Avenues of trees are some of the most striking and important structural planting to be found in a designed landscape. In most cases the trees planted in an avenue will be of the same species, so as to give a uniform appearance along the full length of the avenue.

Growing concerns around biosecurity have caused questions around the wisdom of this approach and how best to plant avenues with biosecurity and biodiversity in mind.

Over the last decade, as awareness around biosecurity, plant health and biodiversity has grown, single species avenues of trees have started to be seen as a fairly high-risk approach. Many of our once dependable trees have been hit by pest and disease problems, such as the Elms, our lovely Ash and recently even the majestic Oak.

With the knowledge of this and understanding that our trees may face further problems in the future, it makes sense to try and be as diverse as possible with our species selection.

Mixed Avenue Planting

Mixed avenues are designed with a diverse range of tree species that are complementary in size, form and scale and as such the avenue is still unified. A mixed avenue will be far more robust and reliable and better equipped to face the ecological and climatological realities of today`s world.

A very successful mixed avenue that Hillier supplied was at the Queen Elizabeth Olympic Park, this was designed by LDA Design in collaboration with Hargreaves Associates. Another more recent example of a mixed tree avenue was Sauchiehall Street for Glasgow City Council.

This generation of avenues puts the trees into the heart of the city and the species selected were mixed, all deciduous and designed to complement each other in form and ornamental features.

Pilot Avenues Project in Glasgow City Centre

In 2018, we supported the first project within a £115 million‘Avenues’ transformation programme by Glasgow City Council for the development of Sauchiehall Avenue. This runs from the west of the city into the centre and, prior to the programme was a dominantly traffic-filled area.

The ‘Avenues’ programme is intended to deliver an integrated network of continuous pedestrian and cycle routes across the city centre, making the city more sustainable and economically competitive. When complete, 17 streets and adjacent areas will be transformed, improving the environment and introducing green infrastructure across the city.

The pilot area, Sauchiehall Avenue, had never had trees planted down it before. The brief to Hillier, from Glasgow City Council and landscape contractor idverde, was for trees that would clearly mark out the new cycle route, as well as bringing great benefits to the appearance and environment of the avenue.

While one of the important factors driving tree selection for this project was size, in order to create instant impact, biosecurity and biodiversity were also key. From a biosecurity point of view, the project favoured British-grown trees. And to support biodiversity, the avenue was planned with a mixture of tree species.

Varieties of tree chosen were:

  • Acer campestre ‘William Caldwell’
  • Carpinus betulus ‘fastigiata’
  • Acer platanoides
  • ‘Deborah’ and Gingko biloba

All of these are similar in that they exhibit a fairly upright habit and are tolerant of urban situations, making them ideal for the planting environment and complementary choices for mixed avenue planting. Once selected, all the trees were containerised into Spring Ring or Air-Pot containers at Hillier Container Tree Nursery in Hampshire to give them the best possible chance of successfully establishing when planted on site. Because of the requirement for a three metre clear stem, Hillier carefully raised the canopy on the trees.

This project was commended at the BALI National Landscape Awards 2019, where idverde were an Award Winner within the Soft Landscaping Construction (Non-Domestic) – over £500k category.


Caroline Swann

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