Which trees can take a flood?
When city streets flood, the trees standing in the water are not all equal. In a summer-long experiment, researchers flooded 16 tree species for 3 or 10 days and watched what happened — during the flood and after. The differences were dramatic, and the usual way of judging a tree's toughness turned out to be a poor guide.
Why this matters
Cities are planting more trees to cool streets, soak up stormwater and clean the air. But climate change is bringing heavier rain and more urban flooding, and compacted soil and paving trap water exactly where trees grow. A tree that drowns is a wasted investment — and because many cities plant only a handful of species, one wrong choice gets repeated street after street.
The advice available to city planners is mostly based on experience from other climates and from natural floodplains — not on how trees handle the short, sudden floods that are typical of cities. This study tested exactly that.
The experiment
281 young potted trees of 16 broadleaf species — six native to northern Europe, ten from other regions — spent the summer outdoors at a commercial nursery in south-west Sweden. They were split into three groups: well-watered controls, a 3-day flood and a 10-day flood. The flooding was simple and close to the urban reality: the pots were placed in water until the water sat above the soil.
- Before. Every tree was measured: how fast it photosynthesised, how open its leaf pores were, the health of its light-harvesting machinery, and more.
- Flood. In August 2023, the pots stood in water for 3 or 10 days while the controls were watered normally.
- Recovery. The pots were drained and watered normally for 16 days — the moment of truth for a tree's ability to bounce back.
- Final check. Everything was measured again and compared with the unflooded control trees.
The team also measured 12 standard tree traits on the healthy control trees — things like wood density, leaf size and root-to-shoot ratio — to test whether such traits can predict which species will struggle with flooding.
What they found
3 days: most trees coped
Only hop hornbeam was clearly damaged by the short flood. Wild cherry's photosynthesis dipped and stayed down, and common hackberry also lagged after recovery. For everyone else, three days underwater left little trace.
10 days: the field split
Photosynthesis fell in 10 of the 16 species, and was still down after recovery in seven of them. Vitality dropped in six species, and tulip tree and hop hornbeam lost leaves.
Recovery made the difference
Norway maple, silver maple, sweetgum and small-leaved lime regained photosynthesis during recovery. Tulip tree, hop hornbeam and wild cherry stayed damaged, with combined performance scores below 0.5 — against 1.0 for untouched trees.
Traits couldn't predict it
Wood density, leaf size, root-to-shoot ratio and nine other standard traits showed only weak links to flooding sensitivity. A statistical analysis found no groups of sensitive or tolerant species — the crystal ball was cloudy.
The headline: for flood-prone city sites, how well a tree recovers from a short flood matters as much as how well it survives one — and you cannot read that from the usual trait measurements alone.
Explore this site
The 16 trees
Meet every species, see its photo, and read how it fared. See the trees
Results explained
What photosynthesis, Fv/Fm, vitality and the rest actually mean — with the paper's figures in plain language. Understand the results
What it all means
The authors' conclusions, practical advice for city planting, and the honest limits of the study. Read the conclusion
Pixel art
The whole experiment as one giant pixel-art scene: all 16 trees and the research team measuring them. See the pixel art
The study
This site is a plain-language summary of an open-access study led by Astrid Fridell at the University of Gothenburg:
Fridell, A., Sjöman, H., Uddling, J., Klingberg, J., Gärdenäs, A. I., Labastida Jaimes, D. L., Asplund, I., Benedet, S., & Tarvainen, L. (2026). Identifying trees for flood-prone urban sites: Interspecific variation in flooding sensitivity under controlled conditions was not predicted by measured functional traits. Urban Forestry & Urban Greening 125, 129674. Read the original (free)
Published open access under CC BY 4.0. Tree photos on this site come from Wikimedia Commons under their respective licenses (credited on the trees page); the paper's figures are reused under CC BY 4.0.