The plane trees of Isfahan's and Tehran's streets do not die of a single pest. Soil compaction, chronic drought, de-icing salt, paving and a wrong choice between injection and soil feeding hollow the tree out.
For centuries the plane tree has shaped the face of the streets of Isfahan, Tehran, Shiraz and parts of Qazvin and Tabriz. Over the past decade, shoot dieback, thin foliage, early leaf fall and the gradual death of individual trees have been reported more often in these same cities. The simple story sometimes heard is that a new pest has arrived. The reality is more complicated. An urban plane tree usually does not die of a single agent; it dies of an accumulation of stresses that suffocate the roots, cut the water and leave the vascular system open to a secondary attack. Without separating those layers, any pesticide and any fertiliser changes only the appearance of one season.
Compaction and paving: roots with no air
Most street plane trees were planted in a strip that was later covered with stone, asphalt or concrete. Surface permeability is near zero, oxygen does not reach the root depth, and rainwater leaves by the gutter instead of infiltrating. Pedestrian traffic and parked cars compact that same narrow band of soil. Plane roots are sensitive to oxygen; in compacted ground the fine root hairs die, and the tree takes up nothing even if it gets a surface watering. Yellowing and thin foliage in this situation are usually not a nutrient shortage but a shortage of active roots. Spreading fertiliser over paving, or tipping it at the foot of the trunk without opening up the soil area, leaves that element on a surface the roots cannot reach.
The soil area of a plane tree should be considered at least as large as the canopy shade, not the size of a cement basin at the foot of the trunk. In pavement improvement projects, if that area is destroyed, the tree may die two to four years later — by which time nobody remembers the construction work. Recording the tree's condition before and after paving is part of urban management that is still not institutionalised in many districts. Isfahan with the old planes of Chaharbagh, and Shiraz with its shaded streets, both face the same conflict: the city wants a hard surface, the tree wants living soil.
Urban drought and salt: two pressures that arrive together
Isfahan and Shiraz have hot summers and high evaporation; Tehran shows the same pattern in low-rainfall years. Landscape irrigation is often irregular, network pressure is low, and an old tree with a large crown receives a smaller share of water than it actually needs. Chronic drought lowers the carbohydrate reserve and prepares the tree for attack by bark beetles and diseases of weakness. In winter, salt is used for de-icing on some streets. That salt goes into the root strip, disturbs the osmotic potential, and shows as marginal leaf scorch the following spring, looking like a potassium deficiency. A wrong diagnosis at this point adds more fertiliser to soil that is already salinised.
- Deep, well-spaced irrigation for an old plane tree is more effective than sprinkling the paving surface daily.
- Saline runoff and air-conditioner water must be blocked from reaching the foot of the tree.
- A soil sample from two depths separates salinity caused by de-icer from a real deficiency.
- A sudden heavy pruning after a dry summer empties the tree's reserves further.
Trunk injection or soil feeding: which for an urban plane?
When the roots are out of reach — complete paving, severe compaction, or the risk of digging into utilities — delivering an element, and in specific cases a systemic fungicide or insecticide, through the vascular route becomes logical. Trunk injection is a shortcut, not a replacement for the soil. If the soil area can be restored, improving permeability, mulching and targeted fertigation are more durable. Repeated injection without repairing the root environment makes the tree dependent on an artificial route and stacks up wounds on the trunk. The decision must be per tree: trunk diameter, bark health, the severity of chlorosis, and whether the soil area can be opened. A single prescription for a long street usually over-treats some of the trees and leaves others untreated.
Pests and diseases are usually secondary
Leaf spot, mildew, mite and bark beetles are all seen on urban plane trees. On a vigorous tree, many of these agents remain at the level of cosmetic damage. On a tree under compaction and drought stress, the same agents turn into decline. Spraying the crown without relieving the root stress raises the cost and sometimes removes the natural enemies as well. Monitoring has to start from the state of the soil and the irrigation, and only then arrive at the pest. If bark beetle galleries are active, sanitation of dead branches and reducing water stress in that same season take priority; a systemic injection is justified only when both the pest population and the value of the tree are high and the soil route is impossible.
Do not feed an urban plane tree with the logic of an orchard, and do not abandon it with the logic of a forest. This tree lives in soil the city built; the treatment has to target that same soil.
For a street of old plane trees, a simple record is enough: trunk diameter, percentage of crown dieback, width of the soil strip, type of surface cover, a history of winter salt, and the date of the last heavy pruning. Those few numbers alone prevent a single contract-wide prescription. If the soil strip is less than a metre wide, first agree with the municipality or the client on opening several permeable patches; without that, injection only holds one season of leaves. On Chaharbagh in Isfahan and the old streets of Shiraz, trees of the same age do not respond the same way, because the utilities beneath each of them differ. A summer visit after the heatwave and an autumn visit after leaf fall are the two annual decision points. Take off the dead branches, but do not lighten the crown all at once.
Plane tree decline in Isfahan, Tehran and Shiraz is less the riddle of a new pathogen than the result of compaction, paving, drought and salt, which bring the pest along behind them. Restoring the soil area, deep irrigation, keeping salt away from the foot of the trunk, and a deliberate choice between injection and the soil route form a reasonable framework. On landscaping projects, Farin Kesht Taban first assesses whether the roots can breathe, and only then turns to elements and injection.
