Evaluation of the success of urban tree planting in England between 2012 and 2022

Daisy Brasington, Kieron Doick and Jon Banks

Government-backed and new development planting programmes frequently aim to improve the local environment, support climate change adaptation and increase the delivery of ecosystem service benefits from trees to society. The long-term success of these planting schemes is essential to providing these benefits but is seldom investigated or publicised.

Management practices can significantly affect tree establishment, yet only 37% of tree strategies reviewed in 2018 mentioned planting and establishment protocols and just 14% required compliance with BS 8545 (Hand et al., 2022). Furthermore, and anecdotally, there appears to be a widespread and systematic absence of planting aftercare to support trees to establishment.

The research summarised here – and funded by Fund4Trees – evaluates grant- funding-led and development-led tree planting completed between 2012 and 2022. It investigates 820 individual planting locations at 48 sites across four cities: Bristol, Birmingham, Nottingham and Leeds. This is the first time research which retrospectively investigates the survival and condition of multiple cohorts of recently planted trees across different cities has been carried out.

The objectives of the project included:

• determining whether specified cohorts of trees from each funding source had actually been planted;
• determining whether the planted trees had survived; and
• using structured observations to systematically describe the tree, the site, how planting was carried out and post-planting maintenance characteristics.

The trees were surveyed using an adapted version of the Planted Tree Re-Inventory Protocol, developed by the Bloomington Urban Forest Research Group, which was specifically designed to measure factors which influence tree establishment in the urban environment.

The 820 individual planting locations were surveyed between June and August 2024.

Key findings

Regarding the delivery of approved development proposals, 23% of trees specified were found not to have been planted at all. It was not consistently possible to investigate the delivery of the grant-funding-led trees in the same way due to data availability. However, in one city where proposed planting plans were available, 42% of proposed Urban Tree Challenge Fund trees appeared not to have been planted in the locations specified.

Of the 687 trees which were planted, 79% survived. However, just 42% were found growing in good condition (the highest condition rating). 21% of development-led trees and 20% of grant-funding-led trees were found to have died or been removed at the time of the survey. Development-led trees were significantly more likely to be in poor condition than grant-funding-led trees. Just 3% of the trees planted were found growing ‘unscathed’ at the time of survey (where unscathed is defined as: no dieback, no epicormic shoots, no chlorosis, no lower trunk or other visible damage, a visible root flare, and staked correctly) (Figure 1).

Significantly more development-led trees had crown dieback than grant-funding-led trees (69% and 56% respectively). With dieback grouped into 0%, 1–20% and 20–100% categories, the differences between funding sources were significant in each category. It is unlikely that the trees already expressing over 20% crown dieback (Figure 2) will survive, or if they do, they will not provide a full quantity of ecosystem services due to their reduced condition. Previously, Morin et al. (2012) reported that across five different species, trees expressing over 11% dieback were at significantly increased risk of dying.

Looking at all the trees, those with lower trunk damage, other damage, incorrect staking, no visible root flare, grass at the base of the tree, and/or with visual chlorosis or dieback over 1% were statistically more likely to be in fair or poor condition.

Trees which were incorrectly staked were more likely to have other damage present. Grass under the canopy of the tree was associated with lower trunk damage, and trees with weeds at the base were less likely to have lower trunk damage. These relationships offer evidence of common risk factors that affect establishment success, namely insufficient planting inspection and aftercare provision, coupled with damage sustained in situ post-planting.

Figure 1. Number of trees remaining after filtering for certain conditions.

Figure 2. Crown dieback (total observation n=547; 304 development-led, 243 grant-funding-led).

Based on the findings, the following key considerations should be taken into account prior to planting standard-sized trees in the urban environment:

• Planning – site and species selection, aftercare funding, community engagement, specified monitoring and evaluation mechanism
• Preparation – site and tree preparation on the day of planting (competing vegetation removal, hessian removal, planting depth scrutiny)
• Protection – against predictable forms of damage, within the setting (stem guards, strimmer guards etc.)
• Provision – of water, mulch and long-term maintenance of stakes and guards until established

Common failures

Lower trunk damage, often caused by grass maintenance equipment, was observed regularly during the surveys (image 1). Our findings indicate that trees with grass surrounding the base of the stem are more likely to have poor condition outcomes when compared to those with stems surrounded by bare soil, weeds, organic mulch or a mix of permeable surface types. Trees planted where grass was the predominant ground cover under the canopy were more likely to have lower trunk damage than those with weeds or soil under the canopy.

