Meeting with Professor Kristina Jones

Planting vegetation can be an effective way to mitigate soil erosion because plant roots stabilize soil. To learn more about vegetation selection, Fiona and Mackenzie met with Professor Kristina Jones, Director of the Botanic Gardens.

Selecting the right vegetation for the slopes surrounding the Poilao Dam is challenging because we know so little about our site, as we have not been able to have a conversation with our community partner. But, given one photo of the dam, Kristina was able to give us some valuable insights:

We had been researching vegetation erosion control techniques on slopes, but Kristina advised us to research soil erosion management onroad cuts and other newly cut land features because the dam’s impoundment was cut out of hillsides. Thus, a lot of the topsoil has probably eroded away.

Soil

When choosing plants for a site, it is critical to know what the soil type of the site is. We need to do more research on the soil to learn if it’s sand, clay, or basalt, and if the soil is compacted. Since Cape Verde is a former site of volcanic activity, there is a good chance that our soil is partially basalt. We also want to know what the pH, moisture, and nutrient content of the soil is. Since the slopes have been eroding, much of the organic matter present in the topsoil has probably eroded. This means that organic matter will have to be added to the soil before planting so that the plants have the necessary nutrients. Hugelkultur is a cheap way to increase soil nutrient content: essentially you bury wood debris under the soil and it breaks down slowly over time and creates organic matter.

Vegetation Type

While doing research on vegetation types, we came across conflicting recommendations (ex. Plant grass! DON’T PLANT GRASS!). Kristina told us that we shouldn’t think about trees vs. grass but rather we should ask “do we want fast growing plants or not?” The answer to this depends on how dire the erosion is. Our best plan is probably to plant a fast-spreading groundcover that will quickly stabilize the topsoil. At the same time, we can plant tree and shrub seedlings, which will grow slowly and eventually shade out the groundcover (succession!) and provide deeper structural support against erosion. This approach provides short and long-term solutions to erosion.

Plant Species

Whatever plants we choose will have to be very drought tolerant. We are going to research drought-tolerant willows, which sucker underground to form thickets and grow really quickly. We could try a willow mat – a layering of willow branches that will sprout when the conditions are right. For a cheap groundcover, we can try to source a local plant and divide up and plant its rhizomes. Since a lot of Cape Verde’s plant life is exotic, we will want to be sure that we don’t introduce anything that could be invasive, even if it’s not a native plant.