Invaded: Leonie JoubertDid you know that there is a secret war going on right here in South Africa? That we are being invaded? No, illegal Zimbabweans are not to blame. Instead Leonie Joubert's book refers to the biological invasion of South Africa. No, not biological warfare either, but rather the movement of new species into habitats in South Africa and the ecological impact they have on the environment.

Invaded provides a good overview of the processes that have helped lead to this invasion. Once again man (and womankind), have had a huge role to play. The book's central point is this,- that with the increase in trade and migration of humans, the introduction of new species into different environments has steadily increased. That, coupled with our input into global warming, has also helped to put out the welcome mat for many of these invasive species. Joubert explains the debates and issues behind the current situation in an approachable and engaging manner.

Joubert states in her introduction that “I hope that Invaded will be a book that sits close to the elbow of any nature enthusiast or environmentalist or policy maker. The kind of book that will be picked up from time to time and a different chapter dipped into as a reminder of how serious this problem of invasive alien organisms really is in our country.”

Joubert explores the major ecological and human issues relating to South Africa's water supplies and how they are affected by alien species. Wetlands, which are great reservoirs in our water supply chain, are changing their nature due to human activity and the colonization of new plant species. “South Africa loses nearly 7% of its annual rainfall run-off to invasive plants.” This has a huge impact on our water sustainability for the future, and shows how important a role invasive plants play in our local ecosystems.

The reader is given an easy to follow glimpse into the different kinds of invasive plants and animals that have surreptitiously made themselves at home. In a very reader-friendly manner she talks about the mechanisms behind their incursion and goes on to explain the impact that they are having on the eco systems that they have invaded.

One of my favorite chapters is when Joubert looks at South Africa's own unique biome - the fynbos in the Cape floral kingdom - with a special focus on the threatened renosterveldt, of which there is only 4% left.

One of the central points is, that it is not so much that change is occurring through the movement of species, but rather the rate at which it is happening. The invasive species often quickly take over and squeeze out native species, thereby decreasing biodiversity. For instance in Chapter 2 Joubert mentions that within the Cape Floral Kingdom there are 8 600 species of which 70% occur nowhere else on the planet. These plants need very specific conditions to grow and the result of invasive species is that they change the soil composition, which has created conditions favourable for grass. The increase in grass has in turn lead to an increase in the frequency of fires. Fire is an important part of the life cycle for many fynbos species, however, the increase in the frequency of the fires is having a negative impact on the fynbos.

Joubert looks at the ecological impact invasive species have had on Marion Island and shows how we should learn from what happened. This little island, half way between South Africa and Antarctica has provided a unique opportunity for scientists to look at the impact that invasive species have on ecosystems. The first major invader, rats, arrived with the first ships - so cats were introduced to curb their number. Good plan right? Well, it backfired when the cats bred like, well rats, and decided that they had a particular fondness for local birds which were easier to catch than the rats they were introduced to kill, thereby having a further detrimental impact on the local species. The lesson in this is that once a new species has made itself comfortable, it is often hard to show it the door.

“An invasive species is like a cancer of the ecosystem, for which there may be no chemotherapy,” this is how Dr Guy Preston, chairperson of the Working for Water program describes the situation in the final chapter entitled, Staging a defense. We can do our best to curb the spread of an invasive species and try to stop any more from entering into our ecosystems, but this is an uphill battle. The South African Working for Water Programme is one of the biggest and most well known success stories, cited as an example of how to deal with invasive species.

Invaded is a very approachable book, that is a great introduction into the debates surrounding invasive species in South Africa. In a time where we should all be taking the environment and its future seriously, it is well worth knowing who the culprits are in all their forms.