Astronomically speaking, the first day of spring in the Northern Hemisphere is when the sun shines directly on the equator and the length of day and night are nearly identical. In 2023, this will be March 20.
Meteorologists define spring and other seasons in three-month periods, with spring being March 1 to May 31.
The seasons can also be defined through phenology. This is the study and recording of dates of recurring plant and animal life cycle events, such as when plants start to bloom, leaves begin to appear, frogs first croak, insects emerge or migratory birds arrive.
The timing of these biological events is important because many are highly sensitive to climate change, so shifting earlier or later over time can cause disruptive mismatches with other events in an ecological community. For example, the emergence of insects and migration of birds is closely synchronized with the onset of leaf growth, flowering and/or fruiting of plants.
Changes in ecosystems impact timing and severity of allergy season, carbon capture, pollination, proliferation of insect pests and invasive plants and crop productivity.
Phenology can involve the study of indicator species, which are animals, insects, plants or other organisms whose presence, absence or abundance reflect environmental change, level of diversity and overall condition. Some indicator plants reflect the presence of certain pests and when they are most vulnerable. Moss indicates acidic soil.
Phenology is a real science with many practical applications. It helps farmers know when to plant, prune, apply fertilizer and apply pesticides and herbicides, especially on invasive insects and plants. It helps identify when wildfire risks are greatest and predict timing of allergy season.
A nationwide organization exists to collect, store and share phenological data collected and reported by thousands of volunteers.
The U.S. Geological Survey-funded USA National Phenology Network, hosted within the University of Arizona College of Agriculture and Life Science’s School of Natural Resources and the Environment, has enabled volunteer observers across the country to record and share information on phenology of plants and animals since 2009.
The information is submitted to the network’s program, Nature’s Notebook. Observers set up observation sites in backyards or participate through local organizations. These citizen-scientists typically visit their sites once or twice a week to observe and record plant and animal activity changes throughout the seasons.
Specific campaigns that individuals or groups can join include “Green Wave,” which records when deciduous trees leaf out; “Nectar Connectors,” which focuses on timing of nectar sources for monarch butterflies and other pollinators; “Pest Control,” for reporting sightings of insect pest species harm trees; and observations of life cycle events of lilacs and dogwoods.
Nature’s Notebook volunteers collected and reported information on invasive, non-native shrubs, documenting that they leaf out earlier in the spring and hold onto leaves longer in the fall than natives. They out-compete native plants and shade the forest floor at times when native species previously were able to get sunlight.
Authors of a new study used this data to determine that the leaf period for invasives was up to 77 days longer than for native plants. Better knowledge of how invasive shrubs negatively impact natives can help stem the spread of these plants by humans and protect native species and their ecosystems.
Phenology is important because it involves whether plants and animals thrive or survive in their environments. Ultimately, human food supplies depend on the timing of phenological events.
For more information on joining Nature’s Notebook, go to https://www.usanpn.org/natures_notebook.
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