Central Otagoa Changing Grassland Scene

New Zealand Journal of Agriculture, Volume 95, Issue 3, 16 September 1957, Page 238

Central Otago — a Changing Grassland Scene

FOR many years the low-rainfall areas of Central Otago have been of note for their rich historical interest, their rabbits, and their large area of grey, mat-forming scabweed. For a long time also investigations have been carried out with the object of replacing the scabweed with useful pasture plants, but though much information was secured on grasses which would grow provided they were protected from grazing by sheep and rabbits, if was never possible for any of this information to be put into practice by those who farmed the land. COLD winters and hot, dry summers were thought to be one of the major factors limiting improvement, yet within the fenced-off areas a surprising variety of grasses and clovers would grow and survive. Climate was

one limiting factor, but the most important and destructive one was the rabbit. Rabbits were so plentiful and so voracious that they left the ground denuded except for the patches of scabweed, which were quite unpalatable to sheep and rabbits. For many years grasses and clovers have been tried out by the Extension Division of the Department of Agriculture at Earnscleugh, Wanaka, Ardgour Valley, the Dunstan Range, Pisa Flats, Bannockburn, Springvale, Ophir, Fruitlands, Hawea Flat, and many other places. Hardly ever could the information secured be put into practice because of the ever-present hordes of rabbits. Under these conditions the work was discouraging to those who were carrying it out and whose only hope was that some day the rabbit would be destroyed. The work was carried on under considerable difficulties, always with the rather forlorn hope that the time would come when the rabbit would be so reduced that the information gained would be put into practice. For years the fenced-off, rabbit-free areas, whether large or small, stood out as monuments of unfulfilled hopes in an apparently endless sea of scabweed, rocks, and rabbits. Dramatic Change . Today all this is changing: The rabbit has been made worthless through the action of the Rabbit Destruction Council. Rabbit boards have carried out a concentrated plan of destruction. As a result rabbits have been so reduced that in many areas they are no longer the chief agent limiting the growth and survival of palatable plants. A few rabbits are still seen, but only in the early morning and in the evening. No longer are the roads littered With the carcasses of rabbits run over by night travelling cars; no longer do the hawks obtain easily secured meals on the roads. This wholesale destruction of the rabbit is now effecting, certainly slowly, a transformation in the depleted country of Central Otago. For many years scabweed has been regarded as a worthless plantquite unpalatable and therefore of no use. If rabbits can be kept down, there is little doubt that, in retrospect, the

value of the scabweed will be appreciated, because over the years it has acted as a caretaker of the soil. As the result of wind and water erosion enormous quantities of soil have been blown and washed away, but the scabweed has played a very important part in soil retention. Its spreading habit has not only provided a windproof blanket for the soil, but over the years has trapped at least some of the windand waterborne, dusty soil. Unquestionably the .much maligned scabweed has been a blessing in disguise. A visitor now passing through this country; after an absence of a few years is amazed to find that the; sea of dull grey scabweed he has so long associated with this depleted area no longer dominates the landscape. In spring and autumn he sees a tinge of green over the hills and flats; in summer he sees the thin brown veneer of sun-dried grass. The face of Central Otago’s problem lands is changing from year-round grey to alternating green and brown as one season follows another. Scabweed Being Replaced The scabweed is still there, but it is being overtopped by grasses, mainly annuals. Hairgrasses and brome grass are increasing rapidly and the not very useful haresfoot trefoil is spreading slowly. A community of annuals is gradually replacing the scabweed. Dead and dying scabweed is abundant. This soil- and moisture-conserv-ing organic matter provides an excellent seed-bed in which plants can establish. A mild winter in 1956 and the wet summer which followed both did much to speed up the ingress of this annual vegetation. The information gained from years of experiment during the period of rabbit infestation can now be put into practice. Many of the trials laid down by the Department of Agriculture have included a wide range of droughttolerant pasture species as well as some of the commonly used plants, such as ryegrass, crested dogstail, and cocksfoot. In many places cocksfoot, white clover, and red clover have established and grown well. There has, however, always been the suspicion that some unusual conditions were favouring their survival.

Surface Sowinas y Surface sowings by runholders during the last year or two have shown that cocksfoot and white and red clovers will establish and survive, at least in the valley floors and on shady faces. Experimental evidence shows nn^nfrv WiU alS ° SrW ° n thiS y- ■ All the evidence available indicates that the introduction of cocksfoot, lucerne, and, on valley floors and shady faces, white and red clovers is likely to give satisfactory results. Several other soecies of grass such as Bromus inermis Bromus marginatus and tall oat grass look promising, but cannot be evaluated until grazing trials lasting a year or two have been conducted. Grazing trials are essen-

tial to ensure not only that the grasses will grow but that they will be grazed readily by sheep. For example, love grass (Eragrostis curvula) established an ft grew well in plant nurseries, but was completely neglected when an area o f ft was opened for grazing by sheep. Numerous trials carried out by the Department of Agriculture have shown that pasture species can be introduced most satisfactorily by burying the seed i n the ground. Several makes of machine are now available which either disturb the soil or make grooves into which the seed can falL Wherever it; is possible to take Wheeled machinery this method is advocated. Where machinery cannot be taken the only method of introduction is surface sowing. This can now be done

—— rapidly by the use of aeroplanes and with this method the cost is a great deal less than that for hand sowing, However, the strike of seed resulting from aerial sowing on the ground is not nearly as good as that. from mechanical sowing of the seed m the ground. go far the ingress of the annual plants and the introduction of perennial grasses ana clovers have been considered. It is necessary to realise that native grasses, too, are recovering.

All through the tussock country small, isolated communities of native grasses have managed to survive in places such as rock crevices and damp areas. Where rabbits could not kill them out these plants are now recovering rapidly and are setting and shedding their seed. Within a few years a marked increase in the native grasses can confidently be expected. Blue wheat grass, fescue, silver and blue tussocks, and plume grass are now conspicuous in areas where a few years ago only odd plants were seen.

New Era All in all there is every indication that within the next 10 years or so the depleted country of Central Otago will be transformed. Already annual grasses and clovers have started to replace the scab weed and there is every reason to believe that on much of the country perennial grasses and legumes will replace much of the annual grass. , The easing of grazing pressure on the plant cover by the destruction of rabbits has brought one problem in its train: The better conditions assist the growth of some weeds as much as they benefit useful species. This was foreseen a number of years ago when in enclosed areas unpalatable plants such as sweet brier, matagouri, and native broom became established. For some years the Department of Agriculture has been experimenting with various chemicals with the object of controlling sweet brier. Considerable progress has been made and established bushes can be controlled individually, but no satisfactory method has yet been found for controlling seedling plants economically.

The future of the depleted land of Central Otago has never looked brighter. Native grasses are regenerating and the sowing of introduced grasses and legumes has passed beyond the experimental stage. A watch must, however, be kept on the ingress of unpalatable plants, > such as brier, gorse, and broom, which unless checked when in small amounts could eventually take charge.