To date mulching has gained wider acceptance and has been adopted by several corporate growers. Residue management is an operation which takes place prior to planting in silviculture and mulching as a residue management operation is gaining momentum. It is becoming a common practice in forestry re-establishment operations. Mulching is known as a process of breaking down fuel load or residues mechanically using a machine equipped with head containing a drum or disc with teeth. Mulching heads mounted on excavators and wheel loaders are capable of pushing and mulching standing trees when a relatively young stand needs to be cleared quickly. This method provides more control over the process and prevents running the head into the dirt. Mulchers are a versatile piece of equipment and not all their potential has been fully recognised/realised. With their continued use in forestry new techniques and applications are bound to be explored.
Concept of clearing standing trees using a mulcher.
Mulchers are commonly used for breaking up tops, branches and stumps after harvesting has taken place to manage post-harvest slash. They can also be used to push and mulch standing young trees when needed. This is more prevalent when a young stand has been damaged by a pest, disease, drought, fire and poor form and consequently no longer economically viable to grow because the yield at rotation end will be adequate. Other prevalent methods include using chainsaws to fell and crosscut the trees or use a dozer to push the standing trees and a chopper roller to break up the trees into smaller pieces for better access. There are benefits and limitation to the different methods and to appreciate the full benefits, one needs to consider the bigger picture of mulching as process of stand preparation and re-establishment.
After the clearing and mulching of trees has taken place, it is important to re-establish the stand. Depending on the age of the trees and the level of mulching achieved weeds may grow on-site at a variable rate. If the trees are older, they can be a barrier for the mulching drum to reach the stand ground level. Company standards determine the mulch quality, but the preferred mulch quality is medium to fine sized chips after mulching. With drum mulchers, mulching standing trees requires repetitive number of passes to reach a mulch quality of medium to fine chips which may increase the operational costs of the operation. With disc mulchers the process is normal not repetitive. This type of mulching head contains a disc that rotates to break down the standing tree biomass. Its application is similar to a mulching head containing a drum with teeth. It is suitable for clearing and mulching residues left on site after harvesting moreover it can be used to grind down stumps to the surface, thus preparing the site for other silvicultural activities to take place. Containing teeth located on top and bottom it can break down wood biomass efficiently and it is suitable for small excavator-based carriers.
Tree clearing with mulchers can be a viable option as it eliminates harvesting costs while providing good access on the site for silvicultural operations such pitting and planting. Stand clearing with a mulcher has been observed on trees of less than seven years with heights ranging from 5 to 7 meters and DBH’s ranging from 9 to 19 cm. With different mulcher head sizes being manufactured, the concept of clearing trees required a robust machine with a highly skilled operator.
Benefits and limitations of mulching standing trees.
Mulching standing trees is not a common practice applied in forestry. Therefore, one needs to consider the option very carefully prior to full implementation. Some considerations:
• If timber can be recovered and sold at a profit then that option must be considered before clearing to waste.
• If biomass markets are able to recover and use the material then that option should also be considered.
The limitation of this operation is that more time is spent on mulching as each tree needs to be thoroughly broken down to small pieces thus a second pass is necessary. Depending on the sizes of the trees felled to an extent silviculture operations such pitting and planting maybe difficult if the trees are not thoroughly mulched. Therefore, this may increase the cost of the operation and constant maintenance may be required on the machine.
Disc mulcher (diamondmowers.com)
The application of mulchers depends on a specific grower company’s objective, and it is important to consider the financial and environmental limitations and benefits before choosing mulching as a stand clearing management option. Productive tree growth requires a healthy soil habitat which is achieved through maintaining the original state of the forest floor. Tree clearing using mulchers can be viable concept, and finding the right systems to meet productivity expectations while delivering a consistent quality of mulch is critical hence needs careful considerations.