Publication Summary

The advance in the timing of spring events is well documented in scientific research. However, changes have not been the same for all species and can even differ among populations of the same species in distinct locations. A team of researchers compiled an extensive dataset of phenology observations from the published literature and from phenology networks including USA-NPN. They estimated whether the average date that a life cycle stage occurs has shifted since 1980, assessed the extent to which those shifts were driven by changes in temperature or precipitation, and explored whether climate change was increasing the likelihood of phenological mismatches for species that occur in the same location. The authors found that for plants, spring and summer events like leaf out, flowering, and fruiting are occurring earlier than they did 40 years ago, with later stages like flowering and fruit ripening advancing faster than earlier stages. Climate had much weaker effects on the timing of animal activity, which has implications for mismatches in the timing of plants and animals that rely on synchronization of their life cycle stages.

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.

Grasslands are among the most disturbed ecosystems globally. In the areas that remain, managers must balance practices such as mowing and burning that maintain natural systems while avoiding nesting periods for grassland birds. The authors of this study used information about nest survival from scientific literature as well as climate information and the USA-NPN’s Spring Bloom Index to develop models to predict the expected nest departure timing for 36 grassland bird species. This information can provide more localized information about nesting timing to better time management actions to avoid this critical period.

Ash trees on are the decline, and the main culprit is emerald ash borer (EAB), an invasive pest that has killed millions of ash trees in the United States. Knowing where and when to expect EAB emergence gives managers an advantage in controlling this pest, helping them to know when to take actions to control the pest. In this article, Barker et al. evaluated a model that predicts activity of EAB, taking into account both phenology and locations that have suitable climate for this pest. They used observations of EAB, including those from Nature’s Notebook, to test their model and found that it correctly estimated over 99% of presence records and predicted dates of adult EAB emergence within 7 days. This paper demonstrates how your observations can be used in the realm of invasive species, helping to improve management and ultimately conserve the unique ecosystems that we care about.

Pollen alerts give allergy sufferers the potential to reduce their exposure and the negative health impacts that result. An emerging data source for alerts is observations of flowering phenology, which can be highly correlated with the presence of airborne pollen. The authors of a new study compared data from National Allergy Bureau stations on daily pollen concentrations to flowering and pollen cone data from Nature’s Notebook. They found that the strength of the relationship between open flowers and pollen cones and pollen concentration varied by the type of plant, with the best agreement for Oaks (Quercus) and walnuts (Juglans). More specific data on the timing of open flowers and pollen release, like those that you collect in Nature’s Notebook, could lead to create real-time pollen alerts with local specificity.

The ability to predict spring plant phenology has implications for ecosystem services and forest management. The amount of heat that has accumulated at a given location, called growing degree days, is one method for prediction. The authors compared phenology data collected by the Tree Spotters (a Nature’s Notebook Local Phenology Program) at an urban arboretum, to those collected in a rural forest, Harvard Forest, and found that the urban site actually required fewer GDDs than trees at the rural site, possibly due to other phenological cues such as light and a higher amount of accumulated winter chill than predicted.