[graphic] Link to USDA Forest Service web site
 
In this section  
  corner
Need help?

If you need assistance while using this site, please contact web support.

 

Got photos?

We are seeking photos to help illustrate examples of forest conditions and treatments. Find out how you can contribute to this web site.

 
[graphic] Rounded corner
Harvesting systems

The process of timber harvesting is comprised of five basic tasks:

  1. Timber acquisition (moving to the tree).
  2. Felling and preparing the tree for extraction (delimbing, topping, and segmenting).
  3. Extracting the tree to a central location or landing (skidding or forwarding).
  4. Loading the tree for transport to the mill.
  5. Transporting the tree to a mill.

The processing of the tree into individual products (e.g., veneer logs, sawlogs, pulpwood) may occur at either the stump or at the landing. A variety of equipment options can be used to accomplish each task (Tables 1 and Table 2 below).

 
   

Harvesting systems are named based on the form in which the wood arrives at the landing. The three general types of harvesting systems include shortwood, tree-length, and full-tree. We will focus our discussion on the tasks of moving to the tree, felling the tree, processing it at the stump, and transporting the tree to the landing.

There are a variety of equipment options that can be used with each harvesting system. While a given harvest system can be used to accomplish any silvicultural objective (Table 3 below), there are distinct advantages and disadvantages for each that need to be considered (Table 4 below). While a shortwood system is suited to all types of management, a full-tree system is better suited to a production requirement because equipment frequently tends to be larger and to operate faster than for the other systems.

Light-on-the-land operations

Light-on-the-land (LOL) is an approach to timber harvesting that uses techniques and equipment designed to minimize site and stand impacts. To be successful, business owners and on-the-ground operators need to understand and apply light-on-the-land approaches too. Operators who have and apply a light-on-the-land ethic are critical. As all sites and conditions do not require the same treatment, and there may be many ways to accomplish a silvicultural objective through logging, it is important to recognize where LOL approaches are needed. The need for LOL increases as:

  • the silvicultural prescription includes more residual trees because of the need to protect those remaining trees from scarring and rot damage and because it takes more time and care to work around residual trees, and;
  • site conditions warrant (e.g., soils that are wet, non-frozen, or have more loam, silt, or clay; steep topography).

Light-on-the-land techniques

Individual state best management practices or forest management guidebooks often include a wealth of LOL techniques to protect water quality and site productivity such as:

  • Combine and integrate management activities to reduce trafficking on the site
  • Avoid unnecessary stand re-entry
  • Operate on snow or when soils are frozen or dry
  • Avoid operating during periods when insect infestations are possible
  • Avoid rutting within the site and hydrologic impacts from roads and skid trails
  • Divert water from roads, skid trails, and landings
  • Revegetate exposed areas
  • Infrastructure (roads, skid trails, and landings)
    • Minimize within the harvest site
    • Share between harvest sites
    • Plan during stand establishment
    • Use designated trails
  • Avoid full-tree harvesting on nutrient-sensitive sites
  • Retain or redistribute slash on nutrient-sensitive sites
  • Operate machinery along the contours, rather than up and down slopes
  • Store lubricants and fuels in appropriate (e.g., approved, labeled) containers that are located away from water
  • Incorporate and administer appropriate regulations in the timber sale contract

Techniques that do not often appear in guidebooks include:

  • When thinning a stand, mark it so that there is enough room for equipment to operate
  • Final cuts in shelterwood, seed tree, or other situations where natural regeneration has established should be planned for winter when snow cover protects seedlings and the soil is frozen
  • Swing trees out of sensitive areas using felling machinery. Use the full reach of a mechanical boom whenever possible.
  • Minimize turning and curves when planning skidding trails during thinning operations. The best skid trail route is generally the straightest possible, over the most level terrain.
  • Locate skid trails to accommodate future as well as current harvests. Use designated skid trails to reduce trail density and to control the path of skidders and forwarders.
  • Select open areas along skid trails where skidders and forwarders can turn around and then back up to a load.
  • Consider the dimensions of logging equipment when planning trails and roads. Where possible, match equipment size to the size of the timber to be harvested. Because they are shorter and can maneuver more easily through residual trees, horses and forwarders may be a better choice than skidders.
  • For thinning operations,
    • Consider use of a tree-length or shortwood harvesting system as the tree size (i.e., length or the material and elimination of the branches and top material) is reduced as compared to the full-tree system.
    • Use directional felling techniques to align stems at a thirty to forty-five degree angle to the trail to limit trafficking
    • Cut stumps as low as possible on skid trails to reduce load shifting.
    • Designate bumper/rub/turn trees at curves and turns in the skid trail to protect the residual trees from scarring.
  • If ground strength permits, maximize payloads to reduce the number of required trips.
  • Communicate the harvest plans to the buyer and on-the-ground operator(s) through an on-site walkover conducted prior to commencing any harvesting activities.

