Invasive Blooms: Mapping Ireland’s Rhododendron Problem
Monitoring the spread of invasive plant species is crucial to protecting and managing our native tree and plant species.
Typically, monitoring the spread of an invasive species on a national scale has been difficult.
However, Remote Sensing technology is helping to advance our understanding of the spread of invasive species. Mallon colleague Michael O’Connor has created the following images, which identify the spread of an invasive species across Ireland.
Classification of Blooming Rhododendron Ponticum Through Aerial and Satellite Imagery
Rhododendron Ponticum is an invasive plant species introduced to Ireland in the 18th Century. It forms dense thickets and can outcompete native plants for resources such as sunlight and nutrients,
resulting in a loss of biodiversity.
Using high–resolution ortho–imagery and low–resolution satellite imagery, we have been able to identify Rhododendron Ponticum during its blooming period in the Vee Pass, Co. Tipperary (May/June 2023).
The Vee Pass, Co. Tipperary
The primary characteristic that distinguishes Rhododendrons is their distinctive pink or purple colour when in bloom. Mapping the precise location of the plant focused on its contrast to other vegetative features during its bloom period,
with emphasis on spectral vegetation indices, reflectance and colour contrast. The images below show the blooming Rhododendron, visible in its purple hue, and the identified blooms, classified in red.
N.B. Ortho–imagery was purchased from the Bluesky Mapshop, 2025. Available at: https://www.blueskymapshop.com/ [Accessed 04 April 2025], Bluesky International Ltd, UK.
Vee Pass Example 1
Vee Pass Ortho Image
Vee Pass Sentinel Image 1
Delineation of Rhododendron Ponticum using classification technique based on High–Resolution (BlueSky, top images) and Low–Resolution (freely available Sentinel–2, bottom images).
Vee Pass Example 2
Vee Pass Ortho Image 2
Vee Pass Sentinel Image 2
Delineation of Rhododendron Ponticum using classification technique based on High–Resolution (BlueSky, top images) and Low–Resolution (freely available Sentinel–2, bottom images).
How can Earth Observation help track invasive Rhododendron outbreaks?
Despite the difficulties in identifying Rhododendron Ponticum using aerial imagery, the work we have undertaken to identify and classify the outbreaks will hopefully lead to an improvement in their detection.
We initially used high–resolution imagery for our maps but were able to transfer the results to lower–resolution imagery. This, combined with the positive identification of species location, could lead to a breakthrough in the ability to easily track and monitor rhododendron outbreaks.
Further Information
For further information about the methods used to produce the images above or to discuss your Earth Observation requirements, please get in touch with us below.
