THE CASEBOOK OF DR. D. R. SLATER - No. 2 - A Bad Start...

Challenges facing car park trees

The car parks around our retail parks and supermarkets could be green oases in our towns and cities if they invested in the provision of greenery.

Establishing good tree cover is particularly important in these acres of tarmac where the surface gets hot, the cars get hot and you get hot lugging your shopping back to your vehicle. Unfortunately, a lack of investment in landscaping is common at present and more needs to be done about this.

At my local supermarket, the pictured multi-stemmed birch (Betula pendula Roth) has been planted between two concrete kerb edges and a pathway – and provided with an inadequate soil volume. The initial consequence of this was that it suffered drought damage and dieback in its first full season (2006).

Revisited 10 years later, this tree has not developed into the ‘green asset’ that one might hope: it is likely to remain at this sort of size, as a bonsai, due to a lack of investment in producing a good planting location. Trees need soil in quantity and quality. Where space seems ample for planting in a retail car park, there is often underground compaction, excess concrete haunching for the kerb edges and very little good quality soil. Much better landscaping specifications are needed as this is no legacy to pass on to future generations.

Wire and trees – no more please!

It is a common error to get trees in contact with steel wire. Wire is so unforgiving a material – and how many arborists have experienced cutting into a tree to find wire occluded inside? I blunted one of my Samurai saws last year with just such an incident.

Pictured are hybrid poplars planted in a park, but with wire ties on a single stake system to support them. This is a mistake as the wire is not flexible, but the trunks of these young trees are, and in 2006 their trunks were already deviating from a straight line by pivoting on the wire.

Revisited in 2018, this whole line of poplars has multiple branches – all arising where the metal ties used to be at c.1.3 metres. It is not a coincidence and they have snapped, been strangled or bent over where they touched the wire as this was the wrong support system for these trees. Establishing young trees is very much about mimicking nature and protection and support systems should be discrete, flexible and ideally biodegradable. For me, steel wire is a no-no.

The lesson here is that you would not use wire to tie two children’s ankles together for a three-legged race so why would you use it to tie a tree to a stake?

Being ribbed

As tree planting technology progresses, are the teams installing it up to date with training? Pictured is a Liquidambar styraciflua L. that was planted in 2010–11 at a supermarket near me. I was walking by at the time, as two landscapers were putting in the root barrier for the planting pit.

“You’re putting that root barrier in the wrong way round,” I said, “the ribs need to go on the inside, the smooth surface on the outside.” They looked at me as if I were a bit strange, told me that they knew what they were doing and carried on installing the thick bit of black plastic the wrong way around.

This heavy standard died back shortly afterwards (as shown left), but is now growing into a reasonable specimen (as shown right). However, with the root barrier installed the wrong way around, won’t the roots just be circling round and round? What seems simple and self-explanatory to some may be confusing to others. Try putting flat-pack furniture together!

Cumbria is not Crete

Going back to trees over 10–12 years later has led to a lot of ‘out-takes’ – many trees now missing, presumed felled. Pictured is an olive (Olea europaea L.) growing in an historic garden in Cumbria.

‘Olives in Cumbria?’ you might ask. Well, that was optimistic planting. Climate change predictions for Cumbria are that it will get ‘a bit warmer’ and ‘a lot wetter’ in the next few decades, but it’s not going to have that dry Mediterranean heat on a regular basis that an olive would want – this summer being the exception. So I was not surprised to find that this tree had been replaced with a whitebeam (Sorbus aria (L.) Crantz) upon my return, 10 years later.

Climate changes are predicted to be gradual rather than dramatic. In 50 years’ time, northern England may have a climate rather like Brittany in France has now and it makes sense to plant accordingly.

Robust adaptable trees of a diverse range of species may be the best way to ‘hedge our bets’, but it’s not time for citrus fruit in Lancashire just yet.

It’s the pits!

This row of pin oaks was planted at the University of Manchester in 2010. By 2014, some were chlorotic and most had crown dieback. Revisiting in 2018, many of these trees have really gone backwards. I’m not surprised – I don’t suppose the planting pit design is up to much probably because of the ‘concrete coffin’ design so favoured by developers. I am regularly surprised, though, by how most members of the public do not really notice these things. They don’t notice when trees are dying, for instance.

I have encountered this ‘lack of tree awareness’ many times. When I used to survey trees for schools, I would say to the headteacher: “OK, so you’ve called me in to look at the dead tree by your front entrance, right?”. And he would reply: “What dead tree?” - even though he must be driving past it every day when coming to work - and it can be seen through his office window. Once you look at trees on a technical level, you observe what most people are oblivious to: dead trees, dying trees, hazardous trees. I used to think this would destroy my enjoyment of the landscape - but now I enjoy spotting the warning signs before they become problems.

*THIS ARTICLE FIRST APPEARED IN PRO-ARB MAGAZINE - JULY 2018*