Light-on-the-land equipment

In addition to the techniques identified above, existing equipment may be modified or other equipment used to address specific concerns. Some of the possible options are noted below.

  • Equipment modifications
    • Swing-to-tree vs. tree-to-tree felling equipment
    Swing-to Tree Harvester Tree-to-tree feller buncher
    [photo] Swing-to Tree Harvester [photo] Tree-to-tree feller buncher
    • Cable vs. grapple skidding

    Cable skidder Grapple skidder
    [photo] Cable skidder [photo] Grapple skidder
    • Aerial yarding systems from stump to landing

    [photo] Aerial yarding systems from stump to landing

    • Spread equipment weight over a wider area to reduce the pounds/square inch of weight (low ground pressure options)

      High flotation tires Dual tires
      [photo] High flotation tires [photo] Dual tires
         
      Wheel tracks Tracked machinery
      [photo] Wheel tracks [photo] Tracked machinery
         

    • Reduce machine weight/small-scale equipment
  • Apply temporary crossing structures over areas with weak soils
Wood mats Wood pallets
[graphic] Wood mats [photo] Wood pallets
   
Drive on slash mats or corduroy Wood aggregate
[photo] Drive on slash mats or corduroy [photo] Wood aggregate
   
HDPE plastic  
[photo] HDPE plastic  

Tree-to-tree feller-bunchers traverse more of the area and lead to more scarification than excavator-type feller-bunchers or chain saw felling

As compared to tree-length skidding, full-tree skidding increases scarification because limbs act as a rake. If organic matter is thick or understory vegetation is dense the opposite may be true.

Skidding increases the amount of scarification over forwarding since limbs or tops are allowed to drag.

Felling machines with the ability to remove trees from both the front and side of the machine allow you to thin within leave rows. Select machinery with zero or minimal tail swing so that the machine’s width is no wider than the tires or tracks.

Availability of a small felling machine with a narrow forwarder or skidding allows you to specify a narrower thinning corridor. The tradeoff may be that you remove more rows because of the limited reach of the machinery.

Mechanical fellers (e.g., cut-to-length feller processor) with a telescoping boom better protect the overhead components of the stand than does a knuckleboom.

Table 1. Basic harvesting components, associated activities, and options for accomplishing each component.

Component

Possible activities

Options

Timber acquisition

Move to tree prior to felling

WalkMachine (rubber or tracked)

Drive-to-tree
Swing-to-tree

Felling

Fell, limb, top, buck into individual products

Chain sawMechanical

Bunching operation
No bunching

Primary transportation

Move felled tree(s) to central landing

Animal

Horse

Skidder (rubber or tracked)

Cable
Grapple
Clambunk
Forwarder
Cable yarding

Processing

Delimb, buck/slash into individual products, debark, chip, or no processing

DelimberChain saw buckingMechanical slasherDebarkerChipper

Loading

Load products onto or into over-the-road vehicle

LoaderForwarder

Secondary transport

Over-the-road vehicle transports products to mill

TrailerChip van

- TOP OF THE PAGE -

Table 2. Characteristics of timber harvesting systems in Minnesota.

Characteristic

Shortwood

Tree-length

Full-tree

Felling equipment

Chain saw
Harvester

Chain saw
Feller-buncher
Harvester

Chain saw
Feller-buncher

Off-road transport equipment

Forwarder
Cable skidder (limited use)

Cable skidder
Grapple skidder
Cable yarder
Horses

Delimbing and topping location

Stump area

Stump area
Cut-over (concentratedwithin cut-over)

Roadside
Not delimbed

Bucking location

Stump area

Roadside
Off-site
Not bucked

Slash distribution

Evenly spread
Windrows

Evenly spread
Small piles

Roadside piles
No slash left

Roadside landing requirements and impact

Small

Large

Largest

Maximum effective off-road transport distance 

2000 ft.

