Spanish heath should be taken seriously

Press, 2 August 1985, Page 19

Spanish heath should be taken seriously

Spanish heath should be taken seriously in areas where it is rampant, according to a research scientist, Ms Louise Mather. Ms Mather has just completed a year-long contract with the Noxious Plants Council and the Botany Division of the D.S.I.R. She investigated the

plant’s ecology in the hope of finding a weakness which could be used to help control it. Spanish heath grows mainly on marginal hill country throughout New Zealand. Several counties have become so alarmed about its spread that they have asked the Noxious

Plants Council to classify it as a noxious plant or to fund special control projects. Ms Mather’s report is now being considered by the council’s classification committee, which is expected to make a recommendation on control policy for Spanish heath later this year.

At present, the Noxious Plants Council’s policy on this weed states that control of Spanish heath must be part of an over-all farm management strategy including raising the fertility of the soil and establishing a good pasture cover to exclude this plant. The council asked Ms Mather to investigate the plant’s distribution, how significant it is as a weed in different land use situations and soil conditions, its potential to spread, and to give recommendations for future control. A member of the Erica family, Spanish heath can still be bought from plant nurseries as an ornamental plant even though it poses a threat to grazing on low fertility marginal hill country. It bears pretty bellshaped flowers in winter with pink buds which later turn white. It can spread rapidly — a specimen planted on a Scotsman’s grave in Picton in the early 1900 s is credited with being the source of infestation in the Marlborough Sounds area. Spanish heath is not really a problem in any other country. Like many of our scrub weeds, it comes from the Mediterranean and is particularly well adapted to our climate. The hardy plant can live for more than 40 years. Sheep and cattle do not like eating it and Spanish heath plants can form impenetrable stands so dense that farmers cannot use the land for grazing, particularly in areas where over-sowing and fertiliser applications are neglected. Much of the marginal land infested with Spanish heath has been planted with pine trees. Although the heath is not a problem for forestry at the present, plants are persisting and flowering beneath heavily thinned and pruned stands. So when trees are har-

vested, Spanish heath may cause problems for the establishment of the second crop — depending on how long their seeds remain viable in the soil. There are certainly no easy answers to controlling Spanish heath, Ms Mather said. “If the land can be worked Spanish heath will be eliminated as it is susceptible to root disturbance. Good management of the land must follow and be maintained over a long term,” she said. The plant only seems to be vulnerable when the seedlings are establishing themselves. “If you manage to put down a good pasture sward, then the seedlings may suffer from competition and I have shown this in experiments.” As farmers in areas infested with Spanish heath know, the young plants are remarkably resilient. “I have cut seedlings down and they have still managed to regrow shoots. Putting a fire through Spanish heath doesn’t work either — it just rejuvenates the plants and they regenerate. “You also get seedling establishment on the bare ground after a fire,” Ms Mather said. “However, these plants can also slowly invade improved pasture. Farm animals can clear ground with their hooves and since there are such large numbers of seeds in the soil, this can encourage seedling establishment,” she said. Her research report is based on work at two study sites — one at Okuti Valley

on Banks Peninsula near Christchurch and the other at the Kakahu forest area, south of Geraldine. Moisture and the warmer temperatures of the lower altitude at Okuti Valley resulte'd in more vigorous plants. Seeds can remain dormant in the ground for many years, even in areas which have been sprayed with herbicide. Seed production is prolific. Each flower produces 80 to 100 seeds. Understandably, Ms Mather did not attempt to count flowers as each stem larger than 50cm bears at least 5000 flowers. The seeds are so tiny and light that the wind disperses them over great distances. Some seeds remain in the flower capsules and can get caught in the wool of sheep brushing past. Many of the seeds fall from the parent plant and become incorporated into a gigantic “seed bank.” As many as 200,000 seeds per square metre are found underneath established heath stands in the top scm of soil. These seeds germinate in autumn and spring. Plenty of work remains to be done on the plant to reveal its weaknesses. Ms Mather has recommended that future research should concentrate on the effects of competition from other plants and stock management, including the use of goats. Finding out how long the seeds remain viable in the soil could also be useful, as could research on biological control and root growth associated with different soil types.