🌳 Flood-tolerant city trees

The 16 trees and how they fared

Sixteen broadleaf species — six native to northern Europe and ten from elsewhere — were flooded for 3 or 10 days and compared with well-watered control trees.

The badge on each card shows how the tree coped. After 10 days of flooding, each tree got a combined performance score (SPI, 1.0 = same as unflooded): Coped well 0.75–1; Moderately affected 0.5–0.75; Strongly affected below 0.5.

Norway maple (Acer platanoides)

Norway maple

Acer platanoides Native Moderately sensitive

Photosynthesis dipped during the 10-day flood but rose again during recovery — a quick bounce-back.

Coped well SPI 0.75–1

Silver maple (Acer saccharinum)

Silver maple

Acer saccharinum Eastern North America Moderately tolerant

Among the least affected of all 16 species. Photosynthesis and pore openness rose during recovery, and the leaf-machinery measure (Fv/Fm) dipped at the end of the 10-day flood but fully recovered.

Coped well SPI 0.75–1

Silver birch (Betula pendula)

Silver birch

Betula pendula Native Sensitive

Coped well overall. The only sign of stress was lower leaf water potential after recovery from the 10-day flood.

Coped well SPI 0.75–1

European hornbeam (Carpinus betulus)

European hornbeam

Carpinus betulus Native Sensitive

Coped well, with no significant declines reported.

Coped well SPI 0.75–1

Common hackberry (Celtis occidentalis)

Common hackberry

Celtis occidentalis North-eastern and central North America Moderately sensitive

Photosynthesis fell after recovery from the 3-day flood. After the 10-day flood, photosynthesis, pores and leaf machinery were all still reduced after recovery — delayed damage.

Moderately affected SPI 0.5–0.75

Goldenrain tree (Koelreuteria paniculata)

Goldenrain tree

Koelreuteria paniculata Northern and central China Sensitive

Leaf machinery (Fv/Fm) fell by the end of the 10-day flood but recovered. Leaf nitrogen fell, without a drop in photosynthesis.

Moderately affected SPI 0.5–0.75

Sweetgum (Liquidambar styraciflua)

Sweetgum

Liquidambar styraciflua North and central America Moderately tolerant

Among the least affected; photosynthesis and pore openness rose during recovery.

Coped well SPI 0.75–1

Tulip tree (Liriodendron tulipifera)

Tulip tree

Liriodendron tulipifera North America Sensitive

Hard hit: leaf machinery was still damaged after recovery from the 10-day flood, and vitality dropped with leaves lost.

Strongly affected SPI below 0.5

Kobus magnolia (Magnolia kobus)

Kobus magnolia

Magnolia kobus Japan Moderately sensitive

Delayed damage: leaf machinery fell only after recovery, leaf nitrogen dropped, and vitality declined.

Moderately affected SPI 0.5–0.75

Black tupelo (Nyssa sylvatica)

Black tupelo

Nyssa sylvatica North and central America Moderately sensitive

Coped well, with no significant declines reported.

Coped well SPI 0.75–1

Hop hornbeam (Ostrya carpinifolia)

Hop hornbeam

Ostrya carpinifolia Southern Europe, Balkans and Caucasus Sensitive

The most sensitive species in the study: the only one clearly hurt by just 3 days of flooding — photosynthesis, pores, vitality, leaf loss and leaf water potential were all affected. After the 10-day flood, leaf machinery was still damaged after recovery.

Strongly affected SPI below 0.5

Wild cherry (Prunus avium)

Wild cherry

Prunus avium Native Sensitive

Hurt by both treatments: photosynthesis and pores were down after 3 days and still down after recovery from 10 days; leaf machinery fell after recovery and leaf nitrogen dropped.

Strongly affected SPI below 0.5

Swedish whitebeam (Sorbus intermedia)

Swedish whitebeam

Sorbus intermedia Native Sensitive

Leaf nitrogen fell after the 10-day flood without a photosynthesis drop; coped well overall.

Coped well SPI 0.75–1

Service tree of Fontainebleau (Sorbus latifolia)

Service tree of Fontainebleau

Sorbus latifolia Central Europe Sensitive

Vitality and leaf nitrogen were down after the 10-day flood.

Moderately affected SPI 0.5–0.75

Wild service tree (Sorbus torminalis)

Wild service tree

Sorbus torminalis Central and southern Europe Sensitive

Coped well, with no significant declines reported.

Coped well SPI 0.75–1

Small-leaved lime (Tilia cordata)

Small-leaved lime

Tilia cordata Native Sensitive

Photosynthesis and pore openness rose during recovery — a quick bounce-back; coped well.

Coped well SPI 0.75–1

Summary table

Tree Native to Expected flooding tolerance Performance after 10-day flood
Norway maple Northern Europe Moderately sensitive Coped well
Silver maple Eastern North America Moderately tolerant Coped well
Silver birch Northern Europe Sensitive Coped well
European hornbeam Northern Europe Sensitive Coped well
Common hackberry North-eastern and central North America Moderately sensitive Moderately affected
Goldenrain tree Northern and central China Sensitive Moderately affected
Sweetgum North and central America Moderately tolerant Coped well
Tulip tree North America Sensitive Strongly affected
Kobus magnolia Japan Moderately sensitive Moderately affected
Black tupelo North and central America Moderately sensitive Coped well
Hop hornbeam Southern Europe, Balkans and Caucasus Sensitive Strongly affected
Wild cherry Northern Europe Sensitive Strongly affected
Swedish whitebeam Northern Europe Sensitive Coped well
Service tree of Fontainebleau Central Europe Sensitive Moderately affected
Wild service tree Central and southern Europe Sensitive Coped well
Small-leaved lime Northern Europe Sensitive Coped well

Photo credits

The tree photos are illustrative images of each species from Wikimedia Commons (not the experimental trees). They are shown under the licenses listed; click a file name to see the original and the full license terms.