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Backhoes needed to take out invasive mega grasses

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Napier grass (Pennisetum purpureum).

One of the most vivid insights from my first safari to Africa was understanding the significance of the African megafauna elephants, rhinoceros, hippopotamus and giraffe whose impact on the land is sufficient to create the natural highways that safari vehicles can use in the absence of man-made roads.The reason that megafauna survived in Africa and almost nowhere else, least of all in the New World, is because Africa is where humankind evolved, giving the wildlife time to co-evolve and adapt to our ever more deadly weapons. In the New World, where man’s arrival was so recent, the megafauna had no time to adapt at all, resulting in many extinctions.Of course Bermuda, as an isolated oceanic island, had no mammals at all other than bats, let alone megafauna, so you might well ask what all this has to do with this week’s Green Pages topic of invasive grasses?Well, let’s take a look at two of those invasives, both, incidentally, imported from Africa, and you will understand.They are so tall and woody that, as grasses go, they can be described as megaflora to match the megafauna and once fully mature it is only elephants, rhinos and hippos that can effectively browse them down.The two species are Cow-cane, Arundo donax, and Napier grass, Pennisetum purpureum, and both were originally imported here as fodder grasses for cattle. Cow-cane was imported more than a century ago. It is so tall and woody-stemmed that most people mistake it for bamboo.Fortunately, it does not seem to self-seed in Bermuda, spreading instead by robust rhizomes underground. If not controlled it can eventually spread to form impenetrable thickets of cane too dense to walk through and too tough for cows to control. Although typically a grass of river flood plains in Africa, here in Bermuda it can grow anywhere and is typically dispersed in loads of rubble fill.Once established in filled areas it can be extremely difficult to eradicate because the buried rhizomes can push up shoots through as much as four feet of rubble!Napier grass is of much more recent introduction in the 1960s or 1970s. As with cow-cane it was imported as a fodder crop for cattle and is still grown in some dairy farm fields. Unfortunately, however, this species does self-seed in Bermuda and has started to become invasive in the wet pasture fields around the edge of our marshes.In Devonshire marsh it is now growing so tall and raggedy that it looks untidy and is beginning to block that once grand view across the marsh, just as dense thickets of cow-cane and cattail have long since blocked the view of Pembroke marsh pond from Bernard Park. These two mega grasses, together with two other lower growing fodder grasses that have also become invasive paragrass, Brachiaria mutica and Paspalum urvillei are now so common that they are gradually replacing the native bush and sedge flora that once dominated the wetter parts of our peat marshes.No, I am not suggesting that we import elephants and hippos to keep them under control, but I can assure you from bitter experience in managing nature reserves that where control is necessary only our machine equivalent of the megafauna the backhoe is capable of doing the job!

Photos by Lisa GreeneCow-cane (Arundo donax) was imported to Bermuda more than a century ago.