Progress report for GNE24-309
Project Information
Climate change is shortening winters in the northeast in turn
initiating earlier sapflow during the maple season. Larger
maple operations responsible for installing many taps may adapt
to this pressure by tapping earlier in winter dormancy, ensuring
they capture sap when it begins to flow. We know that the
tree’s wound response is temperature dependent and diminished
during dormancy. Trees respond to tapholes, and other
wounds, by compartmentalizing the affected tissue and surrounding
area, results in the cessation of sap flow, thus the name
Non-Conductive Wood (NCW). It is vitally important to the
tree that this portion be minimized in volume by generating a
rapid and robust wound margin. In the context of maple
sugaring, not all tapping practices generate the same volume of
NCW yet the sustainability model is fundamentally tied to the
relationship between the trees annual increment and the volume of
NCW generated. This project aims to quantify the
non-conductive portion of sapwood generated in response to
tapholes installed at 6 different points throughout the dormant
season to understand this relationship if one exists.
Objective 1. Establish relationships between taphole wounding and
timing of installation as they apply to the maple sugaring
industry. The response variable will be the volume of NCW
generated by tapholes installed at 6 different time periods
within dormancy. These data will let us determine whether
there is a difference in NCW formation across the 6 treatments,
and if there is, where the greatest differences are.
The purpose of this project is to assess whether the time of year when installing a taphole in the stem of a maple tree impacts the sustainability of the tapping practice. Collecting maple sap requires the annual introduction of a relatively small wound into the stem vessels of a maple tree. The tree responds by compartmentalizing an area around the wound to permanently restrict the flow of water transport through this area, creating non-conductive wood (NCW) and forming a barrier to pathogens from entering the tree’s healthy vessels [1, 2]. Theoretically, annual tapping and sap extraction can be sustainable if the tree is able to compensate for the loss of conductive wood through the annual increment accumulated during the following growing season [3]. In the hierarchy of metabolic demands, radial growth is the last process a tree will expend resources on [4]. This means that if a tree can accumulate sufficient radial growth to compensate for the NCW generated during sap extraction, one can assume the quantity of carbohydrate extracted, and tapping practice did not diminish the trees health enough to consider it unsustainable [5]. Additionally, the working model of sustainable tapping states the proportion of functional sapwood in the tapping zone should be greater than 90%. Practices that minimize the accumulation of NCW are more likely to be considered sustainable and conversely practices that generate more NCW are more likely to be considered unsustainable or unfavorable. Choosing practices that limit the accumulation of NCW and maximize yield sustainably will help to optimize a sugarmakers long term production. As stewards of their working forests, sugarmakers need to have information available to them that informs management, ensuring their practices maximize the health of their trees and forests for their lifetime and future generations.
As soon as a taphole wound is introduced, it becomes vitally important to the tree that it limits the spread of infectious pathogens, which in turn needs to colonize as much tissue as possible at the cost of viable sapwood. One of the first lines of tree defense comes through the formation of phenols, antimicrobial defense compounds [2, 6]. These compounds gather at the margin of infection known as the reaction zone and work to limit the spread of pathogen [6]. The reaction zone is not always immediately successful which can lead to a larger column of NCW above and below the taphole wound if penetrated [2, 7]. Among other factors, the success of forming a stable reaction zone is likely dependent on the time of year and pathogenic potential of the microorganisms present at the time of infection [2, 8, 9]. Unfortunately, wound response and accumulation of phenolic defense compounds is a temperature dependent process, requiring periods of warm temperature brought by the following growing season [2, 8] potentially leaving tapholes defenseless against pathogen for an extended period.
|
Year |
Number of taps |
Number of farms |
|
2022 |
5,828,040 |
223 |
|
2017 |
3,614,782 |
147 |
A combination of shorter winters and the growing number of large maple farms requires some sugar makers to install taps earlier in winter dormancy [3]. The National Agriculture Statistics Service (NASS) reported an increase of 2.2 million taps installed on operations that have 10,000 taps or more from 2017 to 2022 (Table 1.) Producers of this size represent almost 6 million trees tapped in the state of Vermont (Table 1.) showing that these practices, if restricted to this class of producer, have the potential to impact a substantial portion of Vermont’s maple resource.
