The Wuhlf 960-2 wheeled mulcher is designed and manufactured in South Africa for African conditions.
The Wuhlf team put their big Wuhlf 960-2 wheeled mulcher through its paces at York’s Jessievale plantation in Mpumalanga in late October under close scrutiny from York’s forestry team as well as Brad Shuttleworth of Forestry Solutions, who was there to do a detailed productivity study to gauge its performance.
The Wuhlf 960-2 wheeled mulcher is a 276kW machine designed and manufactured by Pretoria-based Wuhlf Equipment. According to the Wuhlf team it compares favourably with any of the imported mulchers in terms of durability, reliability and productivity, with an additional advantage: It is designed and manufactured in SA specifically to suit conditions in Africa, so the purchase price is significantly cheaper than comparative imported machines while the spares, maintenance and technical skills required to keep it working productively are available on our doorstep. Electronics on the mulcher are kept to a minimum and there is no high-tech computer gadgetry requiring specialised skills to maintain. The machine can be repaired and serviced by any qualified hydraulic and diesel mechanics.
This compartment has been mulched clean after clear felling, and is ready for the planting operation to follow.
The Jessievale trials saw the mulcher clean up the stumps and slash left behind four months after clearfelling 20-25 year old Pinus patula grown for sawlogs. The slash conditions were ranked in three classes for purposes of the trial: Light slash; Medium; and Difficult (with big branches, stumps & high slash piles):-
Pass length
Light
Medium
Difficult
100 m
2.0 hrs/ha
2.6 hrs/ha
3.5 hrs/ha
200 m
1.8 hrs/ha
2.4 hrs/ha
3.3 hrs/ha
300 m
1.7 hrs/ha
2.3 hrs/ha
3.2 hrs/ha
Above is a quick snapshot of the time trial results. Note that the shorter the pass length the more time it takes to mulch a hectare due to the increased number of turns that the machine has to make. Also note that Brad said that the mulcher operator used in the trial was relatively inexperienced, and he would expect that a more experienced operator would improve productivity by 10-15%.
The Wuhlf mulcher busy mulching the post-harvest slash.
The aim of the mulching operation is to reduce the slash and stumps to a mulch blanket which covers the soil and protects it from erosion and moisture loss, while providing easy access for the pitting and planting operations to follow. Mulching also eliminates the need for a controlled burn of the slash which carries a fire risk and can damage the soil.
According to Wuhlf Sales Executive Grant Moodley, the 960-2 performed well at Jessievale and the York team were suitably impressed. It was trialled on compartments with light, medium and heavy slash to properly gauge its performance under different conditions.
Wuhlf started designing and building mulchers in 2013 and have a number of different machines in production including a T90 tracked mulcher for use in under-canopy mulching, a 930 (129 kW) medium size wheeled mulcher and the big 960-2 wheeled machine.
These stumps have been reduced to ground level.
The mulcher heads, canopies, hydraulic pipes and brackets etc are manufactured in-house, the Danfoss hydraulic pumps are sourced from a local manufacturer, while the chassis, wheels, gearbox, diffs and engine are imported. The machines are assembled in the Wuhlf manufacturing facility in Pretoria. The mulchers come with a 12 month/1 000 hours warranty, with more extended warranty options available.
The Wuhlf mulchers will be on show at the Focus on Forestry Conference taking place in Karkloof in the KZN midlands from 7-9 November, so go along to meet the team and see the mulchers in the flesh.
Red flag over deteriorating health of forest soils
Planting successive rotations of the same tree species on the same piece of land over and over is likely to have a negative impact on soil health and long term productivity of the site will decline – especially when the residue from the previous harvest has been burnt off, leaving the soil unprotected from the elements, as is the case with this community forestry enterprise in Eastern Cape.
Planting the same tree species over successive rotations carries a high risk of deteriorating soil health, say FABI researchers …
It is widely accepted in agriculture circles that practicing crop rotation is beneficial for soil health. This is because the continuous cultivation of the same plant species on the same piece of land over and over again impacts negatively on soil health, and leads to a build-up of harmful micro-organisms. There is plenty of scientific evidence to support this theory.
To address this issue, good farmers all over the world practice crop rotation, planting different crops over successive rotations, or do inter-cropping where for instance they will plant a legume in between rotations to improve soil health and biodiversity.
Many small-scale tree farmers in Zululand practice inter-cropping, planting mielies, beans or peanuts in between their Eucalyptus seedlings when they are still small, and before the canopy closes. This could be beneficial for soil health.
So why not treat short rotation tree crops the same way – and if we don’t, and we keep on planting the same species rotation after rotation, will we eventually find that soil health deteriorates to the point where the trees will no longer grow properly?