Cable & grapple skidders - 1000 ft.

Access road requirement1

27 ft./acre

Cable & grapple skidders - 40 ft./acre

Area with vehicular traffic

Low

Cable & grapple skidders - heavy

Ground disturbance - dry

Low

Moderate

Heavy

Ground disturbance - frozen

Minimal

Low

Low

Ground disturbance - wet

Moderate

Heavy

Heavy

Protection of residual trees and regeneration

Good

Moderate

Poor

Source: Jaako Pöyry Consulting, Inc. 1992. Harvesting systems: A background paper for a Generic Environmental Impact Statement on timber harvesting and forest management in Minnesota. Jaako Pöyry Consulting, Inc., Tarrytown, NY. 50 p.
1 Length of road required, on average, to access an area for logging.

- TOP OF THE PAGE -

Table 3. Applicability of timber harvesting systems to silvicultural systems and operations.

Operation

Shortwood

Tree-length

Full-tree

EVEN-AGE

clearcutting

clearcutting w/ standing snags & live trees

patch cutting

alternate strip cutting

progressive strip cutting

Good

shelterwood cutting

Good

Moderate

Poor

seed tree cutting

Good

Good

Moderate

UNEVEN-AGE

individual tree selective cutting

Good

Poor

Poor

group selective cutting

Good

Moderate

Poor

OTHER

selective thinning

Good

Poor

Poor

row thinning

Moderate

overstory removal (shelterwood & seed tree)

Source: Jaako Pöyry Consulting, Inc. 1992. Harvesting systems: A background paper for a Generic Environmental Impact Statement on timber harvesting and forest management in Minnesota. Jaako Pöyry Consulting, Inc., Tarrytown, NY. 50 p.

- TOP OF THE PAGE -

Table 4. Advantages and disadvantages for the three harvesting systems.

Harvesting system

Advantages

Disadvantages

SHORTWOOD

Low initial investment and operating costs (sometimes)Less adverse site impactsStems remain clean and are less prone to breakageResidues remain at the stumpBranches and slash may be left on skid trails, protecting soil and rootsLess support equipment neededSmaller landings neededSkid trails may be meanderingNarrower skid trails needed

High initial investment and operating costs (sometimes)Lower productionMay be labor intensive (skilled labor, workers' compensation)Can't put on a heavy load on steeper slopesSlash mat may be inadequate to fully support some equipment

TREE-LENGTH

Branches remain at the stumpIn-stand residue helps to protect the soil from machine trafficRoadside slash is greatly reducedLandings are somewhat smallerSkid trails don't have to be as wideBumper trees for load compression are less critical

Wood tends to be dirtySoil damage in skid trails may be greater if branches are not left on the trailsDamage to residual trees and seedlings may be greater/Bumper trees are needed

FULL-TREE

Maximizes volume recovery/unit area  Highly mechanized with high productivity  Less labor/unit volume  Concentrates many operations at a central point, permitting bulk operations.  This is a particular advantage when trees are small  Softwood limbs reduce soil disturbance and damage to residual stand  Cutover area is left clear of residue, minimizing site preparation and planting costs  Generally the lowest possible harvest cost/unit

High initial investment and operating costRequires a lot of support equipment/larger landing space is requiredMoves are more expensive  More timber required in short- and long-runMachines may be heavy, causing root damage, soil compaction, and possible ruttingHigh flotation tires may be needed, thus increasing cost and minimum trail widthLimbs increase load width and may cause damage to residualsLoss of high value may occurMay result in more slash at the landingResidues are not left at the stumpMore seed cones and nutrients are removed from the forest

 

 
[graphic] Rounded corner
 
[graphic] Rounded corner


North Central Region Forest Management Guide: A cooperative project of the USDA Forest Service and University of Minnesota.
USDA Forest Service - Northern Research Station
Last Modified:  05/25/2006