Publication Summary

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 So, researchers gathered data from published scientific papers, unpublished reports, and observations submitted to community science programs like USA-NPN’s Nature’s Notebook to see whether combining information from all these sources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.

Plants growing in the forest understory, including spring ephemerals, which are short-lived herbaceous plants, are important members of the forest plant community. A team of Appalachian Mountain Club scientists evaluated observations of leaf out and flowering in 11 understory plant and 14 tree species to help address the outstanding question of which plant group is shifting their springtime activity more. Overall, understory plants are advancing the timing of their activity twice as much as trees under warmer conditions. Interestingly, plants of the mid-Atlantic region – comprising the “middle” section of the Appalachian Trail – showed substantially more advancement than plants to the north or the south. And finally: when they looked at differences among the plant groups by region, they only saw evidence of greater advancement among understory plants in the north. The findings of this analysis are good news for the understory plants. Greater advancement in the springtime activity of these plants compared to leaf-out in the overstory canopy means more time for them to grow prior to being shaded out by the larger trees.

Understanding how climate change is affecting species is especially important for threatened or endangered species, which already exhibit perilously low species numbers. A research team led by Jeremy Yoder at California State University, Northridge sought to determine the environmental conditions that Joshua trees must experience to trigger flowering. Using over 10,000 images of Joshua tree contributed to iNaturalist, the team predicted whether and when Joshua trees flowered in years past, back to 1900, and tested the performance of the model in predicting the timing of flowering by comparing the predictions to observations contributed to Nature’s Notebook. They determined that over the past 120+ years, the trees have increased how frequently they flower, as a result of progressively warmer temperatures and more variable rainfall over the period.

In many deciduous forests, understory plants such as spring blooming wildflowers depend on a critical period of sunlight before overstory tree leaves block out the sun. Climate change has caused a shift to earlier leaf out in many plants, but not all taxa are shifting at the same rate. Two recent studies found conflicting results about whether wildflowers are advancing their springtime activity in step with overstory trees. The authors of the studies came together to investigate what might be behind the difference in results and found that difference in the types of data used, herbarium data in one and Nature’s Notebook data in the other, along with the geographic and temporal extent of the datasets evaluated, were likely the cause. The study demonstrates the importance of both types of data to explore these types of complex ecological questions. Once the methods of the two studies were adjusted to be more similar, the results indicated that wildflowers in the southern part of eastern North America are less sensitive to changes in temperature than overstory trees and that phenological activity was earlier in warmer years and in warmer locations.

Invasive hemlock woolly adelgid (Adelges tsugae or HWA) has caused widespread decline and mortality in hemlock trees, an important foundation species in the Eastern U.S. One method used for control of this species is the release of specialist predators at two life cycle stages: emergence from summer dormancy in early fall and egg laying in late winter. Authors of this study engaged Nature’s Notebook observers to collect data on HWA. The authors found that emergence of HWA from summer dormancy was consistent, starting at the end of September in each year of the study, while the start of egg laying in late winter was much more variable. Better knowledge of when to take management actions to reduce HWA will help preserve these important trees.

Dioecy, defined as distinctly male or female individuals in a species, is uncommon in plants, occurring in only about 5% of species. Consequently, our understanding of how this group of plants is being affected by climate change is limited. A group of researchers based at Purdue University in Indiana, USA asked two questions: 1) is the synchronicity in flowering in male and female trees changing? and 2) is the timing of leaf-out and flowering changing at different rates? The researchers found that male trees are advancing their flowering time at a greater rate than female trees. This is potentially bad news for these species; this pattern could reduce pollen transfer from male to female trees and negatively impact reproductive success in these trees. The researchers also found that flowering, which occurs before leaf-out in the species evaluated in this study, is advancing more rapidly than leaf-out. This finding is good news; the increasing temporal gap between flowing and leaf-out means less interference for the transfer of pollen from male to female trees.