ISLAND CONSERVATION-Invasive agave – more than just a thorn in one’s side |11 September 2006

I  I’m not going to pretend that I haven’t done it too – as a hormone-crazed teenager I  inscribed quite a few “Pat loves XX” on the leaves of agaves growing in a certain church garden that I walked through on my way home!

Fortunately, these plants, called lalwa or lalwes in Creole from the French l’aloès, are not part of the native vegetation of Seychelles. They come all the way from Central and South America and were introduced all over the tropics as a source of sisal fibre. This is obtained from the leaves and in Madagascar, East Africa and elsewhere is still used for making ropes and twine that are strong and durable (they do not deteriorate in seawater).

In Seychelles, the days of homegrown sisal fibre are over, but the plants persist as cultivated “ornamentals” or as wild populations that are gradually invading not only glasi areas in the granitic islands but also large tracts of some of our outer, coralline, islands. We were discussing this recently in the Island Conservation Society (ICS) because sisal has overrun parts of several islands that we hope to be able to rehabilitate, such as Anonyme and Cosmoledo.

It is interesting that, in their native habitats in tropical America, agaves grow and reproduce slowly – whereas in many areas where they have been introduced they grow and reproduce very fast (reproduction is mainly by “bulbils” that drop from the flower spikes and take root as well as by rhizomes or special stems that grow into separate plants).

A few years ago scientists working in south-east Spain reported that agave plants growing in sandy soils there produce nine times more bulbils than those in the clay soils of their native habitats; and in sandy soils bulbils are 30 per cent heavier and are more likely to survive. Perhaps the thriving expanses of lalwa in some of the outer islands have something to do with this: it certainly looks like “sand enhances the potential of clonal reproduction in these species” in the words of the Chilean and Spanish scientists who did the study.

Agaves can be dangerous too. The tips of the leaves are needle sharp – indeed, it is these very leaf tips that we break off and use to scratch those graffiti phrases into the leaves.

I experienced their dangerous nature myself when I was on the island of Menai in the Cosmoledo group some time back. I was reaching over a large rosette of agave leaves to peer at a yellow butterfly that I had not seen before. Suddenly I felt a literally stabbing pain just above my right foot. I glanced down to see blood spurting from where a leaf tip had pierced into my shin.

Fortunately the wound was very small and after I had bathed it in seawater the bleeding stopped.

An American teenager in Texas was not so lucky three years ago when he fell backward from a fence onto the rigid terminal spine of an agave plant. The American Journal of Roentgenology reported that he had to have surgery to extract the five centimetre-long “needle” from his spinal cord.

How to check the spread of invasive agave is going to be a thorny problem in more ways than one for conservationists!

The Island Conservation Society promotes the conservation and restoration of island ecosystems.

by Pat Matyot