Latest Score:

3.1/5

in 2018

score trend is down over time
Weight: 15%

As trees experience stress or decline, they begin to reduce resources to the outermost leaves and branches, leading to crown dieback. This fine-scale measurement allows for a more detailed assessment of the tree's overall health and vigor -- it is an early indication of declining health. In any one year, a tree may exhibit short-term dieback due envrionmental stressors, like drought or insect damage. However, trends in crown condition provide an early warning sign of forest decline. Canopy dieback is estimated as the percentage of missing foliage from the upper and outer areas of a tree’s crown. The current year is scored as a proportion between the long-term mean and the maximum value in the record.

The current score highlights the trend that crown dieback is increasing in Vermont's forests, and has been since data collection began. An average of 10% dieback is not indicative of tree decline, but average dieback ratings greater than 15% are cause for concern.

Interpretation provided by:

Josh Halman, Forest Health Specialist; Vermont Department of Forests, Parks and Recreation

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The score is calculated using a target value and the historical range of the the entire long-term dataset. The higher the score, the closer this year's value is to the target.

Once the score is computed for each year, the trend in scores over time is calculated. If the trend is significantly positive or negative, the long-term trend is marked as increasing or decreasing respectively.

Component Description
Scored as

Distance between target and maximum (scaled between 1 and 5)

Target value

Long-term mean

Directionality of scores

Lower values in the data are better

Minimum value used in scoring

Long-term mean

Maximum value used in scoring

Data maximum + 10% of the range

Crown dieback is a visual assessment of the percentage of the tree’s crown that has recent fine twig mortality. Crown dieback has been assessed annually on Vermont Forest Health Monitoring1 (FHM, a collaboration between FEMC and VT FPR) and North American Maple Project (NAMP) plots2. For the FHM program, plots have been assessed annually since 1994, but between 2008 and 2013, plots were assessed on a 3-year rotation. To generate values for the missing years of 2009 and 2012, we used the average dieback from 2008-2010 and 2011-2013, respectively. FHM dieback scores were averaged per plot per year of survey data for dominant and codominant trees of all species. NAMP plots have assessed on an annual basis, beginning in 1988. While maple species are the focus of the NAMP project, co-occurring species have also been assessed. To approach the unequal species composition on NAMP plots, we selected only those plots that where dominant and codominant trees were less than 80% sugar maple. We averaged dieback within species in a plot prior to averaging across plots. We then computed the mean crown dieback for all species across all plots per year in NAMP. From these two data sources, we computed an overall mean crown dieback for all species for each year by taking the mean of the NAMP and FHM yearly dieback averages. For crown dieback, the target was set as the long-term mean. We computed the current year score was the distance between the target and the upper scoring bounds (maximum value in the dataset plus 10% of the range), scaled to be between 1-5. Values below the target were scored as 5.

1 Pontius J., S. Wilmot. 2017. Forest Health Monitoring. FEMC. Available at: https://www.uvm.edu/femc/data/archive/project/forest-health-monitoring
2 Wilmot, S., Halman, J. 2018. North American Maple Project. Vermont Department of Forest Parks and Recreation.

CONDITION INDICATORS