Global commitments to tree planting have surged in response to the climate and biodiversity crises, bringing closer attention to the practices of the tree planting industry. Given that the UK government is currently missing its tree planting target of 30 million trees per year by 86%, the pressure to improve this figure is intensifying. Concerns have been raised regarding the capacity of the industry to meet these targets, with bottlenecks arising from limited tree planter availability and shortages in sapling supply from nurseries. These challenges exacerbate the missed planting targets and highlight the critical importance of ensuring the survival of each planted sapling, making protection from herbivore damage imperative.
Plastic tree shelters offer numerous benefits for saplings. However, historically, these shelters have either been left uncollected or disposed of in landfills, contributing to the proliferation of discarded plastic tubes in the environment. A recent initiative by a tree shelter manufacturer aims to address this issue by implementing a straightforward recycling program to incentivize tube collection. Additionally, biodegradable tree tubes are now widely available at scale, using a variety of materials from sheep wool to cardboard. A recent study suggested that tree shelters could potentially be circumvented altogether to mitigate the carbon footprint of tree planting and eliminate plastic pollution. With increasing efforts to reduce plastic usage, does the argument for employing plastic tree shelters still hold? Can recycling serve as an effective means to both reduce plastic waste and enhance sapling survival rates?
Why do we use tree shelters?
The primary purpose of tree shelters is to protect growing saplings from browsing animals such as deer, rabbits, and voles. A recent report indicated that 40% of woodland is in poor condition due to herbivore damage, and the deer population is increasing every year, putting more pressure on growing saplings. There has been an explosion in deer numbers as a result of reduced demand for venison, particularly during the Coronavirus pandemic, so browsing pressure is set to increase even further. Deer browsing not only reduces seedling density but also hampers the growth of surviving saplings, affecting both the height and shape of trees and the speed of forest regeneration. The economic costs associated with deer management and preventive measures can be considerable and reached £8.7 million between 2018 and 2019 in Scotland alone.
There are a number of ways to prevent deer browsing, including culling, fencing, encouraging weed growth, and using individual tree shelters. Tree shelters offer significant advantages over other methods by protecting the saplings from other mammals in addition to deer. They have been shown to significantly enhance sapling survival rates, with protected trees exhibiting survival rates ranging from 67 to 100% compared to unprotected tree survival rates of 2-90%. The shelters do need to be of sufficient height to protect the trees and taller tree shelters can eliminate deer browsing altogether. In a recent meta-analysis of how to reduce deer browsing and increase sapling growth, tree shelters came in third place behind fencing and cages, both of which are more expensive than tree tube protection. Tree shelters also provide protection against land operations such as mechanical weeding and the application of herbicides or pesticides.
Originally intended for species like oak that have slower establishment rates, tree shelters are now commonly used for a wide range of species. One of their unique attributes is the creation of a microclimate within the shelter, which accelerates tree growth. Light, heat, carbon dioxide, and moisture interact within the shelter to regulate photosynthesis, respiration, and transpiration, providing the ideal microclimate, which can significantly increase the height of saplings. While this accelerates above-ground growth, it may potentially hinder the development of extensive root structures below ground.
Alternatives to tree shelters
Several alternatives to plastic tree shelters exist to protect trees from herbivore browsing or rubbing damage. These include biodegradable shelters made from materials such as wool, cardboard, and plant-based materials, which are currently undergoing extensive testing. However, many of these alternatives still require removal as they will degrade in situ, leaving debris, or because they require industrial composting to break down. They also lack the microclimate benefits associated with polypropylene shelters, which promote accelerated tree growth.
Other alternatives include fencing, which also protects woodland ground flora but can be costly and less economically viable for smaller plots of land. A recent study found that fencing is the most effective method for reducing deer browsing and enhancing sapling survival, but it does not exclude other herbivores like voles and rabbits. Planting techniques, such as the Miyawaki Method can also reduce deer damage, as saplings are planted very densely and deer cannot access them. Allowing weed growth between seedlings is another technique that can protect the trees although that can increase vole numbers and damage. Tree shelters are the only option that protects the trees against all browsing species.
Recycling tree shelters
The biggest drawback of traditional polypropylene tree shelters is the significant portion that remains uncollected or ends up discarded in the environment, littering the countryside with plastic. An estimated 13 million tree shelters are used annually in the UK alone and while some contain recycled plastic, each tube has a manufacturing carbon footprint of 0.44kg CO2. A recent life cycle analysis study recommended avoiding tree shelters altogether due to the environmental impact caused by degrading plastics left onsite. Even if collected and recycled, the brittle nature of polypropylene plastic can result in microplastic particle residue. The study concluded, however, that tree shelters are essential in certain circumstances, and that polypropylene tubes can have a lower environmental impact than those made from biodegradable materials due to manufacturing processes. The preferred option of the researchers was replacing trees rather than trying to protect them, although this does constitute additional pressure on the tree supply chain.
It is essential to retrieve and recycle tree tubes to minimise their environmental impact and prevent plastic pollution. Initiatives like the Tubex collection scheme facilitate the collection and recycling of used tubes, reducing plastic waste, and closing the manufacturing loop. The schemes need to be scaled up, however, as of the 13 million tree shelters used annually only 150 thousand were recycled in 2021. The Tubex collection scheme arranges for the collection of tubes once they have been used or can arrange drop offs at a series of collection hubs. Polypropylene tubes can be recycled even after 8 to 10 years onsite, making them an excellent option for long-term tree protection. The tubes are processed into pellets and then repurposed into new tree shelters or other products.
What changes are needed to facilitate more tree shelter recycling?
Recycling plastic tree shelters is vital for minimizing their environmental impact and enabling forest creation schemes to benefit from their increased sapling survival rates without contributing to plastic pollution. Government woodland creation grant schemes typically mandate the removal of individual tree protection after 10 to 15 years, yet there is no requirement for recycling or additional provision for recycling costs. Including provisions for recycling costs in grant schemes would incentivize applicants to incorporate recycling into their projects, thereby reducing the environmental footprint of plastic tree shelters.
While optimised recycling schemes exist, the process of tube removal can be laborious and challenging. Considering additional costs for labour in tube removal, particularly in inaccessible areas, may further incentivize recycling efforts.
Plastic tree shelters remain an indispensable tool for woodland creation, but their retrieval and recycling are crucial for minimising environmental impact. The forestry industry should advocate for government support to integrate recycling provisions into grant schemes, ensuring responsible and sustainable tree planting practices.
