Agroforestry trials established

Press, 5 October 1984, Page 26

Agroforestry trials established

Four agroforestry demonstration plots are being established in Canterbury, including two on Banks Peninsula, by the Forest Service.

The trials will show fanners how low density forestry and grazing by stock can be combined.

The Canterbury trials are a small part of the agroforestry research being done throughout New Zealand. Part of the Lands and Survey Department’s Okuku Pass station, near Rangiora, is devoted to agroforestry and other projects are under way at Rotorua and in Otago. According to M.A.F., economic analyses show that under present prices for clearwood, combined with reasonable levels of management, agroforestry has a similar profitability to conventional agriculture or forestry. Banks Peninsula has been selected as one area for agroforestry trials because of the district’s pockets of micro-climates where trees will grow quickly. One 3ha site om the peninsula is being planted with trees which provide speciality timbers, including Douglas fir, black walnut, blackwood, macrocarpa and eucalyptus regnans. This site will later be grazed by deer.

Another Banks Peninsula plot planted in radiata will be grazed by sheep and cattle. In North Canterbury, 4ha was planted in radiata about seven years ago and this block might be divided into four areas under different management techniques. A site at Yaldhurst was planted last year to demonstrate the benefits of shelter. As well as creating a micro-climate to enable faster grass growth and less stress on stock, the trees will provide timber. Forestry and agriculture are proving compatible on two trial sites in south-east Otago, according to Mr Gordon Crossens, an agronomist at the Invermay Agricultural Research Centre of the M.A.F. These trials, run in conjunction with the Forest Service, were started about 10 years ago and involve grazing by stock under radiata trees. One set of trials is located on 7ha of cultivated, high fertility, rolling pasture on the Invermay farm.

The other covers about 40ha of low fertility, oversown tussock country in the Akatore area of the Forest Service’s Otago coast forest, 50km south of Dunedin.

Open pasture at the Invermay site has a livestock carrying capacity of 20 stock units per ha, compared with nine stock units per ha at Akatore. Trees were planted on the Invernmay site in 1974 at two initial densities (400 and 750 stems per ha) and the pasture underneath grazed by sheep.

In three operations over the last 10 years — in 1979, 1981 and 1984 — the trees have been progressively thinned to a final density of 70 to 110 stems per ha and pruned up to 6m in height. Similar trials, but with initial tree densities of 600 and 1200 stems per ha, were established at Akatore in 1975 and 1976, and are being grazed by sheep and cattle. Following progressive thinning, tree densities this year — the ninth year after planting — are 200, 400 and 600 stems per ha. The trees will be given a final thinning later this year to give a tree stocking rate of about 100 stems per ha. Although Invermay research information only covers up to 10 of the 30 year tree rotation, indications are that agroforestry will provide greater net returns in the long term than either forest or pasture alone.

For the total 30 year period, economists predict that net profits from agroforestry on the Invermay site will be about 10 per cent greater than those which could be expected from open pasture on the same land.

On the Akatore trials, an increase of about six per cent in net profit is projected.

These results are dependent on agroforestry being at a final tree density of 100 stems per ha. They are based on estimates of future prices for pastoral products and current domestic prices for timber. Because they were calculated to show the returns from a national viewpoint, they do not take into consideration existing subsidies for forestry or pastoral farming. Economists say the actual increase in profits to the farmer could be even greater because of such factors as the availability of forestry encouragement grants.

Cost savings could also be made if the fanner had the time to carry out thinning and pruning operations himself. Contract rates were used in the calculations for Invermay and Akatore.

Account has been taken of the cost associated with

tying up capital in agroforestry for 30 years and forgoing the interest which could have been gained on that money. When considering the projected increase in profits from agroforestry, it must be remembered that most of the tree income will not become available until the end of the 30 year tree rotation when the trees are logged and the timber sold. In the intervening years, a reduction in cash in-flow can be expected, due to the decreased livestock carrying capacity on pasture under trees.

This reduction is particularly noticeable in the first three years after planting when stock carrying capacity is severely restricted because of the need to protect young trees from browsing damage. It is also likely to be marked in years 17 to 30 when stock carrying capacity is expected to be relatively. low, due to increased tree canopy cover reducing available light and limiting pasture growth. This interim reduction in cash inflow could be alleviated and long-term profits further increased if the farmer was able to lift stock carrying capacity on his remaining farm land.

Other significant indications from Invermay research are that the best balance of tree and animal productivity, giving the highest possible returns, is likely to be achieved with a final tree density of 70 to 110 stems per hectare. This is provided thinning and pruning operations are completed in three lifts by the tenth year after planting, Mr Cosswns says.

Under such a regime, pasture under radiata can be expected to support an average of 50 per cent of the livestock numbers carried by open pasture over a 30 year tree rotation. From years four to 17, it can be expected to support no less than 55 per cent and up to 85 per cent of the livestock numbers carried by open pasture. During the last 13 years (years 17 to 30) stock carrying capacity can be expected to drop from 55 per cent to no less than 30 per cent of that of open pasture. However, if the final tree stocking rate is higher than 150 stems per ha 10 years after planting, stock carrying capacity is likely to drop much more rapidly. This is due to increased tree canopy cover which has a more severe impact in reducing available light and limiting pasture growth.

Mr Cossens says the amount of first quality timber is also likely to decrease at tree stocking rates above 150 stems per ha after year 10. These points have not yet been demonstrated conclusively by Invermay scientists because the trials so far only cover 10 years of the tree rotation.

But Mr Cossens says they are fairly reliable predictions, based on existing data on forest tree growth and the results of the first 10 years of agroforestry research in south east Otago and on other New Zealand trial sites.

For example, the fact that pasture yield under trees at Invermay was 13 per cent lower than open pasture in 1983-84 was clearly due to the increas-

ing canopy cover as trees at densities of 185 and 200 stems per ha matured. When the trees were thinned to 100 stems per ha in January, 1984, pasture growth responded rapidly. Although pasture production under trees remained as high as that of open pasture in the first seven years after planting, Mr Cossens says stock carrying capacity was severely restricted in the first three years because of the need to protect young trees from browsing damage. The importance of correctly timing introduction and removal of stock to prevent serious tree damage was demonstrated in the trials on the Invermay site when 50 stock units to the ha were grazed on the pasture beneath the trees directly after planting. Within a month, 20 per cent of the trees had been seriously damaged.

In contrast, when stock were introduced later uid at lower stocking rates on the Akatore site, only six per cent of the trees were seriously damaged.

Mr Cossens recommends that pasture under trees be left ungrazed for the first two years unless the farmer is prepared to look at his trees every day and remove stock immediately damage occurs.

From year four to 10 of the tree rotation, stock carrying capacity fluctuatted slightly, according to the presence and absence of slash from pruning and thinning operations. Mr Cossens says slash on pasture appears to have only a slight affect in restricting the amount of grass available for grazing, provided pruning and thinning operations are carried out in three lifts by year 10 of the rotation.