Pruning of Broadleaf Trees in the UAE

Split branch in mature ghaf, fallen int its neighbour

I have said elsewhere that the landscapes of Dubai and Abu Dhabi are growing (no pun intended) at an extraordinary rate and that the knowledge and skills needed to care for the landscapes as they mature are not keeping pace.  This is especially true when it comes to trees.

Palm trees are familiar to the region as a crop tree; they are tough, easy to move without too much worry and of simple form which does not necessitate any complex pruning.  Broadleaf trees however, demand more than the crude lopping they are so often subject to, especially in urban spaces where there are issues of health and safety.  Bad pruning, but also lack of pruning can lead to dangerous conditions.

The following two pictures show dangers from no pruning care taken:

Delonix split branch
Lack of awareness – split Delonix branch over public path. Here, lack of any pruning leads to a potential danger to the public.
Years of neglect for these trees
A fallen Albizia tangled into a Ficus – caused by years of neglect

Often a tree’s lifespan and health are determined even before they are planted on a site. Many problems come from lack of formative pruning right at the nursery stage and roots may be damaged during lifting or potting on.

Poor care at the nursery stage has caused significant damage
Poor care at the nursery stage has caused significant damage. The tree may never regain its health or vigour.
Lack of care and attention in the nursery has damaged these trees for life
Lack of care and attention in the nursery has damaged these trees; pruning to correct poor shape is easy if done when very young, difficult to correct in trees like these (removing one of the co-dominant stems in the left picture will unbalance the tree, leaving it will ensure future failure). Such faults left in the tree, however,  may be impossible to alter as it matures.  It doesn’t need training to know that you remove tree-ties before they get trapped.

So many trees are off to a poor start before they are even planted but once they are, environmental factors will kick in.  How well they are planted and irrigated will effect their health.  Assuming they survive and grow (and the average life-span of a UK planted urban tree is less than 10 years) then they have to cope with the occasional pruning that they are given and the damage that this may cause.

We have to understand that trees never heal.  They survive damage by a process of isolation, or compartmentalisation, whereby cells surrounding damage isolate this area from the remaining areas of the tree.  Unfortunately, bad pruning tends to rip right through these natural defenses, opening up the tree to infection and decay.  Key to this is understanding the correct and   way to place cuts.  Here’s how you DON’T do it:

Stubs with tears on a Delonix caused by incorrect pruning methods
Stubs with tears on a Delonix caused by incorrect pruning methods. Tears have ripped through the collar.
Incorrect pruning has torn through the collar and the natural defense mechanism of this ghaf
Incorrect pruning has torn through the collar and the natural defense mechanism of this ghaf
These may "only" be damas trees (and best not planted) but this is still a terrible abuse
These may “only” be damas trees (and best not planted) but this is still a terrible abuse. Excuse the poor photo, snapped in Abu Dhabi.

All these abuses and bad practices can be seen anywhere in the world, even in the UK which has a thriving profession of arboriculture.  Trees in hot climates are critical, however, to the health of people and the city overall.  As the landscapes of our modern cities and mega-cities continue to grow, and the effects of climate change become more severe, we need to look after our trees – everywhere – to a much higher standard than our current levels.

Trees deserve our respect – and our thoughtful care.  More, they deserve active and knowledgeable management and the correct level of arboricultural skill and care to ensure they thrive and serve us, and our built environments, as best they can.  The more we give, the more we get back.

Irrigation of Native and Exotic Trees in Arid Climates

This article first appeared in Pro Landscaper Gulf.   It is based on tree consultancy work I have undertaken in Abu Dhabi in recent years.


Irrigation is taken as a necessity when landscaping in arid climates.  It is a view that I wouldn’t like to completely contradict, yet I have seen a fair bit of evidence that tells me many plantings, and trees especially, are over-watered.  Of equal importance is the fact that many of the irrigation methods are wasteful of water and sometimes damaging to the trees themselves.

 

Tree sprinkler damage

Lawn Watering with sprinklers is damaging the trunk of this Millingtonia

 

We have to discern the different needs of trees and understand that what is necessary for one species is overkill for another.  I particularly speak of natives verses exotics.  Ghaf and Sidr you will see growing wild and without irrigation but imported exotics need a regular supply.  I have seen Ghaf blown over in irrigated plantings, caused by shallow rooting from an easy water supply.

Bacterial wetrot in Delonix

Bacterial wetwood in Delonix regia caused by overwatering. It also reduces the flowering, for which these trees are famous.

How the water is put on is just as important; pop-up sprinklers in lawns can damage the trunks of trees, causing aerial rooting in species like palm or fig, discolouring bark and causing stress-induced rots to occur in others.  Exotics like the Flame tree (Delonix regia) get over-watered, causing a reduction in flowering and a susceptibility to bacterial wetwood (slime flux). Even drip irrigation is not ideal, as it applies the water at the surface and promotes shallow rooting.  Trees with shallow roots are vulnerable to drought and so dependent upon the irrigation supply – a vicious circle.

Excess surface irrigation is wasteful.

Excess surface irrigation is wasteful.

In the UK, we are used to putting in a subterranean irrigation ring around trees, which gets water to the tree roots at a deeper level.  For watering established trees, perforated tubes can be utilised, inserted vertically throughout the root zone and either manually watered, or connected to standard irrigation systems.  Supplying water at a slightly deeper level means less water used and wasted. A word of warning though – most feeding roots occur in the top 300 – 500mm of soil, so watering too deeply can also be wasteful.

Tree roots growing along the line of irrigation pipes

Tree roots growing along the line of surface irrigation pipes

In coastal cities, problems can arise from a naturally high-level, saline water table.  Halophytes (salt tolerant plants) have evolved to cope with this, but for some imported species, salinity can be a problem.  You also have to be aware of the quality of the irrigation water itself, which if drawn from the ground, may have a high saline content. Get your water supply tested if you are unsure.

 

Ultimately, I believe that planting styles and expectations of “landscape” must change.  A more natural style, with more xeriscaping and use of natives or other arid loving plants from different parts of the world (but from similar conditions), will emerge.  More important, in my view, than using strictly native species, is building plant communities that function and thrive in place without much human care or maintenance.  As climate zones shift rapidly around the world, nature cannot keep up and it will be down to us to create landscapes that sit well in their altered environments, whether native or not.  I believe we can do this with considerably less use of irrigation.  The water we do use should then be grey water (from taps and sinks), which is a much better way to conserve processed water use.

Canopy of Delonix regia

Canopy of Delonix regia

The goal has to be minimal water use, natural, ecologically benign planting and urban environments which feed our biophilic needs for connection to nature.

Zizyphus spina-christi

Zizyphus spina-christi, crown of thorns tree. A native of the UAE