Article written by Jeneya Smith, Research Forester, NHRI. Adapted from Jeneya’s technical note; Understanding fall phenology of red maple and sugar maple. Available here

In October 2023, the NHRI team sat down to discuss the potential for an exciting new project involving fall phenology. Our goal? To improve the identification of temperate deciduous tree species using remote sensing. The first step was to determine a spectral classification system to distinguish different species via remote sensing… and what’s one of the most distinctive features of deciduous trees? Their fall colours! Each species boasts a unique autumn foliage palette: sugar maples turn vibrant orange, red maples become deep red, and beeches and oaks turn brownish and retain their leaves through the winter.

These vibrant colours, along with their timing, seemed like ideal markers for identifying species through satellite imagery. However, to leverage these fall colours, we needed satellite imagery captured at just the right time. This led to many hours spent downloading imagery mosaics, only to find out we’d missed the peak colours by a week or more. It felt like we were working blind, trying to catch the perfect snapshot of fall foliage. It became clear that predicting the timing of fall colours could streamline our data acquisition process.

Why Study Fall Phenology?

Fall phenology provides more than just aesthetics; it plays an important role in forest processes, influencing the risk of frost damage, nutrient cycling, biotic interactions, and growing season length. Additionally, the vibrant fall foliage acts as a major tourist attraction, significantly contributing to New Brunswick’s economy. Despite its importance, research on fall phenology is relatively underexplored compared to phenomena like budburst. Consequently, the timing of peak fall colours remains less understood, underscoring the need for further research in this area.

Our Approach

To tackle this challenge, we aimed to map the timing of peak fall colours for two key temperate deciduous tree species of the Acadian Forest—red maple (Acer rubrum L.) and sugar maple (Acer saccharum Marsh) across New Brunswick. We collected data from 266 CLI plots across the province, focusing on sites dominated by these species. Using satellite-derived phenology timing and climate data, we identified the day-of-year when leaves fell to 50% of their peak greenness—our marker for peak fall colours.

To model the timing of peak fall colours, we used the Delpierre senescence model (Delpierre, 2009). This model simulates the mechanisms driving leaf colour change. Essentially, as daylength shortens and temperatures drop, a threshold is reached that signals to the tree that it’s time to prepare for winter, triggering leaf colour change.

Left: Red maple; Right: Sugar maple

What We Found

During our model testing phase, we found that the senescence model tended to underpredict the variability in peak fall colour timing across New Brunswick, showing an early bias of about 5-8 days. This finding aligns with other research on peak fall colour timing and highlights that while we understand the key mechanisms influencing fall foliage colouration, certain variables are still not fully captured. Nonetheless, our modeling successfully identified overall trends and distinct patterns in the timing of peak fall colours across the province. In the warmer southeastern, low-elevation regions of New Brunswick, peak colours generally occur the latest, while in the cooler northwestern, high-elevation regions, peak colours occur the earliest. Specifically, peak colours for red maple ranged from September 15th to October 3rd, and for sugar maple from September 18th to October 8th.

Final map of the 5-year mean (2019-2023) of peak fall colour timing for red maple. Colour gradient shows the variability in timing, and the grey lines represent the borders of the New Brunswick ecoregions.

Final map of the 5-year mean (2019-2023) of peak fall colour timing for sugar maple. Colour gradient shows the variability in timing, and the grey lines represent the borders of the New Brunswick ecoregions.

Why It Matters

Understanding the timing of fall phenology has practical applications. For forest managers, it aids in planning silvicultural treatments and ensuring the health and sustainability of our forests. For the tourism industry, accurate predictions of peak fall foliage can help attract visitors. For us, these maps will be invaluable in quickly locating satellite imagery that captures fall colours, enhancing our ability to identify species via remote sensing. Additionally, these maps can help to delineate stands with species of interest, such as tolerant hardwoods, and proactively schedule drone flights in the fall.

Looking Ahead

With the framework for mapping the timing of peak fall colours now developed, we can expand this project. We have the opportunity to map other phenological events, such as the timing of budburst or the peak growing season. This will enable us to examine past events and make future projections, helping us understand how climate change will affect these phenomena and allowing us to be proactive in our management decisions.

Conclusion

At the Northern Hardwoods Research Institute, we are committed to enhancing our understanding of New Brunswick’s forests and promoting sustainable management practices. By studying fall phenology, we not only celebrate the beauty of our natural landscapes but also equip ourselves with the knowledge to protect and preserve them for the future.

For more detailed information and to access our full technical note on this project, please follow the link below. Stay tuned for more updates on our research and how we are adapting our sustainable management practices for the future.

Full technical note can be accessed here