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Updated: May 11, 2025

Forced Flowering in Mandarin Trees under Phytotron Conditions
Published on: March 6, 2019
Long-term trends in global flowering phenology
David R Williamson1, Tommy Prestø1, Kristine B Westergaard1
1Department of Natural History, NTNU University Museum, Norwegian University of Science and Technology, Trondheim, 7012, Norway.
Climate change impacts flowering times globally. Digitized herbarium data reveals varied phenological trends, with low latitudes showing greater shifts in flowering dates and season duration over the past century.
Area of Science:
- Ecology
- Botany
- Climate Change Science
Background:
- Flowering phenology serves as a critical indicator of climate change impacts on ecosystems.
- Long-term ecological data is scarce, hindering comprehensive analysis of climate change effects over extended periods.
- Herbarium specimens offer a vast, yet underutilized, historical record of plant life.
Purpose of the Study:
- To investigate global temporal trends in flowering phenology using digitized herbarium specimens.
- To quantify shifts in mean flowering date and flowering season duration across various ecoregions.
- To explore latitudinal variations in phenological trends and their potential drivers.
Main Methods:
- Digitization of millions of angiosperm herbarium specimens to create a large-scale dataset.
- Development and application of a convolutional neural network (CNN) model for classifying flowering status from specimen images.
- Analysis of inferred flowering data from approximately 8 million specimens spanning a century to assess phenological trends.
Main Results:
- Significant diversity in temporal trends of flowering seasonality was observed across ecoregions.
- A median absolute shift of 2.5 days per decade in flowering date and 1.4 days per decade in flowering season duration was detected.
- Phenological trend variability was notably higher at low latitudes compared to high latitudes.
Conclusions:
- Digitized herbarium specimens are invaluable for studying long-term ecological dynamics and climate change impacts.
- Observed phenological shifts highlight the sensitivity of plant life cycles to changing climatic conditions.
- Higher variability at low latitudes may be attributed to combined shifts in temperature and precipitation seasonality, alongside photoperiodic factors.
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