AEMS

Napoleon’s Trees: Planting Shade for the Future

Conor Molloy

TLDR: This was the coolest summer of the rest of your life. Plant trees now for shade later.

The Value of Shade

To make some small amends for the CO2 of my business flights, on time off I try to travel by bicycle, train, and ferry. During a recent trip, I cycled the Canal des Deux Mers—a 750 km route from the Atlantic to the Mediterranean. Officially, the route goes from Royan to Sète, but logistical challenges (including train cancellations on older tracks due to the heat) meant I covered 522 km from Bordeaux to Agde, where the Canal du Midi ends in a unique circular three-way lock and entrepôt.

Figure 1: A Garmin bike computer showing a temperature of 40.3°C during the ride.

Below 20°C, shade is a luxury. In 30°-40°C+, it’s a necessity. My bike computer, which tracks, navigates and reminds me to hydrate, also displays the temperature. I noticed a 3–4°C drop under the shade of the ancient plane trees along the canal’s towpaths compared to areas where the trees had died off. The peak temperature I saw was 44°C, but most of my ride through southern France saw temperatures between 30–35°C— cooler than my 2025 trip along the Loire, where 37–38°C forced me to cut my journey short and return to Ireland from Nevers.

Figure 2: Cycling along the remaining shaded towpath of the Canal du Midi.

Figure 2: Cycling along the remaining shaded towpath of the Canal du Midi.

Napoleon and the Plane Trees

The Canal du Midi, a 17th-century engineering marvel, was built to bypass Britain’s control of Gibraltar by connecting the Mediterranean Sea to the Atlantic. Today, it’s an UNESCO World Heritage site and a popular route for cyclists and driving tourists alike. The canal is lined with plane trees, which are widely credited as a favourite of Napoleon’s—apparently, they reminded him of his native Corsica.

However, there is limited historical evidence that Napoleon directly ordered the planting of trees along French roads or canals. While his affection for plane trees is well-documented, their presence along the Canal du Midi predates his era. For more on Napoleon’s botanical legacy, see Europeana’s exhibition on Napoleon and Botany.

Figure 3: Plaque commemorating the Canal du Midi as an International Historic Civil Engineering Landmark.

Figure 3: Plaque commemorating the Canal du Midi as an International Historic Civil Engineering Landmark.

A Crisis for the Canal’s Trees

The plane trees of the Canal du Midi are under threat. Since 2006, canker stain, a microscopic fungus, has decimated these trees, killing them in a matter of months. The only solution is to cut down and burn infected trees and replant with new species. This effort is ongoing, as documented by Replantons le Canal du Midi.

Figure 4: Key figures of the replanting program. Since 2011, 19,230 trees have been replanted, and 32,000 plane trees have been felled due to canker stain

Figure 4: Key figures of the replanting program. Since 2011, 19,230 trees have been replanted, and 32,000 plane trees have been felled due to canker stain.

Lessons for the Future

The Canal du Midi offers a powerful lesson: trees are not permanent. They require management, care, and replanting over time. This is especially relevant today, as cities worldwide grapple with the dual challenges of urban heat and active travel infrastructure development to reduce our CO2 emissions.

Urban Heat and Tree Cover

In Madrid, over 1,300 trees will be cut down to make way for a new metro line, sparking political debate. Similarly, in Ireland (see BusConnects), where our tree cover is the amongst the lowest in Europe—a fact that underscores the urgency of planting native, deciduous species to cool streets and restore ecosystems. For more on Madrid’s tree controversy, see this Reuters article.

In my view, arguing over older trees that have served their purpose is a waste of time. While these trees may be beloved, their lifespan is finite. The focus should be on planting millions of new trees to ensure our cities, streets, and cycleways remain usable in the decades to come.

Practical Advice for Planting

If you’re considering planting trees, here are a few tips:

I’m no arborist, so here’s some useful links to the debate and commercial services

Conclusion: A Call to Action

The story of the Canal du Midi and Napoleon’s plane trees reminds us that tree shade is not a given—it’s a legacy. To combat rising temperatures and create liveable urban spaces, we must plant, manage, and replant trees with intention.

Whether you’re a cyclist, a city planner, or simply someone who enjoys a cool walk on a hot day, the message is clear: Plant trees now for shade later.

Footnotes

  1. I’m grateful to Mark Daly at Eninserv for the title and for reminding me of the life-threatening nature of heatwaves and their accompanying wildfires.
  2. The Canal des Deux Mers is a 750 km route from Royan to Sète. For full route details, accommodation, and terrain, see France Vélo Tourisme. Note: When they say “mountain bikes,” they mean it—5 cm tires minimum are recommended for the soft gravel paths, my 4cm tyres sank repeatedly.
  3. For updates on the replanting effort, visit Replantons le Canal du Midi.
  4. A stunning example of “Napoleon’s Trees” can be seen on the approach to Amboise on the Loire. Explore the tree lined approach via D731 Avenue de Tours in  Google Maps or visit by bike using the https://www.loireavelo.fr/ (I can highly recommend this route from Saint Nazaire to Nevers).
Screenshot from Google Maps because I missed this on my cycle in to Amboise
My route and stats from Strava (because if its not on Strava it didn’t happen 😊)
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