Aim Numerous studies have reported changes in first flowering day (FFD‐changes) in response to changes in climate. However, regarding the direction (advances versus delays) and the intensity (number of days/decade) of FFD‐changes, species show differences even when observed in the same location. Here, we examine the extent to which plant traits can explain observed differences in the response of flowering phenology in trees, shrubs, herbs and grasses. Location Eighteen sites distributed over the Northern Hemisphere. Methods We compiled data from the literature on FFD‐changes over recent decades for 562 species (648 observations). We related FFD‐changes to predictor variables associated with (a) changes in climate, (b) local site conditions and (c) traits. Results Of all FDD‐changes, 80.4% were FFD‐advances, 69.9% not exceeding 5 days/decade, and 10.5% exceeding 5 days/decade, whereas 19.6% reported delays. The intensity of FFD‐advances could be explained by several predictor variables from all three groups (a–c). The importance of these variables differed between the growth forms. Overall, decreasing precipitation was more important than increasing temperature in explaining FFD‐advances. FFD‐advances were strongest in polar tundra and in dry and warm habitats. Traits related to competition and growth rate, like plant height, specific leaf area and leaf dry matter content, had substantial explanatory power in the models. Traits had the highest overall importance in trees and grasses. In herbs they were of equal importance with changes in climate. In shrubs, variables related to site conditions best explained the intensity of FFD‐advances. Main conclusions Plant traits are important to understand species‐specific and growth form‐specific differences in phenological responses to climatic changes. Hence, in future observations and predictions of plant phenology, traits should be taken into consideration, especially those related to competition and growth rate, as they improve our understanding of adaptations leading to phenological changes.

Phenological responses to changing temperatures are known as “fingerprints of climate change,” yet these reactions are highly species specific. To assess whether different plant characteristics are related to these species‐specific responses in flowering phenology, we observed the first flowering day (FFD) of ten herbaceous species along two elevational gradients, representing temperature gradients. On the same populations, we measured traits being associated with (1) plant performance (specific leaf area), (2) leaf biochemistry (leaf C, N, P, K, and Mg content), and (3) water‐use efficiency (stomatal pore area index and stable carbon isotopes concentration). We found that as elevation increased, FFD was delayed for all species with a highly species‐specific rate. Populations at higher elevations needed less temperature accumulation to start flowering than populations of the same species at lower elevations. Surprisingly, traits explained a higher proportion of variance in the phenological data than elevation. Earlier flowering was associated with higher water‐use efficiency, higher leaf C, and lower leaf P content. In addition to that, the intensity of shifts in FFD was related to leaf N and K. These results propose that traits have a high potential in explaining phenological variations, which even surpassed the effect of temperature changes in our study. Therefore, they have a high potential to be included in future analyses studying the effects of climate change and will help to improve predictions of vegetation changes.