Did you know that tree bark is actually a widely used material, not just something you get rid of as garbage. In todays forestry and wood-processing industries, bark is no longer viewed as a low-value residue, but instead as a versatile biomass resource. It can be converted into biofuel, soil amendments such as mulch, raw material for panel boards, a source of extractives (e.g., tannins, resins, and phenolics), or even a component in advanced bio-based materials. With appropriate processing, bark becomes a standardized, valuable product rather than a heterogeneous waste stream. This shift in perspective plays a large role in sustainable forestry and circular bioeconomy strategies – and it is precisely where technologies like screener and crusher buckets play a transformative role in their turn.
First things first – how much bark does a tree have?
The proportion of bark in a tree, of course varies significantly depending on species, age, and growth conditions. In general, bark accounts for approximately 10–20% of the total stem volume in most commercial tree species, which is quite a lot. Conifers such as pine and spruce tend to fall within the lower to mid-range, while some hardwoods may exhibit higher bark fractions due to thicker protective layers.
From a mass perspective, bark can contain an even larger share because of its relatively high density and moisture content. In industrial terms, this means that a considerable fraction of harvested biomass – often underestimated – is bark! In a typical sawmill processing thousands of cubic meters of timber daily, bark quickly accumulates into a substantial material flow that must in turn be handled efficiently.
The moisture content of bark – quite high!
Fresh bark is characterized by high moisture content, typically ranging between 40% and 65% (wet basis), although values can exceed this range depending on tree species and environmental conditions. Compared to wood, bark often contains more bound water and a higher proportion of extractives, which influence drying behavior and combustion properties.
This high moisture content has several implications. For energy use, it reduces the calorific value per unit mass, meaning that pre-drying or blending with drier materials may be required. For mechanical processing, moisture affects particle cohesion and flowability – wet bark tends to clump and can be more difficult to screen uniformly. On the other hand, some moisture is beneficial during crushing, as it reduces dust generation and wear on equipment.
Debarking a tree – how it’s done
To “shave” off the bark, more commonly known as de-barking, is a common industrial operation, typically performed before the logs enter the main sawmill processing line. The primary reasons are actually to protect saw blades from abrasion, reduce contamination, and improve the quality of final wood products.
There are several common debarking methods:
- Mechanical drum debarking: Logs are rotated in large drums where friction between logs and internal structures removes bark.
- Ring debarkers: Logs pass through a ring of rotating tools that strip bark efficiently, often used in high-throughput sawmills.
- Hydraulic debarking: High-pressure water jets are used, though this method is less common due to water consumption and wastewater handling requirements, of course.
In forestry operations, partial debarking may also occur at roadside processing sites using harvesters, but full industrial debarking is typically done at sawmills.
The output of these processes is a heterogeneous mixture of bark fragments, fibers, and sometimes small wood particles – this is where bark processing begins.
Now it’s time for bark processing – but what is it really?
Bark processing is the mechanical and sometimes thermal treatment of raw bark material to produce a more uniform and therefore usable product. The goal is quite simple, it is to transform irregular, bulky, and moisture-rich bark into a consistent fraction suitable for specific applications.
Typical steps in bark processing include:
- Size reduction (crushing, shredding)
- Screening and classification
- Drying (if required, that is)
- Contaminant removal (stones, metals, oversized wood pieces)
Traditionally, this processing has been carried out in stationary facilities using large shredders and screening plants. However, mobile solutions – particularly crusher and screener buckets mounted on excavators or loaders – are increasingly being adopted for smart and cheap on-site processing.
Advantages of a crushing bucket and screener bucket for the process
The use of crusher and screener buckets is a major shift toward flexible, on-site material handling. These attachments can be mounted on common carrier machines such as excavators, wheel loaders, or backhoe loaders, enabling bark processing directly where the material is generated.
One of the primary advantages is logistical efficiency. Transporting unprocessed bark is costly due to its bulk and moisture content. By reducing volume and homogenizing the material on-site, operators can significantly decrease transportation costs and improve downstream handling.
Another key benefit is process adaptability. Screener buckets allow operators to adjust output size fractions by changing screening shafts or meshes. This makes it possible to tailor bark products for specific applications, such as coarse mulch or fine biofuel feedstock, without investing in multiple dedicated machines.
Crusher buckets, on the other hand, are effective for breaking down larger bark chunks and agglomerates, especially when bark is mixed with wood residues or compacted during storage. The combination of crushing and screening enables a closed-loop processing approach in a single workflow.
