MÔN QUẢN LÝ THẢM THỰC VẬT RỪNG: EVEN AGED MANAGEMENT (LEC 14)

A stand of trees composed of a single age class in which the range of tree ages is usually ±20 percent of rotation (SAF, 2008) In natural an even – age stand exists in a short period of time regeneration established relatively synchronously within a short period following a major disturbance It is the stand initiation stage of forest succession

Natural Even-aged stand

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A stand of trees composed of a single age

class in which the range of tree ages is

usually ±20 percent of rotation (SAF, 2008)

• In natural an even – age stand exists in a short period of time

• regeneration established relatively synchronously within a short period following a major disturbance

• It is the stand initiation stage of forest succession

Forest succession

Stand initiation stage

• Follows major disturbances (wind, fire, clear-cut)

• Regeneration of open space

• Pioneer species occupy

• One cohort or age class

• Generally an even canopy (although even-aged species mixtures can form two- or

multi-• layered stands)

• High density

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Artificial Even-aged stand

Stands normally consist of trees at the same age

• Afforeststation

• Reforestation

Planted forest

Even-aged harvest and regeneration systems

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• Clearcut

• Shelterwood

• A method used to regenerate a stand by the removal of most or all woody vegetation during the harvest creating a mostly or completely open area leading to the establishment of an even-aged stand

• Regeneration can be from natural seed produced by adjacent stands or from felled tops of harvested trees

• Clearcuts are also used to direct seeding or replanting for artificial regeneration systems

• A remarkable characteristic of this method is that no trees are left in the cut area for seeding purposes

Clearcut

Seed-tree: A method designed to bring about natural reproduction on clearcut harvest areas by leaving enough trees singly or in groups to naturally seed the area with adequate stocking of desired species in a reasonable period of time before the site is captured by undesirable vegetation Seed-trees may be removed after establishment or left indefinitely.

Clearcut vs Seed-tree method

In Vietnam, according to Prof Pham Xuan Hoan (2013), seed – tree is also called clearcut

• High forest

• Even-aged stand structure

• Create open environment favorable for

establishment of shade intolerant species

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• Relatively simple

• Light-demanding species

• Creation of even-aged forest patches

• Intensive commercial management

• Most or all trees within a unit are clear-felled at one point in time at the end of the rotation

• Regeneration occurs within a short period after harvest

• Specific regeneration strategies, such as planting, direct seddling or natural regeneration

• With the clearcut system, the opening size and dimensions created is generally large enough to limit significant microclimatic influence from the surrounding stand

Clearcut in lager areas

A clearcut systemis defined as a silvicultural system that removes an entire stand of trees in a single harvesting operation

– Cutting area > 1 ha or greater than 250 m in width (Pham Xuan Hoan, 2013)

– Artificial regeneration (normally)

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Clearcut in small areas

Patch cut systems: cutting area < 1 ha (Pham

The Malayan Uniform System (MUS)

• Silvicultural treatment includes poison girdling of non-commercial tree species to assist in the natural regeneration of seedlings of selected species

The Malayan Uniform System (MUS)

Year Operations

A - (1+1/2) Regeneration survey (4m 2 sample plots )

A - All trees over 45 cm dbh are allowed to be cut if there is sufficient regeneration present

-All remaining defect and unwanted trees will be poison girdled

-The remaining stand consists only regeneration of dipterocarps, temporarily mixed with pioneers

A + 2 TSI , Liberation of saplings of commercial tree species

A + 3 to 5 - Inventory (25m 2 sample plots )

- Climber cutting

- unwanted trees will be cut if necessary

A + 8 to 10 Inventory (100m 2 sample plots ) and the next activities depend of inventory results

The Malayan Uniform System (MUS)

Clear cut in Vietnam

•Patch cut systems:

- Applied in steep areas

- Cutting area < 3 ha

•Strip cut systems:

- Cutting area < 60 m in width when slope < 150

- Cutting area < 30 m in width when slope from150 - 250

Clear cut in Vietnam

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• For planted forests

• Applied when slope < 250

• Climber should be cut be 3 months before felling

• All trees to be cut accept seed tress

• After felling, moving vegetation from the site and manipulating the soil

• Liberation of saplings of commercial tree species in the next 4-5 years

Shelterwood systems

• The shelterwood system is defined as a silvicultural system in which mature trees are removed in a series of cuts to achieve a new even-aged stand under the shelter of remaining trees

