The knowledge gap to de-risking investment into a new-to-Aotearoa New Zealand tree syrup industry is a lack of understanding of sap exudation mechanisms in each potential tree syrup species. This gap limits our ability to predict potential yields, optimise new production systems, confirm economic viability, or identify new sources of tree syrup.
In September 2021, the research project “Non-invasive sap flow measurement and mechanisms for reliable tree syrup yield predictions”, was awarded three years of funding by the Ministry of Business, Innovation and Employment's (MBIE) Endeavour Fund. This project is being led by University of Canterbury.
Despite the long history of tree-syrup production in north-eastern North America, the exact mechanism that drives sap flow is not fully understood, primarily due to the difficulty of directly observing the flow process in trees. We aim to provide a comprehensive understanding of sap exudation phenomena for both juvenile and mature trees.
Using advanced, high-resolution, 3D, in-vivo imaging techniques we will non-destructively image the microstructural changes that occur during freeze-thaw induced sap flow. Our microstructural imaging will examine the interactions between xylem anatomy, the pit membranes that interconnect xylem cells, bubble formation and movement, and the role of pit membranes in generating stem pressure and sap flow.
Our goal is to understand the effect of climate and pruning regimes on potential syrup production. By correlating un-controlled, but measured, climatic factors to measured tree response variables (e.g. tree stem pressure, sap flow and internal tree temperature) we will refine our ability to optimise plantation site requirements.
Trees will be subjected to different pruning regimes to determine whether a single stem yields greater syrup volumes than multiple stems resulting from a coppice regime. Experiments with excised stems, and monitoring of potted and field-planted trees will examine the role of sap sugar and root water uptake in sustaining flow.
The microstructural observations from advanced imaging, augmented with data from instrumented trees on test-sites in Aotearoa New Zealand and around the world, will inform an advanced observation-based sap flow model. This tool that will improve forecasting of tree syrup yields under various climatic conditions and differing harvesting techniques.
The model will be used to predict tree stem pressure, optimum growing conditions and locations in our maritime climate, and sap-harvesting strategies to maximise yield. We will use this model, coupled with other costs to determine the economic viability of establishing a tree syrup industry.