Poplars set for emphatic comeback

Press, 27 June 1987, Page 22

Poplars set for emphatic comeback

Country Diary

Derrick Rooney

Z Clean, white, straight-grained timber, good for posts, decking, jyeneer, framing, or pulp — 20 years after planting as unrooted cuttings directly into stony riverbed land subject to periodic flooding. ' It sounds like a pipedream, but jjt represents a development >which could have considerable for shelter, soil con.servation, and possibly for limber production from otherWise unproductive land in many parts of the. country. . , ' --The poplar is back. ♦tr A decade ago, the poplars, a family of trees which entrenched themselves in the New Zealand .landscape, seemed to be on the way out. .. x Poplar rust, which arrived /from Australia by air on the ifrans-Tasman trade winds about 3973, was hot horticultural news. 'Rust was spreading rapidly and The two favourite poplars — the black poplar and its jjjpright. form, the Lombardy — ■were among the most vulnerable Jto it. Like the elm of England jjifter Dutch elm disease, these -two characteristic trees of. the JNew Zealand farmscape seemed dieaded for oblivion. 5* Predictions were made that ■;ihe face of the landscape would Change, particularly in the inland of the South Island. Happily, the actuality turned 7dut to be less bad than the Lombardy poplars are tjtill a dominant element of the Otago landscape, and, in £nany other areas, big old trees to light up the autumn —. sometimes.

Poplar rust causes leaves to fall prematurely and thus restricts the growth .of the trees. In a bad infestation all the leaves are shed, by late sumiher, and the golden autumn colours for

which poplars are noted fail- to materialise. When the rust arrived, about 20 poplar clones were available for shelter and conservation planting in New Zealand, but only three were widely grown. In fact, these three clones accounted for about 70 per cent of all poplar plantings in the country. All three, plus most of the other 17, were susceptible to rust.

If you think that sounds like a recipe for difficulties, you’re right The few clones resistant to the disease had faults — such as root systems unsuitable for soilconservation plantings; heavy, brittle branching; poor quality timber; or large, spreading crowns that made them unsuitable for horticultural shelter. Since 1973 the National Plant Materials Centre at Aokautere, near Palmerston North, has im-

ported 239 clones of poplar and 290 seedlots of European, Asiatic, and. North American' poplars. A number of hybrids has also been raised at the centre. No shortage of diversify there! So far, only 11 of the “new” poplars have been released for sale, and only three are regarded as suitable for horticultural shelter. Several more are scheduled for release in the next few years, and in the pipeline are promising New Zealand-raised hybrids, of which one, named “Kawa,” has been released.

Some of these new poplars are on trials in parts of the South Island, and a few days ago Dr John Sheppard, of the Ministry of Works : and Development, showed me vigorous young trial stands in the Waimakariri River bermlands at Courtenay. The trees were impressive: well formed, at least as fast-growing as pines and in some cases possibly faster, having had the advantage of thriving on periodic • inundation by floodwaters. In the same situation, pines would peg out. • .

Poplars are not native to New Zealand. They occur naturally in the temperate zone of the Northern Hemisphere and the only species to extend south of the Equator is a tropical one, in East Africa. Poplars are a very minor

part of the timber trade in New Zealand, but. in some Northern Hemisphere countries they are of considerable economic importance, being used for building, firewood, stock fodder, shelter, shade, veneer,, fibre, paper pulp, and. matches. \ * •

As they thrive in wet gullies, bermlands, and swampy areas where the more familiar timber cannot be grown, they have considerable potential, says Dr Sheppard. They are equally valuable for erosion control in hill country. Poplar timber is light and soft, but strong and flexible, and there is a small but steady demand for it. The logs command a higher stumpage price than pine. In the Northern Hemisphere, fibreboard and paper of high qualify are made from poplar

pulp. Its suitability for similar uses in New Zealand is as yet largely an unknown quantity, but the potential of some of the hew varieties is being assessed this year in a trial being held jointly with a North Canterbury manufacturer, says Dr Sheppard. On the farm, poplar has a variety of uses. When treated, poplar makes excellent posts — stronger, some say, than pine posts. In dry periods, the foliage and young shoots can be cut and fed to livestock. Poplar leaves are rich in nitrogen, potassium,

calcium, and zinc; their nutritive value is about equal to that of lucerne hay. In fact, if it weren’t for the recently-arrived diseases, the poplars would be just about the ultimate in your easy-care, no-hassle trees.

