When only focusing on urban sites (Table 5) full flowering of
birch was associated with O3 as significant predictor in the first
model and O3 and temperature in the second model. The model
with another parameter increases R2 by 8.1%. O3 was the only significant
predictor for flowering of horse chestnut. Common hazel,
however, was associated with PM10 in the first model and with
PM10 and O3 in the second model, resulting in an increase of 7.1%.
Linear regressions with solely temperature as predictor yielded in
an R2 of 34.4% (birch), 6.5% (hazel) and 18.8% (horse chestnut),
respectively (data not shown).