Common sense would suggest that this will be the case, but there is no ‘conclusive’ scientific evidence to support this theory. In any event crop rotation in forestry is not so easily done as rotation lengths are long (8 – 20 years), land available for forestry is limited (in South Africa) and only three species are widely grown – eucalypts, pine and wattle – all of which are geared to serve specific markets.
Moreover improvements in silvicultural practices and advances in tree breeding have thus far masked any impacts of deteriorating soil health on successive tree crops, thus reducing growers’ appetite for experimenting with crop rotation...
This Sappi compartment in Zululand has been mulched and the residue retained to cover the soil with a nutrient-rich layer that provides protection, retains moisture and gives the young trees a growth boost.
But now a group of highly regarded researchers have raised a red flag and warned that deteriorating soil health is a real risk for short rotation plantation forestry, as it is practiced in South Africa and in many other parts of the world.
A team of FABI researchers including Dr Tanay Bose, Prof Bernard Slippers, Almuth Hammerbacher, Jolanda Roux and Mike Wingfield, have analysed existing data on soil microbiomes from short-rotation forestry environments around the world which, they say, provides evidence that a build-up of harmful micro-organisms, depletion of beneficial micro-organisms, and deterioration of the physical and chemical properties of soil can result from continuous replanting of the same tree species on the same piece of land.
“Populations of unfavourable microbes can be expected to become more abundant over successive rotations,” state the FABI researchers in an article published in the journal Current Forestry Reports. “This is strongly supported by data from recent soil microbiome studies involving commercially managed forests, which provide convincing evidence of an increase in pathogenic microbes in soils of continuously replanted forests.”
Building on these findings and considering similar approaches in agriculture, the team proposes a number of practical solutions that have the potential to mitigate the deterioration of soil health resulting from planting the same species over successive rotations.
Weza farmer Jon Mackenzie uses a tractor-powered chipping machine to chip the post-harvest residue after clear felling, which is then spread evenly over the site before the re-planting operation begins. This is his strategy to conserve the health of the soil on his farm for the log term.
• Retaining post-harvest residue on the site is likely to result in healthier soils over successive rotations. This is why many growers have stopped burning the post-harvest residues and have opted for mulching or chipping. • Application of biochar has considerable potential to enhance soil properties, nutrients and microbes in continuously replanted forests. Biochar is a carbon-rich, stable organic product made from the pyrolysis of organic biomasses such as leaves, sawdust, animal dung and wood. During carbonization, biochar releases phosphate into the soil along with other mineral nutrients, improving its fertility. Biochar also improves the physical properties and microbial biodiversity of the soil, which could further increase soil nutrient availability and carbon storage. However more research is needed to assess the impact of biochar on plantation soils. • Crop rotation and intercropping could alleviate the negative consequences of continuous replanting of the same species in short-rotation plantation forestry. For example, rotating between eucalypts, black wattle and pine species could prevent the accumulation of harmful soil microbes detrimental to these trees. Rotating nitrogen fixing leguminous tree species such as Acacia with eucalypts or pines has the potential to further promote both soil and tree health increasing the availability of nitrogen in the soil and improving the quality of plant litter. • Practicing agro-forestry, where different crops are inter-planted on the same piece of land, would also have a positive impact on soil health. • Innoculation of tree seedlings in the nursery with beneficial microbes. “Continuous replanting practised in short-rotation plantation forests is likely to be accompanied by a high risk of ‘replanting syndrome’ in plantations. While long-term monitoring programs to document the changes in soil microbiomes are still lacking and should be urgently initiated, the available evidence suggests that short-rotation forest plantation enterprises could be restrictive when successively establishing plots with the same or nearly the same genotypes,” the FABI team concluded.
Mulching after clear felling is an expensive exercise, but many growers have opted for this approach instead of burning off post-harvest residues, in the interests of boosting soil health for the long term.
Brush lines are mulched along timber extraction routes before the shorthaul begins.
Mulching of harvest residues is rapidly gaining ground in South African forestry, and is proving to be a game changer …
Deon Redinger of Savithi Mulching is one of a new crop of contractors flying the flag for mulching as a means of managing post-harvest slash in SA. Deon is a passionate believer in the benefits of mulching over burning slash, and local forestry companies – notably Sappi – have opted for mulching over burning in plantations with sensitive soils.
Historically there has been a reluctance on the part of forestry companies to throw their full weight behind mulching, due to the relative cost of mulching vs burning, which is the traditional South African way of dealing with slash.
This reluctance to engage with mulching has been exacerbated by the fact that it is known to be one of the toughest operations in forestry – on both man and machine. Contractors and growers have had to learn some hard lessons in the process of finding the right systems that can meet productivity expectations while delivering a consistent quality of mulch.
