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Location, location, location and forest management practices: A new way to predict future timber yields

The team behind newly published, FWPA-supported research have gathered a wealth of knowledge to help hardwood growers in Southern Australia make smarter decisions about the location and management of their plantations.

Armed with reliable estimates of the potential productivity of a plantation site under a range of conditions, plantation owners and forest managers can make decisions on the most advantageous locations for plantation establishment, and the management practices that will enable optimum productivity and timber yield.

The team also set out to determine the main causes of the gaps between potential and actual yields within current plantations or earlier rotations, and the extent to which management practices could help to reduce those gaps.

During the project, titled Optimising productivity of hardwood plantations: yield gap analysis for Eucalyptus globulus plantations in southern Australia, the team aimed to develop a forest modelling and prediction framework based on climate and environmental factors to generate yield gap estimations.

John McGrath of McGrath Forestry Services – who led the research alongside Dr Tom Baker of Melbourne University and Dr Philip Smethurst of the CSIRO – said this framework could provide a new methodology for benchmarking Australian plantation performance.

By identifying the environmental and management factors that impact plantation productivity this work will assist in assessing the viability of investment opportunities and the risks associated with various forest management decisions.

“Such knowledge would allow the forestry industry to explore different scenarios that consider a range of key productivity drivers such as water availability, temperature and nutrition,” McGrath said.

The team used the Agricultural Production Systems sIMulator (APSIM) Next Generation Eucalyptus process-based growth model, due to its ability to include complex soils, flexibility around silvicultural practices, science and software engineering credentials, and links to agricultural models and software support.

Based on their observations, the team provided some quantification of the forest management factors that can affect yield, while noting the differences between regions and the extent to which environmental and management factors can impact productivity.

Unsurprisingly, climate, particularly water availability, was determined to be the primary limitation to yield across southern Australia. Observed greater yields were attributed to plantation access to water in addition to rain, such as run-on, groundwater and deep-profile soil water. Regional differences such as temperature and evaporation effects were also discerned.

Another major driver of productivity was nutrient supply, with nitrogen found to be the main nutrient impacting productivity. The analysis of yield gaps using APSIM suggested all plantations modelled would have seen a markedly improved response to additional nitrogen fertiliser, leading the team to recommend multiple applications of nitrogen throughout each rotation.

The impact of variations in potential root depth due to soil properties was also considered, with the researchers recommending the avoidance of planting in shallow rooting-depth soils for improved yields.

Land-use history was also found to be an important contributing factor for productivity, with increased fertility observed on land with prior history of agricultural use.

The negative impacts on yield of high or low stand density, weed competition and coppicing rather than planting were also observed.

The utility of the resultant framework was tested by the research team using case studies based on the annual yields of Eucalyptus globulus plantations aged 10-years. These case studies provided a test of the accuracy and relevance of the modelling approach.

“Overall, the model simulations proved to be a useful way to examine the role of individual factors impacting growth and yield without the confounding effects of un-controlled factors that can arise during analyses,” Smethurst said.

“We hope, with ongoing support and industry training, the sector will adopt this modelling capability and future enhancements, either in-house or through the engagement of external consultants.”

To share the information and knowledge gained during this project, the team hosted seminars and training workshops for industry stakeholders to educate them about forest yield prediction approaches, and how they can be used to inform decision making.

“This work demonstrated the need to improve the modelling capacity available to the plantation sector,” Smethurst said.

“This includes both the capacity for model development and, importantly, the human and technical capacity to deliver the modelling systems in an effective manner for the industry.”

According to the research team, one way this could be achieved is through the availability of improved, nationally consistent soil data, including attributes that can be functionally linked to plantation productivity.

“The analysis of the extensive trial data available from the efforts of industry and research institutions over the past three decades has only received a preliminary analysis in the present study,” McGrath said.

“Further synthesis of this valuable knowledge is now being undertaken in another FWPA-funded project titled Enhancing the knowledge base for hardwood plantation management.”

Posted Date: November 1, 2023

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