Trees with weeds surrounding the base of the stem were less likely to have lower trunk damage, and weeds were more prevalent at grant-funding-led planting sites. However, weeds also present a problem for newly planted trees in terms of competition for water and nutrient resources. It was observed that weedkiller use did not necessarily prevent mechanical damage by grass maintenance equipment. Mowing regimes should be checked and, if necessary, amended prior to planting to prevent trees from becoming damaged.

At development-led planting sites, where trees were staked, they were staked incorrectly 74% of the time. Although not quantified, a large proportion of incorrectly staked trees were categorised as such because their stakes had been left in place too long, and occasionally because they had been installed incorrectly with a nail piercing the tree (image 2). Tree staking maintenance had a significant impact on tree condition outcomes; fewer incorrectly staked trees were found in good condition, and incorrectly staked trees were more likely to be in fair condition. All except 34 trees in this survey had been in the ground for more than 2.5 years since planting; according to best practice guidelines, the stakes should have already been removed. If they are left in place for too many years, trees may then need careful weaning from their support structures to prevent leaning or snapping (Patch, 1989).

A lack of visible root flare was associated with poor condition outcomes, and no root flare was visible at 19% of trees observed in this research, indicating they were planted too deep. The high prevalence of epicormic shoots (39% of trees) and dieback in trees from both funding sources indicates the presence of stressors in the environment surrounding the tree. These findings highlight the importance of proper site selection, site preparation and planting technique to reduce unnecessary and avoidable stress.

1. Strimmer damage is common in areas where grass is maintained.

2. Incorrect staking or maintenance.

3. Common protection methods can cause damage if not regularly inspected/maintained.

Annual mortality rates

The annual mortality rate is the percentage of trees lost each year from a particular cohort. It is useful for comparing mortality between planting cohorts of different ages and is based on the percentage remaining at the time of the survey relative to the total number planted and to how long the trees have been planted. The annual mortality rate was calculated for each of the sites, enabling us to calculate the range and the average annual mortality rate for each of the funding sources and each city.

The annual mortality rate was highly variable: for development-led sites it ranged from 0–21%, and for grant-funding-led trees from 0–100%. The average annual mortality rate for development-led sites was 5%, and the average annual mortality rate for grant-funding-led planting was 7%. However, these results were very sensitive to the incorporation of one grant-funding-led site (comprised of just four planted trees) which had a 100% mortality rate. With this site removed, the annual mortality rate for grant-funding-led sites ranged from 0 to 16%, and the average annual mortality rate for grant-funding-led tree planting was 3%.

If a scenario is imagined in which 20 trees are planted at a new development site, and – on average – 5% are lost each year, then just four trees will remain after 30 years. Recently enacted Biodiversity Net Gain legislation in England now creates a legal requirement for some developments to successfully deliver biodiversity outcomes 30 years after planning permission is granted; some of this is expected to be achieved through new tree planting. The new legislation could lead to an improvement in outcomes for development-led tree planting. However, our research indicates that monitoring and enforcing compliance will be critical if the expectations are to be met. Furthermore, the trees will fail to deliver their intended benefits without an improvement to the post-planting maintenance observed throughout this research.

Condition, survival rates and ecosystem service delivery

The quantity of ecosystem services delivered by an individual tree, such as carbon storage, rainfall interception and air pollution removal, is determined by characteristics including size and condition (Davies et al., 2017; Hand et al., 2022).

The extent of strimmer damage encountered by tree planting organisations in England is not trivial and was cited as a barrier to successful planting outcomes by multiple stakeholders who attended the Tree People conference, hosted by Trees for Cities, in June 2024. Lower trunk damage affected more than half of the trees surveyed for this research and was significantly associated with fair tree condition outcomes. Despite the use of tree guards and tree cages to mitigate strimmer damage and vandalism at some grant-funding-led sites, over half of these were incorrectly installed or maintained, often exacerbating rather than mitigating damage (image 3). High levels of damage by grass management equipment are a global problem; the figures in this study are not dissimilar to the outcomes of research from urban areas in New Zealand, where at least one mechanical damage wound was found on 63% of all surveyed trees (Morgenroth et al., 2015).

The presence of ‘other damage’ (above 45 cm on the trunk) on the surveyed trees was significantly associated with fair and poor condition outcomes. Damage caused by dogs and other forms of vandalism (snapped branches, peeled bark, stripped leaves) were encountered. A resident with a view of a tree at a planting site near a busy children’s play area (where 53% of planted trees had died) stated that the reason the tree in front of their property remained was because they had been regularly intervening to stop children from damaging it.

