Trial weighs up pros and cons of agroforestry in grazing systems

That question formed the basis of a three year silvopastoral system trial in northern Queensland, evaluating integrated systems of forestry, trees and grazing.

The trial examined the merits of the system compared to conventional forestry or grazing systems.

The study took place on a commercial plantation south of Cardwell, across three sites roughly 16ha each.

Kennedy Valley cattle producers Peter and Mariah Chiesa of Palm Creek Brahmans, provided cattle and land for the trial.

Mr Chiesa said they were happy to be involved in the trial as they'd already leased pine forest country adjoining their property.

They run 500 Brahman breeders plus progeny, using a rotational grazing system on both their 130ha home property and 580ha of leased pine country.

"The pine forest is split up into 13 paddocks with electric wire, and we just rotate them around" Mr Chiesa said.

"For me that is the best way to operate cattle and pasture in the pine forest. It allows for sufficient rest for the grass to grow back.

"You can have too much shade and nothing wants to grow, so we let the cattle graze in a paddock, rest it and it grows back better.

"I think they are starting to see a bit of anecdotal evidence about the trees being a bit healthier in the pine forest we are in.

"It makes mustering and managing your cattle a lot easier as well, being able to rotationally graze through that pine."

Mr Chiesa said while the system may not be for everyone, it made sense on their property from a holistic perspective.

"If you want to start doing the full circle approach looking down the lines of carbon farming, it is an achievable goal," he said.

"I don't mind a few trees in a paddock providing a bit of shade, especially up north, it gets hot and humid here.

"I think it's a good thing to keep pushing the boundaries."

Timber Queensland CEO Mick Stephens said silvopastoral systems could include wide spaced trees in a paddock, tree rows, zoning and patches of trees and forests in a landscape.

"It can be planted trees or it can also be, managed natural forests, which occurs in an informal basis across Queensland and a lot of our native hardwood forests," he said.

"One of the challenges is to learn more about how to maximise the benefits for grazing in those forests and it includes all types of livestock."

During the trial, different treatments were applied to each of the three sites.

Mr Stephens said the control site had no thinning and light and heavy thinning treatments were applied to the other two sites.

"There were tree rows planted in between the pasture alleys. Ten and 20 metre alleys were tested to establish if a pasture could be sustained through the life of a rotation," he said.

"Stocking of a normal site is about 800 to 1000 stems. The control site had 808 stems on it.

"There is not a lot of data specific to regional areas and particular species, so one of the main advantages of this experiment was looking at what would normally grow in that area, which is Caribbean pine trees."

Mr Stephens said beef productivity was measured in live weight gain and tree growth data.

Data was collected by an Optiweigh system taking regular measurements of the cattle. GPS collars were also used to track their movements.

Part of the reason the trial was conducted in Cardwell was because broad scale grazing already exists in the area.

"Farmers are looking at ways to become carbon neutral. We know that trees can adapt...helping deal with climate change but also mitigation and sequestering carbon," he said.

"Farmers are also looking for resilience, income diversification and things like carbon and wood products have a lot of potential to do that."

Mr Stephens did however acknowledge there were always trade-offs.

"When we put trees in the landscape, they are taking up soil and water resources and sunlight, that would otherwise be used for cropping or pasture for livestock," he said.

"You need to look at what the gain is by having the trees in the landscape.

"There might be some benefits with improved shelter from wind and erosion and there is also the income from the timber products."

CQUniversity cattle researcher Dr Thomas Williams gave a graziers perspective on the silvopastoral system.

"The Queensland cattle industry is one of our largest manufacturing sectors, it contributes a billion dollars annually to the state's economy and supports over 10,000 jobs across the state," he said.

"They are the custodians of 71 percent of the country and when you start looking at the models for overlaying trees with cattle, there is quite a lot of opportunity there.

"The Fitzroy Basin Association has been pushing trees on productive pasture for a long time, but it's solely from for a natural resource management point of view, not necessarily silvopastoral.

"The FBA are promoting keeping 30 to 40pc cover over grazing land, increased water and nutrient cycling, carbon offset opportunities, increased biodiversity, shelter and reduced heat stress for animals, stabilised soil conditions to reduce sediment and loss and increased resilience in ecosystems.

"That is also what we've been promoting in silvopastoral."

Dr Williams said the reality was producers wanted to know how much they were going to lose by adding or increasing trees to their land.

"If they are going to put trees in they are going to have some form of reduced pasture growth under those trees unless we look to optimising those pasture species," he said.

"We acknowledge it is still an emerging land use, we need more RND to take those principles to other species and other regions because it is so variable in the landscape.

"We are looking at extending the trial to other sites and maintaining measurements on that site."