New revelations on how weed seeds spread

Space invaders (weed plants) are on the increase all over the world. The change in climatic conditions exacerbates this trend and the list is continuously growing.

More resources and smart tools are required to halt this acceleration at all levels. Each individual can help by avoiding planting potential weed species and/or removing space invaders on their own property, or by joining a group of Weedbusters. There is more to find out through research and adjusting control methods according to scientific findings.

Recently published research undertaken by Debra Wotton (Moa’s Ark Research and University of Canterbury), Kate McAlpine (Department of Conservation) and George Perry (University of Auckland) revealed some surprises in the way weed seeds spread.

Traditionally, seed traits, the term for inherited characteristics, are associated with the way seed can disperse from the parent plant. Winged seed is the dispersal mechanism of sycamore and ash. These seeds are carried by wind, as are feathery plumes of pampas, old man’s beard, grey willow, etc. Such seeds are often found several kilometres away from the parent plant. Birds and mammals ingest fleshy berries and fruit such as cherries, barberry, hawthorn, cotoneaster, etc. These are then dispersed via defecation.

Through their research, the trio of scientists discovered many unexpected modes of seed dispersal and concluded that these modes are more important than mechanisms predicted by seed traits.

Many years of data gathering for hundreds of weed species were undertaken. The analysis of the data revealed that 44% of these seeds were dispersed by unexpected mechanisms.

The lead author Debra Wotton explains: "We need to understand how weed seeds are actually getting around in order to predict their spread and their impacts on native ecosystems".

To quote further from the published article: The scientists found that animals are a key culprit in spreading weeds long distances — not only do they disperse more than 60% of weed species, they can move seeds much further than other mechanisms. Wilding pines are a good example of the unexpected ways that animals can transport weed seeds. Pine seeds have wings that assist with wind dispersal, but they can also hitch a ride on animal feathers, fur or feet, in bird nesting material and when water birds swallow them.

"Our research shows the sometimes surprising ways that seeds can move around the landscape and highlights the importance of identifying the full range of dispersal mechanisms used by weeds in New Zealand," Dr Wotton said.

Unexpected seed dispersal mechanisms have rarely been studied in New Zealand; therefore, they may be more common than we know. Further research will be very welcome to provide us with increased knowledge. The research to date will be useful to identify and manage weed threats for native ecosystems.

The findings from the trio’s research are an important aspect when discussing potential grazing of public conservation land in order to control weed species, e.g. pine seedlings. Animals playing such a large part in distributing seeds may well mean that grazing may be counterproductive.

• Ines Stager is a landscape architect based in Geraldine, and a committee member of the local branch of the Royal Forest & Bird Protection Society.