One tapper can reasonably expect to install between 300 and 400 taps in a day, so tapping 10,000 or more trees on a sugarbush is no short task, forcing producers to begin tapping earlier in the year. Historically, town meeting day has been the target date to have taps installed by. However, recent climate trends have made this target unreliable. Early installation maximizes sap yields [3], though it introduces a wound in crop trees during a potentially vulnerable time of year. There are key information gaps on the changes in NCW formation that occur when tapping early in winter dormancy. Paired data comparing the volume of NCW in response to tapholes introduced throughout each month in dormancy prior to sap flow do not exist. This project will generate and analyze these data to better understand the relationship between timing of taphole installation and sustainable yield from our sugarwoods.
Research
20 Sugar maple tree’s were selected from a larger inventory taken from two properties in Underhill VT, resulting in 10 trees on each property during the late summer of 2023. Preliminary work indicates there is no significant site effect on NCW formation so 20 samples were distributed across 2 properties to diminish the burden placed on each landowner (unpublished data). All trees included in the inventory were selected under the conditions they were healthy, mature, dominant or codominant trees with vigor rating 1 as defined by the FEMC forest health field methods to limit variation in NCW volume due to health or canopy status. The original inventory included trees of diameter between 10”-14”. Once inventoried, the final selection limited the variation in tree diameter in the population. Average diameter was 10.84” on site 1 and 10.9” on site 2. On each tree 6 positions were oriented around the north aspect and identified as 1-6. Position 1 was on the north aspect and subsequent positions were equally distributed clockwise around the trunk as a function of tree diameter. Each study unit received one control treatment, a taphole installed on February 15th, and 5 treatments, one taphole each installed in the middle of October, November, December, January, and March resulting in 6 paired groups. Variability between individuals can be high. Pairing the data limits the effect of tree to tree variability on the final analyses. Taphole depth was controlled using a drill bit marked at 1.5”. There is not a universal standard for taphole depth and 1.5” was chosen instead of using other commonly used depths like 2” to decrease the likelihood of wounds merging with existing stem defects, thus rendering that datapoint unusable. To accommodate for variation in taphole size, depth measurements are taken for each treatment prior to sectioning and results will also be reported as a proportion of NCW area to taphole area. Treatment and control tapholes were randomly assigned to one of the 6 positions identified prior. Given that wound response is a temperature dependent process, care was taken to not subject certain treatments to a tree aspect that would subject it to different temperature conditions due to solar warming. The south facing aspect of a tree stem will typically be warmer due to a longer exposure to sunlight than other aspects during the winter months. Local weather conditions are obtained from a database recorded at PMRC. Both sites are within a 3.5 mile radius of the weather station recording temperature data which allow for comparison to time of year and temperature conditions during each treatment period. Following the 2024 growing season, giving the study units an opportunity to form the boundary layer, trees are harvested via felling with a chainsaw, maintaining a continuous 3’ of tissue above and below the whorl of treatment tapholes on the stem. An accurate measurement of taphole depth is taken and an initial cross section is made through the whorl of treatments to initiate the bottom plane of two sections representing “Above” and “Below” the taphole. From this initial plane cross sections are taken to reveal the surface plane every 2” from the treatments until the extent of the boundary is reached. Sections are made by securing the log across two sawhorses, built for this purpose, and cutting cookies using a chainsaw jig to maintain accuracy (Figure 1.) Each cross section is photographed (Figure 2.), and using ImageJ image analysis software, the volume of the compartmented section is quantified for each treatment. Data is reported as a volume of compartmented area and as a proportion of taphole area.
ImageJ is open source image analysis software that can, among other functions, measure the area of features on an image. Images of cross sections are scaled in the software using a 30mm rule and the area of NCW corresponding to each treatment is measured from each 2” cross section (Figure 2). Using these measurements, a final volume of NCW is calculated for each treatment.
