Lasting scars from drought?

Press, 1 March 1982, Page 1

Lasting scars from drought?

By

DERRICK ROONEY

Drought conditions occur regularly in Canterbury during summer, and are largely accepted by the province's farmers and foresters as part of the way of life. But there is growing evidence to suggest that this . summer’s drought, far from causing the usual temporary inconvenience, is going to leave lasting scars on the landscape. Comparisons are being made in some quarters with the Great English drought of 1976, when trees shed their leaves, months of hot, dry weather turned the whole countryside brown, and some wells which had been reliable for centuries dried up. This summer in Canterbury is analogous with that British summer, in that the rainfall on the plains has been only about one-third of the average expected during the period. In January, for example, Christchurch Airport recorded only 12mm,

compared with the monthly average of 47mm; and for • February, up to last Friday, 22mm was recorded, compared with the monthly average of 49mm. But the rainfall figures tell only part ( of the story, and in . themselves do not explain the severity of the drought, which has not only burnt off * pastures but has had an unusually harsh effect on trees in many parts of the province. Dead or disabled trees — not just young trees but mature specimens 10. 20 or more years old — have been reported in many parts of the central plains and foothills, and some foresters are worried more about this than about the extreme fire . hazard, because among the ; worst sufferers are some ; species which have been [. widely planted for shelter or j timber. A Forest Service forestry ■ extension officer, Mr T. Rus- , sell, told the Central Farm

Foresters Association last week that he was concerned about the situation. Experienced farm foresters told the association's meeting that Canterbury farmers may have to think again, in the light of this year's experience, about their choices of shelter trees. One of the most widely affected trees is the Douglas fir. which has been extensively planted in recent years as a premium timber tree. This year it has given Canterbury’ farmers a sharp reminder that it comes from a zone of higher, rainfall than the Canterbury Plains. Losses of recently planted Douglas fir are believed to run into many thousands, and over a wide area of the central plains older trees are dying, too. A similarly worrying aspect of the drought for many farmers is that some of the trees which are dying are species which have in the

past been regarded as highly drought-tolerant. These include Australian eucalypts, Arizona cypresses, and some pines and related coniferous trees. Foresters say that these evergreen species are more likely to suffer permanent damage than are deciduous trees, many- of which have simply shut up shop for the summer, dropped all of most of their leaves, and gone into dormancy. It is considered that these trees will recover next spring. Conifers of many kinds appear to be the worst sufferers. Broadleaf trees, other than some eucalypts. are less widely affected, although it was reported at the weekend that a rare Madrona tree, 60 to 70 years old, was dead at Governor's Bay. Fi-brous-rooted shrubs and small trees, particularly rhododendrons, are dying in i many gardens. ; Even Pinus radiata trees j are showing severe signs of

stress in many shelter belts, as also are Arizona cypresses. Trees of the latter species up to 25 years old are reported dead on some lighter soils in the central plains, and it seems certain that many shelter belts will be left with gaps that will take years to fill. Why this has happened this year is not yet clear, but many foresters believe it is the result of a combination of several factors, among which the low rainfall is not necessarily the most damaging. Very low humidities, coupled with strong sunshine, hot winds, and high day temperatures have been recorded in many districts, and at the same’ time some places suffered low night temperatures in January and early February. Thus some tree’s have been, in effect, cooked by day and frozen at night.

Zero night temperatures have been recorded at least once already in inland Canterbury, and near Hororata a record high of 44deg. was recorded unofficially on February 15. when the official ’ maximum in Christchurch was 38deg. But during that night the thermometer on one Hororata property fell to 6deg.

“These." said a central plains farmer, "are desert conditions, and as we all

know nothing grows in a desert."

During these periods of atmospheric stress, reportedly high soil temperatures have served a further blow to trees struggling to maintain their top growth. The farm foresters were staggered at their meeting last week when Mr P. W. Smail, of Hororata, showed them a graph of January soil temperatures recorded on climate-monitoring equipment installed on his property by the Ministry of Agriculture.

Mr Smail, who is chairman of the Selwyn Plantation Board, is a member of the National Shelter Working Party set up jointly by the Ministry and the D.5.1.R.. and his property is one of anumber throughout the country where-wind, soil and air temperatures, and dry-mat-ter yield are being monitored to gather data on the effect of shelter on growth. The chart for January’ showed soil temperatures. 10cm below the surface, ranging above 30deg. At 30cm below the surface temperatures up to 25deg. were recorded.

These figures had so surprised the scientists running the trials that a technician had been sent out to test the machine. Mr Sniail said.

On Mr Smail’s property, as on many others, most of the deciduous trees have shed most or al) of their leaves. Some species of eucalyptus aged 10 years or more are dead or dying, and some 10-year-old Douglas firs have died in a shelter belt. Nearby, severe losses have occurred in a young Selwyn Plantation Board plantation of Douglas firs. Mr Smail agreed with other farm foresters at last week's meeting that much of this damage was as much the result of sunburn and windburn as of lack of moisture. What is yet to be discovered is the percentage of stressed trees which have suffered permanent damage. Here again comparisons have been made with the English situation of 1976. when heavy September rains broke eight months of drought — just after the British Meteorological Service reported to the emer-gency-appointed Minister of Drought that no change in the weather was expected — and deciduous trees which had shed their leaves prematurely greened up almost overnight. Other parallels with the English drought are seen in the heavy crops being carried by many walnut trees, and heavy crops of pip fruit and stone fruit in many gardens. It remains to be seen whether our March will bring rains that reflect Britain's September.