Poplars and Willows on Farms

Bruce Wills wants to see poplars and willows planted across 700,000 more hectares of steep hill country in New Zealand, and he heads a trust promoting their use and providing research to develop new clones.

In 2007 MAF established a Hill Country Erosion Fund to decrease pastoral hill country erosion through financial support for regional soil conservation projects. New plantings of poplars and willows are a key component of these projects.

In February 2008, $450,000 a year was sought from this fund to develop new poplar and willow material, field check its suitability, bulk up supplies for council nurseries, carry out disease and pest monitoring, research new clone physiology and to provide educational material and services.

In July 2008, MAF agreed to provide $175,000 per annum for four years from their fund, conditional on councils providing a similar amount and a stable funding source being established to provide a secure long term future.

Councils agreed to the proposal and the Poplar and Willow Research Trust was formed in late 2009 with the brief to find and secure funding for poplar and willow research beyond 2012.

The NZ Poplar & Willow Research Trust’s aims are primarily to breed new poplar and willow clones which are more adaptable and for niche sites. And those new clones should give a greater variability within poplars and willows planted in NZ, spreading the risk.

Ian McIvor, senior scientist and plant breeder says “We are looking to produce clones from different parent species: our parent stocks are from either North America, Europe or Asia. Most of our original clones are either pure species or hybrids of European or North American origin. By using Asian species in our breeding programme we can introduce resistance genes to the current prevalent pests and diseases, for example poplar rust.

The breeding programmes for poplars in other parts of the world are focused on timber production. But how we use poplars in NZ is different. We grow our poplars singly out in the landscape. They grow differently than they do in a forest plantation with close spacing and lots of competition for light. Many of the early clones imported to NZ, when given space grew a broad crown which produced lots of shade on the pasture, and made the trees more vulnerable to branches breaking in the wind.

We are looking to grow clones which are more tapered, and have a narrower crown, which is called fastigiate. This shape will also minimise shading on pasture. This upright form also makes the trees less vulnerable to breakage.

This is the familiar shape of Lombardy poplars. However the fastigiate clones bred in NZ have a more vigorous rooting system and better disease resistance and perform better in soil conservation roles.

This year we released six new poplar clones: these were bred through the 1990’s. It has taken 15 years to go through the process of nursery selection, bulking up for field trials, evaluation in the field for 10 to 12 years, and then bulking up for sale.

We aim to breed willows with a reasonably upright form for the same reasons. However the natural habit of willows is to grow several main stems, not just one like poplars.

Willow sawfly arrived in NZ in the mid 1990’s, and caused massive defoliation in riverbank willows, resulting in significant willow deaths and a weakening of flood defences. We brought in seeds of one tree willow not planted in our landscape, which was selected in the first instance because it grows in the natural habitat of the willow sawfly and did not get defoliated.

While it does get eaten by the sawfly, this new willow doesn’t appear to be a favourite part of the sawfly’s diet. In initial trials the caterpillars didn’t eat the leaves of that species as fast as others. We don’t know the exact reason, but it may be the chemical composition in the leaf. Eggs are still laid on the leaves, and the caterpillars will mature right through to adulthood on the leaf, but they are very slow to mature.

If we can increase the length of the sawfly lifecycle by using this new species as a parent in our breeding programme, we could reduce the number of generations of sawfly produced over a season, and that may reduce the sawfly problem.

I have done some experimental work looking at the rate at which new clones produce roots compared with commercial clones. It is an advantage to produce roots faster.

If you plant a 3m long pole into the ground, only 70-80cm of it is actually in the ground. The rest of it is exposed to the air and will lose water. If we can select clones where the poles produce roots at a greater rate, then that’s a good thing.

Any feature we can select for that increases the rate of plant survival and establishment is a good thing. It gives end users confidence in the material.

We did an experiment last summer looking at root development in a number of different willows, mostly hybrids. Two of the hybrid willows stood out as producing quite a lot of root material quickly. We are repeating the experiment with five different clones of each of the hybrids. One set is growing in the ground, and one set is growing in water. We want to know if the rooting behaviour is seen in all of the clones, and if so we have more options for selecting other features.

This other pot trial is about water use efficiency of poplars and how they can handle situations of water shortage. We are testing several different poplar clones in this experiment. The survival of poles in their first two years is quite critical, and water stress is the main factor threatening survival. Those clones which can manage limited water better are a better option for planting.

Poplar clones that are profligate water users have a role in wastewater management so different characteristics can be useful for different purposes, and both poplars and willows are used for multiple purposes.

Bruce Wills, Chairman of the NZ Poplar and Willow Research Trust says, “My message is we need more trees on NZ farmland, and we are promoting their use on farmland by developing some easy, relatively inexpensive trees to grow in grazing regimes.

Most of the Trust’s research at the moment is on root mass, form and wind tolerance.

The results are quite regional, and we don’t have recommended species for the whole country. Species choice for different regions depends on their drought tolerance and wind tolerance for example.

Our Trust is now hosted by Massey University’s Institute of Natural Resources. This is a very good association for us, and we are better linked with the academic teaching staff. We are very pleased with this development.

A lot of the Trust’s work is in technology transfer. We do a lot of work supporting regional council land and river managers in promoting the use of willows and poplars. Our trustees include a river manager and a land manager from separate regional councils. Every regional council in NZ, apart from the Otago Regional Council, helps fund the Trust too. Now Beef + Lamb is on board as a sponsor of the Trust. This enables us to use their network and their ability to hold open days to tell our story across the country.”

I hesitate to use the word passionate, but I really get the importance of poplars and willows on hill country. I have seen the benefits.

Cyclone Bola in 1988 delivered a very strong environmental message that we have some serious mitigation to do on hill country. We proceeded to plant thousands and thousands of trees: about 7000 on our property Trelinnoe. With these trees and all our native bush fenced off, we would have a fraction of the damage that Bola caused. There is no question in my mind that those trees are very efficient at holding hillsides where they need to stay.

Of course, there are all these other benefits too: shade, shelter, erosion control, fodder value, and aesthetics.

Poplars and willows are well proven simple trees that fit well with our existing pastoral farming systems.

We have identified around 700,000ha of medium to steep hill country in NZ that needs these sorts of trees on it: that’s a significant area.

Demand for poles has increased this year. Only part way through the planting season there wasn’t a spare pole to be found. For example the Hawke’s Bay Regional Council produced 35,000 poles this year, and could have easily sold half as many again.

A main focus for the Trust is to get assured funding for on-going research into the better and more suitable varieties of poplars and willows. We’re not a big Trust, with only one employee, Ian McIvor. But our impact is large.

Currently the Trust, which is registered as a charity, has funding of $175,000 from MAF which runs out on 30 June 2012. We hope to replace that with commercial sponsorship.”

More information is available on www.poplarandwillow.org.nz