Shannon Pacilli
What is Phenology?
- Phenology is the branch of science that studies the relationship between the annual life cycles of plants and animals and their responses to climatic change.
- It correlates natural seasonal events with weather and temperature.
People have been collecting phenological information for thousands of years. The first paper on phenology was written in 974 BC; the Japanese have been recording the dates of the first annual cherry blossom blooms since 812 AD; and in 1852, Henry David Thoreau began recording the the first flowering date for many plant species found in the US. In more recent years, phenology has been used to identify when the naturally occurring links between plants and animals are breaking as a result of global warming.
Often phenological studies use indicator plants, such as common lilac and saucer magnolia, as signals for certain biological events and when they are likely to occur. Lilac is the cornerstone for phenological events and is particularly useful when comparing one year to the next. There are many programs in the US and Canada recording stages in the life cycle of common lilac, and climatologists use this information to study the effects of global warming. The saucer magnolia is an indicator of many early spring events. Discrete events in its life cycle, such as pink bud, early bloom, full bloom, past bloom and petal drop, can be associated with an array of insect pests.
When observing phenological events on a large scale, such as when indicator plants bloom, an event tends to progress from west to east and south to north. Hopkin’s Rule states that events are delayed by 4 days per degree north in latitude and by 1 ¼ days per degree east in longitude. It doesn’t, however, account for topography or altitude. When observing discrete phenological events, such as when a garden plant’s leaves open or when various pests are first noticed, it takes several years for patterns to develop. This data, gathered over time, can then be correlated with season, local weather conditions and regional climate changes.
Because phenology can be used to predict insect emergence and when pest control should be initiated, its role in Integrated Pest Management is perhaps the most practical application. Phenological studies enable the development of strategies that properly time controls to target pests at their most susceptible stage of life cycle. Insects are cold blooded and their growth and development directly correlate with temperature and weather. This makes them uniquely suited for phenological based predictions. Coincide, a book by Donald A. Orton, lists hundreds of insect and indicator plant associations.
Plant events and Insect emergence Links:
By studying data gathered over many years, phenologists have developed reliable correlations that aid in garden planning. The blooming time of common flowering plants can be used as a guide for crop planting dates. Because these plants are in tune with local conditions, they act as natural indicators for when conditions are right for planting.
Phenological planting guides:
We are living in a time when past weather patterns are no longer reliable and seasonal weather conditions change dramatically from year to year. The planting and harvesting schedules developed years ago do not necessarily account for “season creep”—a term coined in 2006 that is used to describe the gradual expansion of the spring season. In fact, data has shown that spring is arriving a week earlier than in prior centuries. What we do know for sure is that plants and animals are reacting to these changes. The National Phenology Network calls phenology "Nature’s calendar." If we also pay attention and start accumulating notes of our own on indicator plants uniquely adapted to our gardens, it enables us to tune in to the rhythms of life. We gain the power to react to changes based on observation, to become proactive against the pests that plague us and be more effective stewards of our gardens.
I challenge you to plant a lilac in your garden and begin recording your observations, like Thoreau and the many before him.
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