Highlights from Spring Northern Meet-ups

Midlands Group

On a glorious sunny day, the Midlands group had the privilege of visiting two private woodlands owned by longstanding Observatree volunteer John Pitcairn. Calling these sites "woodlands" barely does them justice. They are part arboretum, part nature reserve, part scientific experiment and, above all, places of remarkable tranquillity and beauty.

John shared the story behind their creation, from what was once ordinary farmland to a thriving and diverse woodland. The first site sits in the Trent flood plain; the site bears the scars of several major floods (approximately every 10 years) and flash floods from the local drainage ditch. The second site is on the edge of the Trent valley – it is prone to standing surface water in hollows in winter, but it does not flood (Figure 1). Nature has certainly shaped this landscape, but so too have pests and diseases.

Like much of Britain, the woods have suffered extensive losses from ash dieback. Yet amongst the casualties were trees showing encouraging signs of tolerance, offering a small reminder that nature often finds ways to adapt. The diversity of species planted throughout the woodland has also helped create a resilient and fascinating landscape.

One species that particularly caught my attention was Robinia (Robinia pseudoacacia), better known as black locust or false acacia. Native to North America and a member of the pea family (Fabaceae), it is perhaps more familiar in parks than woodlands. Its formidable thorns certainly encouraged us to watch where we were walking!

As expected on a floodplain, alder featured prominently, but this was no ordinary collection. John treated us to an impromptu identification masterclass, demonstrating the different alder species growing on the site and the subtle leaf differences (Figure 2). We also examined several alder trees for symptoms of Phytophthora, a group of destructive water moulds that have been affecting alder populations across Europe for more than three decades. Because the pathogen can travel along rivers, flooding provides an ideal route for their spread, making this site particularly vulnerable. 

Unfortunately, we saw several trees with characteristic ‘bleeds’ or tar spots on the stem (Figure 3). Detecting these pathogens is far from straightforward. Chemicals released by infected plant tissue can interfere with DNA testing, while delays between collecting samples and laboratory analysis reduce the chances of successfully isolating the organism. Although laboratory confirmation would be needed, the field symptoms we observed were highly suggestive of Phytophthora infection.

Another alder pest made an appearance in the form of the alder leaf beetle (Agelastica alni), an attractive metallic-blue beetle whose beauty disguises the considerable damage it can inflict. Once considered extinct in Britain, it has returned with a vengeance and is now becoming increasingly common.

Our tour continued with sycamores affected by sooty bark disease (Figure 4), caused by the fungus Cryptostroma corticale. First recorded in Britain in 1945, it particularly affects trees stressed by prolonged hot, dry summers. With warmer summers becoming increasingly frequent, John commented that the disease has become common on roadside trees in the area. This emerging disease is receiving growing attention from plant health specialists.

The day perfectly illustrated why mentoring events are so valuable. Every tree had a story to tell, and John's knowledge transformed a woodland walk into a fascinating lesson in ecology, tree identification and forest health.

Many thanks to Sue Quick and Paul Gill for organising such an excellent meeting, and especially to John Pitcairn for so generously sharing both his remarkable woodlands and his wealth of knowledge.

Northern England Group

In early May, Sara Spillett and Alex Riley led the Northern England mentoring meeting with visits to Grass Wood Nature Reserve (managed by the Yorkshire Wildlife Trust) and Lower Grass Wood (managed by the Woodland Trust), near Grassington in the Yorkshire Dales. Overlooking the River Wharfe, these beautiful ancient woodlands provided the perfect setting to explore tree health in one of England's most spectacular landscapes.

We began among an impressive stand of mature beech, including one of Sara's Sentinel Trees (Figure 5). It provided an excellent opportunity to discuss long-term monitoring and how repeated observations can reveal subtle changes in tree health over time. Several trees displayed old bleeding cankers consistent with Phytophthora, although the lesions appeared dry and inactive.

The woods also highlighted another growing challenge: deer. Fresh browsing damage was evident throughout the site, and Sara explained how heavy grazing pressure is preventing natural regeneration across large areas of woodland.

As we continued, the list of interesting finds seemed endless. Ring spot symptoms on elm hinted at a possible viral infection before we encountered one of the day's most striking sights — bird cherry almost completely enveloped in silken webbing created by the bird cherry ermine moth (Yponomeuta evonymella). Although dramatic in appearance, these outbreaks have been especially noticeable and common following this year's warm spring.

Passing the sign for the prehistoric settlement at Fort Gregory reminded us that people have shaped this landscape for thousands of years. More sobering, however, was the widespread impact of ash dieback, with extensive areas having already been felled (Figure 6). It served as a stark reminder of the scale of this disease and its lasting impact on Britain's woodlands.

Nearby, we examined spruce showing possible signs of the great spruce bark beetle before crossing into the Yorkshire Wildlife Trust reserve, where further evidence of ash dieback reinforced just how severely the disease has affected the Yorkshire Dales.

One particularly memorable practical demonstration came from Sara, who showed how woven brash can be used to create natural barriers around young trees to prevent deer browsing (Figure 7).

Our thanks go to Sara Spillett and Alex Riley for organising such an informative and enjoyable day. We are already looking forward to the next meet-up.

Like the Midlands visit, the day combined excellent company with a wealth of learning. Observatree meet-ups are about far more than identifying pests and diseases — they are an opportunity to share knowledge, learn from one another and spend time exploring some truly remarkable woodlands.