As part of the “Prioritisation of productive tree species for Wales” project, funded by the Welsh Government and led by Forest Research, a database of information about wood properties and products is being created covering all long-listed productive tree species. Wood Knowledge Wales is leading the stakeholder engagement aspects of the overall project and providing specialist inputs relating to the wood properties and end use. This specialist input is being done in collaboration with Bangor University and Edinburgh Napier University.

This page is a work in progress and will be updated as this database is assembled.

About the project

The forest and timber sector in Britain is heavily dependent on a very small number of productive tree species. With the increasing threat from pests and diseases and the effects of climate change, it is essential to identify a shortlist of alternative species that the whole sector can agree upon, to diversify the composition and increase the resilience of our woodlands and forests.

The need for such a shortlist for Wales has been highlighted in the Welsh Timber Industrial Strategy. A similar project has recently been completed in Scotland funded by Scottish Forestry, and another is underway in England funded by Defra. The project for Wales runs in parallel with the England work, creating synergies that benefit all three countries. The shortlists in each country allow joined up investment in tree breeding, plant and seed supply, growth, yield and carbon modelling, silvicultural knowledge exchange and training, timber research and development, processing capacity and market development, and incentives to target species for planting.

The project uses a multi-criteria assessment (MCA) framework to assess the performance of a longlist of species against a comprehensive set of criteria covering a range of benefits, constraints and risks associated with productive forestry throughout the wood value chain. The framework will be complemented with additional datasets, and practical knowledge elicited through stakeholder engagement, that help interpret the data and add nuances that cannot be captured through the MCA scores alone. You can read the Scottish report to find out more about the criteria and what they cover.

“Wood properties and end uses” is one of the criteria and it combines diverse metrics related to harvesting, processing, manufacturing, markets and end uses. This page provides information about the component metrics involved.

First, what exactly do we mean by species?

This describes the type of tree, but in forestry and timber the word species is often not used in the strict botanical sense (as it is not so useful). Sometimes we talk about things as the same species when, scientifically speaking, they are different species, and sometimes we talk about things as being different species when, scientifically speaking, they are the same.

Many important wood properties vary by growth conditions and the timber grown in one country might be quite different from that grown in another, even though the species is the same. For that reason, the growth area is often also part of the distinction.

Also, while there can be many things that matter about species for forestry – for wood products the exact species might not matter much at all. Some species are processed and sold without differentiation, and, for the wood value chain, they are considered to be the same “species”, even though they might actually be a completely different genus. The way timber species are grouped can differ between places and product types.

There are also some types of timber that can vary quite a lot even within a single species, and the timber trade makes distinctions that are, scientifically speaking, at the “infraspecific” level, such as subspecies and varieties. Hybrids and cultivars can make this even more complicated, as does genetic complexity and unsettled taxonomy.  In our longlist, “sorbus” and poplar are perhaps the biggest headaches; more so for poplar because the cultivars and hybrids can have very different properties, yet poplar is often treated as a single group. However, the problem is not so much about always being scientifically precise, but about being able to separate trees sufficiently well for the things that matter in this context.

For our wood properties and products database that means:

• Being able to map the wood properties concept of “species” onto the forestry one, and have that connection work in both directions.
• Being able to record information about specific species, as well as species combinations, and cope with the fact that often wood properties research is not very specific as to exactly what species where tested.
• Recording also the growth area information, which cannot really be separated from species for many wood properties. For preference we seek information from timber grown in UK and Ireland, but in a lot of cases we can only obtain data from abroad.
• The database information includes relevant common names, the full scientific name and taxonomy (as class, order, family, tribe, genus, subgenus, species, subspecies), NCBI taxid number, and commonly used synonyms and alternative names.

The scoring

The way in which the scores are calculated for wood properties and products is being re-examined as part of this Welsh project. In summary, we need to cover the technical potential of the wood, the compatibility with the current value chain, and the level of confidence we have in the information.

The wood properties that matter for different uses vary greatly, so there is no single measure of what “good timber” means. However, since the UK forests need to provide mills with sufficient material to make a basket of fundamental high-volume products, we do know that it is important to consider the requirements of construction timber (structural and non-structural), pallets and packaging, fencing, and wood-based panel products. It is also important that co-products such as bark and chip are suitable for other key industries, including agriculture. There are numerous components to this, but they broadly fit into things relevant to:

• Modern uses (e.g. strength, hardness, appearance, natural durability)
• Processing (e.g. stem form, debarking, drying, workability, treatability, health risks)
• Markets (e.g. familiarity, coverage by standards, competition from abroad)

As mentioned above, for many uses, the exact species often does not matter to markets and as part of the scoring we are looking at how well species fit into familiar “archetypes”. For Wales, these are (currently), spruce-like, oak-like, and Douglas-fir-like. These are comparing the factors related to processing and end use rather than to growing, but species that grow well together in the forests also have advantages if they can be processed and sold together.

The sub-metrics and why they matter

Short explanations of the following are currently being written, but the component metrics in the database cover:

• Existing interest in forestry as a potential timber species
• Wood type (hardwood/softwood, end grain type, heartwood-sapwood distinction)
• Colour
• Workability
• Drying and seasoning (including kiln schedule type, difficulty, and degrade such as blue-stain)
• Natural durability against fungi
• Treatability of sapwood and heartwood
• Extractives content and extraction method)
• Moisture movement
• UK market familiarity
• Stem form (length, straightness, taper, fluting etc)
• Reaction wood
• Branches and knots
• Reported (existing) uses (grouped by service class – indoor or outdoor)
• Appearance grading
• Strength grading (visual and machine), existing possibility and work required to establish
• Density
• Mechanical properties (of clear wood and full size), covering bending strength, modulus of elasticity, hardness