Financial implications

A study from America demonstrated that trees can be expected to provide an overall increase in annual benefit provision during the 10 years after planting if the annual survival rate is higher than 93% during the establishment period, but with lower annual survival, incremental increases in benefit delivery due to tree growth did not make up for the decrease in benefit due to tree loss (Widney et al., 2016). Similar results were found from investigations in the UK, which looked at break-even and payback points for delivering canopy cover under different growing conditions (GreenBlue Urban, 2018). This research indicates annual mortality rates close to and over these thresholds at some sites. For both funding mechanisms considered here, the investment in tree planting risks failing to reach break-even under the current trajectory of loss.

Conclusion

The survey recorded high levels of physical damage and signs of establishment stress across both planting types, with poorer outcomes overall for development-led planting compared to grant-funding-led planting. The findings reinforce the importance of proper site preparation, planting technique, and regular quality maintenance throughout establishment.

Recommendations

To support trees to establishment and improve return on investment, those planning, planting and maintaining new planted trees should:

• Provide or ensure sufficient revenue funding for multi-season post-planting maintenance in all urban planting schemes, with accountability for successful establishment, not just planting. Address common failures, e.g. eliminate grass surrounding the tree before planting (screefing), remove stakes and ties when required, ensure correct planting depth and adequate quantity and quality of soil, and enforce any required remediations identified by inspections, until the tree is established.
• Require minimum compliance with BS 8545 planting and establishment standards, and utilise standardised post-planting monitoring tools such as the Planted Tree Re-inventory Protocol to assess and report survival and condition.
• Incentivise community engagement in the planting and aftercare of urban trees, especially for projects near private property and parks.

Future evaluation of the trees surveyed during this research is recommended to help evidence the long-term implications of poor establishment practice, including our prognosis for those trees already with greater than 20% dieback.

The full report on this investigation is published on the Fund4Trees website at www.fund4trees.org.uk

Acknowledgements

The authors wish to extend gratitude to all those who spared their time to provide invaluable support and guidance during this project. They include, but are not limited to, Dr Madalena Vaz Monteiro, Carl Lothian, Dr Dean Bell, Sarah Bryce. We would also like to thank Dr Lara Roman and the Bloomington Urban Forest Research Group who developed the Planted Tree Re-inventory Protocol at the Center for the Study of Institutions, Population and Environmental Change at Indiana University. A final and important acknowledgement goes to Fund4Trees, its trustees and its donors.

Daisy Brasington BSc is a freelance professional, often working with Crown Tree Consultancy and Avon Needs Trees. In 2024, Daisy was awarded a grant from Fund4Trees to carry out this research.

Dr Kieron Doick is Head of the Urban Forest Research Group at Forest Research.

Dr Jon Banks is the Research Lab Manager for the UK Bartlett Tree Research Laboratory.

References

Davies, H., Doick, K., Handley, P., O’Brien, L., & Wilson, J. (2017). Delivery of Ecosystem Services by Urban Forests. Forestry Commission, Scotland.

GreenBlue Urban (2018). Street Tree Cost Benefit Analysis. Accessed 9.10.24 via www.treeconomics.co.uk/wp-content/uploads/2018/08/GBU_Street-Tree-Cost-Benefit-Analysis-2018.pdf

Hand, K. L., Rix, H., Stokes, J., & Doick, K. J. (2022). The creation, content and use of urban tree strategies by English local governments. Arboricultural Journal 44(4), 183–207.

Morgenroth, J., Santos, B., & Cadwallader, B. (2015). Conflicts between landscape trees and lawn maintenance equipment – The first look at an urban epidemic. Urban Forestry and Urban Greening 14(4), 1054–1058.

Morin, R. S., Steinman, J., & Randolph, K. C. (2012). Utility of tree crown condition indicators to predict tree survival using remeasured forest inventory and analysis data. In Moving from Status to Trends: Forest Inventory and Analysis Symposium.

Patch, D. (1989). Tree Staking. Arboriculture Research Note 40, The Tree Advice Trust. Accessed 3.6.25 via www.trees.org.uk/Trees.org.uk/files/a5/a57529ea-49b4-4686-99ab-965c1c0475eb.pdf

Widney, S., Fischer, B. C., & Vogt, J. (2016). Tree mortality undercuts ability of tree-planting programs to provide benefits: Results of a three-city study. Forests 7(3).

This article was taken from Issue 210 Autumn 2025 of the ARB Magazine, which is available to view free to members by simply logging in to the website and viewing your profile area.