• The intent of these cuttings is to:

- Provide shelter with sufficient overstorey trees to improve conditions of the site, promoting establishment

of an even-aged stand under leave-trees from a mature stand

- Potentially provide seed and an environment (shelter) for natural regeneration

- Provide site occupancy and volume increments by retaining mature trees during the regeneration phase

Shelterwood systems

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There can be up to three cut phases in a shelterwood system:

• Preparatory cuts

• Regeneration or seeding cut

• Overstorey removal cut(s)

Overstorey removal cuts

• Once regeneration is established and stocking is acceptable, removal of the sheltering overstorey is a common option

• Protecting the vigorous, well-distributed young age class of a desirable species established under the partial canopy

Shelterwood systems

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There can be up to three deferent methods of shelterwood system:

• Strip shelterwood system

• Group shelterwood system

• Irregular shelterwood system

• …

Strip shelterwood system

• A strip shelterwood system involves a series of progressive, usually linear cuts in narrow successive strips

• The basic principles influencing strip shelterwood

- Minimizing damaging effects on the residual stand (e.g., wind),

- Maximizing shading of cut strips by the uncut areas,

- Accommodating terrain

Strip shelterwood system

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Group shelterwood system

• In a group shelterwood system, small openings are created in the stand such that the adjacent trees shelter the new regeneration

• The size or density of leave-tree groups will decrease through one or more future stand harvests, until the mature overstorey has been completely removed

• Regeneration methods for the final area to be harvested may include natural or artificial regeneration or a combination of both

Group shelterwood system

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Irregular shelterwood system

• Established the vigorous, well-distributed young age class of a desirable species under the partial canopy

• Residual trees are left for long periods beyond the regeneration phase (e.g., from 20 per cent of the rotation to several rotations)

• Keep and improve good stand condition for non-timber products

Irregular shelterwood system

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CC with Natural Regeneration

– Which forest types?

– For exposure-tolerant species

– Advance regeneration usually shade-tolerant

• Many deciduous trees regenerate vegetatively

• Dominant species establish soon, later germinants fail or never become part of the main crown canopy

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CC with Natural Regeneration

• Natural dispersal distance varies inversely with distance

from the source  CC-size limited to 1-6 times the height

of adjacent trees (mostly 100-300 ft) if relying on seed!

CC with Artificial Regeneration – Plantation Silviculture

• Most efficient operationally: size & pattern of cutting areas not limited, no need to protect seedlings

from hazards bypassed in nursery, no residual trees obstruct the use of fire, herbicides, machinery

during site preparation

• Trees in rows, uniform spacing, site completely restocked

• Limited vertical structural diversity

• No large snags or additions of CWD

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Some examples of inappropriate clearcutting

Some examples of inappropriate clearcutting

• Unsuitable for LSOG (late sucessional/old growth)-species

• Changes animal behavior

– Black bears avoid centers of large clearcuts  no escape cover,

sensitive to heat stress

– Deer & elk tend to

primarily feed along

edges of larger openings

Some disadvantages of CCs

Where to avoid clearcuts

• Riparian zones

• Special plant & animal habitats, habitat corridors

• Small woodlots  residual forests of adequate area

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Avalanche-prone areas

Where to avoid clearcuts

• Difficult-to-regenerate sites

Where to avoid clearcuts

• Recreation & tourist areas

• Aesthetically valuable areas

• Heritage or

culturally

sensitive

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Keep clearcut edges away from…

• Topographic features that funnel winds & accelerate the velocity  saddles along ridges, ridge lines,

indentations on slopes

• Poorly drained & shallow soils

• Signs of old blowdown

• Concentrations of unsound trees with decayed roots or trunks

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Keep clearcut edges away from…

Ecological Consequences of CC

How many red spots make a white cow red? How many clearings make a forest, prairie?

A score? More? A coalescing core? A threshold reached?

(Landscape Ecology, Forman and Godron 1986)

Modifications: Altering the Configuration of Clearcuts

• Configurations with long edges can

– Increased probability of disturbance (wildfire & windthrow)

– Wildlife is highly sensitive to structural changes

Patch CC

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Strip CC

Alternate-Strip Alternate-Patch Clearcut

Width: 1-2 times the height of adjacent trees

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