Delayed Biodegradation  – the answer to ‘single-use’ plastic tree guard pollution?

July 24, 2023

As part of an Innovate UK project, SCG visited the beautiful Avoncliff Wood in Wiltshire to investigate and understand the surprisingly complex subject of delayed biodegradation for tree guards (or as I’ve discovered, more professionally referred to as ‘tree shelters’).

In 2019, the Woodland Trust established the Avoncliff site to test the new plastic-free products coming onto the market. The trial is one of the longest running in the UK and now has different types of non-plastic tubes in use across 5,000 new trees, with more models being added regularly.

The UK government has committed to increase new planting of woodland to 30,000 hectares a year. In the quest for Net Zero carbon accounting, other organisations will increase this figure.

The UK’s independent climate advisory body has recommended increasing national forest cover from 13% to up to 19% by 2050, which the Woodland Trust equates to planting more than 1.5 billion trees. The National Trust – which is among the biggest landowners in the country – aims to plant 20 million trees by 2030. This means that a significant number of tree shelters will be needed to support these targets.

The Innovate UK project was established to support development of a suitable biodegradable tree guard that protects trees over time, a suitable testing regime, and a certification scheme to independently validate that the materials have met the requirements.

What is the purpose of a tree shelter?

A tree shelter is a structure that protects planted tree saplings from browsing animals (dear, rabbits and voles) as the trees grow. They are solid or mesh tubes that are placed over a seedling to provide favourable environmental conditions for seedling growth.

These can be made from a wide range of materials. To date, most have been made from plastics made from petrochemicals. These are not biodegradable and must be removed after use and recycled. Others use petrochemically derived plastics, but have additional materials that result in the tree shelter or guard breaking down into small pieces. However, the small fragment size means they cannot be recovered from the environment. More recent designs use organic sources, compressed paper, or cardboard. Issues have arisen over the longevity of these as they need to be designed and constructed to provide adequate protection throughout the establishment of the tree.

There are some manufacturers that use organic sources to make tree shelters from biodegradable materials, such as British wool, polyol made from cashew nutshell liquid and castor oil, and custom polymers.

One of these is NeXGen, who are partners on this Innovate UK project, and who’s trial we went to see as part of the visit.

While tree shelters are an effective means of establishing trees, there are some problems associated with them. For example, when their job is done (e.g. after 5 years), they do not simply disappear. They must either be collected and recycled, or begin to biodegrade to prevent killing the tree. The latter of these is referred to as ‘Delayed Biodegradation Products’ (DBP).

Positive points

Plastic tree shelters are used for their longevity and effectiveness when it comes to protecting young trees from damage. After the tree has become established, they can be collected and recycled.

DBP – after the tree has grown to a robust size over time, the tree shelters break off and biodegrade into the soil, negating collection time and costs and preventing plastic pollution.

Negative points

  • Plastic: It can be considered as a contradiction that more trees are being planted to help fight climate change, but the people who work with trees use plastic guards that are typically only used once. Because of the increasing focus on ‘single-use plastics’, governments and people who work with trees are under pressure to find a new kind of tree shelter that is better for the environment.
  • Unless collected the plastic tree shelters will either remain, damaging the tree, or they will fall to the ground, and contaminate eco systems as plastic litter, harming wildlife and pets, or ultimately as marine pollution when they (eventually) reach the sea.
  • In a carefully managed environment (usually commercial) collection is less of a problem, but there is an associated labour cost. There is also the question of if that organisation will still be in existence (e.g. 5 years later) when they need collecting.

  • DBP: The efficacy of DBP’s has been a major problem for producers. Getting a material to biodegrade is difficult, getting one to biodegrade after a set period of time is even more so. During the site visit we saw ‘biodegradable’ examples that had disintegrated, and alternatively ones that looked like they would last until the next century, with no damage or sign of degradation after several years of being in-situ.
  • Once the DBP tree shelter breaks away, it does not biodegrade immediately, instead breaking up into increasingly smaller pieces over time, until biodegrading into the soil. During this intermediate period, the DBP tree shelters can have the same littering effect as the more durable plastic equivalents. Therefore and enclosed or controlled area/site may be required to prevent escape until biodegradation is complete.

SCG’s Role

SCG’s role in the project is to create a certification scheme for DBP’s.

This will provide independent validation of products that are designed to biodegrade after a set period of time. At the moment we are piloting this on tree shelters, but expect more agri-sector based products to be considered in future. To ensure we have an informed DBP Certification scheme, we’ve gathered an number of independent experts to form a Technical Advisory Group. This passionate group of industry practitioners and technicians ensure that the scheme will challenge and bring value to those who choose to adopt it.

