Considering the importance of a well-developed tree-planting strategy to improve diversity in the tree population.

AS recently as April 2021, I used these columns to argue the case for tree diversity in urban tree populations. Such diversity creates resilience against the impact of pests and diseases and resistance to the likely impact of climate change. 

Government initiatives at both local and national level have stimulated a focus on tree planting, with demand being higher and more sustained than I have known in a career spanning 40 years or more. With a lead time of between 5 and 7 years necessary to produce a typical 12–14 cm girth street tree (dependent on species and production method), such accelerated demand has produced shortages of trees at the nursery. It is the trees that are produced in smaller numbers which tend to be the trees that are underrepresented in our urban tree populations, yet are those which are most necessary if diversity is to be achieved.

READ MORE: UK Forest Market Report 2021: Another record-breaking year for industry

It is a constant surprise to me that species such as Styphnolobium japonicum, Koelreuteria paniculata, Ostrya carpinifolia and Celtis australis (to name just a few) are rarely used to enhance the populations of our towns and cities. It is true that tree managers are beginning to look at a wider palette only to find the specimens at the nursery have been sold because there were so few of them to start with. Faced with a politically driven tree-planting numbers game – which is well intentioned with a level of investment that is to be commended – managers are invariably having to fall back on the limited palette available, and it is diversity which suffers.

Developments in i-tree Eco have facilitated the use of local authority and other tree inventories to produce i-tree studies with all the features of conventional sample surveys included, without the need for data collection in the field. Several local authorities in the UK have now used their inventories, working with Treeconomics and Kenton Rogers, to produce such studies. These include the London Boroughs of Ealing and Camden, Newcastle City Council and others such as the 10 authorities comprising the Greater Manchester area. 

Forestry Journal: Styphnolobium japonicum, a species rarely used in the UK.Styphnolobium japonicum, a species rarely used in the UK.

Many authorities and other landowners and managers are now looking into using the information to produce tree-planting strategies, but why are such strategies necessary? There are many answers to this question, but one of the most pertinent is that strategic thinking facilitates planning, which enables diversity to be factored in. 

At this moment in time, tree planting is very fashionable with politicians, both national and local, rather belatedly but commendably recognising that trees provide many benefits and are an essential part of urban infrastructure. However, planting targets are often reduced to promises and commitments based on numbers or percentages such as ‘across the country we will plant 22,000 large trees and 28,000 small trees from Thanet to Middlesbrough and Merseyside to Bristol’ (first round of the government’s tree-planting challenge 2020) or ‘we will increase the capital’s tree canopy cover by 10 per cent by 2050’ (Sadiq Khan, London Assembly).

Such aspirations are to be welcomed, but often they are not based on any factual information as to what is there now and any real knowledge as to whether such aspirations are actually achievable or whether the desired benefits, even if they have been identified, can or will ever be achieved. In short, there is rarely any coherent planting strategy in place.

A recent Treeconomics webinar, in conjunction with USA tree care company Davey, focused on the subject. There were over 190 attendees with feedback excellent.

During the webinar it was suggested the tree-planting process should be strategised and the process divided into several interrelated and co-dependent elements. These are:
•    Create a vision: what is wanted based on a thorough understanding of what is there now
•     Set targets and goals which are achievable and deliverable
•     Create an action plan comprising where to plant, what to plant, how to plant, management and maintenance necessary.
•     Monitor and review.
    It was argued that such strategising would offer several advantages:
•     Allow uniformity and planning
•     A clear vision to be articulated
•     Realistic and achievable goals and targets to be set
•     Suitable and appropriate species to be selected
•     Informed planting techniques to be specified and adhered to
•     Programming of appropriate management and maintenance
•     Progress to be monitored and reviewed.

The case study of the London Borough of Islington was discussed where opportunity mapping by ward had been undertaken. Potential planting space had been identified on a ward-by-ward basis, with priority planting areas identified according to a range of indicators such as areas with high pollution, flood potential and existing areas with low canopy cover. Planting can then be strategised to meet the priority needs of Islington.

Forestry Journal: Koelreuteria paniculate – an underused tree.Koelreuteria paniculate – an underused tree.

Such articulated and defined tree-planting strategies allow for new and underused species to be factored into the process and the creation of long-term targets with regard to diversity. The Trees and Design Action Group’s publication ‘Trees in the Hard Landscape’ features a notable case study showcasing the Greater Lyon in France. There, the tree manager Frederick Segur began managing the tree population with a view to diversification. In 1994, Platanus hispanica accounted for 53 per cent of the total tree population, but in 2013 the same species accounted for just 26 per cent. In 2013, over 254 species were growing successfully in the hard landscapes of Lyon, which represented an increase of species used by 69 per cent.

This dramatic diversification exercise was only achieved with clear strategic thinking over time. Such planning produced many other advantages, including the contract growing of trees which would not normally be available in the numbers required at nurseries. 

It is clear that if diversity within our tree populations is to be achieved and is valued, then clear strategic planning of tree planting is a necessity. Such information can then be communicated to politicians, the public and other stakeholders, who ideally should be involved in the entire process, with all parties understanding why planting is taking place, why certain areas have been prioritised, why certain species have been selected and, most importantly, over what timescale goals and targets will be met.

Lack of space prevents a more detailed discussion of the subject in these pages, but further information about tree-planting strategies can be obtained from Kenton Rogers at Treeconomics Further information about contract growing and the advantages it offers can be obtained by emailing me at