Saving Rare Sea Cliff Plants

The intervention

Invasive plant removal and community engagement

We are organizing events with local volunteers to help remove the invasive ice plant from the area where it is competing with the rare cliff plants. This is done by manually pulling the plants and removing them from the area. With these events we are aiming to:

• stop the invasion before it spreads further and control efforts become unfeasible;
• take direct action to restore diverse cliff plant communities (similar efforts have been successful elsewhere);
• spread awareness about these species to prevent any damage by park visitors;
• encourage dialogue between all the groups involved in protecting, studying and enjoying the area.

Monitoring with a drone and photogrammetry

We will be capturing drone images to survey inaccessible cliffs and ensure we have the evidence needed to guide our conservation actions. We expect the technology will have multiple uses:

• detecting the presence of rare plant species in hard to access locations;
• monitoring the distribution of the invasive ice plant and use this data to coordinate removal events;
• monitor the vegetation before and after ice plant removal to check if the vegetation is recovering as expected or if further intervention is needed.

How did the invasive plant get here?

One serious threat for these rare species is the spread of ice plant (Carpobrous edulis) in the area. This is an invasive succulent plant that forms dense mats which change the soil composition and displace native species that have been evolving together for millennia. It can spread rapidly on dunes and coastal cliffs wiping out entire plant communities. As in other European countries, the species was introduced in Portugal during the 1900s because it was thought to help prevent coastal erosion. It is currently widespread along the Portuguese coast.

Using a drone for cliff plant monitoring

Current methods for monitoring these rare endemic species are very time consuming making it impractical to carry out population surveys with the accuracy and frequency needed to detect population trends and threats. Both species have a very narrow range but their habitat is very hard to access.

If no other monitoring approach is used, we would have to invest substantial time in continuously monitoring these populations. Accurate population size estimates would require very thorough sampling using abseiling and rock climbing techniques. Other than being logistically complex, this type of survey would be intrusive and could inadvertently disturb the cliff ecosystem.

To address this, we are using a drone to capture high resolution images which can later be processed to detect where the individuals of each species are present. After being validated and refined, we hope this approach will provide a reproducible and cost effective way to monitor the abundance and distribution of these rare species.

We also aim to use the drone and photogrammetry software to create orthophotomaps of the areas where C. edulis is to be removed. The resulting maps will help to plan the removal events but, more importantly, they provide a baseline scenario for monitoring the impact of this intervention on native vegetation. By creating the same maps every year, we hope to capture the process of recolonization by native vegetation. These surveys may demonstrate the success of the intervention or a failure of native plants to recolonize the area which would suggest that assisted revegetation may be appropriate. Finally, we expect the maps will prove useful as a way of identifying C. edulis resprouts that could be missed otherwise.