Being close to nature is for most of us city dwellers a free health medicine. It makes you relax, decreases anxiety, make your blood circulate better and sharpens your mind.
But for some, a walk in the woods can be very stressful indeed. The reason? Some plants around shouldn’t be there. The so called invasive alien plants, non-native species or exotics. Plants that we humans transported to places where they did not grow before, sometimes purposefully, sometimes accidentally. The alien plants behave like deadly diseases – a cancer killing the resident plants of the place. In turn, it reduces the resilience of the native ecosystems, which little by little will spiral out of control and collapse, bring other native species and its interactions to become rarer and rarer or to disappear altogether.
In the island of Mauritius, in the Western Indian Ocean, this process is happening in from of our eyes. The very few best preserved and protected native forests are today dominated by…alien species! If you are a good observer, you will realise that in most of the native forest left on the island you are surrounded by a ‘sea’ of strawberry guava (a species from the Atlantic forest of Brazil). Well, you don’t need to be a great observer as, in average, nearly 80% of the stems are of non-native species. Worrisome is that it does not stop here: the invasion is progressing.
Strawberry guava is also a major problem in other tropical islands around the world. It is considered the worst invasive species of Hawaii. To avoid the full destruction of unique species and its ecosystems, it is necessary to control alien invasive plants. Both on Mauritius and Hawaii, manual removal of stems of these alien plants are done on regular basis. But such approach can only be effective on small areas. Biocontrol, a much used tool for agriculture, when conducted carefully and well-studied is arguably the only way to reverse the fate of today invaded forest and bring it back to a more pristine state and to avoid extinctions of unique species. Luckily, an effective and specific biocontrol has been found for strawberry guava. It was introduced in some selected areas of Hawaii in 2011.
Understanding the problem is the beginning of the solution to bring back a world where all green is good for all.
Florens et al 2016. Invasive alien plants progress to dominate protected and best-preserved wet forests of an oceanic island. Journal for Nature Conservation 34: 93–100