Wind- and Dust-Resilient Trees in Iran: From Zabol to Tehran

Spring gales, the dust of Khuzestan, the 120-day winds of Sistan and the wind channels between Tehran's towers bring trees down every year. A tree planted for quick shade and never structurally pruned behaves like a sail in those flows. Resilience means the right species, roots in enough soil, a crown with one clear framework, and soil moisture before the windy days. Farkesht has felt this repeatedly in industrial landscaping east of Isfahan and in the open compounds of Yazd: a good tree is quiet in the wind, a bad one becomes a story.

Understand Iran's wind by its local pattern

The 120-day wind blows from the Afghan side into Zabol and the Sistan plain: dry, dust-laden and persistent. Ahvaz and Abadan more often meet gales carrying dust and sometimes humidity. Yazd has wind channelled between walls and sunken courtyards. Tehran combines a westerly, the channelling of north-south streets, and the pressure on trees behind a tower. A planting design has to see the prevailing wind direction, the hard surfaces around, and the distance to the façade. A wall of identical trees, all the same height and planted at once, behaves like dominoes in the first gale. Mixing heights, spacings and species with permeable crowns spreads the load.

Choose the species for wind and dust, not for the catalogue

• In Sistan and around Zabol, native species adapted to drought and salinity, with relatively open crowns, work better than a thirsty, heavy plane tree.
• In Ahvaz, avoid trees with broad, succulent leaves and shallow roots in an open compound with no windbreak; plan alongside date palm and mesquite rather than instead of them.
• In Yazd and Kashan, Mediterranean cypress, wild pistachio and undemanding species under light pruning break less often than an unpruned, overgrown Lombardy poplar.
• In Tehran, keep plane and pine only where soil and water are sufficient; on a narrow median in a wind tunnel, a smaller species with a stronger framework makes more sense.

Besides the mechanical wind, dust blocks the stomata and reduces photosynthesis. After a dust event, a gentle wash of the crown in the cool hours helps if the water is not saline, but the priority is keeping the roots alive. A tree whose soil was completely dry before the wind has a root plate that behaves like a light pot and lifts. A tree with moist soil at root depth has far more friction with the ground.

Structural pruning instead of topping

Topping the crown to reduce wind load in practice builds a weak sail: whippy shoots grow from the cut, their attachment is poor, and in the next wind they break off in bunches. The right way is to reduce the weight at the ends of long branches, keep one clear leader or framework, and open the crown so that wind passes through the branches rather than pushing against a single sheet of foliage. This work belongs before the windy season, not the day after the damage. In Zabol and Ahvaz the window for structural pruning is usually late autumn and winter, so the wound is not left open in the peak of heat and dust.

Root space, staking and soil before the wind

A tree in a thirty-centimetre median or a bed boxed in with stone has no anchor roots, however tough the species. At a minimum, give it uncompacted, permeable soil to a radius several times the trunk diameter. Do not tie a sapling to a single stake against the trunk; two stakes outside the root mass, with a broad strap and a little free movement, build a strong trunk. Take the stakes off after one or two seasons once the roots have taken. A permanent stake means the tree never builds its own trunk, and when the tie rots it breaks in the first gale. Mulch on the surface reduces evaporation and stops the surface soil turning into drifting powder.

Set the soil moisture before the weather warning

When the forecast announces a gale or a dust event, a surface watering of the lawn that same day does the tree little good. If a deep irrigation under the canopy was done two or three days earlier, the soil profile is heavier and more cohesive. In the salinity of Ahvaz and Yazd, apply enough volume for a little leaching but without flooding the collar. After the wind, look at the tree from the side opposite the lean: if the soil has a crescent crack or the roots have parted from the ground, do not fix it with three spadefuls of soil; assess the stability.

In an open factory or school compound, a windbreak row of tough species on the windward side lowers the pressure downwind for the shade trees. The spacing and permeability of the windbreak matter; a completely closed wall throws the flow over and around it and sometimes shakes the tree behind it harder. After a dust event, do not wash coated leaves with a very high-pressure jet, or the tissue is injured. If the trunk carries an old wound, that point is the first place to fail in a gale and should be checked before the windy season.

If you want to carry one instruction from Zabol to Tehran, it is this: choose the species by the prevailing wind and the water you have, plant a small sapling correctly, stake it properly for two years, correct the framework every winter, and moisten the soil deeply before the windy season. If a municipality or a client buys nothing but a number of trees, they buy that same number again after the first gale. Resilience costs less than replanting, provided the wind path was thought about from day one. In Zabol, after weeks of continuous wind, do not mistake abraded foliage for root dieback; look first at deep moisture and at the health of the collar. In Tehran behind new towers, the wind channel changes from year to year, and a tree that has stood quietly for five years may suddenly break after the neighbouring building goes up. At that moment review the distance to the façade and the need for reduction pruning again, rather than immediately cutting the whole crown.