Publication Summary

Temperature is important, but not the only factor in determining when plants leaf out in spring or lose their leaves in autumn. Species traits, like leaf size or thickness, also play an important role. To understand whether some plants may be more sensitive to increasing temperatures, researchers gathered data from warming experiments as well as observational data from Nature’s Notebook and a phenology network in China. They found that plants with thinner leaves and higher nutrient concentrations are more sensitive to temperature increases. These plants will typically leaf out earlier and lose their leaves later in warm years. Plants with thicker, longer-lived leaves are less likely to shift their growing seasons in response to warming temperatures. These results identified important patterns that can help refine predictions about how plant communities will respond to future climate change.

The appearance of bright pink flowers on eastern redbud trees is a reliable indicator that spring has arrived in the eastern U.S. However, the timing varies across the species’ range and not much is understood about the climate conditions that trigger flowering. A team of researchers used Nature’s Notebook observations from more than 150 sites across the eastern U.S. to identify how temperatures and daylength influence flowering in eastern redbuds. They used a novel modeling approach to show that both the amount of cold in winter and warmth in spring are important. However, the relative amount of cold and warmth needed to trigger flowering differed among sites. Trees in the north needed more cold and less heat to flower than trees in the south. Using these results, researchers can make accurate predictions about redbud flowering given recent climate conditions and better understand the potential impacts of climate change.

The timing of phenological events in autumn like leaf color and leaf fall have important consequences for nutrient cycling, species interactions, and even tourism. However, there has been less research on autumn phenology than spring phenology and the effects of temperature, precipitation, and day length are not well understood. To fill this gap, researchers used Nature’s Notebook observations of autumn phenology from woody plant species across the U.S. They found strong regional differences. Leaf color in the eastern U.S. was driven primary by summer temperatures, whereas in the western U.S., leaf color change was influenced more strongly by precipitation that occurred more than six months prior. Given these differences, the effects of climate change are likely to be complex. Increased temperatures may extend the growing season for some plants and increased drought may shorten the growing season for others.

Global temperatures are increasing and the impacts are numerous and wide ranging. Temperatures have been rising at a particularly fast rate in the northeastern U.S., including many densely populated areas like New Jersey. To document environmental changes and better understand the impacts of climate change in this region since the mid-1960s, researchers gathered data on sea and air temperatures, lake ice, and snowfall. They complemented the weather data with observations of spring leaf-out and flowering in local lilac plants. The researchers found clear evidence of climate change, with notable increases in both daytime and nighttime temperatures and earlier spring plant activity. These changes will have numerous economic, social, and ecological impacts. Among other effects, earlier spring onset has the potential to alter plant-pollinator interactions and the length of the pollen and growing seasons.

Insect pests, like emerald ash borers and spongy moths, pose a significant threat to forests in North America. Management of these pests depends on information about which trees are at greatest risk and which treatments are likely to be most effective. Outbreaks of spruce budworm can devastate fir and spruce forests in the northeastern U.S. and Canada, but the risk to other tree species has not been well documented. Researchers in Maine used Nature’s Notebook observations and tree ring data to show that spruce budworms also feed on eastern hemlock trees, which leaf out at the same time as fir and spruce trees. Understanding the risk to eastern hemlock trees is important because the trees play a unique role in eastern forests and are also harvested commercially.

Results from many small-scale studies have shown that warming temperatures are causing plants to leaf-out and flower earlier than they have in the past. However, it has been difficult to know whether these patterns hold true for a wide variety of plant species at a continental scale. To answer this question, researchers used thousands of observations of plants in the eastern U.S. that were submitted to Nature’s Notebook, mainly by volunteers. They found that leaf-out and flowering occurred earlier with warmer temperatures, but the effects varied among species and locations. Invasive species, shrub species, and species at southern latitudes were more sensitive to warming temperatures than other species. These patterns were similar to results from analyses of data collected by professionals and consistent with results from previous scientific studies, demonstrating the value of Nature’s Notebook observations.

As the world becomes increasingly urban, it will become more important to maintain diverse plant communities in and around cities. A diverse plant community provides many benefits to people and wildlife inhabiting urban areas. In many cities, we have incomplete information about plant species and distributions. So, researchers gathered data from published scientific papers, unpublished reports, and observations submitted to community science programs like USA-NPN’s Nature’s Notebook to see whether combining information from all these sources provided a more complete picture of urban plant biodiversity. They compiled more than 171,000 observations of plants in the Chicago, Illinois area and documented more than 2,200 plant species. Community science programs contributed more observations of more plant species in more diverse locations than scientific studies or reports. However, professional scientists documented a significant number of native species with limited distributions that were not observed by community scientists. In all, the study highlighted the value in combining different types of data to better characterize and manage plant communities in urban areas.

As the climate changes, there has been a significant increase in the frequency of extreme weather events like heat waves, droughts, and hurricanes. We know that increases in average temperatures affect the timing of plant and animal activities, but the effects of extreme weather events are largely unknown. To address this knowledge gap, researchers used millions of photos of plants, butterflies, and moths that were submitted to iNaturalist between 2016 and 2022 to evaluate the effects of extreme heat, cold, dry, or wet conditions on the timing of plant flowering and adult insect activity. The results showed that the onset and duration of plant and animal activities were impacted by extreme events and not just changes in average climate conditions. However, the effects of extreme weather were complex, often differing between plants and animals and varying regionally. Results from this study can help us predict how plant and insect populations will respond to extreme weather events, which are likely to occur more often with climate change.

Many trees in the Northern Hemisphere are leafing out earlier as the climate warms. But with leaves emerging earlier in the season, there is an increased risk of damage from a late spring frost. Researchers used experimental and observational data – including thousands of records from Nature’s Notebook – to evaluate the effects of late spring frosts on hundreds of tree species. The results indicated that late spring frosts have both short-term and long-term effects on tree growth and phenology. In the short-term, late spring frosts damage young leaves and limit tree growth that year. But more notably, late spring frost events also limit the amount of resources a tree can store that year, which results in delayed leaf emergence and reduced productivity the next calendar year. These results illustrate that the effects of extreme climate events on plant phenology and productivity may extend months, or years, into the future. The results may also help scientists generate more accurate predictions of how forests will respond to future climate change.