Moreover the additional and hidden benefits of mulching are not easily quantifiable. It impacts on almost every facet of growing and harvesting trees, so to appreciate the full benefits you have to consider the bigger picture - not just short term rands and cents.
Productive tree growth requires a healthy soil habitat which is achieved through maintaining the pristine state and balance of soil physical, chemical and biological properties. Numerous local and global studies have demonstrated the extreme negative impact of organic matter loss due to repeated residue removal, burning (and subsequent erosion) on the soil health and productivity of sensitive soils. Residues left behind after harvest contain large quantities of organically bound nutrients and carbon. Mulching compared to burning or residue removal directly conserves the soil health. This retained organic matter feeds the trees and soil microbes as a slow release organic fertiliser and carbon source for much of the subsequent rotation. Healthy soil microbes contribute to tree nutrition and are believed to also act as the soils immune system by outcompeting soil pathogens.
Before: stumps and brush left in-field after clearfelling creates access problems for the pitting and planting operation to follow.
After: the mulcher has prepared the way for follow-up pitting and planting operations.
Further benefits measured after mulching are increased soil water due to reduced surface evaporation, reduced weed growth and increased percolation; and stabilisation of soil temperature by eliminating extreme heat and cold. Prevention of soil erosion and compaction through surface protection are further major benefits.
In addition, greenhouse gas emission due to fuel use during mulching is far less than the methane and nitrous oxide release during residue burning.
Residue mulching through these benefits can potentially mitigate the effects of climate change.
Forwarders haul timber along mulched extraction routes … no stumps, no tyre damage, soil protected by the mulch layer which reduces soil compaction.
No more burning
Sappi was one of the first large grower companies to adopt mulching of slash as a strategy in their Zululand plantations. Work by Sappi’s research team to gauge the cost benefit based on trials concluded that at rotation end the additional growth benefit was three times the cost of mulching. This research was used to motivate for the decision to proceed with mulching in Zululand.
The mulcher clears a burnt compartment...
... young saplings and all.
Sappi started doing trials in 2010, and by 2014 were mulching 100% of their Zululand coastal plantations, stretching from Richards Bay to north of Mtubatuba. No more burning of slash takes place on these plantations.
Mulching solved a lot of problems for Sappi in Zululand, reducing temporary unplanted areas dramatically, improving seedling survival and growth, removing old stumps thus paving the way for better access for modernised silviculture operations and fire prevention; as well as more productive future harvesting operations, whilst protecting and nourishing the sensitive soils with a mulch blanket.
Much work has been carried out by Sappi in quantifying the financial benefits of mulching due to improved growth at rotation age. Their research team has installed mulch/burn twin plots to directly measure and compare the effects of mulching on soil water, soil health and tree growth.
The Merensky forestry team inspects the Tigercat M726G wheeled mulcher operated by Savithi during an in-field demo.
This work has led to a study currently being undertaken by Leeshan Mahadeo, a BSc Forestry graduate from Stellenbosch University, to gauge the impact of mechanical mulching on subsequent pitting and planting operations in both pine and Eucalyptus. The study, supervised by Bruce Talbot and Simon Ackerman of Stellenbosch University, is being implemented on sites in Zululand, KZN midlands and the Mpumalanga Highveld.
This study will provide useful data that will help to clarify the operational cost/benefits of mulching while developing drone-based methods for residue load assessment.
Negative impact of residue removal
According to Sappi research scientist, Steven Dovey, productive tree growth requires a healthy soil habitat which is achieved through maintaining the pristine state and balance of soil physical, chemical and biological properties. Numerous local and global studies have demonstrated the extreme negative impact of organic matter loss due to repeated residue removal, burning (and subsequent erosion) on the soil health and productivity of sensitive soils, he says.
Big old stumps left in-field create headaches for foresters and contractors, hindering access and mechanised operations.
The same compartment after mulching...
Residues left behind after harvest contain large quantities of organically bound nutrients and carbon. Mulching compared to burning or residue removal directly conserves the soil health, he says. This retained organic matter feeds the trees and soil microbes as a slow release organic fertiliser and carbon source for much of the subsequent rotation. Healthy soil microbes contribute to tree nutrition and are believed to also act as the soil’s immune system by outcompeting soil pathogens.
Further benefits measured after mulching are increased soil water due to reduced surface evaporation, reduced weed growth and increased percolation; and stabilisation of soil temperature by eliminating extreme heat and cold. Prevention of soil erosion and compaction through surface protection are further major benefits.
In addition, greenhouse gas emission due to fuel use during mulching is far less than the methane and nitrous oxide release during residue burning. Thus residue mulching can potentially mitigate the effects of climate change, says Steven.
The mulcher can work on fairly steep sites, and can go wherever skidders can go.