You don’t have to mess about raising them from seed (like pines) or gentling them along-in a nursery bed. Just cut rods up to 'three metres long in winter, -/ plant them with about one-third of their length in the ground (same as fence posts), and within

a couple of years you have a small tree with most of its foliage above stock reach. In riverbed lands, poplar poles can be "ploughed in” behind a bulldozer, like willow poles. What the Ministry’s Water and Soil Directorate would like to see, says Dr Sheppard, is about 25 to ,30 poplar clones being widely planted.

This ■ would broaden the genetic base of the resource, and at the same time lessen the chance of mass wipe-outs if another . new pest or disease arrives.

Quarantine precautions have ensured that no new pest or disease has arrived with any of the imported material but, says Dr Sheppard, the poplar rust and other recent undesirable arrivals were self-introduced. It is significant, he says, that the last three new poplar diseases have arrived here within a year of their first appearance in Australia. the latest arrival is a leaf spot which defoliates silver poplar, one of the most familiar soilconservation species. This fungus was first reported in New Zealand in 1985, and year had spread throughout the country.

Most of the new poplars from Aokautere, including two clones and two hybrids of silver poplar, are resistant to leaf spot and to the surviving poplar , rust (the other-rust died out soon after its arrival in New Zealand; for lack of a suitable host to cany it, through the winter). But, says Dr Sheppard, until the number of different clones being planted is

greatly increased, the risk of widespread disease remains. There mdy be other ways around the problem. One of these, in the pipeline, is a range of new plane trees selected for their good form and ease of propagation from cuttings. Someone thought there might be a future for these as an alternative to poplars for pole planting. . , - •

A number of new willows are in the offing, also, and as with the poplars the Ministry is keen to see these widely distributed. The willows comprise a much bigger family than the poplars, with about 300 species, mostly in the temperate Northern Hemisphere, and though largely unknown and unexploited in New Zealand these have numerous potential uses from stock fodder to bee foraging (for pollen and nectar), basketry, timber, fire- . wood, and soil stabilisation. Weeping willows, a notable feature of the central Christchurch riverbanks, were first grown in New Zealand almost 150 years ago, and the most common species — the crack willow — has been here about 130 years. . ; . Fifty years ago, the Christchurch Botanic Gardens, on behalf of the ? Waimakariri River Trust, imported about 60 kinds of 'willow from the Royal Botanic Gardens, Kew, and planted them on bermlands and swamps in the Chaneys area, but I don’t know if - anyone could say how many of - these survive today, /or even identify them. In fact, until quite recent times fewer than 20 wil-

low varieties were commercially available, and only a handful of these were widely planted. Interest in willows has now increased, and many clones have been imported • both by the Aokautere centre and by private growers. More than 200 different willows are now being grown at Aokautere. - Small groups selected from these — and including New Zealand-raised, hybrids — are on trial in the Waimakariri riverbed near Christchurch. Airport. Some are the shrubby, multi-stemmed !: osier types, which include the willows, and some are j tree willows.-. The latter, since the arrival of poplar rust, have commanded increasing interest for shelter planting, and in recent years hundreds of kilometres of the Chinese willow (Salix matsudana) have been planted in shelter belts for orchards and market gardens. Increasing interest also in coppicing (for firewood) and in alternative timber species has led to extensive hybridising of the Chinese willow, mainly with the more familiar white willow, and a number of clones have been released from Aokautere. Five of them are on trial in the Waimakariri, and are shoeing considerable promise. Planted as rods, they have grown

mostly at the rate of more than a

. metre a year and although they have had minimal or no silviculture, most are of excellent form. All five are named after soilconservation stations: Adair,

Aokautere, Hiwinul, Moutere, and Wairakei.

Dr Sheppard is keen to see catchment authorities and farmers not only making more extensive use of these new willows, but also pruning and tending them, to obtain crops of timber from areas that are now wastelands, with little or no wildlife or recreational values. At present, he says, most catchment authorities plant a restricted number of clones. As a consequence, there is a real fear of insufficient genetic- diversify in New Zealand willows to resist any disease that might arrive.d Even the new Chinese-white willow hybrids carry some risk, because, all the current clones have a single tree of Salix matsudana as the female parent. To counter this risk, the Aokautere station has imported new strains of matsudana willow from different parts of China, and will broaden the genetic base of local willow strains by breeding from these. ......

In due course, a wide variety of clones of these fast-growing willows, which establish quickly and easily from cuttings, will be available for planting. Their usefulness will not be confined to river lands, because.wiljows are also good for stabilising slipprone soils in hill country. Will they be among the timber trees of the future? Dr Sheppard likes to think so. Recently, he says, the North Canterbury Catchment Board found a keen buyer when it put up a block of Waimakariri poplar for tender among local sawmills. He believes the new willows will yield timber at least as good as poplar, and may well grow it at a faster rate.