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(a) maple sap exudation from tapping a spout into the sapwood. (b) Tubing network for collecting maple sap prior to processing into syrup. Photos are Copyright University of Vermont and courtesy of Mark Isselhardt, used with the permission.
Source publication
Maple syrup is strongly associated with North America in the same way that wine was once associated with France. Parts of New Zealand (NZ) have growing conditions suitable for maple trees to grow and exude sap to be used for the production of maple syrup. While traditional production requires mature trees, recent research in the United States sugge...
Contexts in source publication
Context 1
... process of extracting sap from the trees, known as tapping, is accomplished by drilling a hole into the sapwood of the tree allowing the natural pressures within the tree to exude the sap. With properties consistent to water, maple sap flows from the trees through extensive networks of tubing ( Figure 1) to be collected and processed into syrup. Maple syrup is only classified as such if it has between 66.9-68.9 ...
Context 2
... process of extracting sap from the trees, known as tapping, is accomplished by drilling a hole into the sapwood of the tree allowing the natural pressures within the tree to exude the sap. With properties consistent to water, maple sap flows from the trees through extensive networks of tubing ( Figure 1) to be collected and processed into syrup. Maple syrup is only classified as such if it has between 66.9-68.9 ...
Citations
... However, recent developments in sap extraction methodologies has allowed for (in theory) commercially viable maple syrup yields from small diameter maple saplings (5-10 cm) [16,17]. This offers up potential new regions for syrup production, as small diameter saplings mean less extreme freeze thaw cycles may be required to induce sap flow, opening up production to warmer climates [18]. However, there is currently a lack of detailed anatomical information on xylem elements within juvenile sugar maple. ...
New methodologies have enabled viable sap yields from juvenile sugar maple trees. To further improve yields, a better understanding of sap exudation is required. To achieve this, the anatomy of the xylem must first be fully characterised. We examine juvenile maple saplings using light optical microscopy (LOM) and scanning electron microscopy (SEM), looking at sections cut along differing orientations as well as macerations. From this we measure various cell parameters. We find diameter and length of vessel elements to be 28 ± 8 μm and 200 ± 50 μm, for fibre cells 8 ± 3 μm and 400 ± 100 μm, and for ray parenchyma cells 8 ± 2 μm and 50 ± 20 μm. We also examine pitting present on different cell types. On vessel elements we observe elliptical bordered pits connecting to other vessel elements (with major axis of 2.1 ± 0.7 μm and minor 1.3 ± 0.3 μm) and pits connecting to ray parenchyma (with major axis of 4 ± 2 μm and minor 2.0 ± 0.7 μm). We observe two distinct pit sizes on fibres with circular pits 0.7 ± 0.2 μm in diameter and ellipsoidal pits 1.6 ± 0.4 μm by 1.0 ± 0.3 μm. We do not observe distinct pitting patterns on different fibre types. The various cell and pit measurements obtained generally agree with the limited data available for mature trees, with the exception of vessel element and fibre length, both of which were significantly smaller than reported values.
We demonstrate the application of synchrotron x-ray microtomography (microCT) to non-invasively examine the internal structure of a maple and birch sapling. We show that, through the use of standard image analysis techniques, embolised vessels can be extracted from reconstructed slices of the stem. By combining these thresholded images with connectivity analysis, we map out the embolisms within the sapling in three dimensions and evaluate the size distribution, showing that large embolisms over 0.005 mm3 in volume compose the majority of the saplings' total embolised volume. Finally we evaluate the radial distribution of embolisms, showing that in maple fewer embolisms are present towards the cambium, while birch has a more uniform distribution.
Freeze-thaw cycles, where temperatures fluctuate above and below 0 °C, are the cause of elevated stem pressures that drive sap flow from within the sugar maple. This temperature-dependency has historically limited the production of maple syrup to select regions of North America. The plantation method of sap harvesting (which uses densely planted saplings instead of mature trees) now raises the possibility of a New Zealand-based maple syrup industry. In this study, a transient 2D heat transfer model was developed to predict freeze-thaw events in trees, and thereby evaluate potential plantation locations based on their climate. The heat transfer phenomena which have been modelled are bulk thermal diffusion, diffusion across discrete wood layers, convection, infrared radiation and solar radiation. Through experimental validation the model was found capable of predicting temperatures in real-life trees with high accuracy. Sensitive parameters were the bark absorptivity and sapwood diffusivity. Simulation results also indicate that the frequency of freeze-thaw cycles increase dramatically in saplings, as compared to mature trees, making maple syrup production potentially viable in locations that would otherwise fail when using traditional methods.
