How consistently do species leaf-out or flower in the same order? Understanding the factors that shape this characteristic of plant communities

Plant species are frequently reported to undergo leaf-out and flowering in a consistent order from 1 year to the next; however, only a limited number of these findings arise from studies encompassing many species or sites. Here, we evaluate the consistency in the order species leafed out in the northeastern United States using observations contributed to the USA National Phenology Network’s Nature’s Notebook platform. We repeated this analysis for flowering, evaluating a total of 132 species across 84 sites. We documented a relatively high degree of consistency in the order of both events among individual plants, with higher consistency in flowering. A small number of species pairs exhibited very high consistency in phenological order across several sites. The majority of species pairs exhibited variability in how consistently they underwent either leaf-out or flowering from site to site, which could be the result of either plastic or locally adaptive responses. Our investigation revealed that neither functional type nor seasonal position played a major role in shaping how consistently species leafed out or flowered in the same order. Instead, we found the number of days separating the events and interannual variability in timing to be the most influential factors driving the consistency in ordering.