Analysis of the resulting data will use ANOVA to compare the mean volume of each treatment. A sample size of 20 will be sufficient for inference using this method. However, if enough NCW columns are unusable the sample size for that group will be reduced making non parametric testing such as the Kruskal-Wallace test a more reliable analysis.
In 2021 these same methods were used to determine the NCW area generated by various taphole refreshing that were developed to delay tapholes from “drying up” in the spring when tapped earlier in the season [10]. Similar methods have also been used in in determining NCW generated by different size tapholes and tapping depth [5].
Outreach Plan:
This project is intended to be viewed as a pilot project. Nuanced guidance leading to meaningful policy may require more in-depth studies investigating the processes involved which are beyond the scope of this project and require additional years of data. While the results of this project may not be appropriate to inform policy or tapping guidelines yet, they will provide needed guidance to producers as they are making management decisions. Outreach will come in 2 primary forms, publishing in 2 primary newsletters distributed across the maple producing region and presentations at the Vermont Maple Sugar Makers Association Vermont Maple Conferences (link to 2023 meeting brochure: https://www.uvm.edu/sites/default/files/Agriculture/maple/2023-vt-maple-conference-brochure.pdf) attended by industry professionals and maple producers alike.
Articles will be submitted to both the Maple news and Maple Syrup Digest for publication. The Maple News is an industry publication widely distributed to producers and other members of the industry, containing stories, events, classifieds, and research reports (https://www.themaplenews.com/). The Maple Digest is the quarterly publication of the North American Maple Syrup Council and has served as a valuable method of distributing research reports to the maple community since its origins in the 1960’s (http://northamericanmaple.org/index.php/maple-syrup-digest/). Because of the applied nature of the work, other publications wouldn’t be expected to reach the target audience. Though it’s generally the goal of research to be published in journals recognized by the scientific community, there is no cost of publication with the outlets were pursuing and it is one of the most effective ways of reaching maple producers, the community this study is designed to help.
The annual Vermont Maple Conferences hosts maple producers and professionals for a day to distribute information to the maple community. From forest managers and researchers to manufacturing and packer representatives, these conferences engage the maple community with current research topics strategically scheduled immediately prior to that year’s production season. These meetings will be an opportunity to present research results and hold open discussions with the maple community.
Education & Outreach Activities and Participation Summary
Participation Summary:
This project is intended to be viewed as a pilot project. Nuanced guidance leading to meaningful policy may require more in-depth studies investigating the processes involved which are beyond the scope of this project and require additional years of data. While the results of this project may not be appropriate to inform policy or tapping guidelines yet, they will provide needed guidance to producers as they are making management decisions. Outreach will come in 2 primary forms, publishing in 2 primary newsletters distributed across the maple producing region and presentations at the Vermont Maple Sugar Makers Association Vermont Maple Conferences (link to 2023 meeting brochure: https://www.uvm.edu/sites/default/files/Agriculture/maple/2023-vt-maple-conference-brochure.pdf) attended by industry professionals and maple producers alike.
Articles will be submitted to both the Maple news and Maple Syrup Digest for publication. The Maple News is an industry publication widely distributed to producers and other members of the industry, containing stories, events, classifieds, and research reports (https://www.themaplenews.com/). The Maple Digest is the quarterly publication of the North American Maple Syrup Council and has served as a valuable method of distributing research reports to the maple community since its origins in the 1960’s (http://northamericanmaple.org/index.php/maple-syrup-digest/). Because of the applied nature of the work, other publications wouldn’t be expected to reach the target audience. Though it’s generally the goal of research to be published in journals recognized by the scientific community, there is no cost of publication with the outlets were pursuing and it is one of the most effective ways of reaching maple producers, the community this study is designed to help.
The annual Vermont Maple Conferences hosts maple producers and professionals for a day to distribute information to the maple community. From forest managers and researchers to manufacturing and packer representatives, these conferences engage the maple community with current research topics strategically scheduled immediately prior to that year’s production season. These meetings will be an opportunity to present research results and hold open discussions with the maple community.