WOOD SCIENCE AND TIMBER TREATMENT
Managing for quality in silviculture Jez Ralph of Timber Strategies encourages readers to think wood science when growing trees for timber.
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s we move towards more complex silvicultural systems (at least in many lowland areas) where we take more notice of individual trees it gives us a chance to consider quality as well as quantity in our standing resource. Continuous cover forestry (CCF), agroforestry, urban forestry and even small farm woodlands present huge opportunities to expand what we think of as “conventional” forestry. These systems potentially enable us to look more closely at what we have. With increased management time comes increased need to garner as much value from individual stems as possible. This won’t likely come from forcing sales into volume/commodity markets but will come from managing for quality. It’s not for everyone, it isn’t the answer for all forestry, but it is a poten-
tially large and generally untapped area of development. To do this we, as an industry, as individual owners and managers, need to understand quality by stepping outside the forest gate and looking back in. From the point of view of timber users, R&D scientists and future generations, what does quality mean, and how do we adapt our silviculture to suit it?
Macro scale quality Understanding the anatomy of a tree and the anatomy of useable timber helps to understand how silviculture can make or break the end quality and value of timber. As an example, let’s take the proportion of juvenile core to heartwood in a tree. Juvenile core is the soft, bendy, early wood that allows saplings and tree tips to
respond to environmental stress such as wind or snow loading. It works extremely well up to a certain point at which time the tree needs to become a stiffer solid column. It is the heartwood the tree generates to become stiff that is of interest to us, that will maximise the good, gradeable timber within the tree. Ideally we want to minimise juvenile core and maximise heartwood and we can go some way to doing this through how we plant and how we thin to get stems over the juvenile core stage as quickly as possible. Whilst we understand this, new silvicultural systems allow us the intimacy of knowledge in a forest to see where this is going to work, perhaps where it isn’t. New extreme examples, such the Myawaki Method of planting that has roots (sorry!) in environmental urban forestry, maybe deserve more attention as a silvicultural method for quality timber? Then let’s consider knottiness. Most timber users, especially for structural purposes, hate knots. Knot-free timber will always be at a premium, if nothing else it reduces the need for cross-cutting and finger jointing at timber-engineering plants. It will also, along with ring-width, significantly increase the grade timber could attain. Reducing knottiness is a matter of species selection, genetics, planting spacing and thinning. It’s complex but can be significantly enhanced by the oh-so out-of-fashion and oh-so rewarding practice of high-pruning. To carry a pruning saw on a walk-through small woodland or CCF stand is no great burden but has the potential to create knot free timber in selected trees from an early age (note: bad pruning can be as counter-productive as good-pruning can be productive, think of it as a craft worth learning). I could go on and on about increasing target diameters but let’s leave that here hanging for a big debate sometime.
Micro Scale Quality
Photo credit: Timber Strategies
On a macro scale we can see the effects our silvicultural interventions have but what happens on a micro scale is more difficult to see and understand but no less important. The work of many scientists, not least at the Centre for Timber Engineering and other UK research groups, is enabling us to match factors such as density, durability and stiffness through micro-fibril angle to how we grow trees. Again, new systems such as small coupe fellings or small-woodland management may offer the chance to experiment without pushing the whole forest into a particular system for a desired outcome. They offset risk and may offer high reward. Stiffness is a good example of this. If we can grow stiffer timber we can increase the potential structural grade a tree can reach, enhancing the value. As with the macro scale, species selection and environment helps but we can bring
38 FORESTRY & TIMBER NEWS • December 2021
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