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.

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The Phenophase Primer for Flowering Plants: Understanding Plant Phenophases for Nature's Notebook, is finally here!

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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.