What is a weed to one person can be a valued plant to another. Just think of Agapanthus, wilding pines, puwha or watercress or, in dunes (and increasingly inland), pink ragwort.
The single worst environmental weed at Gordon Park is Tradescantia (wandering jew) where it threatens all native ground cover plants and regenerating seedlings and it has to be totally eradicated there. However, before it was controlled at Virginia Lake Reserve, Tradescantia used to be one of the best nutrient filters for run-off into the lake and was nesting habitat for ducks, pukeko and other water birds.
The trees at the lake do not depend on natural regeneration, so why does our council spend so much in trying to remove Tradescantia where it threatens nothing at all? I outlined this in the Chronicle (December 20, 2007) but our council continues to seek engineering rather than ecological solutions to the lake's algal blooms.
Other examples of unjustified "weed management": much herbicide is used each year around Wanganui on roadside fennel (an occasional culinary herb), perhaps in the mistaken view that it is poisonous hemlock? Brush wattles along road and river margins are felled with almost religious fervour yet the much more invasive old man's beard, pampas and other weeds among them are left to grow. Our fire authorities have advocated removing native toetoe when it is pampas grass that is the harmful invader.
In the past several years, unselective herbicide has been used on all our railway margins and sidings, producing gravel deserts, but why?
Early last year (March 16, 2011) I wrote that Wanganui's controversial vacant land on the corner of Maria Place and St Hill St would have produced almost 10 billion seeds of fleabane. What I didn't say then was that fleabane was only one of many weeds there.
For the last eight summers, all the visible plants were listed (the last two years from outside the fence only) but the variety changed rather little from year to year. That's despite different management of the site between years, including slashing, spraying and excavation.
Over the eight years 138 species were seen. Clearly, there is a "rain" of seeds reaching the site, mostly by wind and birds - a lottery helped by factors like proximity of the parent plant and which birds are around. Of these seeds, only some establish, depending on which plants are suited to the harsh nature of the site. But spending money on control of these weeds makes little difference to next year's crop.
Such examples show us that weeds need to be identified correctly and their control justified and targeted ... and some weeds should be controlled in specific places but not others.
