Green waste at the Patea River
So what does grow from green waste in coastal dunes?
Weeds establishing from illegally dumped garden waste are a problem throughout the country. Such dumps are seldom in mobile coastal dune systems and are seldom legal. In the Tongariro/Whanganui/Taranaki Conservancy we're unfortunate enough to have a legal garden waste dump site on the dunes at the mouth of the Patea River. Although DOC doesn't approve of stabilising mobile dune systems with garden waste, it has given us the opportunity to determine what can establish from ordinary garden waste.
Agapanthus
So what does establish?
Well, anything that's dumped, really! Over a period of four years we've recorded 249 species of exotic weed. There are also six indigenous species that have established from garden refuse. Virtually every common vegetable has established, with pumpkins and potatoes flourishing. Bulbs love the sand, and vines such as blackberry, convolvulus and climbing dock flourish. Tree mallow seems to persist as the canopy.
The most disturbing aspect is the number of weeds that are considered problems or are included in the Taranaki Regional Council plant pest management strategy. Madeira vine is rampant, brush wattle and gorse have established from garden waste, and pampas is present. I wonder if strategy rules about distributing weed species applies to garden refuse that has a good chance of establishing. There are also weeds that are of concern in other areas of the country, e.g. tamarisk, boxthorn and three willow species have established from cuttings, and agapanthus, arums and cannas have taken hold.
Several weeds that are new to the country have been found at the Patea dunes dump, e.g. pineapple flower Eucomis comosa.
Obviously not all weed species persist at the site, as the garden waste is covered by a layer of clay occasionally. But several species do survive this clay topping and continue to flourish. The major concern remains the ease with which most groups of plants establish in nutrient-poor dune sand. The number of potential weeds at the site is probably governed by the number of plants in gardens around Patea. So if you have mobile dunes, don't think that they're safe from a variety of weeds.
And in case you're wondering how we got to such a high number of weeds, we managed to get our retired botanist interested in the site.
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