Harvesting Systems

Timber/Wood/Pulp Harvesting Systems

Introduction

Over the years, the forests of southern New England have seen several different timber and wood/pulp harvesting systems.  Until the advent of the internal combustion engine, all felling and bucking was done with axes and hand saws; all skidding was done with horses or oxen.  In the 1930's, chainsaws and crawler tractors (bulldozers) began to replace axes, handsaws, and draft animals.  In the 1960's, 4-wheel-drive, rubber-tired skidders began to replace crawlers.  Now, as we approach the turn of the century, fully mechanized harvesting systems are beginning to replace chainsaws and skidders.  The following will describe and discuss these harvesting systems, all of which (except axes and handsaws) are still in use in this area. 

Horses or Oxen

Logs are loaded onto a low-to-the ground sled or attached at one end with choker chains to a 2-wheel forecart which are pulled by the horses/oxen.  The animals are specially bred and have been trained for their work.  Some are capable of skidding from stump to log landing and back unassisted.

The main advantage of horse/oxen skidding is the very low level of damage to the residual trees and the forest soils.  The main disadvantage is the low limit on skidding distance for which draft animals are economical.  Uphill skidding on grades steeper than 10% is generally not feasible.  Unless skidding distances are very short, draft animal skidding will cost $20-$30/Mbf more than skidder work (i.e., $90-$110/Mbf as compared to $70-$90/Mbf for skidders).

Crawler Tractors

Crawlers run on metal tracks which give them excellent traction and maneuverability.  They most often have a cable winch attached to the rear end with several log choker chains attached to the cable.  The chains may be attached to logs (or whole stems) lying close to each other.  When the cable is winched in, the logs come together to form a hitch which is then skidded out to the log landing.

The main advantage of crawlers is that they compact the soil less than rubber-wheeled skidders because their weight is spread out over a much larger tractive surface area.  They are also able to do road construction work with their blades, and their manueverability can help avoid damage to residual stands.  The main disadvantage for crawlers, as for draft animals, is the cost factor.  Tracks require more maintenance than wheels and they limit the speed of the machine.  Some land is too rocky to operate with crawlers because rocks can damage tracks and the low-slung undercarriages of crawlers.  Crawler skidding will cost at least $10-$20/MBF more than skidder work (i.e., $80-$100/MBF as compared to $70-$90/MBF for skidders).

Rubber-Wheeled Skidders

Skidders use winches in the same way as crawlers to haul out logs or tree stems.  Their axles move independently in the vertical plane.  They are articulated (jointed) in the middle to allow full independent movement of front and rear sections.  They have high ground clearances so they can operate on all kinds of terrain.  They can haul much faster than draft animals or crawlers.

The main advantages of skidders are their speed and ability to operate under all but the most adverse conditions.  Therefore, they are the lowest-cost harvesting systems.  The principal disadvantages are the relatively higher levels of damage to residual stands and skid roads, plus increased soil compaction.  However, these disadvantages may be minimized or even eliminated when the equipment is run by a careful operator who carefully plans his hitches and skid roads, and avoids skidding when soils are wet (to reduce soil compaction).  Such careful skidder operation would have a cost at the high end of the $70-$90/MBF range indicated previously.

Other Systems

In regions of the country with relatively flat, rock-free soils, other harvesting systems have become popular.  They are now also being used in southern New England.  Large, hydraulically-operated sawheads and stem gathering systems mounted on tracked or rubber-wheeled tractors are very fast and safe for operators.  These equipment systems, called feller-bunchers, leave bunches of tree stems along skid roads which are run by forwarders or grapple skidders.  Forwarders pick up and carry cut logs; grapple skidders drag whole trees.

A forwarder has a front section like a skidder, but instead of a cable winch, has a hydraulic knuckle-boom log loader behind the cab and a small log deck above the rear axle.  Forwarders are used with conventional chainsaw felling and feller-bunchers.  When loaded, the forwarder has a high center of gravity which makes it unsuited to steep or rough terrain.  Grapple skidders have a large grapple mounted on the rear; they may also have a cable winch.

Other Considerations

Many landowners are concerned about the amount of tree tops, or slash, which is left in the woods after a harvesting operation.  Most timber cutting operations will remove the stems down to about 10" diameter in the tip.  Cordwood and pulp cutters will remove stems down to about 6" in the tip.  The remaining slash is normally left to lie no higher than 3-4' from the ground.  Complete utilization of the tree is generally not practiced in this region, partly because of absence of markets for the small diameter wood and partly because of the damage caused to the residual stands by removing whole trees.

It is possible and aesthetically desirable to lop or run over the remaining tree tops so that they will lie closer to the ground.  The cost of lopping or flattening will depend upon how high the tops are to be left.  Lopping to lie within 2' of the ground would cost about $5/MBF extra.

Another aesthetic consideration is the appearance of the log landing after the harvesting operation.  The normal procedure is to push the chunks (crooked sections cut out in the process of cutting stems into logs) to the side of the landing and smooth out any ruts; grass seed may also be spread.  It is possible to remove all the chunks from the property for an additional cost that will depend on the number of chunks.  Complete seeding of the landing and all major skid roads is also possible for a cost that will depend upon the extent of the skid road system.

Generally speaking, heavier equipment will have a greater impact, although the skill of the operator is an extremely important and under-appreciated factor.  The difference between some horse logging operations and some large skidder operations are, believe it or not, quite minimal, especially after a few years of regrowth.  Tracked harvesting equipment is becoming more prevalent in western Massachusetts.  Because of their low ground pressure, these huge machines will have lower impact than skidders.   

Horse logging, farm tractors, or crawler tractor systems are not economical for skidding trees long distances.  Therefore truck roads or forwarder roads need to be built to reduce skidding distances for these systems.  Where frequent entries to remove low volumes are anticipated, the investment in good road systems makes sense, particularly where they increase access for fire protection and recreational uses.

Conclusions

In planning a harvesting operation, all the equipment systems described above should be considered along with their associated costs and benefits.  Independent of the harvesting system chosen, additional consideration should be given to the disposal of slash and the clean-up and seeding of landings and skid roads.  Since the effects of a harvesting operation are visually and ecologically long-lasting, these considerations deserve careful attention.

February, 1998