Identifying trees for flood-prone urban sites: Interspecific variation in flooding sensitivity under controlled conditions was not predicted by measured functional traits

Tree species selection for flood-prone urban areas is an important aspect of urban forests' climate resilience. However, most current knowledge of flooding tolerance comes either from natural stands or long-term experimental studies that may not well reflect responses to the shorter flooding episodes common in urban settings. We examined the sensitivity to, and the ability to recover from, flooding of 16 broadleaf tree species with varying traits, natural habitats, and expected levels of stress tolerance. Young potted trees growing outdoors were exposed to one out of three treatments: control (watered regularly), short flooding (SF; 3 days), or long flooding (LF; 10 days). A variety of ecophysiological, morphological, and structural response variables and traits were measured before and at the end of the flooding periods, and after a 16-day recovery period. Net photosynthesis ( A net ) decreased significantly in two species in response to SF and in ten species in response to LF. Reduced A net and the ability to recover were linked to reduced stomatal conductance and/or maximum quantum efficiency of photosystem II. The vitality response, estimated from wilting and leaf discoloration, also differed significantly among species and treatments. Low vitality was often associated with lower capacity for physiological recovery. While some correlations between the measured functional traits and ecophysiological responses were observed, no clear patterns emerged between trait combinations and species’ flooding sensitivity. When selecting species for urban sites prone to sporadic flooding, the ability to recover from short-term flooding events is an important factor, alongside the ability to tolerate flooding stress.