

: trees whose crown extends above the general level of the main canopy of even-aged stands, or in uneven-aged stands, above the crowns of the tree's immediate neighbors and receiving full light from above and partial light from the sides.

codominant

: a tree whose crown helps to form the general level of the main canopy in even-aged stands, or in uneven-aged stands, the main canopy of the tree's immediate neighbors, receiving full light from above and comparatively little from the sides.

intermediate

: trees with crowns either below or extending into the canopy formed by

codominant

and dominant trees; receiving little direct light from above and none from the sides; usually with small crowns considerably crowded on the sides.

overtopped

: trees with crowns entirely below the general level of the crown cover receiving little or no direct light from above or from the sides

.

Slide5

Crown Competition

Slide6

Growth and Yield

Growth

is the change in

biomass, size

volume, weight or

other characteristic of interest over a specified time period

.

Yield

is the existing amount of that characteristic of interest for a particular type of forest stand by species, site, stocking, and management regime at a specified point in

time.

Slide7

Growth and Yield

Growth

 

example

, let's say your stand of slash pine might increase in volume by 2,000 cubic feet over 10 years.  If we state this as an annual increment, we would say that the stand's growth is equal to 200 cubic feet per year (2,000 cubic feet per year / 10 years). 

Yield

 actually has 2 meanings.  It is

:

the

amount of some characteristic that can be harvested per period, or

the total amount that could be removed at any time

Slide8

Organism and Population Idealized Growth Curve

Slide9

Annual Increments

Current (CAI) – the increment over a period of one year at any stage in a tree’s life

MAI = yield @ age A/Age A

PAI = Yield @ age A

2

– Yield @ age A

1

------------------------------------------

age A

2

– age A

1

PAI = sum of CAI from age A

2

to A

1

-----------------------------------

age

A

2

– age

A

1

Slide10

Annual Increments

Slide11

Yield

Age X MAI

Sum of CAI from 0 to Age A

Slide12

It is all about the Leaves

Slide13

Leaf Area Index

Slide14

Stand Density Index

A measure of

the stocking of a stand of trees based on the number of trees per unit area and diameter at breast height of the tree of average basal

area (QMD)

Slide15

Stand Density Index

log

10

SDI

= log

10

N + 1.605 log

10

D - 1.605

Example: Given BA = 150

sq

ft

and N = 400 trees per acre, the QMD =

= 8.29

Thus

log

10

SDI = log

10

(400) + 1.605log

10

(8.29) - 1.605 = 2.47

SDI = 10

2.47

SDI =

295

BA used instead since easier to calculate and well-correlated to SDI

 

Slide16

3/2 Law of Self-Thinning

For pure even aged stands crowded to the point of self thinning the mathematical relationship exists

Log (mean tree volume) = -3/2 log (tree density) + C

C is a constant that varies by species

Mathematically equivalent to SDI

Slide17

Maximum Crown Area

A – unit area (43560 ft

2

or 10000 m

2

)

Slide18

Relative Spacing

RS =

N

= number of trees per acre

H

= average Height of the dominant canopy in feet

 

Slide19

Relative Spacing

Slide20

Crown Competition Factor

Measure of stand density

Independent of site quality, stand age, stand structure (even or uneven-age stands)

Definition: Area available to the average tree in a stand compared to the maximum area used by an open-grown tree with the same diameter

Crown Width (CW) vs. DBH – linear relationship

Maximum crown area (MCA): crown area of an open-grown tree of diameter DBH, expressed as % of unit area (1 ac or 1 ha)

Slide21

Crown Competition Factor

Slide22

Harvesting, Regeneration and Thinning

coppice method

 - the main regeneration method is vegetative sprouting of either suckers (from the existing root system or cut

trees)

or shoots (from cut stumps).

even-aged methods

 - a regeneration method designed to regenerate and maintain a stand with a single age class and includes:

clearcutting

 - the cutting of essentially all trees, producing a fully exposed microclimate for the development of a new age class.

seed tree

 - an even-aged regeneration method in which selected trees (seed trees) are left standing after the initial harvest to provide a seed source for 

natural regeneration

. Seed trees can be left uniformly distributed or in small groups. Although regeneration is generally secured naturally, it may be augmented by planting. Seed trees are often removed once regeneration is established or may be left as reserves.

shelterwood

 - a regeneration method in which trees are removed as a series of cuts designed to achieve a new 

even-aged stand

 under the shelter of remaining trees

.

Slide23

Continued

two-aged methods 

- a regeneration method designed to regenerate and maintain a stand with two age classes, usually through the retention of reserve trees in the

overstory

.

uneven-aged methods 

- (also known as selection methods) a regeneration method designed to create or maintain and regenerate an

 uneven-aged stand 

structure, including:

single tree selection

 - a regeneration method in which individual trees of all size classes are removed more or less uniformly throughout the stand to promote growth of regeneration.

group selection

 - a regeneration method which removes trees and facilitates regeneration in small groups.

Slide24

Thinning

thinning from below

 - (also known as ordinary, German, or low thinning) the removal of trees from the lower crown classes to favor those in the upper crown classes.

thinning from above

 - (also known as French or crown thinning) the removal of trees from the dominant or

codominant

crown classes to favor the best trees of those same crown classes.

selection thinning

 - the removal of trees from the upper crown classes to favor trees in the lower crown classes.

row thinning

 - (also known as mechanical or geometric thinning) the removal of trees in rows, strips, or using fixed spacing intervals.

Slide25

Released by thinning

Slide26

Thinning results

Slide27

Thinning

Slide28

Fire and Fuels Management

Timber managers

may be interested in decreasing

wildland

fire hazard

.

To do so,

they need

to understand the fire types such as 

surface

passive

 

and active

crown 

fires and their effects on stands

.

In addition,

managers

may

want to look

at stand attributes such as 

canopy bulk density

 and 

canopy base

height.

This information can help predict fire types and spread so they can be managed or prevented.

Thinning reduces and redistributes fuel loads thus fire hazards.


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