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A full-scale fire test of the Cupressus arizonica as part of the WUIVIEW project

The role of ornamental vegetation in community fire resilience  

By Knowledge Network – Staff memberPublished on

Ornamental vegetation is a common feature of gardens and hedgerows in the wildland-urban interface (WUI) - basically the area where human development meets wildland vegetation – but it can also pose a hidden fire hazard. Recent research shows that different ornamental species vary dramatically in flammability, and plant selection around homes and communities can significantly impact fire safety. 

Traditionally, flammability has been assessed through small-scale laboratory tests. While useful, these do not capture how entire plants behave when exposed to flames. To address this, an EU Civil Protection Mechanism (UCPM)-funded project (WUIVIEW UCPM-2018-PP-AG) developed a full-scale experimental method to rank ornamental vegetation according to realistic burning behaviour, classifying species into three levels:  

  • low flammability – vegetation resists ignition and does not sustain flames; 
  • medium flammability – vegetation ignites and produces vertical flares, acting as ‘ladder fuels’ that can transmit fire to roofs, power lines or nearby trees; 
  • high flammability – vegetation quickly ignites and sustains large flames, spreading fire both vertically and horizontally.  

Four common Mediterranean ornamental species were tested under different watering conditions. The results showed clear differences:  

  • Cherry laurel (Prunus laurocerasus) consistently showed low flammability, resisting ignition and preventing flame spread; 
  • Leyland cypress (Cupressocyparis × leylandii) and northern white-cedar (Thuja occidentalis) exhibited medium to high flammability, depending on plant condition and moisture stress, as drought and poor maintenance significantly increased their fire risk; 
  • Arizona cypress (Cupressus arizonica) proved to be the most flammable species, often producing intense, fast-spreading flames.  

This evidence highlights two clear lessons for WUI residents. Plant choice matters: opting for low-flammability species such as cherry laurel can reduce ignition potential and limit fire spread near homes, whereas highly flammable conifers such as the Arizona or Leyland cypress should be avoided or carefully managed, especially in hedgerows close to structures. Maintenance is equally critical: even moderately flammable species can become highly hazardous if left drought-stressed, untrimmed, or dead.  

At the community level, these findings point to the need for landscaping guidelines and fire-wise programmes that explicitly address ornamental vegetation, not just native plants. Locally adapted lists of recommended and discouraged species could help residents make safer choices and strengthen collective resilience. 

A Cupressus arizonica hedgerow near unprotected glass
The hedgerow Cupressus arizonica in a residential area near the wildland–urban interface

Overall, ornamental vegetation is not a neutral design choice – it can either shield homes from flames or create dangerous fire pathways. By considering plant flammability in both gardening decisions and community planning, residents and policymakers have a simple, affordable and highly effective tool to reduce wildfire risk. 

by Prof. Elsa Pastor Ferrer - Technical University of Catalonia (UPC)