Half the saplings Trees for Cities planted in London died in this summer's heat and drought

Kew's collection holds 11,000 trees ^[1], so Martin's estimate of at least 400 deaths comes to about 3.6 per cent ^[1]. That is his estimate for the season. It equals the 2022 record but does not pass it ^[2]. The losses followed successive heatwaves and a severe drought, and stressed trees dropped their leaves early to survive ^[4].

The sharper number comes from the young trees. Trees for Cities says half the saplings it planted in London over the past year died this summer ^[6]. In a normal year 80 to 90 per cent survive ^[7]. That puts the usual loss at 10 to 20 per cent, and this summer's at 2.5 to 5 times that ^[2]. The charity did not say how many saplings that half represents. "I've never seen anything like it," said Georgie Power of Trees for Cities ^[8].

This summer's evidence points at young trees more than old ones. City trees deal with hotter air, pollution and compacted soil on top of the drought. According to the New Scientist report, mature city trees are more resilient, while younger ones are in dire straits ^[5]. At Kew, Martin singled out common beech. "I'd be surprised if I've got any common beech left in this garden, because they are all very, very poorly. Because they can't deal with the heat," he said ^[3]. He expects the older trees to follow over the coming decades. "I think we will see quite a few mature trees that will have a big impact on our landscapes disappear," he said ^[17].

The case for planting different species rests on modelling that Martin's team published in November 2025 ^[15]. The model uses the climate forecast for London in 2090 and assumes continued high greenhouse gas emissions. On that basis, 73 per cent of the city's public trees would die or struggle to thrive ^[15]. Just 0.38 per cent of current trees are rated highly suitable ^[16]. Victorian planners lined the main roads with limes and London planes, and parks and squares hold oaks, birch, cherries and magnolias. New Scientist reports that these trees will not cope with the change ^[14].

Martin said the south-east is moving from a moist, temperate climate to a semi-arid one, with hotter summers and flat rainfall ^[10]. The report says rainfall further north and west will keep pace with rising temperatures ^[13]. "The plants need more water to deal with the heat, but there isn't any more water coming," Martin said ^[11]. "We have to get our mind set that, although we're a small island, we're going to have two very different ecosystems," he said ^[12].

In my view the evidence supports changing species more firmly than it supports a record die-off of established trees. The record is one curator's estimate that ties 2022. The heaviest measured losses were among saplings, at half against about 3.6 per cent of Kew's collection ^[6][1]. The species argument comes with one condition set by the model itself: a high-emissions path to 2090 ^[15].

Sadiq Khan, the mayor, wants more canopy cover ^[18]. Friends of the Earth research credits London's trees with cooling the city by up to 5 degrees C ^[9]. Martin wants the replanting spread over decades so the canopy does not disappear all at once ^[19]. He would also remove some sick older trees before they die. "I do think we are going to have to accept that some of the older trees that are really sickly, we'd be better off moving them out, removing them proactively, then planting the next generation," he said ^[20].