Revisiting the railway hedges of Hadley Wood

Biodiversity blooming eight years on...

The Tree Council (blue hats) joins Network Rail on a visit to Hadley Wood station in north London

The Tree Council’s science and research team re-visited our railway hedge trials at Hadley Wood station to check in on progress and found a station buzzing with biodiversity. Now in its eighth season of growth, we visited to check in on the hedges, and learn more about how they have integrated into the wider landscape.

Once fairly widespread, the traditional “railway hedge” was replaced with fencing over the years. We wanted to experiment with bringing it back as a way of boosting biodiversity, alongside providing protection for the lineside. We worked with Network Rail and local community groups to establish a series of trial plots on the embankment area at Hadley Wood train station in north London. Trial plots included a traditional technique of planting whips in rows (hawthorn, field maple, dog rose, dogwood and wayfaring tree), seeded plots using three different sowing techniques, and leaving plots to colonise naturally without human intervention.

Read about the trial details and previous observations here:

Eight years later

The original hedge trials have developed significantly. The volunteer-planted trees, in particular, have grown impressively tall (some hawthorn are up to 4.6m metres) and are now flowering and fruiting well. As they continue to mature, we might expect some natural thinning, with the structure shifting from dense hedge to more individual trees, unless actively managed to encourage bushier growth. Pruning the tops of these trees would likely stimulate denser growth closer to the ground, helping to create a more traditional hedge structure.

The contractor-planted trees are also performing well, though they remain approximately one metre shorter than those planted by volunteers.

Volunteer planted trees are creating an overhead canopy

The seeded trial plots—particularly those where seeds were sown approximately 5 cm below the surface—are now thriving. These areas have developed into dense, impenetrable, hedge-like structures and are roughly comparable in height to the contractor-planted plots. They continue to be dominated by hawthorn and dogwood.

Hawthorn and dogwood dominate in seeded plots

Where the initial natural regeneration trials were less successful, two years ago we undertook replanting in partnership with Network Rail and the local community. Two new hedges were established: one with mushroom compost added to improve the heavy clay soil, and one without.

Both hedges are establishing well, though the compost-improved strip is, on average, 60% taller. Adding the compost required trenching, and a precautionary ground scan revealed a potential underground obstruction. As a result, the position of the hedge was adjusted - locals may notice that one strip does not extend fully to the boundary fence, for this reason.

Trees planted with compost (left image foreground) are growing taller than other trees (right image foreground)

With repeated site visits, we’ve been able to observe the changes to these hedges over time. Areas once dominated by bramble now show increased structural and species diversity after 8 years, with planted tree species beginning to emerge more clearly.

Interestingly, what initially appeared to be competition from bramble may have played a protective role, the dense cover it provided likely acted as a nurse layer, sheltering young trees through challenging periods, most notably the 2020 drought. It is worth remembering the old maxim ‘ the thorn is the mother of the oak’.

Field maple thriving in coppiced shade

The joy of scrub

Looking more broadly across the site, biodiversity is recovering from the widespread vegetation clearance eight years ago. Trees have regrown from untreated stumps and a number of characteristic scrub species have established naturally.

This is not woodland, nor is it a direct replacement for the trees that may have once stood here. However, the new area is already providing valuable food resources and habitat for a wide range of species. This developing habitat is currently best described as scrub—a dynamic and often underappreciated habitat type. Unlike formal hedgerows or managed woodland, scrub is often irregular and patchy in distribution. It may include species such as hawthorn, blackthorn, dog rose, bramble, elder, and self-seeded open grown trees like oak, ash, or field maple. These species often establish without being ‘planted’ through natural seed dispersal by birds and mammals.

Peacock butterfly caterpillars

In ecological terms, “scrub” refers to vegetation dominated by shrubby species like hawthorn and blackthorn, young trees and vigorous woody plants like bramble, forming through natural regeneration on previously open ground. It is often thought of as a transitional stage between grassland and mature woodland - but importantly can also persist as a stable habitat in its own right, depending on management, soil, and disturbance regimes.

The structure of ‘scrub’ is usually characterised by a mosaic of plant heights and densities—ranging from low thorny bushes to taller saplings. This creates a complex habitat with lots of ‘edges’ - something described as an “ecotone community”. This structural diversity is one of the reasons scrub supports disproportionately high levels of biodiversity relative to its area.

Scrub can therefore be somewhat analogous to the edge of a woodland —a habitat that typically supports a rich mix of species due to both open and shaded conditions.

This habitat provides valuable pollen and nectar sources for insects such as butterflies and solitary bees, while its dense structure offers nesting and foraging opportunities for birds and small mammals. Scrub also plays an important role in soil protection, helping to stabilise ground and reduce erosion.

Wide vista of site from above the lineside at Hadley Wood station

It is difficult to specifically quantify whether biodiversity at the station has increased or decreased overall, as this was an establishment trial rather than a biodiversity trial, and no formal baseline survey was conducted prior to the original works by Network Rail. Nevertheless, what is very clear is that, in its current scrubby form, the site is supporting a wealth of wildlife; from Whitethroats to Blackcaps, and Peacock butterflies to Jersey Tigers.

Looking ahead, some intervention may be needed if trees pop up from the scrub and develop too close to the railway infrastructure. However, this can be managed selectively and sensitively - avoiding the need for large-scale clearance - maintaining continuity for both wildlife, and the local community.

We love having the opportunity to keep going back to our trial sites to gather data and see how things are progressing.

MORE: Nigel Adams on hedgerow species and planting considerations

Find out more about The Tree Council at treecouncil.org.uk. Sign up to our monthly newsletter The Leaflet, and follow our social accounts: Instagram, TikTok, Facebook, LinkedIn, X/Twitter, YouTube.