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You can learn more about recent phenology research in the publication summaries below.

What puts plants most at risk of late spring freezes?

The number of early springs followed by late freeze events, called false springs, is predicted to increase due to climate change. To determine the likelihood of damage from a late spring freeze in temperate forests, the authors evaluated several datasets that reflect the start of spring including the USA-NPN’s spring leaf index. Many factors play a role in the susceptibility of plants to damage from false springs, including the plant’s life stage, functional group, morphology, and phenological traits such as whether the plant puts on buds early. A clearer understanding of how to estimate the risk of false springs for various species/functional types improves estimates of the future frequency of false springs under different climate change scenarios and can help improve models of species range shifts, carbon budgets and even feedback loops between climate shifts and forest composition.

Integrating herbarium specimens with observed phenology data

Integrating herbarium data with contemporary phenology data requires standardized terminology, definitions, and principles. The authors of a new study in Applications in Plant Sciences describe the Plant Phenology Ontology, an effort to integrate herbarium and field data. They demonstrate the use of this framework by combining herbarium data and observations from Nature’s Notebook to show that in North America, flowering time for black cherry (Prunus serotina) has been steadily accelerating since 1873.

Nature’s Notebook data show shift to earlier milkweed flowering

Nature’s Notebook data were used to evaluate how common milkweed flowering is responding to changes in climate. With each degree of maximum temperature increase, the mean flowering date for milkweed shifted nearly four days earlier. The shift occurred across first, last, and mean flowering dates but did not extend to initial growth or fruit ripening. The shift became more significant over the period of 2011 to 2016. These findings will help managers develop conservation plans for this species and its pollinators.

Overlooked climate factors predict flowering phenology best

Researchers at UC Santa Barbara combined herbarium records with observations contributed by Nature’s Notebook participants to assess the impact of climate variables on timing of flowering in 2,500 species of plants. The authors found that maximum temperature, the number of frost-free days, and the quantity of precipitation as snow were the best predictors of flowering time for both herbarium and observed data. A better understanding of the climate variables that drive flowering phenology can help us anticipate how future changes in climate might impact flowering. 

With the right resources, untrained observers record high-quality data

In order to better understand precision and accuracy in phenology data collection and how that varies by training level, researchers at Acadia National Park’s Schoodic Institute compared data from three different observer types – expert professional scientists, trained citizen scientists, and untrained citizen scientists. The authors found that untrained citizen scientists recorded data that was as precise and sometimes more accurate than trained citizen scientists, likely due to a misinterpretation of materials presented at trainings. The authors recommend that informative datasheets, mid-season assessments and calibration trainings may help to ensure high-quality data. 

Seed dispersing bears influence plant community composition

In a new study, researchers at Oregon State University sought to quantify the role bears in Alaska play in dispersing seeds. The authors estimated that brown and black bears disperse over 200,000 seeds per hour per square km while foraging for fleshy fruits and then excreting them on the landscape. Brown bears disperse more seeds than black bears overall, and at different times of the year. Because bears disperse a large percentage of the seeds of fleshy-fruit bearing species, they have a great influence on the species composition of plants in their ecosystems. If populations of bears are reduced, the number of fleshy-fruited shrubs may also decline and be replaced by wind-dispersed plants.

Linking time-lapse camera data to phenology observations

To better link phenology data from time-lapse cameras and on-the-ground observations, authors of a new study in Ecosphere compared digital images of tree foliage color from spring to autumn to observations made using the USA-NPN protocols. The authors also found that chill and minimum temperature in autumn, drought stress in autumn, and heat stress in summer are all important factors to the timing of peak fall foliage color.

Teasing apart the phenology of parasitic plants and their hosts

Mistletoes, a group of parasitic plants comprising over 1,500 species, have intricate relationships with different host species, pollinators, and seed dispersers to carry out their life cycle. The authors from a new study in Oecologia used data from the USA-NPN’s National Phenology Database from Arizona and California to look for consistencies in the leafing, flowering, and fruiting phenology between desert mistletoe and their host plants. The authors found that mistletoes are not constrained by their hosts when it comes to phenology, and use diverse strategies to maintain reproductive success.

Linking phenology data from the past and present

Authors of a new study published in Nature Ecology & Evolution analyzed data from three sources – Henry David Thoreau’s observations recorded over 150 years ago in Massachusetts, four decades of observations collected at the Rocky Mountain Biological Laboratory, and recent observations contributed by Nature’s Notebook participants across the U.S. – to demonstrate how these disparate data sources can be combined to detect changes in flowering phenology over time.  The authors found increasing variability in the timing of flowering in recent years across datasets. This suggests that plants may be reaching the limit of how much they can advance their flowering to keep up with changing climate conditions. 

Linking bird migration with the USA-NPN’s Spring Index

The authors of this study used data from two continental-scale observation networks to explore the relationship between migratory birds and environmental cues - observations of migratory birds submitted to eBird and weather surveillance radar, which can detect large groups of migrating birds. They compared the observation data to measurements of vegetation green-up collected via satellites and the USA-NPN’s Spring Leaf Index. The Spring Leaf Index was strongly related to both the estimates of bird species richness from eBird observations and migration intensity collected via weather radar. By better understanding how birds and the habitat on which they rely are responding to climate change, managers will be more equipped to take actions to promote and conserve habitat where it is needed.