Considered Solutions

As is not uncommon in a circular economy situation, a ‘one stop’ solution is possibly not the best option, so a range needs to be considered for specific scenarios.

Reduce: The most sustainable tree guard is no tree guard at all! The environmental performance of protecting seedlings with plastic tree shelters for afforestation in temperate oceanic regions: A UK case study shows that planting seedlings without tree shelters is the environmentally preferable option. Planting techniques and processes that avoid the use of individual tree protection are available – but they can be more cost intensive or require more time

Possible solutions cover overplanting, to compensate for the attrition rate, timber fencing or thorn trees to protect from deer and rabbits, or ‘direct’ wildlife control measures (possibly contentious). These more ‘nature friendly’ solutions can be adopted for low level planting by small estates, NGO’s (e.g. Wildlife Trusts) or conservation volunteers

Reuse and Recycle: The aforementioned case study mentions that in carefully managed tree production that use plastic tree shelters for collection, reuse and recycling, provide the next best environmental options. Trials by the Woodland Trust have shown that some tree guards can be used up to three times, and recycled when no longer fit for purpose.

Using these options may be financially detrimental in terms of collection labour and recycling. However, Life Cycle Assessments should consider the scope (including collection), environmental impacts, (risk of plastic pollution) and associated legal and remediation costs – which also leads to a loss in reputational collateral.

Biodegradation: Residual Flows used in Industry and subsequent Composting: Composting is the microbial breakdown of organic matter in the presence of oxygen. The process is biological and involves naturally occurring microorganisms, such as bacteria and fungi.

These components can be used to biodegrade specifically designed tree shelters made of organic elements (residual flows) such as British wool and cashew nut shell oil. This process should leave no toxic residues, and as the material breaks down into the soil it does not require collecting or recycling. This is generally an initial greater cost than cheaper plastic examples, but negates the need to employ staff or rely on volunteers (or worse – fines and environmental clean-up operations) so could prove cheaper across the product life cycle. As such, this would be a suitable solution for tree planting where there is a risk of the shelters not being collected after the required growth has been achieved, several years later.

SCG’s Role

The caveat for both recycling of plastic tree shelters and biodegradation is that it should be independently validated through certification.

SCG provide certification for Recyclers to validate recycled content (e.g. polypropylene tree shelters) whilst identifying associated carbon savings. When the DBP Certification Scheme has been finalised it will validate that testing on the biodegradable materials involved has been approved.

These schemes effectively validate that whichever solution you choose – collection and recycling or delayed biodegradation – it is independently checked so that it fulfils the intended purposes of –

  • Increased tree robustness(survivability)
  • More tree production (yield)
  • Less plastic pollution (environmental impact)
  • Increased carbon sequestration (climate mitigation)


Our development of the Delayed Biodegradation Products Certification is ongoing, but we have learned much though the discussions we’ve had.

On one side we have the ‘single-use plastic’ camp, who champion delayed biodegradation as an answer to plastic pollution for both land and water.

On the other we have highly experienced tree producers, with managed tree production and collection of tree shelters, utilising a plastic product that has been effectively guarding trees since the 1970’s.

What for myself started as ‘let’s come up with scheme to stop plastic tree guards strangling trees’ has become an unexpected journey of application and learning. From biodegradability, to accelerated weathering and eco-toxicity testing, to the circularity principles of the R-ladder and Biological nutrient cycles.

The expertise of the Technical Advisory Group have effectively challenged the scheme’s development, with the ‘system nerds’, ‘lab boffins’ and the ‘tree people’ learning each other’s ‘language’, coming together to understand and develop a robust approach to validating those who choose to create delayed biodegradable materials.

The solutions of reduction, reuse and recycle, or delayed biodegradation are a classic example of ‘what works for one person might not work for another’.

Choosing the appropriate solution that works for both your operation, and the environment, has to be the way forward. Regardless of if your motives are commercial, carbon based, or recreational ‘shinrin yoku’, there is one thing for sure – there’s going to be a lot of trees that need protecting!

SCG : Sustainable Certifications Group develops Certification Schemes to assure the sustainability of materials and products, whilst identifying low carbon savings.

Our sustainability focused Certification Schemes support recyclers, manufacturers and brand owners to certify low-carbon material choices and their environmental impacts across the supply chain. This provides evidence for retailers to validate the environmental claims of the products they sell to an increasingly demanding and challenging marketplace (avoiding ‘greenwashing’), whilst effectively supporting  the route to ‘net-zero’

If you would like to know more, or to discuss one of our Certification Schemes with you, please visit our website –