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Researchers from the California Phenology Project compared observations of leaf budburst, flowering, fruiting and leaf drop with climate variables such as temperature and rainfall. The authors found that in all four species, at least one phenophase responded to higher winter low temperatures with delayed onset. Generally, precipitation strongly influenced leaf phenology, while both precipitation and temperature were important for flower and fruit phenology.

Using data from phenology observation programs, including Nature’s Notebook, the authors found that leaf unfolding is triggered more by daytime temperatures than by nighttime temperatures. This knowledge can lead to better predictions of when leaf-out might occur and improve vegetation models to estimate how phenology will change over different parts of the globe.

For many plants, it appears that the amount of heat needed to begin leaf growth in spring is related to temperatures in the preceding winter. Under increasing temperatures in the Northern Hemisphere, many temperate woody plants may no longer be exposed to the necessary cold temperatures in winter to meet their chilling requirement, leading to delays in leaf-out.

Most scientific studies that have looked at mismatch have focused solely on relationships between plants and their pollinators. This study takes a step back, and instead of looking at the impact of mismatches, looks at the causes. The authors determine what it is about mutualistic partnerships that make them more likely to experience mismatch.

Increasing winter temperatures could cause a delay in the onset of budburst, as well as a change in the order of when species undergo budburst. This means that in a warmer world, we could see pioneer and invasive species having an even higher advantage, which could result in decreased biodiversity and a more uniform landscape.

There has thus far been no clear agreement on whether autumn phenology events such as leaf color are more influenced by day length or temperature in temperate systems. The authors found that both have an influence.

Temperature and daylight length strongly influence the range of ragweed, an invasive weed. Ragweed can only reproduce in areas where its seeds can mature before the winter frost. This means that as the climate warms, ragweed will be able to grow in more places.

Warming temperatures are prompting many trees in temperate regions to put on leaves in the spring earlier than they have in the past. Climate change models predict continued warming of up to several degrees C by 2100. A team of researchers at Princeton University, led by David Medvigy, developed a nuanced model to predict the timing of leaf-out in the future.

Spring leaf-out phenology observations have proven valuable in predicting how arctic plant communities may change in coming decades. Models used to predict changes in plant communities have traditionally taken phenology into account, but have used a single date for leaf-out averaged across all plant species. As participants in Nature’s Notebook know first-hand, the timing of leaf-out varies by species.