What is ‘shake’ in wood?
Ring Shake & Star Shake
When you’re shopping around for high-quality timber, you need to watch out for is something called ‘shake’. Shake is an industry term that refers to a series of internal cracks that run inside the tree itself. Shake comes in two forms, star shake and ring shake:
Star Shake
Star Shake appears as long, thin lines running across the growth rings.
Ring Shake
Ring Shake appears as broad circles splitting the wood along its growth rings.
The Problems
Shake is a crucial problem for the timber industry. It can lead to a large quantity of wasted material due to it weakening the trees it appears in. This structural weakness can pass on to products made from timber affected by shake.
Shake appears in commercial products infrequently, due to being relatively easy to spot. However, most of the time, shake can only be discovered after the tree is felled, and cladding, beams, joists, and other commercial construction or support structures can easily become less stable if shake is present in their timber.
While there are few ways of resolving shake in a tree, there are signs you can watch out for to mitigate the chance of your tree having shake in the first place.
Environmental Factors Causing Shake in Trees
A number of studies conducted over the past fifty years have narrowed down the factors inherent in causing shake. A number of these may not cause the shake itself but can damage the tree, open it up to the environment, or affect its growth patterns, which in turn makes it more vulnerable to shake occurring.
Cell Size
While a number of these factors are strong indications of shake, one that is always a reliable indicator of shake is that of the tree’s cells being larger.
Larger cells in the wood are more likely to lead to cell wall fractures, local issues which commonly grow into larger faults, most often ring shake.
A number of factors in the environment can lead to a tree’s cells being larger than normal. Chief among them is increased rainfall or moisture present in the early months of a tree’s lifespan (or the springtime generally), either as a result of the tree’s enclosed location (inside a shelter) or the type of soil it’s planted in (acidic or sandy soil that allows free drainage).
Cold & Frost
Cold and frost, especially in particularly cold climates and regions, can also increase shake risk. Severe cold can cause cells to distort and cause damage all around the ring of a tree’s stem, creating a circle pattern known as a ‘frost ring’.
This expands with the tree as it grows, creating lasting instability. This same severe cold can also cause fluid stored in wetwood, or previous shakes to expand outwards, creating a ‘frost crack’: a harsh break in the tree’s bark, which can lead to further shakes.
Hot and Droughts
In hot conditions, sudden droughts can lead to abrupt reductions in ring width, as can insect-led defoliation. A sudden change in ring width like this can lead to ring shake, especially in soils where water uptake, moisture retention, and nutrient availability is limited.
Wounding and Issues in Forest Management
Wounding, or general injuries to the tree’s bark and wood, can come from any number of sources, ranging from human tampering (including pruning or using harvesting machinery) to excessive temperatures. Different parts of the tree being wounded can result in different types of shake. Ring shakes tend to result from damage to the tree’s trunk, while star shakes often result from damage to the tree’s roots. Natural conditions such as regions of heavy wind can cause stem wounds or abrasion.
While wounds never cause shake directly, they open up the interior of the tree to the elements, which lets air in and separates the new wood that grows over the wound from the wood beneath, leading to shake and general instability.
This new wood is often called a ‘barrier zone’, which is relatively small-scale at first, but can lead later to very extensive gaps in the wood, sometimes called ‘traumatic shake’.
Wound points can also act as entryways for fungi and anaerobic bacteria, which colonise the wounded tissue and break down the bonds between cells, making them at greater risk for shake. They do so most often when the wood is naturally very moist. In severely cold climates, this can lead to frost cracks.
How Soil Quality Affects Shake in Trees
The following factors in the environment can cause shake in trees:
- A poor soil nutrient regime
- Sandy, stony, or gravelly soil
- Shallow soil
- Disturbed ground or engineered soils
- Low (or very high) soil clay content
- Site types or soil textures prone to seasonal waterlogging
- Site types or soil textures prone to drought
- A fluctuating water table.
The soil the tree is planted in is one of the most important factors in estimating the presence of shake. There should be a good balance of essential soil nutrients, and an absence (or reduced presence) of toxic elements.
The soil content, flora and fauna, and condition of the site a tree is planted in can help indicate your tree’s shake risk. A shake-prone site has an acid-brown earth, which is low in calcium, and high in aluminium, or a gravelly or sandy-brown earth with rapid drainage and restrictions on the tree’s roots. It will also likely contain plants like heather, bracken, or rhododendrons, which all favour free-draining and acidic soils. One of the worst elements to have in high concentration is aluminium, which is toxic to plants.
A shake-free site, on the other hand, will have a forest-brown earth, rich in nutrients; a dense, loamy soil which favours water retention; and may feature plants such as bluebells, which prefer heavy, moisture-rich soils. The best nutrients for a soil to be rich in are potassium, magnesium, and calcium.
Solutions to Tree Shake
Ultimately, there are a wide number of potential indicators of increased shake risk, and few are universally applicable. Some trees which are in a high-risk area can healthily grow with no shake at all, and others in supposedly shake-free areas can develop it for unforeseen reasons. However, prevention and management are always worth it, to help create a healthier and more productive forest overall, and many of the signs we’ve discussed have ways to address them.
Planting Tubes/Tree Shelter.
When it comes to avoiding wounds, a tree shelter (such as planting tubes or guards) can work wonders in preventing outside interference, be it from nature or humanity. However, a shelter that limits the growth of the tree’s roots or exposes them to the elements can be equally hazardous. When planting the sheltered tree, you should also avoid areas of wetwood, waterlogged soil, or frost hollows.
Management
The role of the forest manager is also very important here, ensuring the trees maintain a constant growth rate. During thinning, the manager should keep a close eye for frost cracks, as these often indicate the presence of wetwood, which can be removed during thinning. Careful timing of the thinnings is very important, especially in the early-to-mid growth cycle of trees, ensuring the trees aren’t competing against each other.
Soil Qualities
Soil pH is a broad but often effective way of measuring how shake-prone a tree might be. Shake-prone sites have acidic soils (low pH), while shake-free sites have alkaline soils (high pH). You should ensure the soil isn’t shallow, as that can limit root growth. Ensuring the tree roots well in the soil, and that the soil retains moisture, can also help with some of the issues inherent to sudden ring growth as a result of unexpected drought or defoliation.
In Summary
While shake has a great many potential sources, all of these have a solution. Ultimately, the key to ensuring you’re not buying a product at risk of shake lies in making sure the site you’re buying from is temperate, in good-quality soil, and, most importantly, is well-managed and regularly maintained.
