Stand Density

Basic Concepts•Growth and yield•Harvesting•Regeneration•Thinning•Fire and fuels

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.

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.

Crown Competition

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.

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

Organism and Population Idealized Growth Curve

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 A2 – Yield @ age A1

------------------------------------------age A2 – age A1

• PAI = sum of CAI from age A2 to A1 -----------------------------------

age A2 – age A1

Annual Increments

Yield•Age X MAI

•Sum of CAI from 0 to Age A

It is all about the Leaves

Leaf Area Index

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)

Stand Density Index• log10SDI = log10N + 1.605 log10D - 1.605

• Example: Given BA = 150 sq ft and N = 400 trees per acre, the QMD = = 8.29

• Thus • log10SDI = log10(400) + 1.605log10(8.29) - 1.605 =

2.47• SDI = 102.47

• SDI = 295

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

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

Maximum Crown Area

A – unit area (43560 ft2 or 10000 m2)

Relative Spacing• RS = • N = number of trees per acre• H = average Height of the dominant

canopy in feet

Relative Spacing

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)

Crown Competition Factor

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.

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.

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.

Released by thinning

Thinning results

Thinning

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.