Pollution adversely affects vegetation; however, its impact on phenology and leaf morphology is not
satisfactorily understood yet. We analyzed associations between pollutants and phenological data of
birch, hazel and horse chestnut in Munich (2010) along with the suitability of leaf morphological parameters
of birch for monitoring air pollution using two datasets: cumulated atmospheric concentrations
of nitrogen dioxide and ozone derived from passive sampling (short-term exposure) and pollutant information
derived from Land Use Regression models (long-term exposure). Partial correlations and
stepwise regressions revealed that increased ozone (birch, horse chestnut), NO2, NOx and PM levels
(hazel) were significantly related to delays in phenology. Correlations were especially high when rural
sites were excluded suggesting a better estimation of long-term within-city pollution. In situ measurements
of foliar characteristics of birch were not suitable for bio-monitoring pollution. Inconsistencies
between long- and short-term exposure effects suggest some caution when interpreting short-term data
collected within field studies.