Of course, there are also buckets incorporating both the capability to crush and screen at the same time and in a single step, such as many products from ALLU, for example.
From a technical standpoint, these buckets are designed to handle heterogeneous and moisture-rich materials, making them particularly suitable for bark. Their relatively simple mechanical design also translates into lower maintenance requirements compared to large stationary systems.
Importantly, on-site processing is entirely feasible. In forestry operations, sawmill yards, or recycling facilities, operators can process bark directly at the source, reducing the need for intermediate storage and handling. This aligns well with modern lean logistics and sustainability goals.
What can bark be used for after processing?
Once processed into fine and homogeneous particles, bark becomes a versatile industrial resource. One of the most common applications is bioenergy production. Processed bark can be used as fuel in biomass boilers, combined heat and power (CHP) plants, or district heating systems. Its relatively high ash content compared to wood requires proper combustion control, but it remains an important renewable energy source.
Another major application is in horticulture and landscaping. Screened bark is widely used as mulch, where it helps retain soil moisture, suppress weeds, and regulate soil temperature. Its natural composition also contributes to soil structure over time as it decomposes.
In the materials sector, processed bark can be incorporated into composite products, such as particleboards, insulation materials, or bio-based polymers. Bark contains valuable chemical compounds – tannins, for instance – that can be extracted and used in adhesives, corrosion inhibitors, or even in pharmaceutical applications.
Emerging research is also exploring bark as a feedstock for biochar production, carbon sequestration, and advanced biorefinery processes. In these contexts, consistent particle size – achieved through proper processing – is crucial for process efficiency and product quality.
Unprocessed bark – is it just garbage?
Tree bark that hasn’t been processed, that it to say unprocessed bark, still has practical uses, though they are generally less efficient or less controlled. It is often used as a low-grade fuel in industrial boilers, particularly in sawmills where it is generated. However, its irregular size and high moisture content can lead to inconsistent combustion.
In some cases, raw bark is applied directly as coarse ground cover in forestry or landscaping. While this requires minimal processing, it lacks the uniformity and aesthetic quality of screened products.
Unprocessed bark may also be stockpiled for later use, but this can lead to biodegradation, odor generation, and even self-heating, which poses a fire risk. From both economic and environmental perspectives, leaving bark unprocessed is generally not the greatest thing to do.
Trivia: Is everything reused or recycled in logging and sawmill waste?
In todays forestry and wood-processing industries, the ambition is to achieve near-total utilization of biomass, and significant progress has been made toward this goal. Wood residues such as chips, sawdust, and shavings are routinely used in pulp production, panel manufacturing, or energy generation.
Bark, historically considered a lower-value by-product, is now increasingly integrated into this circular system. However, it is not entirely accurate to say that everything is reused, because that would be almost impossible. Losses still occur due to contamination, handling inefficiencies, or economic constraints. For example, very fine fractions or heavily contaminated materials may be difficult to recover profitably.
That said, the trend is clearly toward maximizing resource efficiency. Technologies like screener and crusher buckets contribute to this by enabling more flexible and localized processing, reducing waste, and increasing the proportion of material that can be valorized.
Flashback: What we’ve learned about bark and its processing
Tree bark, once overlooked as a by-product, is now recognized as a valuable resource within the forestry and bioeconomy sectors. It typically constitutes of as much as 10–20% of a tree’s volume and exhibits a high moisture content of 40–65%, making its handling and processing both a challenge and an opportunity at the same time.
Debarking is usually performed before logs even enter the sawmill, producing a heterogeneous bark stream that requires further processing. Through size reduction and screening, bark can be transformed into uniform material suitable for a wide range of applications, from bioenergy and mulch to advanced materials and chemical extraction.
The use of crusher and screener buckets provides a flexible, efficient approach to bark processing. These attachments enable on-site treatment, reduce transport costs, and allow operators to tailor output to specific needs. Their compatibility with common machinery such as excavators and loaders makes them particularly attractive in decentralized operations.
Processed bark unlocks higher-value uses and supports sustainable resource management, while unprocessed bark remains limited in application and efficiency. Although not all forestry residues are fully recycled, the industry is steadily moving toward greater circularity.
In short, bark is no longer something to discard – it is something to process, optimize, and actually use. With the helping hand of right technology and approach, even the outermost layer of the tree can play a key role in a more sustainable and resource-efficient future.