Savithi Mulching
Savithi Mulching, equipped with a fleet of tough-as-teak Tigercat wheeled mulchers, are currently mulching for Sappi in Zululand, and have now started mulching for Sappi in the KZN midlands around Ixopo, Highflats and Bulwer as well.
Deon Redinger established Savithi Mulching in 2010, initially using tracked machines but now has graduated to wheeled Tigercat M726G machines.
“We started slowly and learnt a lot of lessons along the way,” says Deon. “We started with tracked machines, but when we got wheeled machines we came right.”
Deon Redinger of Savithi Mulching … at the business end of a Tigercat wheeled mulcher, KZN midlands.
The three most important ingredients in the mulching business, according to Deon, are the quality of your ‘pilot’ (operator), effective maintenance and spares availability.
It’s no coincidence that he calls his operators ‘pilots’. This is because it takes training, skill and concentration to operate a mulcher properly. The importance of effective machine maintenance and spares availability in this extremely tough operating environment speaks for itself.
Every compartment presents different conditions and different challenges, says Deon. Tree species require different mulching tactics due to the quantity and nature of the slash left behind. Some stumps are much harder to grind down than others; ground conditions, weather, slope and the turnaround space at the compartment edges - all of these factors impact on the mulching operation.
Savithi’s ‘pilots’ prepare for take-off.
“The challenge is to get the mulch to cover the soil evenly like a blanket (not to mix the mulch up with the soil) and to reduce stumps to ground height.”
He says the mulcher will run over a brushline two or three times to get an even distribution of mulch that you can plant into.
It can take anything from two to six hours to mulch one hectare (in Zululand), depending on conditions, so Savithi generally works on an average of three hours per hectare. He says they average around three hectares per machine per day, and do not operate at night.
Deon says that 350 horse power is the minimum grunt required for an effective mulcher. He’s also convinced that wheeled machines are better than tracked because they can be moved around from compartment to compartment without the need for a lowbed trailer.
He says they are operating right behind the harvesting team, and as soon as they’re done mulching the planting team moves in. They are also mulching the routes that will be used to extract the harvested timber from in-field, so mobility of the mulching machines between adjacent compartments is essential. This operation speeds up the shorthaul, reduces tyre damage and protects the soil from compaction.
All post plant and future harvesting operations are made easier and cheaper in compartments that have been mulched.
Deon says Savithi has mulched 13 000 to 14 000 ha in Zululand over the past few years, and just this year will mulch 3 000 to 4 000 ha in the KZN midlands.
“We can work in fairly steep slopes – where a skidder can go our mulchers can go,” he said.
Savithi has also been mulching old forestry compartments for private farmers that are converting land to other crops like macadamias, avos and pecans.
Deon has been doing a lot of work to find an effective way to accumulate mulch for further downstream processing opportunities that he believes will be viable in future, and likes to refer to mulched material as “unutilised biomass”.
The Tigercat M726G wheeled mulcher, operated by Savithi Mulching.
Sappi’s Zululand Area Manager, Sandile Nkosi, says mulching has enabled the Sappi forestry team to keep temporary unplanted areas below 1.5% throughout the year, thanks to the speed of mechanised operations and the extended planting window that mulching has given them. Furthermore it has enabled Sappi Zululand to maximise silviculture mechanisation, improving compartment access for planting, weeding and fire fighting.
He says they have had fewer fires since they started mulching, and are able to put fires out quickly as they don’t spread so fast. He says all the Sappi foresters have observed improved survival and growth in mulched compartments.
Sappi’s Silviculture Manager for KwaZulu-Natal, Jeffrey le Roux, has seen the benefits of mulching in post harvesting operations, reduced TU as well as tree growth and yield. Here he inspects a mulched compartment in Zululand, 10 months after planting. The mulch has given these trees an excellent start.
This adjacent compartment was planted at the same time as the photo above – the difference being that the post harvest slash was burnt – not mulched. Soon after planting strong winds commonly experienced in coastal Zululand sand-blasted the young trees, many of which did not survive. Extensive blanking was required, but still the productivity of this compartment will be poor compared to the adjacent, mulched compartment.
Says Deon: “the mulching operation returns organic matter back into the soil and increases plant growth by 5-10%.
“The benefits of mulching harvesting residues are infinitely preferable to burning them. It has taken some time, but the benefits of the mulching process are finally being recognised by the forestry industry.”
The last page of Sappi’s 2019 Corporate Citizenship report focuses on the company’s mulching strategy in their South African plantations, and states: “The value of the estimated additional timber produced exceeds the current mulching costs.”
There you have it! With the right team, the right equipment and sufficient commitment and experience, mulching can be a game changer in the South African forestry environment.
